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data/en.wikipedia.org/wiki/A_Philosopher_Lecturing_on_the_Orrery-0.md

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+---
+title: "A Philosopher Lecturing on the Orrery"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/A_Philosopher_Lecturing_on_the_Orrery"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:37:31.008006+00:00"
+instance: "kb-cron"
+---
+
+A Philosopher Lecturing on the Orrery, or the full title, A Philosopher giving that Lecture on the Orrery in which a lamp is put in place of the Sun, is a 1766 painting by Joseph Wright of Derby depicting a lecturer giving a demonstration of an orrery – a mechanical model of the Solar System – to a small audience.  It is now in the Derby Museum and Art Gallery The painting preceded his similar An Experiment on a Bird in the Air Pump (National Gallery, London).
+The first of Wright's candlelit masterpieces, Three Persons Viewing the Gladiator by Candlelight, was painted in 1765, and showed three men studying a small copy of the "Borghese Gladiator". The Gladiator was greatly admired; but his next painting, The Orrery, caused a greater stir, as it replaced the Classical subject at the centre of the scene with one of a scientific nature. Wright's depiction of the awe produced by scientific "miracles" marked a break with previous traditions in which the artistic depiction of such wonder was reserved for religious events, since to Wright the marvels of the technological age were as awe-inspiring as the subjects of the great religious paintings.
+In both of these works, the candlelit setting had a realist justification. Viewing sculpture by candlelight, when the contours showed well, and there might even be an impression of movement from the flickering light, was a fashionable practice described by Goethe. In the orrery demonstration the shadows cast by the lamp representing the sun were an essential part of the display. But there seems no reason other than heightened drama to stage the air pump experiment in a room lit by a single candle, and in two later paintings of the subject by Charles-Amédée-Philippe van Loo the lighting is normal.
+
+
+== Context ==
+The painting was one of a number of British works challenging the set categories of the rigid, French-dictated, hierarchy of genres in the late 18th century, as other types of painting aspired to be treated as seriously as the costumed history painting of a Classical or mythological subject. In some respects the Orrery and Air Pump subjects resembled conversation pieces, then largely a form of middle-class portraiture, though soon to be given new status when Johann Zoffany began to paint the royal family in about 1766. Given their solemn atmosphere however, and as it seems none of the figures are intended to be understood as portraits (even if models may be identified), the paintings can not be regarded as conversation pieces. The 20th-century art historian Ellis Waterhouse compares these two works to the "genre serieux" of contemporary French drama, as defined by Denis Diderot and Pierre Beaumarchais, a view endorsed by Egerton.
+An anonymous review from the time called Wright "a very great and uncommon genius in a peculiar way".
+
+
+== Provenance, and portraits ==
+
+The Orrery was painted without a commission, probably in the expectation that it would be bought by Washington Shirley, 5th Earl Ferrers, a British Royal Navy officer who had an orrery of his own, and with whom Wright's friend Peter Perez Burdett was staying while in Derbyshire. Figures thought to be portraits of Burdett and Ferrers feature in the painting, Burdett taking notes and Ferrers seated with a youth next to the orrery.
+Ferrers purchased the painting, which was displayed at the Exhibition of 1766 of the Society of Artists, for £210, but the 6th Earl auctioned it off, and it is now in the Derby Museum and Art Gallery, where it is on permanent display, close to a working replica of a full-sized mechanical Grand Orrery.
+A biographer of Wright, Benedict Nicolson, argued in 1968 that John Whitehurst was the model for the lecturer, while another commentator points out the figure's resemblance to "a painting of Isaac Newton by Godfrey Kneller". Close observation of the adult faces in the picture reveals that each one demonstrates one or other of the main phases of the Moon – new moon, half moon, gibbous moon and full moon. Jonathan Powers, in The Philosopher Lecturing on the Orrery, claims that 'the Philosopher' was John Arden, a scholar and lecturer best known for teaching the young Mary Wollstonecraft.
+A working reconstruction of the grand orrery depicted in Joseph Wright's painting was commissioned by Derby Museums in 1993. It was built by clock and orrery-maker, John Gleave, and is displayed alongside the original work in the museum's art gallery.
+
+
+== Notes ==
+
+
+== References ==
+Baird, Olga (2003). "Joseph Wright of Derby: Art, the Enlightenment and Industrial Revolution". Revolutionary Players—Museums, Libraries and Archives—West Midlands. Archived from the original on 29 September 2007. Retrieved 10 April 2007.
+Brooke, John Hedley (1991). Science and Religion: Some Historical Perspectives (Cambridge Studies in the History of Science). Cambridge University Press. p. 434. ISBN 0-521-28374-4.
+Egerton, Judy (1990). Wright of Derby. Tate Gallery. p. 296. ISBN 1-85437-037-5.
+Egerton, Judy (1998), National Gallery Catalogues (new series): The British School. catalogue entry pp. 332–343, ISBN 1-85709-170-1
+Elliott, Paul (1 January 2000). "The Birth of Public Science in the English Provinces: Natural Philosophy in Derby, c. 1690–1760". Annals of Science. 57 (1): 61–100. doi:10.1080/000337900296308. S2CID 145603120.
+Guilding, Ruth; et al. (2004). William Weddell and the transformation of Newby Hall. Jeremy Mills Publishing for Leeds Museums and Galleries. ISBN 0-901981-69-9.
+Jones, Jonathan (1 November 2003). "Yes, it is art". The Guardian. Retrieved 12 January 2007.
+Kimmelman, Michael (7 September 1990). "Review/Art; In Praise of a Neglected Painter of His Time". The New York Times. Retrieved 10 April 2007.
+Nicolson, Benedict (1968). Joseph Wright of Derby. The Paul Mellon Foundation for British Art Pantheon Books.
+Uglow, Jenny (2002). The Lunar Men. London: Faber and Faber. p. 588. ISBN 0-571-19647-0.
+Waterhouse, Ellis, (4th Edn, 1978) Painting in Britain, 1530–1790. Penguin Books (now Yale History of Art series), ISBN 0-300-05319-3

data/en.wikipedia.org/wiki/Abu-Mahmud_Khujandi-0.md

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+---
+title: "Abu-Mahmud Khujandi"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Abu-Mahmud_Khujandi"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:00.430468+00:00"
+instance: "kb-cron"
+---
+
+Abu Mahmud Hamid ibn al-Khidr al-Khujandi (known as Abu Mahmood Khujandi, al-khujandi or Khujandi, Persian: ابومحمود خجندی, c. 940 – 1000) was a Transoxanian astronomer and mathematician. He was born in Khujand (now part of Tajikistan) and lived in the late 10th century. He helped build an observatory, near the city of Ray (near today's Tehran), in Iran.
+
+
+== Astronomy ==
+
+Khujandi worked under the patronage of the Buwayhid Amirs at the observatory near Ray, Iran. There he is known to have constructed the first huge mural sextant in 994 AD, intended to determine the Earth's axial tilt ("obliquity of the ecliptic") to high precision.
+He determined the axial tilt to be 23°32'19" for the year 994 AD. He noted that measurements by earlier astronomers had found higher values (Indians: 24°; Ptolemy 23° 51') and thus discovered that the axial tilt is not constant but is in fact (currently) decreasing. His measurement of the axial tilt was however about 2 minutes too small, probably due to his heavy instrument settling over the course of the observations.
+
+
+== Mathematics ==
+Khujandi stated a special case of Fermat's Last Theorem for n = 3, but his attempted proof of the theorem was incorrect. The spherical law of sines may have also been discovered by Khujandi, but it is uncertain whether he discovered it first, or whether Abu Nasr Mansur, Abul Wafa or Nasir al-Din al-Tusi discovered it first.
+
+
+== Notes ==
+
+
+== References ==
+O'Connor, John J.; Robertson, Edmund F., "Abu Mahmud Hamid ibn al-Khidr Al-Khujandi", MacTutor History of Mathematics Archive, University of St Andrews
+
+
+== External links ==
+Brummelen, Glen Van (2007). "Khujandī: Abū Maḥmūd Ḥāmid ibn al‐Khiḍr al‐Khujandī". In Thomas Hockey; et al. (eds.). The Biographical Encyclopedia of Astronomers. New York: Springer. pp. 630–1. ISBN 978-0-387-31022-0. (PDF version)
+Tekeli, Sevim (2008) [1970-80]. "Al-Khujandī, Abū Maḥmūd Ḥāmid Ibn Al-Khiḍr". Complete Dictionary of Scientific Biography. Encyclopedia.
+History of Islamic Science Archived 2011-06-05 at the Wayback Machine

data/en.wikipedia.org/wiki/Al-Zarqali-0.md

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+---
+title: "Al-Zarqali"
+chunk: 1/2
+source: "https://en.wikipedia.org/wiki/Al-Zarqali"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:18.928040+00:00"
+instance: "kb-cron"
+---
+
+Abū Isḥāq Ibrāhīm ibn Yaḥyā al-Naqqāsh al-Zarqālī al-Tujibi (Arabic: إبراهيم بن يحيى الزرقالي); also known as Al-Zarkali or Ibn Zarqala (1029–1100), was an Arab maker of astronomical instruments and an astrologer from the western part of the Islamic world.
+Although his name is conventionally given as al-Zarqālī, it is probable that the correct form was al-Zarqālluh. In Latin he was referred to as Arzachel or Arsechieles, a modified form of Arzachel, meaning 'the engraver'. He lived in Toledo, Al-Andalus before moving to Córdoba later in his life. His works inspired a generation of Islamic astronomers in Al-Andalus, and later, after being translated, were very influential in Europe. His invention of the Saphaea (a perfected astrolabe) proved very popular and was widely used by navigators until the 16th century.
+The crater Arzachel on the Moon is named after him.
+
+== Life ==
+Al-Zarqālī, of Arab origin, was born in a village near the outskirts of Toledo, the then capital of the newly established Taifa of Toledo. He started work after 1048 under Said al-Andalusi for the Emir Al-Mamun of Toledo and also under Al-Mu'tamid of the Taifa of Seville. Assuming a leading position under Said, Al-Zarqālī conducted solar observations for 25 years from 1050.
+
+He was trained as a metalsmith and due to his skills he was nicknamed Al-Nekkach "the engraver of metals". His Latinized name, 'Arzachel' is formed from the Arabic al-Zarqali al-Naqqash, meaning 'the engraver'.
+He was particularly talented in geometry and astronomy. He is known to have taught and visited Córdoba on various occasions, and his extensive experience and knowledge eventually made him the foremost astronomer of his time. Al-Zarqālī was also an inventor, and his works helped to put Toledo on the intellectual center of Al-Andalus. He is also referred to in the works of Chaucer, as 'Arsechieles'.
+In the year 1085, Toledo was taken by the Christian king of Castile Alfonso VI. Al-Zarqālī and his colleagues, such as Al-Waqqashi (1017–1095) had to flee. It is unknown whether the aged Al-Zarqālī fled to Cordoba or died in a Moorish refugee camp.
+His works influenced Ibn Bajjah (Avempace), Ibn Tufail (Abubacer), Ibn Rushd (Averroës), Ibn al-Kammad, Ibn al-Haim al-Ishbili and Nur ad-Din al-Betrugi (Alpetragius).
+In the 12th century, Gerard of Cremona translated al-Zarqali's works into Latin. He referred to Al-Zarqali as an astronomer and magician. Ragio Montanous wrote a book in the 15th century on the advantages of the Sahifah al-Zarqalia. In 1530, the German scholar Jacob Ziegler wrote a commentary on one of al-Zarqali's works. In his "De Revolutionibus Orbium Coelestium", in the year 1530, Nicolaus Copernicus quotes the works of al-Zarqali and Al-Battani.
+
+== Science ==
+
+=== Instruments ===
+Al-Zarqālī wrote two works on the construction of an instrument (an equatorium) for computing the position of the planets using diagrams of the Ptolemaic model. These works were translated into Spanish in the 13th century by order of King Alfonso X in a section of the Libros del Saber de Astronomia entitled the "Libros de las laminas de los vii planetas".
+He also invented a perfected kind of astrolabe known as "the tablet of al-Zarqālī" (al-ṣafīḥā al-zarqāliyya), which was famous in Europe under the name Saphaea.
+There is a record of an al-Zarqālī who built a water clock, capable of determining the hours of the day and night and indicating the days of the lunar months. According to a report found in al-Zuhrī's Kitāb al-Juʿrāfīyya, his name is given as Abū al-Qāsim bin ʿAbd al-Raḥmān, also known as al-Zarqālī, which has made some historians think that this is a different person.
+
+=== Theory ===
+Al-Zarqali corrected geographical data from Ptolemy and Al-Khwarizmi. Specifically, he corrected Ptolemy's estimate of the width of the Mediterranean Sea from 62 degrees to the correct value of 42 degrees. In his treatise on the solar year, which survives only in a Hebrew translation, he was the first to demonstrate the motion of the solar apogee relative to the fixed background of the stars. He measured its rate of motion as 12.04 arcseconds per year, which is remarkably close to the modern calculation of 11.77 arcseconds.  Al-Zarqālī's model for the motion of the Sun, in which the center of the Sun's deferent moved on a small, slowly rotating circle to reproduce the observed motion of the solar apogee, was discussed in the thirteenth century by Bernard of Verdun and in the fifteenth century by Regiomontanus and Peurbach. In the sixteenth century Copernicus employed this model, modified to heliocentric form, in his De Revolutionibus Orbium Coelestium.

data/en.wikipedia.org/wiki/Al-Zarqali-1.md

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+---
+title: "Al-Zarqali"
+chunk: 2/2
+source: "https://en.wikipedia.org/wiki/Al-Zarqali"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:18.928040+00:00"
+instance: "kb-cron"
+---
+
+=== Tables of Toledo ===
+Al-Zarqālī also contributed to the famous Tables of Toledo, an adaptation of earlier astronomical data by Al-Khwarizmi and Al-Battani, to locate the coordinates of Toledo. His zij and almanac were translated into Latin by Gerard of Cremona in the 12th century, and contributed to the rebirth of a mathematically based astronomy in Christian Europe and were later incorporated into the Tables of Toledo in the 12th century and the Alfonsine tables in the 13th century.
+Famous as well for his own Book of Tables, of which many had been compiled. Al-Zarqālī's almanac contained tables which allowed one to find the days on which the Coptic, Roman, lunar, and Persian months begin, other tables which give the position of planets at any given time, and still others facilitating the prediction of solar and lunar eclipses. This almanac that he compiled directly provided "the positions of the celestial bodies and need no further computation", it further simplifies longitudes using planetary cycles of each planet. The work provided the true daily positions of the sun for four Julian years from 1088 to 1092, the true positions of the five planets every 5 or 10 days over a period of 8 years for Venus, 79 years for Mars, and so forth, as well as other related tables.
+In designing an instrument to deal with Ptolemy's complex model for the planet Mercury, in which the center of the deferent moves on a secondary epicycle, al-Zarqālī noted that the path of the center of the primary epicycle is not a circle, as it is for the other planets. Instead it is approximately oval and similar to the shape of a pignon (or pine nut).  Some writers have misinterpreted al-Zarqālī's description of an earth-centered oval path for the center of the planet's epicycle as an anticipation of Johannes Kepler's sun-centered elliptical paths for the planets. Although this may be the first suggestion that a conic section could play a role in astronomy, al-Zarqālī did not apply the ellipse to astronomical theory and neither he nor his Iberian or Maghrebi contemporaries used an elliptical deferent in their astronomical calculations.
+
+== Works ==
+Major works and publications:
+
+Al Amal bi Assahifa Az-Zijia
+Attadbir
+Al Madkhal fi Ilm Annoujoum
+Rissalat fi Tarikat Istikhdam as-Safiha al-Moushtarakah li Jamiâ al-ouroud
+Almanac Arzarchel
+
+== See also ==
+Islamic astronomy
+Islamic scholars
+List of Arab scientists and scholars
+
+== Notes ==
+
+== Further reading ==
+Puig, Roser (2007). "Zarqālī: Abū Isḥāq Ibrāhīm ibn Yaḥyā al-Naqqāsh al-Tujībī al-Zarqālī". In Hockey, Thomas; et al. (eds.). The Biographical Encyclopedia of Astronomers. New York: Springer. pp. 1258–60. ISBN 978-0-387-31022-0. (PDF version)
+Vernet, J. (1970). "Al-Zarqālī (or Azarquiel), Abū Isḥāqibrāhīm Ibn Yaḥyā Al-Naqqāsh". Dictionary of Scientific Biography. New York: Charles Scribner's Sons. ISBN 0-684-10114-9.
+E. S. Kennedy.  A Survey of Islamic Astronomical Tables, (Transactions of the American Philosophical Society, New Series, 46, 2.)  Philadelphia, 1956.
+
+== External links ==
+Muslim Scientists Before the Renaissance: Abū Ishāq Ibrāhīm al-Zarqālī (Arzachel) Archived 2013-11-11 at the Wayback Machine
+'Transmission of Muslim astronomy to Europe'
+'An Extensive biography'

data/en.wikipedia.org/wiki/Al-ʻIjliyyah-0.md

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+---
+title: "Al-ʻIjliyyah"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Al-ʻIjliyyah"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:35:47.719208+00:00"
+instance: "kb-cron"
+---
+
+Al-ʻIjliyyah bint al-ʻIjliyy (Arabic: العجلية بنت العجلي) was a 10th-century maker of astrolabes active in Aleppo, in what is now northern Syria.
+She is sometimes known in modern popular literature as Mariam al-Asṭurlābiyya (Arabic: مريم الأسطرلابية) but her supposed first name 'Mariam' is not mentioned in the only known source about her life.
+
+
+== Life ==
+According to ibn al-Nadim, she was the daughter of another astrolabe maker known as al-ʻIjliyy; she and her father were apprentices (tilmīthah) of an astrolabe maker from Baghdad, Nasṭūlus.
+Al-ʻIjliyyah manufactured astrolabes, an astronomical instrument, during the 10th century; she was employed by the first Emir of Aleppo, Sayf al-Dawla, who reigned from 944 to 967.
+Beyond that information, nothing is known about her. Her supposed name, "Mariam", is not supported by sources from her time, and the phrase "al-Asturlabiyy" in the names by which she and her father are known simply means "the astrolabist", and indicates their profession; astrolabes were long known by her time.
+
+
+== Legacy ==
+The main-belt asteroid 7060 Al-ʻIjliya, discovered by Henry E. Holt at Palomar Observatory in 1990, was named in her honor. The naming citation was published on 14 November 2016 (M.P.C. 102252).
+She inspired a character in the 2015 award-winning book Binti and Netflix series Vikings: Valhalla. She was named an extraordinary woman from the Islamic Golden Age by 1001 Inventions.
+
+
+== See also ==
+Astronomy in the medieval Islamic world
+List of Muslim astronomers
+List of women astronomers
+Timeline of women in science
+
+
+== References ==
+ 
+
+
+== External links ==
+Astrolabe: the 13th Century iPhone – Daily Sabah
+GPS and its Islamic origins,  The Star Online, 3 October 2013

data/en.wikipedia.org/wiki/Alidade-0.md

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+---
+title: "Alidade"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Alidade"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:20.541498+00:00"
+instance: "kb-cron"
+---
+
+An alidade () (archaic forms include alhidade, alhidad, alidad) or a turning board is a device that allows one to sight a distant object and use the line of sight to perform a task. This task can be, for example, to triangulate a scale map on site using a plane table drawing of intersecting lines in the direction of the object from two or more points or to measure the angle and horizontal distance to the object from some reference point's polar measurement. Angles measured can be horizontal, vertical or in any chosen plane.
+The alidade sighting ruler was originally a part of many types of scientific and astronomical instrument. At one time, some alidades, particularly using circular graduations as on astrolabes, were also called diopters. With modern technology, the name is applied to complete instruments such as the 'plane table alidade'.
+
+
+== Origins ==
+
+The word in Arabic (الحلقة العضدية, al-ḥilqa al-ʿaḍudiyya, lit. 'the ruler'), signifies the same device. In Greek and Latin, it is respectively called δίοπτρα, "dioptra", and linea fiduciae, "fiducial line".
+The earliest alidades consisted of a bar, rod or similar component with a vane on each end. Each vane (also called a pinnule or pinule) has a hole, slot or other indicator through which one can view a distant object. There may also be a pointer or pointers on the alidade to indicate a position on a scale. Alidades have been made of wood, ivory, brass and other materials.
+
+
+== Examples of old alidade types ==
+
+The figure on the left displays drawings that attempt to show the general forms of various alidades that can be found on many antique instruments. Real alidades of these types could be much more decorative, revealing the maker's artistic talents as well as his technical skills. In the terminology of the time, the edge of an alidade at which one reads a scale or draws a line is called a fiducial edge.
+Alidade B in the diagram shows a straight, flat bar with a vane at either end. No pointers are used. The vanes are not centred on the bar but offset so that the sight line coincides with the edge of the bar.
+The vanes have a rectangular hole in each with a fine wire held vertically in the opening. To use the alidade, the user sights an object and lines it up with the wires in each vane. This type of alidade could be found on a plane table, graphometer or similar instrument.
+Alidades A and C are similar to B but have a slit or circular hole without a wire. In the diagram, the openings are exaggerated in size to show the shape; they would be smaller in a real alidade, perhaps 2 mm or so in width. One can look through the openings and line the openings up with the object of interest in the distance. With a small opening, the error in sighting the object is small. However, if a dim object such as a star is observed through a small hole, the image is difficult to see.
+This form is shown in the diagram as having pointers. These can be used to read off an angle on a scale that is engraved around the outer edge (or limb) of the instrument. Alidades of this form are found on astrolabes, mariner's astrolabes and similar instruments.
+Alidade D has vanes without any openings. In this case, the object is viewed and the alidade is rotated until the two opposite vanes simultaneously eclipse the object. With skill, this sort of alidade can yield very precise measures. In this example, pointers are shown.
+Alidade E is a representation of a very interesting design by Johannes Hevelius. Hevelius was following in Tycho Brahe's footsteps and cataloging star positions with high accuracy. He did have access to the telescopic sights that were being used by astronomers in other countries, however, he chose to use naked-eye observations for his positional instruments. Due to the design of his instruments and the alidades, as well as his diligent practices, he was able to yield very precise measures.
+Hevelius' design featured a pivot point with a vertical cylinder and a vane at the observer's end. The vane had two narrow slits that were spaced precisely the same distance apart as the diameter of the cylinder (in the diagram, the portion of the vane between the slits is removed for clarity; the left and right edges of the opening represent the slits). If the observer could sight a star on only one side of the cylinder, as seen in F, the alignment was off. By carefully moving the vane so that the star could just barely be seen on either side of the cylinder (G), the alidade was aligned with the position of the star. This could not be used with a closely located object. A star, being so far away as to exhibit no parallax to the naked-eye, would be observable as a point source simultaneously on both sides.
+
+
+== Modern alidade types ==
+
+The alidade is the part of a theodolite that rotates around the vertical axis, and that bears the horizontal axis around which the telescope (or visor, in early telescope-less instruments) turns up or down.
+In a sextant or octant the alidade is the turnable arm carrying a mirror and an index to a graduated circle in a vertical plane. Today it is more commonly called an 'index arm'.
+Alidade tables have also long been used in fire towers for sighting the bearing to a forest fire. A topographic map of the local area, with a suitable scale, is oriented, centered and permanently mounted on a leveled circular table surrounded by an arc calibrated to true north of the map and graduated in degrees (and fractions) of arc. Two vertical sight apertures are arranged opposite each other and can be rotated along the graduated arc of the horizontal table. To determine a bearing to a suspected fire, the user looks through the two sights and adjusts them until they are aligned with the source of the smoke (or an observed lightning strike to be monitored for smoke). See Osborne Fire Finder.
+
+
+== See also ==
+Gunsight
+Pelorus (instrument)
+
+
+== References ==
+
+Gerard L'E. Turner, Nineteenth Century Scientific Instruments, Sotheby Publications, 1983, ISBN 0-85667-170-3
+Gerard L'E. Turner, Antique Scientific Instruments, Blandford Press Ltd. 1980, ISBN 0-7137-1068-3
+
+
+== External links ==
+
+ This article incorporates text from a publication now in the public domain: Chambers, Ephraim, ed. (1728). Cyclopædia, or an Universal Dictionary of Arts and Sciences (1st ed.). James and John Knapton, et al. {{cite encyclopedia}}: Missing or empty |title= (help)

data/en.wikipedia.org/wiki/Almucantar-0.md

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+---
+title: "Almucantar"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Almucantar"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:21.691077+00:00"
+instance: "kb-cron"
+---
+
+An almucantar (also spelled almucantarat or almacantara) is a circle on the celestial sphere parallel to the horizon. Two stars that lie on the same almucantar have the same altitude. 
+The term was introduced into European astronomy by monastic astronomer Hermann Contractus of Reichenau, Latinized from the Arabic word al-muqanṭarah ("the almucantar, sundial", plural: al-muqanṭarāt), derived from qanṭarah ("arch, bridge")
+
+
+== Almucantar staff ==
+An almucantar staff is an instrument chiefly used to determine the time of sunrise and sunset, in order to find the amplitude and consequently the variations of the compass.  Usually made of pear tree or boxwood, with an arch of 15° to 30°, it is an example of a backstaff.
+
+The sun casts that shadow of a vane (B in the adjacent image) on a horizon vane (A).  The horizon vane has a slit or hole to allow the observer to see the horizon in the distance.  The observer aligns the horizon and shadow so they show at the same point on the horizon vane and sets the sighting vane (C) to align his line of sight with the horizon.  The altitude of the sun is the angle between the shadow vane and the sighting vane (B-A-C).
+
+
+== Solar almucantar ==
+The almucantar plane that contains the Sun is used to characterize multiple scattering of aerosols. Measurements are carried out rapidly at several angles at both sides of the Sun using a spectroradiometer or a photometer. There are several models to obtain aerosol properties from the solar almucantar. The most relevant were developed by Oleg Dubovik and used in the NASA AERONET network, and by Teruyuki Nakajima (named SkyRad.pack).
+
+
+== See also ==
+Circle of equal altitude
+
+
+== References ==
+
+Adelaide Observatory: Almucantar graphs of hour angles, Adelaide, R. E. E. Rogers, Govt. printer, 1927.
+Chandler, Seth Carlo, (1846–1913): The almucantar, Cambridge, J. Wilson and Son, 1887.
+Dubovik, O. and M. D. King, 2000: A flexible inversion algorithm for retrieval of aerosol optical properties from Sun and sky radiance measurements," Journal of Geophysical Research, 105, 20 673-20 696   pdf version
+Nakajima T, Tonna G, Rao RZ, et al.:Use of sky brightness measurements from ground for remote sensing of particulate polydispersions, Applied Optics 35 (15), 2672–2686, 1996
+
+
+== External links ==
+"Compendium on Using the Device Known as the Almucantar Quarter" is an Arabic manuscript from 1757 about the Almucantar Quarter
+
+ This article incorporates text from a publication now in the public domain: Chambers, Ephraim, ed. (1728). Cyclopædia, or an Universal Dictionary of Arts and Sciences (1st ed.). James and John Knapton, et al. {{cite encyclopedia}}: Missing or empty |title= (help)

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+title: "An Experiment on a Bird in the Air Pump"
+chunk: 1/5
+source: "https://en.wikipedia.org/wiki/An_Experiment_on_a_Bird_in_the_Air_Pump"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:37:00.402844+00:00"
+instance: "kb-cron"
+---
+
+An Experiment on a Bird in the Air Pump is a 1768 oil-on-canvas painting by Joseph Wright of Derby, one of a number of candlelit scenes that Wright painted during the 1760s. The painting departed from convention of the time by depicting a scientific subject in the reverential manner formerly reserved for scenes of historical or religious significance. Wright was intimately involved in depicting the Industrial Revolution and the scientific advances of the Enlightenment. While his paintings were recognized as exceptional by his contemporaries, his provincial status and choice of subjects meant the style was never widely imitated. The picture has been owned by the National Gallery in London since 1863 and is regarded as a masterpiece of British art.
+The painting depicts a natural philosopher, a forerunner of the modern scientist, recreating one of Robert Boyle's air pump experiments, in which a bird is deprived of air before a group of onlookers. The group members exhibit a variety of reactions, such as grief, disbelief and dismay, but for most of the audience scientific curiosity overcomes concern for the bird. The central figure looks out of the picture as if inviting the viewer's participation in the outcome.
+The painting was featured in the 1980 BBC Two series 100 Great Paintings.
+
+== Historical background ==
+
+In 1659, Robert Boyle commissioned the construction of an air pump, then described as a "pneumatic engine", which is known today as a "vacuum pump". The air pump was invented by Otto von Guericke in 1650, though its high cost deterred most contemporary scientists from constructing the apparatus. Boyle, the son of the Earl of Cork, had no such concerns—after its construction, he donated the initial 1659 model to the Royal Society and had a further two redesigned machines built for his personal use. Aside from Boyle's three pumps, there were probably no more than four others in existence during the 1660s: Christiaan Huygens had one in The Hague, Henry Power may have had one at Halifax, and there may have been pumps at Christ's College, Cambridge, and the Montmor Academy in Paris. Boyle's pump, which was largely designed to Boyle's specifications and constructed by Robert Hooke, was complicated, temperamental, and problematic to operate. Many demonstrations could only be performed with Hooke on hand, and Boyle frequently left critical public displays solely to Hooke—whose dramatic flair matched his technical skill.
+Despite the operational and maintenance obstacles, construction of the pump enabled Boyle to conduct a great many experiments on the properties of air, which he later detailed in his New Experiments Physico-Mechanicall, Touching the Spring of the Air, and its Effects, (Made, for the Most Part, in a New Pneumatical Engine). In the book, he described in great detail 43 experiments he conducted, with occasional assistance from Hooke, on the effect of air on various phenomena. Boyle tested the effects of "rarified" air on combustion, magnetism, sound, and barometers, and examined the effects of increased air pressure on various substances. He listed two experiments on living creatures: "Experiment 40", which tested the ability of insects to fly under reduced air pressure, and "Experiment 41," which demonstrated the reliance of living creatures on air for their survival. In this attempt to discover something "about the account upon which "respiration" is so necessary to the "animals" that Nature hath furnished with Lungs." Boyle conducted numerous trials during which he placed a large variety of different creatures, including birds, mice, eels, snails and flies, in the vessel of the pump and studied their reactions as the air was removed. Here, he describes an injured lark:
+
+... the Bird for a while appear'd lively enough; but upon a greater Exsuction of the Air, she began manifestly to droop and appear sick, and very soon after was taken with as violent and irregular Convulsions, as are wont to be observ'd in Poultry, when their heads are wrung off:  For the Bird threw her self over and over two or three times, and dyed with her Breast upward, her Head downwards, and her Neck awry.
+By the time Wright painted his picture in 1768, air pumps were a relatively commonplace scientific instrument, and itinerant "lecturers in natural philosophy"—usually more showmen than scientists—often performed the "animal in the air pump experiment" as the centerpiece of their public demonstration. These were performed in town halls and other large buildings for a ticket-buying audience, or were booked by societies or for private showings in the homes of the well-off, the setting suggested in both of Wright's demonstration pieces. One of the most notable and respectable of the travelling lecturers was James Ferguson FRS, a Scottish astronomer and probable acquaintance of Joseph Wright (both were friends of John Whitehurst). Ferguson noted that a "lungs-glass" with a small air-filled bladder inside was often used in place of the animal, as using a living creature was "too shocking to every spectator who has the least degree of humanity".
+
+The full moon in the picture is significant as meetings of the Lunar Circle (renamed the Lunar Society by 1775) were timed to make use of its light when traveling.
+Wright met Erasmus Darwin in the early 1760s, probably through their mutual connection, John Whitehurst In 1767, Wright first consulted Darwin regarding health concerns and stayed with the Darwin family for a week. The energy and vivacity of both Erasmus and Mary (Polly) Darwin impressed Wright. In the 1980s Eric Evans (National Gallery) suggested that Darwin is the figure in the left foreground who holds a watch. As this composed timekeeper is not consistent with Darwin's flamboyant character, it is more likely that this is Dr William Small. The attention to timekeeping fits with Dr Small's role as the social secretary for the Lunar Circle. Small returned from Virginia in 1764 and established his practice in Birmingham in 1765, consistent with this being a meeting in 1767. The profile and wig of this figure are consistent with a contemporary portrait of Small by Tilly Kettle.
+
+== Painting ==

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+title: "An Experiment on a Bird in the Air Pump"
+chunk: 2/5
+source: "https://en.wikipedia.org/wiki/An_Experiment_on_a_Bird_in_the_Air_Pump"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:37:00.402844+00:00"
+instance: "kb-cron"
+---
+
+=== Background ===
+
+During his apprenticeship and early career Wright concentrated on portraiture. By 1762, he was an accomplished portrait artist, and his 1764 group portrait James Shuttleworth, his Wife and Daughter is acknowledged as his first true masterpiece. Benedict Nicolson suggests that Wright was influenced by the work of Thomas Frye; in particular by the 18 bust-length mezzotints which Frye completed just before his death in 1762. It was perhaps Frye's candlelight images that tempted Wright to experiment with subject pieces. Wright's first attempt, A Girl reading a Letter by Candlelight with a Young Man looking over her shoulder from 1762 or 1763, is a trial in the genre, and is fetching though uncomplicated.
+Wright's, An Experiment on a Bird in the Air Pump forms part of a series of candlelit nocturnes that he produced between 1765 and 1768.
+There was a long history of painting candlelit scenes in Western art, although as Wright had not at this date traveled abroad, there remains uncertainty as to what paintings he might have seen in the original, as opposed to prints. Nicolson, who made studies of both Wright and other candlelight painters such as the 17th-century Utrecht Caravaggisti, thought their paintings, among the largest in the style, those most likely to have influenced Wright. However, Judy Egerton wonders if he could have seen any, referring to influences of the far smaller works of the Leiden fijnschilder Godfried Schalcken (1643–1706), whose reputation was much greater in the early 18th century than later. He had worked in England from 1692 to 1697, and several of his paintings can be placed in English collections.
+Although he was the leading expert writing in English, Nicolson does not suggest that Wright is likely to have known of the 17th-century candlelit narrative religious subjects of Georges de La Tour and Trophime Bigot, which, in their seriousness, are the closest works to Wright that are lit only by candle. The Dutch painters' works and other candlelit scenes by 18th-century English painters such as Henry Morland (father of George) tended instead to exploit the possibilities of semi-darkness for erotic suggestiveness. Some of Wright's own later candlelit scenes were by no means as serious as his first ones, as seen from their titles: Two Boys Fighting Over a Bladder and Two Girls Dressing a Kitten by Candlelight.  
+
+The first of his candlelit masterpieces, Three Persons Viewing the Gladiator by Candlelight, was painted in 1765, and showed three men studying a small copy of the "Borghese Gladiator". Viewing the Gladiator was greatly admired; but his next painting, A Philosopher giving that Lecture on the Orrery, in which a Lamp is put in place of the Sun (normally known by the shortened form A Philosopher Giving a Lecture on the Orrery or just The Orrery), caused a greater stir, as it replaced the Classical subject at the center of the scene with one of a scientific nature. Wright's depiction of the awe produced by scientific "miracles" marked a break with traditions in which the artistic depiction of such wonder was reserved for religious events, since to Wright the marvels of the technological age were as awe-inspiring as the subjects of the great religious paintings.
+In both of these works the candlelit setting had a realist justification. Viewing sculpture by candlelight, when the contours showed well and there might even be an impression of movement from the flickering light, was a fashionable practice described by Goethe. In the orrery demonstration the shadows cast by the lamp representing the sun were an essential part of the display, used to demonstrate eclipses. However there seems no reason, other than heightened drama, to stage the air pump experiment in a room lit by a single candle, and in two later paintings of the subject by Charles-Amédée-Philippe van Loo the lighting is normal.
+The painting was one of a number of British works challenging the set categories of the rigid, French-dictated hierarchy of genres in the late 18th century, as other types of painting aspired to be treated as seriously as the costumed history painting of a Classical or mythological subject. In some respects, the Orrery and Air Pump subjects resembled conversation pieces, then largely a form of middle-class portraiture, though soon to be given new status when Johann Zoffany began to paint the royal family in about 1766. Given their solemn atmosphere however, and as it seems none of the figures are intended to be understood as portraits (even if models may be identified), the paintings can not be regarded as conversation pieces. The 20th-century art historian Ellis Waterhouse compares these two works to the "genre serieux" of contemporary French drama, as defined by Denis Diderot and Pierre Beaumarchais, a view endorsed by Egerton.
+An anonymous review from the time called Wright "a very great and uncommon genius in a peculiar way." The Orrery was painted without a commission, probably in the expectation that it would be bought by Washington Shirley, 5th Earl Ferrers, an amateur astronomer who had an orrery of his own, and with whom Wright's friend Peter Perez Burdett was staying while in Derbyshire. Figures thought to be portraits of Burdett and Ferrers feature in the painting, Burdett taking notes and Ferrers seated with his son next to the orrery.
+Ferrers purchased the painting for £210, but the 6th Earl auctioned it off, and it is now held by the Derby Museum and Art Gallery.
+
+=== Detail ===

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+title: "An Experiment on a Bird in the Air Pump"
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+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:37:00.402844+00:00"
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+---
+
+An Experiment on a Bird in the Air Pump followed in 1768, the emotionally charged experiment contrasting with the orderly scene from The Orrery. The painting, which measures 72 by 94½ inches (183 by 244 cm), shows a grey cockatiel fluttering in panic as the air is slowly withdrawn from the vessel by the pump. The witnesses display various emotions: one of the girls worriedly watches the fate of the bird, while the other is too upset to observe and is comforted by her father; two gentlemen (one of them dispassionately timing the experiment) and a boy look on with interest, while the young lovers to the left of the painting are absorbed only in each other. The scientist himself looks directly out of the picture, as if challenging the viewer to judge whether the pumping should continue, killing the bird, or whether the air should be replaced and the cockatiel saved.
+David Solkin suggests that little sympathy is directed toward the bird; the subjects of the painting show the dispassionate detachment of the evolving scientific society. Individuals are concerned for each other: the father for his children, the young man for the girl, but the distress of the cockatiel elicits only careful study. Another reading is that interest in the bird increases from the left side to the right; viewers on the left are scientifically interested (older men and boy) or distracted (young lovers), while those on the right are concerned (girls, older man, assistant) or attending to those who are (father). To one side of the boy assistant at the right side in the rear, the cockatiel's empty cage can be seen on the wall, and to further heighten the drama it is unclear whether the boy is lowering the cage on the pulley to allow the bird to be replaced after the experiment or hoisting the cage back up, certain of its former occupant's death. It has also been suggested that he may be drawing the curtains to block out the light from the full moon. 
+
+Jenny Uglow believes that the boy echoes the figure in the last print of William Hogarth's The Four Stages of Cruelty by pointing out the arrogance and potential cruelty of experimentation, while David Fraser also sees the compositional similarities with the audience grouped round a central demonstration. The neutral stance of the central character and the uncertain intentions of the boy with the cage were both later ideas: an early study, discovered on the back of a self-portrait, omits the boy and shows the natural philosopher reassuring the girls. In this sketch it is obvious that the bird will survive, and thus the composition lacks the power of the final version. Lochlann Jain has analyzed the painting in the context of a contemporary cultural history and medicine of human suffocation and choking.
+Wright, who took many of his subjects from English poetry, probably knew the following passage from "The Wanderer" (1729) by Richard Savage:
+
+So in some Engine, that denies a Vent,
+If unrespiring is some Creature pent,
+It sickens, droops, and pants, and gasps for Breath,
+Sad o'er the Sight swim shad'wy Mists of Death;
+If then kind Air pours powerful in again.
+New Heats, new Pulses quicken ev'ry Vein;
+From the clear'd, lifted, life-rekindled Eye,
+Dispers'd, the dark and dampy Vapours fly.
+
+The cockatiel would have been a rare bird at the time, "and one whose life would never in reality have been risked in an experiment such as this". It did not become well known until after it was shown in illustrations to the accounts of the voyages of Captain Cook in the 1770s. Prior to Cook's voyage, cockatiels had been imported only in small numbers as exotic cage-birds. Wright had painted one in 1762 at the home of William Chase, featuring it both in his portrait of Chase and his wife (Mr & Mrs William Chase) and a separate study, The Parrot. In selecting such a rarity for this scientific sacrifice, Wright not only chose a more dramatic subject than the "lungs-glass", but was perhaps making a statement about the values of society in the Age of Enlightenment. The grey plumage of the cockatiel also shows much more effectively in the darkened room than the small dull-coloured bird in Wright's early oil sketch. A resemblance has been pointed out between the group of the bird and the two nearest figures and a type of depiction of the Trinity found in Early Netherlandish painting, where the Holy Spirit is represented by a dove, to which God the Father (the philosopher) points, while Christ (the father) gestures in blessing to the viewer.
+On the table are various other pieces of equipment that the natural philosopher would have used during his demonstration: a thermometer, candle snuffer and cork, and close to the man seated to the right is a pair of Magdeburg hemispheres, which would have been used with the air pump to demonstrate the difference in pressure exerted by the air and a vacuum: when the air was pumped out from between the two hemispheres they were impossible to pull apart. The air pump itself is rendered in exquisite detail, a faithful record of the designs in use at the time. What may be a human skull in the large liquid-filled glass bowl would not have been a normal piece of equipment; William Schupbach suggests that it and the candle, which is presumably lighting the bowl from behind, form a vanitas—the two symbols of mortality reflecting the cockatiel's struggle for life.
+
+=== Style ===

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+title: "An Experiment on a Bird in the Air Pump"
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+category: "reference"
+tags: "science, encyclopedia"
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+
+The powerful central light source creates a chiaroscuro effect. The light illuminating the scene has been described as "so brilliant it could only be the light of revelation". The single source of light is obscured behind the bowl on the table; some hint of a lamp glass can be seen around the side of the bowl, but David Hockney has suggested that the bowl itself may contain Sulphur, giving a powerful single light source that a candle or oil lamp would not. In the earlier study a candle holder is visible, and the flame is reflected in the bowl. Hockney believes that many of the Old Masters used optical equipment to assist in their painting, and suggests that Wright may have used lenses to transfer the image to paper rather than painting directly from the scene, as he believes the pattern of shadows thrown by the lighting could have been too complicated for Wright to have captured so accurately without assistance. It may be observed, however, that the stand on which the pump is situated casts no shadow on the body of the philosopher, as it could be expected to do.
+Wright's Air Pump was unusual in that it depicted archetypes rather than specific people, though various models for the figures have been suggested. The young lovers may have been based on Thomas Coltman and Mary Barlow, friends of Wright's, whom he later painted in Mr and Mrs Thomas Coltman (also in the National Gallery) after their marriage in 1769; Erasmus Darwin has been suggested as the man timing the experiment on the left of the table, and John Warltire, whom Darwin had invited to help with some air pump experiments in real life, as the natural philosopher; but Wright never identified any of the subjects or suggested they were based on real people.
+In The Orrery, all the subjects have been identified apart from the philosopher, who has physical similarities to Isaac Newton but differs enough to make positive identification impossible. Nicolson detects the strong influence of Frye throughout the picture. Particularly striking is the similarity between Frye's mezzotint Portrait of a Young Man of 1760–1761 and the figure of the boy with his head cocked staring intently at the bird. In 1977, Michael Wynne published one of Frye's chalk drawings from around 1760, An old man leaning on a staff, which is so similar to the observer in the right foreground in Wright's picture to make it impossible that Wright had not seen it. There are other hints of Frye's style in the painting: even the figure of the natural philosopher has touches of Frye's Figure with Candle. Though Henry Fuseli would later also develop on the style of Frye's work there is no evidence of him having painted anything similar until the early 1780s. So, although he had already been in England at the time the Air Pump was produced, it is unlikely that he was an influence on Wright.
+Wright's scientific paintings adopted elements from the tradition of history painting but lacked the heroic central action typical of that genre. While ground-breaking, they are regarded as peculiar to Wright, whose unique style has been explained in many ways. Wright's provincial status and ties to the Lunar Society, a group of prominent industrialists, scientists and intellectuals who met regularly in Birmingham between 1765 and 1813, have been highlighted, as well as his close association with and sympathy for the advances made in the burgeoning Industrial Revolution. Other critics have emphasised a desire to capture a snapshot of the society of the day, in the tradition of William Hogarth but with a more neutral stance that lacks the biting satire of Hogarth's work.
+
+== Reception ==
+
+The scientific subjects of Wright's paintings from this time were meant to appeal to the wealthy scientific circles in which he moved. While never a member himself, he had strong connections with the Lunar Society: he was friends with members John Whitehurst and Erasmus Darwin, as well as Josiah Wedgwood, who later commissioned paintings from him. The inclusion of the moon in the painting was a nod to their monthly meetings, which were held when the moon was full. Like The Orrery, Wright apparently painted Air Pump without a commission, and the picture was purchased by Dr Benjamin Bates, who already owned Wright's Gladiator. An Aylesbury physician, patron of the arts and hedonist, Bates was a diehard member of the Hellfire Club. Wright's account book shows a number of prices for the painting: Pd£200 is shown in one place and £210 in another, but Wright had written to Bates asking for £130, stating that the low price "might much injure me in the future sale of my pictures, and when I send you a receipt for the money I shall acknowledge a greater sum." Whether Bates ever paid the full amount is not recorded; Wright only notes in his account book that he received £30 in part payment. 

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+title: "An Experiment on a Bird in the Air Pump"
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+date_saved: "2026-05-05T09:37:00.402844+00:00"
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+---
+
+Wright exhibited the painting at the Society of Artists Exhibition of 1768 and it was re-exhibited before Christian VII of Denmark in September the same year. Viewers remarked that it was "clever and vigorous", while Gustave Flaubert, who saw it on a visit to England between 1865 and 1866, considered it "charming in naivety and depth". It was popular enough that a mezzotint was engraved from it by Valentine Green which was published by John Boydell on 24 June 1769, and initially sold for 15 shillings. This was reprinted throughout the 18th and 19th centuries, in increasingly weak impressions. Ellis Waterhouse called it "one of the wholly original masterpieces of British art".
+From Bates, the picture passed to Walter Tyrell; another member of the Tyrell family, Edward, presented it to the National Gallery, London, in 1863, after it had failed to sell at an auction at Christie's in 1854. The painting was transferred to the Tate Gallery in 1929, although it was actually on loan to Derby Museum and Art Gallery between 1912 and 1947. It has been lent out for exhibitions to the National Gallery of Art in Washington, D.C., in 1976, the National Museum of Fine Arts in Stockholm in 1979–1980, and Paris (Grand Palais), New York (Metropolitan) and the Tate in London in 1990. It was reclaimed by the National Gallery from the Tate in 1986. They describe its condition as good, with minor alterations visible on some figures. It was last cleaned in 1974. In 2025, it was the subject of its own exhibition at the National Gallery entitled Wright of Derby: From the Shadows. That exhibit prompted a BBC Online article weighing whether it could be considered the first work of modern art.
+The striking scene has been used as the cover illustration for many books on topics both artistic and scientific. It has even spawned pastiches and parodies: the book cover of The Science of Discworld, by Terry Pratchett, Ian Stewart and Jack Cohen, is a tribute to the painting by artist Paul Kidby, who replaces Wright's figures with the book's protagonists. Shelagh Stephenson's play An Experiment with an Air Pump, inspired by the painting, was the joint winner of the 1997 Margaret Ramsay Award and had its premiere at the Royal Exchange Theatre, Manchester, in 1998.
+
+== Notes ==
+
+== References ==
+Baird, Olga (2003). "Joseph Wright of Derby: Art, the Enlightenment and Industrial Revolution". Revolutionary Players – Museums, Libraries and Archives – West Midlands. Archived from the original on 29 September 2007. Retrieved 10 April 2007.
+Boyle, Robert (2003) [1744]. Works of the Honorable Robert Boyle. Kessinger Publishing. p. 740. ISBN 0-7661-6865-4.
+Brooke, John Hedley (1991). Science and Religion: Some Historical Perspectives (Cambridge Studies in the History of Science). Cambridge University Press. p. 434. ISBN 0-521-28374-4.
+Busch, Werner (1986). Joseph Wright of Derby, Das Experiment mit der Luftpumpe: Eine Heilige Allianz zwischen Wissenschaft und Religion. Frankfurt am Main: Fischer.{{cite book}}:  CS1 maint: publisher location (link)
+Egerton, Judy (1990). Wright of Derby. Tate Gallery. p. 296. ISBN 1-85437-037-5.
+Egerton, Judy (1998), National Gallery Catalogues (new series): The British School. catalogue entry pp. 332–343, ISBN 1-85709-170-1
+Elliott, Paul (1 January 2000). "The Birth of Public Science in the English Provinces: Natural Philosophy in Derby, c. 1690–1760". Annals of Science. 57 (1): 61–100. doi:10.1080/000337900296308. S2CID 145603120.
+Harrison, James (2006). Farthing, Stephen (ed.). 1001 Paintings You Must See Before You Die. London: Quintet Publishing Ltd. p. 960. ISBN 1-84403-563-8.
+Hockney, David (2001). Secret Knowledge: Rediscovering the Lost Techniques of the Old Masters. New York: Studio Books. ISBN 0-670-03026-0. OCLC 150844927.{{cite book}}:  CS1 maint: publisher location (link)
+Guilding, Ruth, and others, William Weddell and the transformation of Newby Hall, Jeremy Mills Publishing for Leeds Museums and Galleries, 2004, ISBN 978-0-901981-69-1, Google books
+Jardine, Lisa (2004). The Curious Life of Robert Hooke. HarperCollins. ISBN 0-06-053897-X. OCLC 53276386.
+Jones, Jonathan (1 November 2003). "Yes, it is art". The Guardian. Retrieved 12 January 2007.
+Kimmelman, Michael (7 September 1990). "Review/Art; In Praise of a Neglected Painter of His Time". The New York Times. Retrieved 10 April 2007.
+"An Experiment on a Bird in the Air Pump". The National Gallery. Archived from the original on 7 February 2007. Retrieved 12 January 2007.
+Nicolson, Benedict (1968). Joseph Wright of Derby. The Paul Mellon Foundation for British Art Pantheon Books.
+Shapin, Steven (November 1984). "Pump and Circumstance: Robert Boyle's Literary Technology" (PDF). Social Studies of Science. 14 (4): 481–520. doi:10.1177/030631284014004001. S2CID 5106843. Archived from the original (PDF) on 20 September 2006.
+Solkin, David (1994). "ReWrighting Shaftesbury: The Air Pump and the Limits of Commercial Humanism". In John Brewer (ed.). Early Modern Conceptions of Property (Consumption & Culture in 17th & 18th Centuries). Routledge, an imprint of Taylor & Francis Books Ltd. p. 599. ISBN 0-415-10533-1.
+Uglow, Jenny (2002). The Lunar Men. London: Faber and Faber. p. 588. ISBN 0-571-19647-0.
+Waterhouse, Ellis, (4th Edn, 1978) Painting in Britain, 1530–1790. Penguin Books (now Yale History of Art series), ISBN 0-300-05319-3
+West, John B. (2005). "Robert Boyle's landmark book of 1660 with the first experiments on rarified air". Journal of Applied Physiology. 98 (1): 31–39. doi:10.1152/japplphysiol.00759.2004. PMID 15591301.
+
+== External links ==
+
+Zoomable version of the painting from the National Gallery, London
+An interactive soundscape of the painting

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+---
+title: "Armillary sphere"
+chunk: 1/5
+source: "https://en.wikipedia.org/wiki/Armillary_sphere"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:22.848952+00:00"
+instance: "kb-cron"
+---
+
+An armillary sphere (variations are known as spherical astrolabe, armilla, or armil) is a model of objects in the sky (on the celestial sphere), consisting of a spherical framework of rings, centered on Earth or the Sun, that represent lines of celestial longitude and latitude and other astronomically important features, such as the ecliptic. As such, it differs from a celestial globe, which is a smooth sphere whose principal purpose is to map the constellations. It was invented separately, in ancient China possibly as early as the 4th century BC and ancient Greece during the 3rd century BC, with later uses in the Islamic world and Medieval Europe.
+With the Earth as center, an armillary sphere is known as Ptolemaic. With the Sun as center, it is known as Copernican.
+The flag of Portugal features an armillary sphere. The armillary sphere is also featured in Portuguese heraldry, associated with the Portuguese discoveries during the Age of Exploration. Manuel I of Portugal, for example, took it as one of his symbols where it appeared on his standard, and on early Chinese export ceramics made for the Portuguese court. In the flag of the Empire of Brazil, the armillary sphere is also featured.
+The Beijing Capital International Airport Terminal 3 features a large armillary sphere metal sculpture as an exhibit of Chinese inventions for international and domestic visitors.
+
+== Description and use ==
+
+The exterior parts of this machine are a compages [or framework] of brass rings, which represent the principal circles of the heavens:
+
+The equinoctial A, which is divided into 360 degrees (beginning at its intersection with the ecliptic in Aries) for showing the sun's right ascension in degrees; and also into 24 hours, for showing its right ascension in time.
+The ecliptic B, which is divided into 12 signs, and each sign into 30 degrees, and also into the months and days of the year, in such a manner that the degree or point of the ecliptic on which the sun appears, on any given day, stands over that day in the circle of months.
+The tropic of Cancer C, touching the ecliptic at the beginning of Cancer in e, and the tropic of Capricorn D, touching the ecliptic at the beginning of Capricorn in f; each circle 231⁄2 degrees from the equinoctial circle.
+The Arctic Circle E, and the Antarctic Circle F, each circle 231⁄2 degrees from its respective pole at N and S.
+The equinoctial colure G, passing through the north and south poles of the heavens at N and S, and through the equinoctial points in Aries and Libra, in the ecliptic.
+The solstitial colure H, passing through the poles of the heavens, and through the solstitial points in Cancer and Capricorn, in the ecliptic. Each quarter of the equinoctial colure is divided into 90 degrees, from the equinoctial to the poles of the world, for showing the declination of the sun, moon, and stars; and each quarter of the solstitial colure, from the ecliptic as e and f, to its poles b and d, for showing the latitude of the stars.
+In the north pole of the ecliptic is a nut b, to which is fixed one end of the quadrantal wire.  To the other end is a small sun Y, which is carried around the ecliptic B—B, by turning the nut. In the south pole of the ecliptic is a pin d, on which another quadrantal wire is situated, with a small moon Ζ upon it, which may be moved around by hand. A mechanism causes the moon to move in an orbit which crosses the ecliptic at an angle of 51⁄3 degrees, to opposite points called the lunar nodes, and allows for shifting these points backward in the ecliptic, as the lunar nodes shift in the heavens.
+Within these circular rings is a small terrestrial globe I, fixed on an axis K, which extends from the north and south poles of the globe at n and s, to those of the celestial sphere at N and S. On this axis the flat celestial meridian L is fixed, which may be set directly over the meridian of any place on the globe, so as to keep over the same meridian upon it. This flat meridian is graduated the same way as the brass meridian of the common globe, and its use is much the same.
+To this globe is fitted the movable horizon M, so as to turn upon the two strong wires proceeding from its east and west points to the globe and entering the globe at the opposite points off its equator, which is a movable brass ring set into the globe in a groove all around its equator. The globe may be turned by hand within this ring, so as to place any given meridian upon it, directly under the celestial meridian L. The horizon is divided into 360 degrees all around its outermost edge, within which are the points of the compass, for showing the amplitude of the sun and the moon, both in degrees and points. The celestial meridian L passes through two notches in the north and south points of the horizon, as in a common globe: if the globe is turned around, the horizon and meridian turn with it. At the south pole of the sphere is a circle of 25 hours, fixed to the rings. On the axis is an index which goes around that circle, if the globe is turned around its axis.

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+---
+title: "Armillary sphere"
+chunk: 2/5
+source: "https://en.wikipedia.org/wiki/Armillary_sphere"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:22.848952+00:00"
+instance: "kb-cron"
+---
+
+The globe assembly is supported on a pedestal N, and may be elevated or depressed upon the joint O, to any number of degrees from 0 to 90 by means of the arc P, which is fixed in the strong brass arm Q. The globe assembly slides in the upright piece R, in which is a screw at r, to fix it at any proper elevation.
+In the box T are two wheels (as in Dr Long's sphere) and two pinions, whose axes come out at V and U; either of which may be turned by the small winch W. When the winch is put upon the axis V, and turned backward, the terrestrial globe, with its horizon and celestial meridian, keep at rest; and the whole sphere of circles turns round from east, by south, to west, carrying the sun Y, and moon Z, round the same way, and causing them to rise above and set below the horizon. But when the winch is put upon the axis U, and turned forward, the sphere with the sun and moon keep at rest; and the earth, with its horizon and meridian, turn round from horizon to the sun and moon, to which these bodies came when the earth kept at rest, and they were carried round it; showing that they rise and set in the same points of the horizon, and at the same times in the hour circle, whether the motion be in the earth or in the heaven. If the earthly globe be turned, the hour-index goes round its hour-circle; but if the sphere be turned, the hour-circle goes round below the index.
+And so, by this construction, the machine is equally fitted to show either the real motion of the earth, or the apparent motion of the heavens.
+To reset the sphere for use, one must first slacken the screw r in the upright stem R, and taking hold of the arm Q, move it up or down until the given degree of latitude for any place lies at the side of the stem R; then the axis of the sphere will be properly elevated, so as to stand parallel to the axis of the terrestrial globe, if the globe assembly is to be aligned to north and south by a small compass: once this is done, the user must count the latitude from the north pole, upon the celestial meridian L, down towards the north notch of the horizon, and set the horizon to that latitude. The user then must turn the nut b until the sun Y comes to the given day of the year in the ecliptic, and the sun will be at its proper place for that day.
+To find the place of the moon's ascending node, and also the place of the moon, an ephemeris must be consulted to set them right accordingly. Lastly, the user must turn the winch W, until either the sun comes to the meridian L, or until the meridian comes to the sun (moving the sphere or globe at the user's discretion), and then set the hour-index to the XII, marked noon, the whole sphere will be reset. Then the user must turn the winch, and observe when the sun or moon rises and sets in the horizon. The hour-index will show the times thereof for the given day.
+
+== History ==
+
+=== China ===

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+---
+title: "Armillary sphere"
+chunk: 3/5
+source: "https://en.wikipedia.org/wiki/Armillary_sphere"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:22.848952+00:00"
+instance: "kb-cron"
+---
+
+Throughout Chinese history, astronomers have created celestial globes (Chinese: 渾象; pinyin: húnxiàng) to assist the observation of the stars. The Chinese also used the armillary sphere in aiding calendrical computations and calculations.
+According to Joseph Needham, the earliest development of the armillary sphere in China goes back to the astronomers Shi Shen and Gan De in the 4th century BC, as they were equipped with a primitive single-ring armillary instrument. This would have allowed them to measure the north polar distance (declination) a measurement that gave the position in a xiu (right ascension). Needham's 4th century BC  dating, however, is rejected by British sinologist Christopher Cullen, who traces the beginnings of these devices to the 1st century BC.
+During the Western Han dynasty (202 BC – 9 AD) additional developments made by the astronomers Luoxia Hong (落下閎), Xiangyu Wangren, and Geng Shouchang (耿壽昌) advanced the use of the armillary in its early stage of evolution. In 52 BC, it was the astronomer Geng Shouchang who introduced the first permanently fixed equatorial ring of the armillary sphere. In the subsequent Eastern Han dynasty (23–220 AD) period, the astronomers Fu An and Jia Kui added the ecliptic ring by 84 AD. With the famous statesman, astronomer, and inventor Zhang Heng (張衡, 78–139 AD), the sphere was totally complete in 125 AD, with horizon and meridian rings. The world's first water-powered celestial globe was created by Zhang Heng, who operated his armillary sphere by use of an inflow clepsydra clock.
+Subsequent developments were made after the Han dynasty that improved the use of the armillary sphere. In 323 AD the Chinese astronomer Kong Ting was able to reorganize the arrangement of rings on the armillary sphere so that the ecliptic ring could be pegged on to the equator at any point desired. The Chinese astronomer and mathematician Li Chunfeng (李淳風) of the Tang dynasty created one in 633 AD with three spherical layers to calibrate multiple aspects of astronomical observations, calling them 'nests' (chhung). He was also responsible for proposing a plan of having a sighting tube mounted ecliptically in order for the better observation of celestial latitudes. However, it was the Tang Chinese astronomer, mathematician, and monk Yi Xing in the next century who would accomplish this addition to the model of the armillary sphere. Ecliptical mountings of this sort were found on the armillary instruments of Zhou Cong and Shu Yijian in 1050, as well as Shen Kuo's armillary sphere of the later 11th century, but after that point they were no longer employed on Chinese armillary instruments until the arrival of the European Jesuits.
+
+In 723 AD, Yi Xing (一行) and government official Liang Ling-zan (梁令瓚) combined Zhang Heng's water powered celestial globe with an escapement device. With drums hit every quarter-hour and bells rung automatically every full hour, the device was also a striking clock. The famous clock tower that the Chinese polymath Su Song built by 1094 during the Song dynasty would employ Yi Xing's escapement with waterwheel scoops filled by clepsydra drip, and powered a crowning armillary sphere, a central celestial globe, and mechanically operated manikins that would exit mechanically opened doors of the clock tower at specific times to ring bells and gongs to announce the time, or to hold plaques announcing special times of the day. There was also the scientist and statesman Shen Kuo (1031–1095). Being the head official for the Bureau of Astronomy, Shen Kuo was an avid scholar of astronomy, and improved the designs of several astronomical instruments: the gnomon, armillary sphere, clepsydra clock, and sighting tube fixed to observe the pole star indefinitely. When Jamal al-Din of Bukhara was asked to set up an 'Islamic Astronomical Institution' in Khubilai Khan's new capital during the Yuan dynasty, he commissioned a number of astronomical instruments, including an armillary sphere. It was noted that "Chinese astronomers had been building [them] since at least 1092".
+
+=== Indian Subcontinent ===
+
+The armillary sphere was used for observation in India since early times, and finds mention in the works of Āryabhata (476 CE). The Goladīpikā—a detailed treatise dealing with globes and the armillary sphere was composed between 1380 and 1460 CE by Parameśvara. On the subject of the usage of the armillary sphere in India, Ōhashi (2008) writes: "The Indian armillary sphere (gola-yantra) was based on equatorial coordinates, unlike the Greek armillary sphere, which was based on ecliptical coordinates, although the Indian armillary sphere also had an ecliptical hoop. Probably, the celestial coordinates of the junction stars of the lunar mansions were determined by the armillary sphere since the seventh century or so."
+
+=== Hellenistic world and ancient Rome ===
+
+The Greek astronomer Hipparchus (c. 190 – c. 120 BC) credited Eratosthenes (276 – 194 BC) as the inventor of the armillary sphere. Names of this device in Greek include ἀστρολάβος astrolabos and κρικωτὴ σφαῖρα krikōtē sphaira "ringed sphere". The English name of this device comes ultimately from the Latin armilla (circle, bracelet), since it has a skeleton made of graduated metal circles linking the poles and representing the equator, the ecliptic, meridians and parallels. Usually a ball representing the Earth or, later, the Sun is placed in its center. It is used to demonstrate the motion of the stars around the Earth. Before the advent of the European telescope in the 17th century, the armillary sphere was the prime instrument of all astronomers in determining celestial positions.

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+---
+title: "Armillary sphere"
+chunk: 4/5
+source: "https://en.wikipedia.org/wiki/Armillary_sphere"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:22.848952+00:00"
+instance: "kb-cron"
+---
+
+In its simplest form, consisting of a ring fixed in the plane of the equator, the armilla is one of the most ancient of astronomical instruments. Slightly developed, it was crossed by another ring fixed in the plane of the meridian. The first was an equinoctial, the second a solstitial armilla. Shadows were used as indices of the sun's positions, in combinations with angular divisions. When several rings or circles were combined representing the great circles of the heavens, the instrument became an armillary sphere.
+Armillary spheres were developed by the Hellenistic Greeks and were used as teaching tools already in the 3rd century BC. In larger and more precise forms they were also used as observational instruments. However, the fully developed armillary sphere with nine circles perhaps did not exist until the mid-2nd century AD, during the Roman Empire. Eratosthenes most probably used a solstitial armilla for measuring the obliquity of the ecliptic. Hipparchus probably used an armillary sphere of four rings. The Greco-Roman geographer and astronomer Ptolemy (c. 100 – c. 170 AD) describes his instrument, the astrolabon, in his Almagest. It consisted of at least three rings, with a graduated circle inside of which another could slide, carrying two small tubes positioned opposite each other and supported by a vertical plumb-line.
+
+=== Medieval Middle East and Europe ===
+Persian and Arab astronomers such as Ibrahim al-Fazari and Abbas Ibn Firnas continued to build and improve on armillary spheres. The spherical astrolabe, a variation of both the astrolabe and the armillary sphere, was likely invented during the Middle Ages in the Middle East. About 550 AD, Christian philosopher John Philoponus wrote a treatise on the astrolabe in Greek, which is the earliest extant treatise on the instrument. The earliest description of the spherical astrolabe dates back to the Persian astronomer Nayrizi (fl. 892–902). Pope Sylvester II applied the use of sighting tubes with his armillary sphere in order to fix the position of the pole star and record measurements for the tropics and equator, and used armillary spheres as a teaching device.
+
+=== Korea ===
+
+Chinese ideas of astronomy and astronomical instruments were introduced to Korea, where further advancements were also made. Chang Yŏngsil, a Korean inventor, was ordered by King Sejong the Great of Joseon to build an armillary sphere. The sphere, built in 1433 was named Honcheonui (혼천의,渾天儀).
+The Honcheonsigye, an armillary sphere activated by a working clock mechanism was built by the Korean astronomer Song Iyeong in 1669. It is the only remaining astronomical clock from the Joseon dynasty. The mechanism of the armillary sphere succeeded that of Sejong era's armillary sphere (Honŭi 渾儀, 1435) and celestial sphere (Honsang 渾象, 1435), and the Jade Clepsydra (Ongnu 玉漏, 1438)'s sun-carriage apparatus. Such mechanisms are similar to Ch'oe Yu-ji (崔攸之, 1603~1673)'s armillary sphere(1657). The structure of time going train and the mechanism of striking-release in the part of clock is influenced by the crown escapement which has been developed from 14th century, and is applied to gear system which had been improved until the middle of 17th century in Western-style clockwork. In particular, timing device of Song I-yŏng's Armillary Clock adopts the early 17th century pendulum clock system which could remarkably improve the accuracy of a clock.
+
+=== Renaissance ===
+Further advances in this instrument were made by Danish astronomer Tycho Brahe (1546–1601), who constructed three large armillary spheres which he used for highly precise measurements of the positions of the stars and planets. They were described in his Astronomiae Instauratae Mechanica.
+Armillary spheres were among the first complex mechanical devices. Their development led to many improvements in techniques and design of all mechanical devices. Renaissance scientists and public figures often had their portraits painted showing them with one hand on an armillary sphere, which represented the zenith of wisdom and knowledge.
+The armillary sphere survives as useful for teaching, and may be described as a skeleton celestial globe, the series of rings representing the great circles of the heavens, and revolving on an axis within a horizon. With the earth as center such a sphere is known as Ptolemaic; with the sun as center, as Copernican.
+
+A representation of an armillary sphere is present in the modern flag of Portugal and has been a national symbol since the reign of Manuel I.
+
+== Paralympic Games ==
+An artwork-based model of an Armillary sphere has been used since the March 1, 2014 to light the Paralympic heritage flame at Stoke Mandeville Stadium, United Kingdom.  The sphere includes a wheelchair that the user can rotate to spark the flame as part of a ceremony to celebrate the past, present and future of the Paralympic Movement in the UK.  The Armillary Sphere was created by artist Jon Bausor and will be used for future Heritage Flame events.  The flame in the first-ever ceremony was lit by London 2012 gold medallist Hannah Cockroft.
+
+== Heraldry and vexillology ==

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+---
+title: "Armillary sphere"
+chunk: 5/5
+source: "https://en.wikipedia.org/wiki/Armillary_sphere"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:22.848952+00:00"
+instance: "kb-cron"
+---
+
+The armillary sphere is commonly used in heraldry and vexillology, being mainly known as a symbol associated with Portugal, the Portuguese Empire and the Portuguese discoveries.
+In the end of the 15th century, the armillary sphere became the personal heraldic badge of the future King Manuel I of Portugal, when he was still a Prince. The intense use of this badge in documents, monuments, flags and other supports, during the reign of Manuel I, transformed the armillary sphere from a simple personal symbol to a national one that represented the Kingdom of Portugal and in particular its Overseas Empire. As a national symbol, the armillary sphere continued in use after the death of Manuel I.
+In the 17th century, it became associated with the Portuguese dominion of Brazil. In 1815, when Brazil gained the status of kingdom united with that of Portugal, its coat of arms was formalized as a golden armillary sphere in a blue field. Representing Brazil, the armillary sphere became also present in the arms and the flag of the United Kingdom of Portugal, Brazil and the Algarves. When Brazil became independent as an empire in 1822, the armillary sphere continued to be present in its national arms and in its national flag. The celestial sphere of the present Flag of Brazil replaced the armillary sphere in 1889.
+The armillary sphere was reintroduced in the national arms and in the national Flag of Portugal in 1911.
+
+== See also ==
+
+== References ==
+
+=== Sources ===
+Encyclopædia Britannica (1771), "Geography".
+Darlington, Oscar G. "Gerbert, the Teacher," The American Historical Review (Volume 52, Number 3, 1947): 456–476.
+Kern, Ralf: Wissenschaftliche Instrumente in ihrer Zeit. Vom 15. – 19. Jahrhundert. Verlag der Buchhandlung Walther König 2010, ISBN 978-3-86560-772-0
+Needham, Joseph (1986). Science and Civilization in China: Volume 3. Taipei: Caves Books, Ltd.
+Sivin, Nathan (1995). Science in Ancient China. Brookfield, Vermont: VARIORUM, Ashgate Publishing
+Williams, Henry Smith (2004). A History Of Science. Whitefish, MT: Kessinger Publishing. ISBN 1-4191-0163-3.
+
+== External links ==
+
+Starry Messenger Archived 2014-10-12 at the Wayback Machine
+Armillary Spheres and Teaching Astronomy | Whipple Museum
+AstroMedia* Verlag in Germany offers a cardboard construction kit for an armillary sphere ("Das Kleine Tischplanetarium")

data/en.wikipedia.org/wiki/Astatic_needles-0.md

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+---
+title: "Astatic needles"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Astatic_needles"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:24.009462+00:00"
+instance: "kb-cron"
+---
+
+An astatic system comprises two equal and parallel magnetic needles, but with their polarities reversed. This arrangement protects the system from the influence of the terrestrial magnetic field, as the magnetisms of the two needles cancel each other out. Because of this phenomenon, astatic needles were often used in galvanometers.
+
+
+== References ==
+"Museo Galileo - object description".
+"Static Needles - Joseph Henry Project - Princeton University".

data/en.wikipedia.org/wiki/Astrarium-0.md

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+---
+title: "Astrarium"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Astrarium"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:25.196479+00:00"
+instance: "kb-cron"
+---
+
+An astrarium, also called a planetarium, is a medieval astronomical clock made in the 14th century by Italian engineer and astronomer Giovanni Dondi dell'Orologio. The Astrarium was modeled after the Solar System and, in addition to counting time and representing calendar dates and holidays, showed how the planets moved around the celestial sphere in one timepiece. This was its main task, in comparison with the astronomical clock, the main task of which is the actual reading of time. A complex mechanism, it combined the functions of a modern planetarium, clock, and calendar into a singular constructive device. Devices that perform this function were known to have been created prior to the design of Dondi, though relatively little is known about them. It is occasionally erroneously claimed by the details of some sources that the Astrarium was the first mechanical device showing the movements of the planets.
+
+
+== History ==
+
+
+=== Greek and Roman World ===
+The first astraria were mechanical devices. Archimedes is said to have used a primitive version that could predict the positions of the Sun, the Moon, and the planets. On May 17, 1902, an archaeologist named Valerios Stais discovered that a lump of oxidated material, which had been recovered from a shipwreck near the Greek island of Antikythera, held within it a mechanism with cogwheels. This mechanism, known as the Antikythera mechanism, was recently redated to end of the 2nd century BCE. Extensive study of the fragments, using X-rays, has revealed enough details (gears, pinions, crank) to enable researchers to build partial replicas of the original device. Engraved on the major gears are the names of the planets, which leaves little doubt as to the intended use of the mechanism.
+By the collapse of the Roman Empire, the know-how and science behind this piece of clockwork was lost.
+
+
+=== Middle Ages and Renaissance ===
+According to historians Bedini and Maddison, the earliest astrarium clock with an "almost complete description and incontestable documentation" to have survived is the astrarium completed in 1364 by Giovanni de' Dondi (1318–1388), a scholar and physician of the Middle Ages. The original clock, consisting of 107 wheels and pinions, has been lost, perhaps during the sacking of Mantua in 1630, but de' Dondi left detailed descriptions, which have survived, enabling a reconstruction of the clock. It displays the mean time, sidereal (or star) time and the motions of the Sun, Moon and the five then-known planets Mercury, Venus, Mars, Jupiter, and Saturn. It was conceived according to a Ptolemaic conception of the Solar System. De' Dondi was inspired by his father Jacopo who designed the astronomical clock in the Piazzi dei Signori, Padua, in 1344 – one of the first of its type.
+In later ages, more astraria were built. A famous example is the Eise Eisinga Planetarium, built in 1774 by Eise Eisinga from Dronrijp, Friesland, the Netherlands. It displayed all the planets and was fixed to the ceiling in a house in Franeker, where it can still be visited.
+In modern times, the astrarium has grown into a tourist attraction as a commercially exploited planetarium-showing in IMAX theaters, with such presentations as The History of the Universe, as well as other astronomical phenomena.
+
+
+== See also ==
+Astronomical clock
+Orrery
+Planetarium
+
+
+== References ==
+
+
+== Literature ==
+Giovanni Dondi dell'Orologio – "Tractatus astarii"
+
+
+== External links ==
+Annosphere An electro-mechanical model of the Earth/Sun relationship.
+Science and Society Picture Library: - a picture of De Dondi’s "Astrarium", the world’s first astronomical clock, 1364.
+de Dondi's Astrarium Hi-Tech, 14th Century style
+Het Eise Eisinga Planetarium
+Solar tempometer An astrarium clock running to the Sun.

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+---
+title: "Astrolabe"
+chunk: 1/5
+source: "https://en.wikipedia.org/wiki/Astrolabe"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:26.368952+00:00"
+instance: "kb-cron"
+---
+
+An astrolabe (Ancient Greek: ἀστρολάβος, romanized: astrolábos, lit. 'star-taker'; Arabic: ٱلأَسْطُرلاب, romanized: al-Asṭurlāb; Persian: ستاره‌یاب, romanized: Setāreyāb) is an astronomical instrument dating to ancient times. It serves as a star chart and physical model of the visible half-dome of the sky. Its various functions also make it an elaborate inclinometer and an analog calculation device capable of working out several kinds of problems in astronomy. In its simplest form it is a metal disc with a pattern of wires, cutouts, and perforations that allows a user to calculate astronomical positions precisely. It is able to measure the altitude above the horizon of a celestial body, day or night; it can be used to identify stars or planets, to determine local latitude given local time (and vice versa), to survey, or to triangulate. It was used in classical antiquity, the Byzantine Empire, the Islamic Golden Age, the European Middle Ages and the Age of Discovery for all these purposes.
+The astrolabe, which is a precursor to the sextant,
+is effective for determining latitude on land or calm seas. Although it is less reliable on the heaving deck of a ship in rough seas, the mariner's astrolabe was developed to solve that problem.
+
+== Applications ==
+
+The 10th century astronomer ʿAbd al-Raḥmān al-Ṣūfī wrote a massive text of 386 chapters on the astrolabe, which reportedly described more than 1,000 applications for the astrolabe's various functions.
+These ranged from the astrological, the astronomical and the religious, to navigation, seasonal and daily time-keeping, and tide tables. At the time of their use, astrology was widely considered as much of a serious science as astronomy, and study of the two went hand-in-hand. The astronomical interest varied between folk astronomy (of the pre-Islamic tradition in Arabia) which was concerned with celestial and seasonal observations, and mathematical astronomy, which would inform intellectual practices and precise calculations based on astronomical observations. In regard to the astrolabe's religious function, the demands of Islamic prayer times were to be astronomically determined to ensure precise daily timings, and the qibla, the direction of Mecca towards which Muslims must pray, could also be determined by this device. In addition to this, the lunar calendar that was informed by the calculations of the astrolabe was of great significance to the religion of Islam, given that it determines the dates of important religious observances such as Ramadan.
+
+== Etymology ==
+The Oxford English Dictionary gives the translation "star-taker" for the English word astrolabe and traces it through medieval Latin to the Greek word ἀστρολάβος: astrolábos,
+from ἄστρον: astron "star", and λαμβάνειν: lambanein "to take".
+In the medieval Islamic world the Arabic word al-asturlāb (i.e., astrolabe) was given various etymologies. In Arabic texts, the word is translated as ākhidhu al-nujūm (Arabic: آخِذُ ٱلنُّجُومْ, lit. 'star-taker') – a direct translation of the Greek word.
+Al-Biruni quotes and criticises medieval scientist Hamza al-Isfahani, who stated:
+
+"asturlab is an Arabisation of this Persian phrase" (sitara yab, meaning "taker of the stars").
+In medieval Islamic sources, there is also a folk etymology of the word as "lines of lab", where "Lab" refers to a certain son of Idris (Enoch). This etymology is mentioned by a 10th century scientist named al-Qummi but rejected by al-Khwarizmi.
+
+== History ==
+
+=== Ancient era ===
+An astrolabe is essentially a plane (two-dimensional) version of an armillary sphere, which had already been invented in the Hellenistic period and had probably been used by Hipparchus to produce his star catalogue. Theon of Alexandria (c. 335–405) wrote a detailed treatise on the astrolabe. The invention of the plane astrolabe is sometimes wrongly attributed to Theon's daughter Hypatia (born c. 350–370; died 415 ce),
+but it is known to have been used much earlier.
+The misattribution comes from a misinterpretation of a statement in a letter written by Hypatia's pupil Synesius (c. 373–414),
+which mentions that Hypatia had taught him how to construct a plane astrolabe, but does not say that she invented it.
+Lewis argues that Ptolemy used an astrolabe to make the astronomical observations recorded in the Tetrabiblos. However, Emilie Savage-Smith notes
+
+"there is no convincing evidence that Ptolemy or any of his predecessors knew about the planispheric astrolabe".
+
+In chapter 5.1 of the Almagest, Ptolemy describes the construction of an armillary sphere, and it is usually assumed that this was the instrument he used.
+Astrolabes continued to be used in the Byzantine Empire. Christian philosopher John Philoponus wrote a treatise (c. 550) on the astrolabe in Greek, which is the earliest extant treatise on the instrument.
+Mesopotamian bishop Severus Sebokht also wrote a treatise on the astrolabe in the Syriac language during the mid-7th century.
+Sebokht refers to the astrolabe as being made of brass in the introduction of his treatise, indicating that metal astrolabes were known in the Christian East well before they were developed in the Islamic world or in the Latin West.
+
+=== Medieval era ===
+Astrolabes were further developed in the medieval Islamic world, where Muslim astronomers introduced angular scales to the design, adding circles indicating azimuths on the horizon. It was widely used throughout the Muslim world, chiefly as an aid to navigation and as a way of finding the Qibla, the direction of Mecca. Eighth-century mathematician Muhammad al-Fazari is the first person credited with building the astrolabe in the Islamic world. The earliest Arabic treatise on astrolabes was composed sometime around 815 CE.
+The mathematical background was established by Muslim astronomer Albatenius in his treatise Kitab az-Zij (c. 920 ce), which was translated into Latin by Plato Tiburtinus (De Motu Stellarum). The earliest surviving astrolabe is dated AH 315 (927–928 ce). In the Islamic world, astrolabes were used to find the times of sunrise and the rising of fixed stars, to help schedule morning prayers (salat). In the 10th century, al-Sufi first described over 1,000 different uses of an astrolabe, in areas as diverse as astronomy, astrology, navigation, surveying, timekeeping, prayer, Salat, Qibla, etc.

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+---
+title: "Astrolabe"
+chunk: 2/5
+source: "https://en.wikipedia.org/wiki/Astrolabe"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:26.368952+00:00"
+instance: "kb-cron"
+---
+
+The spherical astrolabe was a variation of both the astrolabe and the armillary sphere, invented during the Middle Ages by astronomers and inventors in the Islamic world.
+The earliest description of the spherical astrolabe dates to Al-Nayrizi (fl. 892–902). In the 12th century, Sharaf al-Dīn al-Tūsī invented the linear astrolabe, sometimes called the "staff of al-Tusi", which was
+
+"a simple wooden rod with graduated markings, but without sights. It was furnished with a plumb line and a double chord for making angular measurements and bore a perforated pointer". The geared mechanical astrolabe was invented by Abi Bakr of Isfahan in 1235.
+The first known metal astrolabe in Western Europe is the Destombes astrolabe made from brass in the eleventh century in Portugal. Metal astrolabes avoided the warping that large wooden ones were prone to, allowing the construction of larger and therefore more accurate instruments. Metal astrolabes were heavier than wooden instruments of the same size, making it difficult to use them in navigation.
+
+Herman Contractus of Reichenau Abbey, examined the use of the astrolabe in Mensura Astrolai during the 11th century.
+Peter of Maricourt wrote a treatise on the construction and use of a universal astrolabe in the last half of the 13th century entitled Nova compositio astrolabii particularis. Universal astrolabes can be found at the History of Science Museum, Oxford. David A. King, historian of Islamic instrumentation, describes the universal astrolobe designed by Ibn al-Sarraj of Aleppo (a.k.a. Ahmad bin Abi Bakr; fl. 1328) as "the most sophisticated astronomical instrument from the entire Medieval and Renaissance periods".
+English author Geoffrey Chaucer (c. 1343–1400) compiled A Treatise on the Astrolabe for his son, mainly based on a work by Messahalla or Ibn al-Saffar.
+The same source was translated by French astronomer and astrologer Pélerin de Prusse and others. The first printed book on the astrolabe was Composition and Use of Astrolabe by Christian of Prachatice, also using Messahalla, but relatively original.
+A simplified astrolabe, known as a balesilha, was used by sailors to get an accurate reading of latitude while at sea. The use of the balesilha was promoted by Prince Henry (1394–1460) while navigating for Portugal.
+
+The astrolabe was almost certainly first brought north of the Pyrenees by Gerbert of Aurillac (future Pope Sylvester II), where it was integrated into the quadrivium at the school in Reims, France, sometime before the turn of the 11th century. In the 15th century, French instrument maker Jean Fusoris (c. 1365–1436) also started remaking and selling astrolabes in his shop in Paris, along with portable sundials and other popular scientific devices of the day. Thirteen of his astrolabes survive to this day.  One more special example of craftsmanship in early 15th-century Europe is the astrolabe designed by Antonius de Pacento and made by Dominicus de Lanzano, dated 1420.
+In the 16th century, Johannes Stöffler published Elucidatio fabricae ususque astrolabii, a manual of the construction and use of the astrolabe. Four identical 16th century astrolabes made by Georg Hartmann provide some of the earliest evidence for batch production by division of labor.
+Greek painter Ieremias Palladas incorporated a sophisticated astrolabe in his 1612 painting depicting Catherine of Alexandria. The painting, entitled Catherine of Alexandria, in addition to the saint, showed a device labelled the 'system of the universe' (Σύστημα τοῦ Παντός). The device featured the classical planets with their Greek names: Helios (Sun), Selene (Moon), Hermes (Mercury), Aphrodite (Venus), Ares (Mars), Zeus (Jupiter), and Cronos (Saturn). The depicted device also had celestial spheres, following the Ptolemaic model, and Earth was shown as a blue sphere with circles of geographic coordinates. A complicated line representing the axis of the Earth covered the entire instrument.
+
+=== Sanskrit works ===
+
+==== Yantrarāja ====
+
+In 1370, the first Indian treatise on the astrolabe was written by the Jain astronomer Mahendra Suri, titled Yantrarāja. With the support and patronage of Firuz Shah Tughlaq, Mahendra Sūri composed the first ever Sanskrit manual on astrolabes. It was Sūri who coined the Sanskrit name "Yantrarāja" ("the king of astronomical instruments") for the astrolabe and he also titled his manual on astrolabes as Yantrarāja. Sūri composed the manual in 1370 CE. Mahendra Sūri's student Malayendu Sūri composed a commentary on Yantrarāja in 1382. Two other commentaries on Yantrarāja are known, one by Gopirāja written in 1540 and other by Yajñeśvara in 1842.
+The Yantrarāja manual in 128 verses is divided into five chapters. The first chapter Gaṇitādhyāya discusses the theory behind the astrolabe. The second chapter Yantraghatanādhyāya is devoted to descriptions of the various components of the astrolabe.  The third chapter Yantraracanādhyāya describes the details of the construction of the astrolabe. The fourth chapter Yantrasodhanādhyāya discusses method for ascertaining whether the astrolabe has been properly constructed. It is in the fifth and final chapter Yantravicāraṇādhyāya one can see descriptions on how to use the instrument for observational and computational purposes. This chapter also dwells on the different types of astronomical and trigonometrical problems that can be solved using the astrolabe.
+While Mahendra Sūri's manual is in 128 verses and contains no data in the form of tables, Malayendu Sūri's commentary is interspersed with neatly prepared tables.
+
+==== Other Sanskrit works on astrolabe ====
+Over the centuries since the publication of Mahendra Sūri's Yantrarāja in 1370, several other Sanskrit manuals on the astrolabe have been composed. These include the following:
+
+Yantra-rāja-adhikāra (Chapter 1 of Yantrakiraṇāvalī) by Padmanābha in 1423
+Turya-yantra-prakāśa by Bhūdhara in 1572
+Yantrarāja-vicāra-vimśādhyāyī by Nayanasukhopādhyāya in 1730
+Yantrarāja-racanā by Savāī Jaya Siṃha (1688 - 1743)
+yantrarāja-kalpa by Mathurānātha Śukla (1782)
+
+=== Astrolabes and clocks ===

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+---
+title: "Astrolabe"
+chunk: 3/5
+source: "https://en.wikipedia.org/wiki/Astrolabe"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:26.368952+00:00"
+instance: "kb-cron"
+---
+
+Mechanical astronomical clocks were initially influenced by the astrolabe; they could be seen in many ways as clockwork astrolabes designed to produce a continual display of the current position of the sun, stars, and planets. For example, Richard of Wallingford's clock (c. 1330) consisted essentially of a star map rotating behind a fixed rete, similar to that of an astrolabe.
+Many astronomical clocks use an astrolabe-style display, such as the famous clock at Prague, adopting a stereographic projection (see below) of the ecliptic plane. In recent times, astrolabe watches have become popular. For example, Swiss watchmaker Ludwig Oechslin designed and built an astrolabe wristwatch in conjunction with Ulysse Nardin in 1985. Dutch watchmaker Christaan van der Klauuw also manufactures astrolabe watches today.
+
+== Construction ==
+An astrolabe consists of a disk with a wide, raised rim, called the mater (mother), which is deep enough to hold one or more flat plates called tympans, or climates. A tympan is made for a specific latitude and is engraved with a stereographic projection of circles denoting azimuth and altitude and representing the portion of the celestial sphere above the local horizon. The rim of the mater is typically graduated into hours of time, degrees of arc, or both.
+Above the mater and tympan, the rete, a framework bearing a projection of the ecliptic plane and several pointers indicating the positions of the brightest stars, is free to rotate. These pointers are often just simple points, but depending on the skill of the craftsman can be very elaborate and artistic. There are examples of astrolabes with artistic pointers in the shape of balls, stars, snakes, hands, dogs' heads, and leaves, among others. The names of the indicated stars were often engraved on the pointers in Arabic or Latin. Some astrolabes have a narrow rule or label which rotates over the rete, and may be marked with a scale of declinations.
+The rete, representing the sky, functions as a star chart. When it is rotated, the stars and the ecliptic move over the projection of the coordinates on the tympan. One complete rotation corresponds to the passage of a day. The astrolabe is, therefore, a predecessor of the modern planisphere.
+On the back of the mater, there is often engraved a number of scales that are useful in the astrolabe's various applications. These vary from designer to designer, but might include curves for time conversions, a calendar for converting the day of the month to the sun's position on the ecliptic, trigonometric scales, and graduation of 360 degrees around the back edge. The alidade is attached to the back face. An alidade can be seen in the lower right illustration of the Persian astrolabe above. When the astrolabe is held vertically, the alidade can be rotated and the sun or a star sighted along its length, so that its altitude in degrees can be read ("taken") from the graduated edge of the astrolabe; hence the word's Greek roots: "astron" (ἄστρον) = star + "lab-" (λαβ-) = to take. The alidade had vertical and horizontal cross-hairs which plots locations on an azimuthal ring called an almucantar (altitude-distance circle).
+An arm called a radius connects from the center of the astrolabe to the optical axis which is parallel with another arm also called a radius. The other radius contains graduations of altitude and distance measurements.
+A shadow square also appears on the back of some astrolabes, developed by Muslim astrologists in the 9th Century, whereas devices of the Ancient Greek tradition featured only altitude scales on the back of the devices. This was used to convert shadow lengths and the altitude of the sun, the uses of which were various from surveying to measuring inaccessible heights.
+Devices were usually signed by their maker with an inscription appearing on the back of the astrolabe, and if there was a patron of the object, their name would appear inscribed on the front, or in some cases, the name of the reigning sultan or the teacher of the astrolabist has also been found to appear inscribed in this place. The date of the astrolabe's construction was often also signed. The inscriptions on astrolabes also allowed historians to conclude that astronomers tended to make their own astrolabes, but that many were also made to order and kept in stock to sell, suggesting there was some contemporary market for the devices.
+
+== Mathematical basis ==
+The construction and design of astrolabes are based on the application of the stereographic projection of the celestial sphere. The point from which the projection is usually made is the South Pole. The plane onto which the projection is made is that of the Equator.
+
+=== Designing a tympanum through stereographic projection ===
+
+The tympanum captures the celestial coordinate axes upon which the rete will rotate. It is the component that will enable the precise determination of a star's position at a specific time of day and year.
+Therefore, it should project:
+
+The zenith, which will vary depending on the latitude of the astrolabe user.
+The horizon line and almucantar or circles parallel to the horizon, which will allow for the determination of a celestial body's altitude (from the horizon to the zenith).
+The celestial meridian (north-south meridian, passing through the zenith) and secondary meridians (circles intersecting the north-south meridian at the zenith), which will enable the measurement of azimuth for a celestial body.
+The three main circles of latitude (Capricorn, Equator, and Cancer) to determine the exact moments of solstices and equinoxes throughout the year.
+
+==== The tropics and the equator define the tympanum ====
+
+On the right side of the image above:

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+---
+title: "Astrolabe"
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+category: "reference"
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+date_saved: "2026-05-05T09:36:26.368952+00:00"
+instance: "kb-cron"
+---
+
+  The blue sphere represents the celestial sphere.
+  The blue arrow indicates the direction of true north (the North Star).
+  The central blue point represents Earth (the observer's location).
+  The geographic south of the celestial sphere acts as the projection pole.
+  The celestial equatorial plane serves as the projection plane.
+Three parallel circles represent the projection on the celestial sphere of Earth's main circles of latitude:
+  In orange, the celestial Tropic of Cancer.
+  In purple, the celestial equator.
+  In green, the celestial Tropic of Capricorn.
+When projecting onto the celestial equatorial plane, three concentric circles correspond to the celestial sphere's three circles of latitude (left side of the image). The largest of these, the projection on the celestial equatorial plane of the celestial Tropic of Capricorn, defines the size of the astrolabe's tympanum. The center of the tympanum (and the center of the three circles) is actually the north-south axis around which Earth rotates, and therefore, the rete of the astrolabe will rotate around this point as the hours of the day pass (due to Earth's rotational motion).
+The three concentric circles on the tympanum are useful for determining the exact moments of solstices and equinoxes throughout the year: if the sun's altitude at noon on the rete is known and coincides with the outer circle of the tympanum (Tropic of Capricorn), it signifies the winter solstice (the sun will be at the zenith for an observer at the Tropic of Capricorn, meaning summer in the southern hemisphere and winter in the northern hemisphere). If, on the other hand, its altitude coincides with the inner circle (Tropic of Cancer), it indicates the summer solstice. If its altitude is on the middle circle (equator), it corresponds to one of the two equinoxes.
+
+==== The horizon and the measurement of altitude ====
+
+On the right side of the image above:
+
+  The blue arrow indicates the direction of true north (the North Star).
+  The central blue point represents Earth (the observer's location).
+  The black arrow represents the zenith direction for the observer (which would vary depending on the observer's latitude).
+  The two black circles represent the horizon surrounding the observer, which is perpendicular to the zenith vector and defines the portion of the celestial sphere visible to the observer, and its projection on the celestial equatorial plane.
+  The geographic south of the celestial sphere acts as the projection pole.
+  The celestial equatorial plane serves as the projection plane.
+When projecting the horizon onto the celestial equatorial plane, it transforms into an ellipse upward-shifted relatively to the center of the tympanum (both the observer and the projection of the north-south axis). This implies that a portion of the celestial sphere will fall outside the outer circle of the tympanum (the projection of the celestial Tropic of Capricorn) and, therefore, won't be represented.
+
+Additionally, when drawing circles parallel to the horizon up to the zenith (almucantar), and projecting them on the celestial equatorial plane, as in the image above, a grid of consecutive ellipses is constructed, allowing for the determination of a star's altitude when its rete overlaps with the designed tympanum.
+
+==== The meridians and the measurement of azimuth ====
+
+On the right side of the image above:
+
+  The blue arrow indicates the direction of true north (the North Star).
+  The central blue point represents Earth (the observer's location).
+  The black arrow represents the zenith direction for the observer (which would vary depending on the observer's latitude).
+  The two black circles represent the horizon surrounding the observer, which is perpendicular to the zenith vector and defines the portion of the celestial sphere visible to the observer, and its projection on the celestial equatorial plane.
+  The five red dots represent the zenith, the nadir (the point on the celestial sphere opposite the zenith with respect to the observer), their projections on the celestial equatorial plane, and the center (with no physical meaning attached) of the circle obtained by projecting the secondary meridian (see below) on the celestial equatorial plane.
+  The orange circle represents the celestial meridian (or meridian that goes, for the observer, from the north of the horizon to the south of the horizon passing through the zenith).
+  The two red circles represent a secondary meridian with an azimuth of 40° East relative to the observer's horizon (which, like all secondary meridians, intersects the principal meridian at the zenith and nadir), and its projection on the celestial equatorial plane.
+  The geographic south of the celestial sphere acts as the projection pole.
+  The celestial equatorial plane serves as the projection plane.
+When projecting the celestial meridian, it results in a straight line that overlaps with the vertical axis of the tympanum, where the zenith and nadir are located. However, when projecting the 40° E meridian, another circle is obtained that passes through both the zenith and nadir projections, so its center is located on the perpendicular bisection of the segment connecting both points. Indeed, the projection of the celestial meridian can be considered as a circle with an infinite radius (a straight line) whose center is on this bisection and at an infinite distance from these two points.
+If successive meridians that divide the celestial sphere into equal sectors (like "orange slices" radiating from the zenith) are projected, a family of curves passing through the zenith projection on the tympanum is obtained. These curves, once overlaid with the rete containing the major stars, allow for determining the azimuth of a star located on the rete and rotated for a specific time of day.
+
+== See also ==
+
+== Footnotes ==
+
+== References ==

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+---
+title: "Astrolabe"
+chunk: 5/5
+source: "https://en.wikipedia.org/wiki/Astrolabe"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:26.368952+00:00"
+instance: "kb-cron"
+---
+
+== Bibliography ==
+Evans, James (1998), The History and Practice of Ancient Astronomy, Oxford University Press, ISBN 0-19-509539-1
+Stöffler, Johannes (2007) [First published 1513], Stoeffler's Elucidatio – The Construction and Use of the Astrolabe [Elucidatio Fabricae Ususque Astrolabii], translated by Gunella, Alessandro; Lamprey, John, John Lamprey, ISBN 978-1-4243-3502-2
+King, D. A. (1981), "The Origin of the Astrolabe According to the Medieval Islamic Sources", Journal for the History of Arabic Science, 5: 43–83
+King, Henry (1978), Geared to the Stars: the Evolution of Planetariums, Orreries, and Astronomical Clocks, University of Toronto Press, ISBN 978-0-8020-2312-4
+Krebs, Robert E.; Krebs, Carolyn A. (2003), Groundbreaking Scientific Experiments, Inventions, and Discoveries of the Ancient World, Greenwood Press, ISBN 978-0-313-31342-4
+Laird, Edgar (1997), Carol Poster and Richard Utz (ed.), "Astrolabes and the Construction of Time in the Late Middle Ages", Constructions of Time in the Late Middle Ages, Evanston, Illinois: Northwestern University Press: 51–69
+Laird, Edgar; Fischer, Robert, eds. (1995), "Critical edition of Pélerin de Prusse on the Astrolabe (translation of Practique de Astralabe)", Medieval & Renaissance Texts & Studies, Binghamton, New York, ISBN 0-86698-132-2{{citation}}:  CS1 maint: work parameter with ISBN (link)
+Lewis, M. J. T. (2001), Surveying Instruments of Greece and Rome, Cambridge University Press, ISBN 978-0-511-48303-5
+Morrison, James E. (2007), The Astrolabe, Janus, ISBN 978-0-939320-30-1
+Neugebauer, Otto E. (1975), A History of Ancient Mathematical Astronomy, Springer, ISBN 978-3-642-61912-0
+North, John David (2005), God's Clockmaker: Richard of Wallingford and the Invention of Time, Continuum International Publishing Group, ISBN 978-1-85285-451-5
+
+== Further reading ==
+For a scanned copy of a manuscript of the treatise Yantrarāja published by S. Dvivedi and Lattara Sarma, Benaras, 1883: Yantraraja (Internet Archive) (Retrieved on 21 December 2023.)
+For a detailed description of an astrolabe constructed in India in 1664 CE and now preserved in Edinburgh Museum: Sreemula Rajeswara Sarma (July 2006). Yantraraja at Edinburgh: On a Sanskrit Astrolabe made for Manirama in ad 1644. Edinburgh: Organising Committee of 13th World Sanskrit Conference. Retrieved 21 December 2023. (In proceedings of the 13th World Sanskrit Conference, held in Edinburgh, 10–14 July 2006, pages 77 – 110)
+Yukio Ohashi (1997). "Early History of the Astrolabe in India" (PDF). Indian Journal of History of Science. 32 (3): 199–295. Retrieved 21 December 2023. This paper includes the full text and English translation of a treatise titled Yantrarāja-adhikāra composed by Padmanābha in 1423 CE.
+Sreeramula Rajeswara Sarma (2008). The Archaic and the Exotic: Studies in the History of Indian Astronomical Instruments. New Delhi: Manohar Publishers and Distributors. ISBN 978-8173045714. Part III of the book containing five articles on astrolabe provides an exhaustive account of the history, construction, distribution and descriptions of the astrolabes in India.
+For a critical assessment of the correctness or otherwise of the statements in Yantrarāja: Kim Plofker (February 2000). "The astrolabe and spherical trigonometry in medieval India". Journal for the History of Astronomy: 37–54. Retrieved 21 December 2023.
+
+== External links ==
+
+Interactive digital astrolabe by Alex Boxer
+A digital astrolabe (HTML5 and javascript)
+Astrolabe Tech Made ... Not So Easy
+Paper astrolabe generator, from the ESO
+Printable astrolabe for every 10° of latitude up to 60°, by John Krieger, Lyncean Education (2023)
+"Hello World!" for the Astrolabe: The First Computer Video of Howard Covitz's Presentation at Ignite Phoenix, June 2009. Slides for Presentation Licensed as Creative Commons by-nc-nd.
+Video of Tom Wujec demonstrating an astrolabe.  Taken at TEDGlobal 2009. Includes clickable transcript. Licensed as Creative Commons by-nc-nd.
+Archive of James E. Morrison's extensive website on Astrolabes
+Fully illustrated online catalogue of world's largest collection of astrolabes
+Mobile astrolabe and horologium
+Medieval equal hour horary quadrant
+A Beginner's Guide to Basic Construction and Use of the Astrolabe (using ruler, protractor and compasses) (PDF), archived from the original (PDF) on 17 June 2015, retrieved 26 October 2018

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+title: "Astronomical clock"
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+date_saved: "2026-05-05T09:36:27.581434+00:00"
+instance: "kb-cron"
+---
+
+An astronomical clock, horologium, or orloj is a clock with special mechanisms and dials to display astronomical information, such as the relative positions of the Sun, Moon, zodiacal constellations, and major planets.
+
+== Definition ==
+
+The term is loosely used to refer to any clock that shows, in addition to the time of day, astronomical information. This could include the location of the Sun and Moon in the sky, the age and Lunar phases, the position of the Sun on the ecliptic and the current zodiac sign, the sidereal time, and other astronomical data such as the Moon's nodes for indicating eclipses), or a rotating star map. The term should not be confused with an astronomical regulator, a high precision but otherwise ordinary pendulum clock used in observatories.
+Astronomical clocks usually represent the Solar System using the geocentric model. The center of the dial is often marked with a disc or sphere representing the Earth, located at the center of the Solar System. The Sun is often represented by a golden sphere (as it initially appeared in the Antikythera mechanism, back in the 2nd century BC), shown rotating around the Earth once a day around a 24-hour analog dial. This view accorded both with the daily experience and with the philosophical world view of pre-Copernican Europe.
+
+== History ==
+
+The Antikythera mechanism is the oldest known analog computer and a precursor to astronomical clocks. A complex arrangement of multiple gears and gear trains could perform functions such as determining the position of the sun, moon and planets, predict eclipses and other astronomical phenomena and tracking the dates of Olympic Games. Research in 2011 and 2012 led an expert group of researchers to posit that European astronomical clocks are descended from the technology of the Antikythera mechanism.
+In the 11th century, the Song dynasty Chinese horologist, mechanical engineer, and astronomer Su Song created a water-driven astronomical clock for his clock-tower of Kaifeng City. Su Song is noted for having incorporated an escapement mechanism and the earliest known endless power-transmitting chain drive for his clock-tower and armillary sphere to function. Contemporary Muslim astronomers and engineers also constructed a variety of highly accurate astronomical clocks for use in their observatories, such as the astrolabic clock by Ibn al-Shatir in the early 14th century.
+
+The early development of mechanical clocks in Europe is not fully understood, but there is general agreement that by 1300–1330 there existed mechanical clocks (powered by weights rather than by water and using an escapement) which were intended for two main purposes: for signalling and notification (e.g. the timing of services and public events), and for modelling the solar system. The latter is an inevitable development because the astrolabe was used both by astronomers and astrologers, and it was natural to apply a clockwork drive to the rotating plate to produce a working model of the solar system. American historian Lynn White Jr. of Princeton University wrote: Most of the first clocks were not so many chronometers as exhibitions of the pattern of the cosmos … Clearly, the origins of the mechanical clock lie in a complex realm of monumental planetaria, equatoria, and astrolabes.
+The astronomical clocks developed by the English mathematician and cleric Richard of Wallingford in St Albans during the 1330s, and by medieval Italian physician and astronomer Giovanni Dondi dell'Orologio in Padua between 1348 and 1364 are masterpieces of their type. They no longer exist, but detailed descriptions of their design and construction survive, and modern reproductions have been made. Wallingford's clock may have shown the sun, moon (age, phase, and node), stars and planets, and had, in addition, a wheel of fortune and an indicator of the state of the tide at London Bridge. De Dondi's clock was a seven-faced construction with 107 moving parts, showing the positions of the sun, moon, and five planets, as well as religious feast days.
+Both these clocks, and others like them, were probably less accurate than their designers would have wished. The gear ratios may have been exquisitely calculated, but their manufacture was somewhat beyond the mechanical abilities of the time, and they never worked reliably. Furthermore, in contrast to the intricate advanced wheelwork, the timekeeping mechanism in nearly all these clocks until the 16th century was the simple verge and foliot escapement, which had errors of at least half an hour a day.
+Astronomical clocks were built as demonstration or exhibition pieces, to impress as much as to educate or inform. The challenge of building these masterpieces meant that clockmakers would continue to produce them, to demonstrate their technical skill and their patrons' wealth. The philosophical message of an ordered, heavenly-ordained universe, which accorded with the Gothic-era view of the world, helps explain their popularity.
+The growing interest in astronomy during the 18th century revived interest in astronomical clocks, less for the philosophical message, more for the accurate astronomical information that pendulum-regulated clocks could display.
+
+== Generic description ==
+Although each astronomical clock is different, they share some common features.
+
+=== Time of day ===

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+---
+
+Most astronomical clocks have a 24-hour analog dial around the outside edge, numbered from I to XII then from I to XII again. The current time is indicated by a golden ball or a picture of the sun at the end of a pointer. Local noon is usually at the top of the dial, and midnight at the bottom. Minute hands are rarely used.
+The Sun indicator or hand gives an approximate indication of both the Sun's azimuth and altitude. For azimuth (bearing from the north), the top of the dial indicates South, and the two VI points of the dial East and West. For altitude, the top is the zenith and the two VI and VI points define the horizon. (This is for the astronomical clocks designed for use in the northern hemisphere.) This interpretation is most accurate at the equinoxes, of course.
+If XII is not at the top of the dial, or if the numbers are Arabic rather than Roman, then the time may be shown in Italian hours (also called Bohemian, or Old Czech, hours). In this system, 1 o'clock occurs at sunset, and counting continues through the night and into the next afternoon, reaching 24 an hour before sunset.
+In the photograph of the Prague clock shown at the top of the article, the time indicated by the Sun hand is about 9am (IX in Roman numerals), or about the 13th hour (Italian time in Arabic numerals).
+
+=== Calendar and zodiac ===
+The year is usually represented by the 12 signs of the zodiac, arranged either as a concentric circle inside the 24-hour dial, or drawn onto a displaced smaller circle, which is a projection of the ecliptic, the path of the Sun and planets through the sky, and the plane of the Earth's orbit.
+The ecliptic plane is projected onto the face of the clock, and, because of the Earth's tilted angle of rotation relative to its orbital plane, it is displaced from the center and appears to be distorted. The projection point for the stereographic projection is the North pole; on astrolabes the South pole is more common.
+The ecliptic dial makes one complete revolution in 23 hours 56 minutes (a sidereal day), and will therefore gradually get out of phase with the hour hand, drifting slowly further apart during the year.
+To find the date, find the place where the hour hand or Sun disk intersects the ecliptic dial: this indicates the current star sign, the sun's current location on the ecliptic. The intersection point slowly moves around the ecliptic dial during the year, as the Sun moves out of one astrological sign into another.
+In the diagram showing the clock face on the right, the Sun's disk has recently moved into Aries (the stylized ram's horns), having left Pisces. The date is therefore late March or early April.
+If the zodiac signs run around inside the hour hands, either this ring rotates to align itself with the hour hand, or there's another hand, revolving once per year, which points to the Sun's current zodiac sign.
+
+=== Moon ===
+A dial or ring indicating the numbers 1 to 29 or 30 indicates the moon's age: a new moon is 0, waxes become full around day 15, and then wanes up to 29 or 30. The phase is sometimes shown by a rotating globe or black hemisphere, or a window that reveals part of a wavy black shape beneath.
+
+=== Hour lines ===
+Unequal hours were the result of dividing up the period of daylight into 12 equal hours and nighttime into another 12. There is more daylight in the summer, and less night time, so each of the 12 daylight hours is longer than a night hour. Similarly in winter, daylight hours are shorter, and night hours are longer. These unequal hours are shown by the curved lines radiating from the center. The longer daylight hours in summer can usually be seen at the outer edge of the dial, and the time in unequal hours is read by noting the intersection of the sun hand with the appropriate curved line.
+
+=== Aspects ===
+Astrologers placed importance on how the Sun, Moon, and planets were arranged and aligned in the sky. If certain planets appeared at the points of a triangle, hexagon, or square, or if they were opposite or next to each other, the appropriate aspect was used to determine the event's significance. On some clocks you can see the common aspects – triangle, square, and hexagon – drawn inside the central disc, with each line marked by the symbol for that aspect, and you may also see the signs for conjunction and opposition. On an astrolabe, the corners of the different aspects could be lined up on any of the planets. On a clock, though, the disc containing the aspect lines can't be rotated at will, so they usually show only the aspects of the Sun or Moon.
+On the Torre dell'Orologio, Brescia clock in northern Italy, the triangle, square, and star in the centre of the dial show these aspects (the third, fourth, and sixth phases) of (presumably) the moon.

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+---
+title: "Astronomical clock"
+chunk: 3/7
+source: "https://en.wikipedia.org/wiki/Astronomical_clock"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:27.581434+00:00"
+instance: "kb-cron"
+---
+
+=== "Dragon" hand: eclipse prediction and lunar nodes ===
+The Moon's orbit is not in the same plane as the Earth's orbit around the Sun but crosses it in two places. The Moon crosses the ecliptic plane twice a month, once when it goes up above the plane, and again 15 or so days later when it goes back down below the ecliptic. These two locations are the ascending and descending lunar nodes. Solar and lunar eclipses will occur only when the Moon is positioned near one of these nodes because at other times the Moon is either too high or too low for an eclipse to be seen on the Earth.
+Some astronomical clocks keep track of the position of the lunar nodes with a long pointer that crosses the dial, with its length extended out to both sides of the dial to pointing at two opposite points on the solar or lunar dial. This so-called "dragon" hand makes one complete rotation around the ecliptic dial every 19 years. It is sometimes decorated with the figure of a serpent or lizard (Greek: drakon) with its snout and tail-tip touching the outer dial, traditionally labelled Latin: "caput draconam" and Latin: "cauda draconam" even if the decorative dragon is omitted (not to be confused with the similar-seeming names of the two sections of the constellation Serpens).
+During the two yearly eclipse seasons the Sun pointer coincides with either the dragon's snout or tail. When the dragon hand and the full Moon coincide, the Moon is on the same plane as the Earth and Sun, and so there is a good chance that a lunar eclipse will be visible on one side of the Earth. When the new Moon is aligned with the dragon hand there is a moderate possibility that a solar eclipse might be visible somewhere on the Earth.
+
+== Historical examples ==
+
+=== Su Song's Cosmic Engine ===
+The Science Museum (London) has a scale model of the 'Cosmic Engine', which Su Song, a Chinese polymath, designed and constructed in China in 1092. This great astronomical hydromechanical clock tower was about ten metres high (about 30 feet) and featured a clock escapement and was indirectly powered by a rotating wheel either with falling water and liquid mercury, which freezes at a much lower temperature than water, allowing operation of the clock during colder weather. A full-sized working replica of Su Song's clock exists in the Republic of China (Taiwan)'s National Museum of Natural Science, Taichung city. This full-scale, fully functional replica, approximately 12 meters (39 feet) in height, was constructed from Su Song's original descriptions and mechanical drawings.
+
+=== Astrarium of Giovanni Dondi dell'Orologio ===
+The Astrarium of Giovanni Dondi dell'Orologio was a complex astronomical clock built between 1348 and 1364 in Padua, Italy, by the doctor and clock-maker Giovanni Dondi dell'Orologio. The Astrarium had seven faces and 107 moving gears; it showed the positions of the sun, the moon and the five planets then known, as well as religious feast days. The astrarium stood about 1 metre high, and consisted of a seven-sided brass or iron framework resting on 7 decorative paw-shaped feet. The lower section provided a 24-hour dial and a large calendar drum, showing the fixed feasts of the church, the movable feasts, and the position in the zodiac of the moon's ascending node. The upper section contained 7 dials, each about 30 cm in diameter, showing the positional data for the Primum Mobile, Venus, Mercury, the moon, Saturn, Jupiter, and Mars. Directly above the 24-hour dial is the dial of the Primum Mobile, so called because it reproduces the diurnal motion of the stars and the annual motion of the sun against the background of stars. Each of the 'planetary' dials used complex clockwork to produce reasonably accurate models of the planets' motion. These agreed reasonably well both with Ptolemaic theory and with observations. For example, Dondi's dial for Mercury uses a number of intermediate wheels, including: a wheel with 146 teeth, and a wheel with 63 internal (facing inwards) teeth that meshed with a 20 tooth pinion.
+
+== Interior clocks and watches ==
+
+=== The Rasmus Sørnes Clock ===
+
+Arguably the most complicated of its kind ever constructed, the last of a total of four astronomical clocks designed and made by Norwegian Rasmus Sørnes (1893–1967), is characterized by its superior complexity compactly housed in a casing with the modest measurements of 0.70 x 0.60 x 2.10 m. Features include locations of the sun and moon in the zodiac, Julian calendar, Gregorian calendar, sidereal time, GMT, local time with daylight saving time and leap year, solar and lunar cycle corrections, eclipses, local sunset and sunrise, moon phase, tides, sunspot cycles and a planetarium including Pluto's 248-year orbit and the 25 800-year periods of the polar ecliptics (precession of the Earth's axis). All wheels are in brass and gold-plated. Dials are silver-plated. The clock has an electromechanical pendulum.
+Sørnes also made the necessary tools and based his work on his own astronomical observations. Having been exhibited at the Time Museum in Rockford, Illinois (since closed), and at the Chicago Museum of Science and Industry, the clock was sold in 2002 and its current location is not known. The Rasmus Sørnes Astronomical Clock No. 3, the precursor to the Chicago Clock, his tools, patents, drawings, telescope, and other items, are exhibited at the Borgarsyssel Museum in Sarpsborg, Norway.
+
+=== Table clocks ===
+There are many examples of astronomical table clocks, due to their popularity as showpieces. To become a master clockmaker in 17th-century Augsburg, candidates had to design and build a 'masterpiece' clock, an astronomical table-top clock of formidable complexity. Examples can be found in museums, such as London's British Museum.
+Currently Edmund Scientific among other retailers offers a mechanical Tellurium clock, perhaps the first mechanical astronomical clock to be mass-marketed.
+In Japan, Tanaka Hisashige made a Myriad year clock in 1851.

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+---
+title: "Astronomical clock"
+chunk: 4/7
+source: "https://en.wikipedia.org/wiki/Astronomical_clock"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:27.581434+00:00"
+instance: "kb-cron"
+---
+
+=== Watches ===
+More recently, independent clockmaker Christiaan van der Klaauw created a wristwatch astrolabe, the "Astrolabium" in addition to the "Planetarium 2000", the "Eclipse 2001" and the "Real Moon." Ulysse Nardin also sells several astronomical wristwatches, the "Astrolabium," "Planetarium", and the "Tellurium J. Kepler."
+
+=== Other examples ===
+Two of Holland America's cruise ships, the MS Rotterdam and the MS Amsterdam, both have large astronomical clocks as their main centerpieces inside the ships' atriums.
+
+== Examples by country ==
+
+=== Austria ===
+Innsbruck. The astronomical clock in the gable of 17–19 Maria-Theresien-Strasse is a 20th-century copy of the astronomical clock of the Ulm Rathaus in Germany.
+Peuerbach. The facade of Peuerbach Town Hall features an astrolabe clock, an enlarged copy of Georg von Peuerbach's original astrolabe of 1457.
+
+=== Belgium ===
+Lier. The Zimmer tower houses an astronomical clock installed by Louis Zimmer in 1930. On twelve dials surrounding a central clockface, it gives indications including the time around the world, the date, the moon phase, and the equation of time, and includes a tide clock.
+Senzeilles. The Senzeilles astronomical clock was constructed by self-taught Lucien Charloteaux between 1896 and 1912. A domestic clock housed in a wooden case, it gives indications including the solar, mean and sidereal time around the world, the positions of the constellations and planets, and the appearance of Halley's Comet.
+Sint-Truiden. The astronomical clock constructed by Kamiel Festraets between 1937 and 1942 is now housed in the Festraets Museum.
+
+=== Croatia ===
+Dubrovnik. The Dubrovnik Bell Tower constructed in 1444 has housed a clock since its creation, though due to earthquake damage, both the tower and the clock were replaced in 1929. A rotating moon ball shows the lunar phase.
+
+=== Czech Republic ===
+
+Prague. The Prague astronomical clock at the Old Town Hall is one of the most famous astronomical clocks. The central section was completed in 1410, the calendar dial was added in 1490. The clock was renovated after damage during World War II, and in 1979. On the hour, Death strikes the time, and the twelve apostles appear at the doors above the clock.
+Olomouc. The Olomouc astronomical clock at the Town Hall is a rare example of a heliocentric astronomical clock. Dated 1422 by legend, but first mentioned in history in 1517, the clock was remodelled approximately once every century; in 1898 the astrolabe was replaced with a heliocentric model of the solar system. Badly damaged by the retreating German army in 1945, the clock was remodelled in socialist realism style in 1955, under the Communist government. The religious and royal figures were replaced with athletes, workers, farmers, scientists, and other members of the proletariat.
+Litomyšl. The tower of the Old Town Hall has an art nouveau astronomical clock, installed in 1907.
+Prostějov. The astronomical clock in the tower of the New Town Hall was installed in 1910.
+Kryštofovo Údolí. The Kryštofovo Údolí astronomical clock is a modern astronomical clock (inaugurated in 2008), built-in a former electrical substation.
+Hojsova Stráž. An astronomical clock in the Bohemian Forest was inaugurated in 2017. It has a concentric dial showing the 24-hour time, the date and zodiac, and the moon phase, and a star map dial with a dragon hand, and indicates the time of sunrise and sunset.
+Třebíč. At the Třebíč Astronomical Observatory, a modern astronomical clock which shows the time in world cities, the time of sunrise and sunset, the date and zodiac, and the orbits of the planets.
+Žatec. The Temple to Hops and Beer, a museum and amusement complex dedicated to beer, has an astronomical clock on which the zodiac indication illustrates the annual processes of beer production.
+
+=== Denmark ===
+Copenhagen. Jens Olsen's World Clock in Copenhagen City Hall was designed by Jens Olsen and assembled from 1948 to 1955.
+
+=== France ===

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+title: "Astronomical clock"
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+category: "reference"
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+date_saved: "2026-05-05T09:36:27.581434+00:00"
+instance: "kb-cron"
+---
+
+Auxerre. The 15th-century clock in the Tour de l'Horloge has a 24-hour sun hand and a moon hand which completes a revolution in a lunar day of 24 hours 50 minutes, and shows the lunar phase on a rotating moon ball.
+Beauvais. The Beauvais astronomical clock in Beauvais Cathedral, constructed 1865–1868 by Auguste-Lucien Vérité, has 52 dials that display the times of sunrise, sunset, moonrise, moonset, the phases of the moon, the solstices, the position of the planets, the current time in 18 cities around the world, and the tidal hours. Its 68 automata enact the Last Judgement on the hour.
+Besançon. The Besançon astronomical clock in Besançon Cathedral (1860) was also constructed by Auguste-Lucien Vérité. Its 70 dials provide 122 indications.
+Bourges. The Bourges astronomical clock in Bourges Cathedral was installed in 1424. It shows the zodiac, and the moon phase and age.
+Chartres. The Chartres astronomical clock in Chartres Cathedral is an astrolabe clock, installed in 1528. It was overhauled, its mechanism replaced by an electric mechanism, in 2009.
+Haguenau. The facade of the Musée alsacien displays an astronomical clock, a modern copy of the clock of the Ulm Rathaus.
+Lyon. The Lyon astronomical clock in Lyon Cathedral was constructed in 1661, replacing a 14th-century original. It has an astrolabe dial and a calendar dial.
+Munster. The Church of Saint-Léger houses the Clock of Creation, installed in 2008. It shows the time, the day of the week, the month and zodiac, and the moon phase.
+Ploërmel. The Ploërmel astronomical clock, constructed 1850–1855, comprises an astronomical clock with 10 dials and an orrery.
+Rouen. The Gros Horloge has a movement built in 1389, with a dial added in 1529. It indicates the moon phase on a rotating sphere above the dial, and the day of the week in an aperture at the base of the dial.
+Saint-Omer. The Saint-Omer astronomical clock in Saint-Omer Cathedral is an astrolabe clock of 1558.
+Strasbourg. The Strasbourg astronomical clock is the third clock housed in Strasbourg Cathedral, following 14th-century and 16th-century predecessors. Constructed by Jean-Baptiste Schwilgué from 1838 to 1843, it shows many astronomical and calendrical functions (including what is thought to be the first complete mechanization of the computus needed to compute Easter) and several automata.
+Versailles. The Passemant astronomical clock in the Palace of Versailles near Paris is a rococo astronomical clock sitting on a formal low marble base. It took 12 years for a clockmaker and an engineer to build and was presented to Louis XV in 1754.
+
+=== Georgia ===
+Batumi. The facade of the former National Bank Building on Europe Square has an astronomical clock based on the clock at Mantua, which shows the positions of the sun and moon in the zodiac, and the moon phase.
+
+=== Germany ===

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+title: "Astronomical clock"
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+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:27.581434+00:00"
+instance: "kb-cron"
+---
+
+A group of interior astronomical clocks of the 14th, 15th and 16th centuries in churches of Hanseatic League towns in northern Germany, known as the Hanseatic clocks (the group also includes the clock at Gdańsk, now in Poland).
+Bad Doberan. At Doberan Minster, an astrolabe clock was installed by Nikolaus Lilienfeld in 1390. Only the dial survives, now positioned above the west door.
+Lübeck. The astronomical clock of St. Mary's Church, constructed 1561–1566, was destroyed in the bombing of Lübeck in 1942. The present clock is a replacement by Paul Behrens, installed in 1967.
+Münster. The Münster astronomical clock of 1540 in Münster Cathedral, adorned with hand-painted zodiac symbols, which traces the movement of the planets, plays a glockenspiel tune every noon.
+Rostock. The Rostock astronomical clock in St. Mary's Church dating from 1472, built by Hans Düringer. Clock with daily time, zodiac, moon phases, and month. With a dedicated electronic database this clock is particularly well documented.
+Stendal. At St. Mary's Church, an astronomical clock of the 1580s, rebuilt in 1856 (and vandalized by the clockmaker), and restored in 1977.
+Stralsund. The astronomical clock in St. Nicholas' Church is an astrolabe clock installed by Nikolaus Lilienfeld in 1394. It has not been in working order since the 16th century.
+Tangermünde. At St. Stephen's Church, Tangermünde, an astronomical clock of the 2023 built by Volker Schulz and Thomas Leu.
+Wismar. The 15th-century astronomical clock in St. Mary's Church was destroyed by bombing in 1945.
+A group of 16th-century clocks on the facade of town halls in southern Germany, which have a 12-hour dial, a moon phase indication, and a calendar dial indicating the positions of the sun and moon in the zodiac, with a dragon hand:
+Esslingen am Neckar. The Clock of Esslingen Old Town Hall, constructed 1581–1586.
+Heilbronn. The Kunstuhr of Heilbronn Town Hall of Isaac Habrecht, installed 1579–1580.
+Tübingen. The clock of Tübingen Town Hall, installed in 1510.
+Ulm. The 16th-century astronomical clock of Ulm Town Hall has a 24-hour astrolabe format, although the zodiac is repeated as a rotating ring of gold sculptures, and the outer ring of the dial is a 12-hour chapter ring.
+Cologne. At the Cologne Planetarium, a modern astronomical clock which shows the hour in regular and sidereal time, the moon phase, positions of the sun and moon in the zodiac, and the rotation of the earth according to the geocentric model.
+Esslingen am Neckar. At the headquarters of Festo, Professor Hans Scheurenbrand has constructed the Harmonices Mundi (named after Kepler's book of the same name), which consists of an astronomical clock, a world time clock, and a 74 bell glockenspiel.
+Görlitz. Görlitz Town Hall and the Church of St Peter and St Paul both have 16th-century clocks which indicate the lunar phase.
+Munich. The Old Town Hall and the Deutsches Museum both have clocks which indicate the moon phase on a rotating ball, and the zodiac on a fixed ring within a 12-hour dial.
+Schramberg. The Town Hall has an astronomical clock installed in 1913. Its indications are similar to the clock of Ulm (except that the outer hour ring is 24-hour), with an offset astrolabe ring repeated as a golden zodiac ring.
+Stuttgart. A modern clock in the tower of Stuttgart Town Hall shows the moon phase and the day of the week.
+Worms. The clock tower Worms Town Hall has a modern calendar dial that shows the month, the positions of the sun and moon in the zodiac, the moon phase, and has a dragon hand.
+
+=== Hungary ===
+Székesfehérvár: A modern astronomical clock with automata and carillon, at the Clock Museum.
+
+=== Italy ===
+
+Arezzo. The clock of the Palazzo della Fraternita dei Laici, installed in 1552, shows the moon phase and age.
+Bassano del Grappa. 24-hour dial with zodiac indication on the Palazzo del Municipio, first installed in 1430, reconstructed by Bartolomeo Ferracina in 1747.
+Brescia. Astronomical clock dated c. 1540–1550 in the Torre dell'Orologio.
+Clusone. Fanzago's astronomical clock at the Palazzo Comunale, built by Pietro Fanzago in 1583.
+Cremona. The 16th-century astronomical clock of the Torrazzo, the bell tower of Cremona Cathedral, is the largest medieval clock in Europe.
+Macerata. An astronomical clock installed in the Torre Civica, a modern replica of the original clock of 1571, which shows the orbits of the planets.
+Mantua. Astronomical clock was installed in 1473 in the Torre dell'Orologio of the Palazzo della Ragione.
+Merano. Clock tower at the entrance to Merano town cemetery, installed in 1908 by Philipp Hörz of Ulm, with a calendar dial showing the month, zodiac, and moon phase.
+Messina. The Messina astronomical clock in the tower of Messina Cathedral. Multi-dial clock equipped with complex automata. Constructed between 1930 and 1933 by the Ungerer Company of Strasbourg. It is one of the largest astronomical clocks in the world.
+Padua. 15th-century astronomical clock in the Torre dell'Orologio.
+Rimini. The clock tower on Piazza Tre Martiri has a calendar dial installed in 1750 showing the date, zodiac, and moon phase and age.
+Soncino. 24-hour dial with zodiac indication in the town hall. The terracotta zodiac dial dates from 1977.
+Trapani. Astronomical clock of 1596 in the Porta Oscura, with a dial for the hours and the zodiac, and a lunar dial.
+Venice. St Mark's Clock, in the clocktower on St Mark's Square, was built and installed by Gian Paulo and Gian Carlo Rainieri, father and son, between 1496 and 1499.
+
+=== Japan ===
+Tokyo: The Shinjuku I-Land clock tower features a clock face that is an exact replica of Prague's astronomical clock. On the other side of the tower is a more conventional analog clock face featuring a rotating planisphere disc that shows the current constellations seen in the night sky over Japan.
+
+=== Latvia ===
+Riga: The clock on the facade of the House of the Blackheads shows the time, date, month, day of the week, and lunar phase.

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+---
+title: "Astronomical clock"
+chunk: 7/7
+source: "https://en.wikipedia.org/wiki/Astronomical_clock"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:27.581434+00:00"
+instance: "kb-cron"
+---
+
+=== Malta ===
+Valletta. The clock of the Grandmaster's Palace, installed in 1745, shows the hour, date, month, and lunar phase, and has bells struck by four jacquemarts.
+Malta has several church clocks that show calendar indications on separate dials, including those of St John's Co-Cathedral, Valletta; St Paul's Cathedral, Mdina; the Rotunda of Mosta; and the Church of St Bartholomew, Għargħur.
+
+=== Netherlands ===
+Arnemuiden. The 16th-century church clock at Arnemuiden indicates the lunar phase and the time of high tide.
+Franeker. The Eise Eisinga Planetarium, built 1774–1781, is an orrery and astronomical clock which shows the movements of the solar system.
+
+=== Norway ===
+Oslo. A 20th-century astronomical clock at Oslo City Hall.
+
+=== Poland ===
+Gdańsk. In St. Mary's Church there is the Gdańsk astronomical clock dating from 1464 to 1470, and built by Hans Düringer of Toruń. It was reconstructed after 1945.
+Wrocław. A 16th-century clock showing the moon phase at Wrocław Town Hall.
+
+=== Slovakia ===
+Stará Bystrica: An astronomical clock in the stylized shape of Our Lady of Sorrows was built in the town square in 2009. The astronomical part of the clock consists of an astrolabe displaying the astrological signs, positions of the Sun and Moon, and the lunar phases. Its statues and automata depict Slovakian historical and religious figures. The clock is controlled by computer using DCF77 signals.
+
+=== South Korea ===
+Honcheonsigye: is an astronomical clock made by  Song Yi-Yeong (송이영; 宋以潁), a professor of Gwansanggam (관상감; 觀象監) (one of the scientific institution of Joseon dynasty) in 1669. It was designated as South Korean national treasure number 230 on August 9, 1985. The clock used the alarm clock technology created by Christiaan Huygens in 1657. This relic shows that Huygens' technology was spread to East Asia in just 12 years. Also, It demonstrates the astronomy and mechanical engineering technology of the Joseon dynasty. Korea has been making armillary sphere since the 15th century as part of King Sejong's technology development policy, and this clock is an important historical document that shows the fusion of East Asian astronomy and European mechanical technology.
+
+=== Spain ===
+Astorga: The interior face of the clock of Astorga Cathedral has a 24-hour dial which shows the lunar phase and the date.
+
+=== Sweden ===
+Lund: Lund astronomical clock in Lund Cathedral in Sweden, (Horologium mirabile Lundense) was made around 1425, probably by the clockmaker Nicolaus Lilienveld in Rostock. After it had been in storage since 1837, it was restored and put back in place in 1923. Only the upper, astronomical part is original, while some of the other remaining medieval parts can be seen at the Cathedral museum. When it plays, one can hear In Dulci Jubilo from the smallest organ in the church, while seven wooden figures, representing the three magi and their servants, pass by.
+Fjelie: Emil Ahrent, the local priest, constructed and donated an astronomical clock to Fjelie Church in 1946.
+Nottebäck: K.L. Lundén, the local priest, installed an astronomical clock in Nottebäck Church in 1954.
+Rinkaby: An astronomical clock was installed in Rinkaby Church in the 1950s. Modelled on medieval clocks, it was made by a local electrician.
+
+=== Switzerland ===
+
+Bern. The Zytglogge is a famous 15-century astronomical clock housed in a medieval fortification tower.
+A set of 16th-century clocks which show the zodiac and the days of the week in concentric rings within a 12-hour clock face, with a moon phase ball above:
+Bremgarten. The clock of the Spittelturm, installed in 1558.
+Diessenhofen. The clock of the Siegelturm, installed in 1546.
+Mellingen. The clock of the Zeitturm, installed in 1554.
+Schaffhausen: The astronomical clock by Joachim Habrecht in the gable of the Fronwagturm, installed in 1564, has five hands, including indications of the positions of the sun and moon in the zodiac, and a dragon hand indicating the lunar nodes.
+Sion: The Sion astronomical clock on the town hall dates from 1667 to 1668. Its current mechanism was installed in 1902.
+Solothurn. This astronomical clock, installed by Lorenz Liechti and Joachim Habrecht in 1545 to replace an original of 1452, shows the positions of the sun and moon in the zodiac.
+Winterthur. This astrolabe astronomical clock was installed in 1529. The building which housed it was demolished in 1870. The clock is now an exhibit at the Museum Lindengut.
+Zug: The astronomical clock of the Zytturm was installed in 1574. Its calendar dial shows the zodiac, the lunar phase, the day of the week and the leap year cycle.
+
+=== United Kingdom ===
+
+A group of four famous astronomical clocks in the West Country, dating from the 14th and 15th centuries, all of which show the 24-hour time and the moon phase:
+Exeter. The Exeter Cathedral astronomical clock (c. 1484)
+Ottery St Mary. The Ottery St Mary astronomical clock (15th century)
+Wells. The Wells Cathedral clock (1386–1392)
+Wimborne Minster. The Wimborne Minster astronomical clock (14th century)
+Durham. Prior Castell's Clock in Durham Cathedral, installed between 1494 and 1519.
+Hampton Court Palace. The Hampton Court astronomical clock (1540) is on the interior façade of the Main Gatehouse. It is a fine early example of a pre-Copernican astronomical clock.
+Leicester. The Leicester University astronomical clock (1989) is on the Rattray Lecture Theatre opposite the Physics department.
+London. The astrological clock of Bracken House was installed in 1959, and depicts the Signs of the Zodiac.
+Snowshill. The Nychthemeron Clock, installed in the garden of Snowshill Manor in Gloucestershire.
+St Albans. A modern clock dating from 1995, built from notes by Richard of Wallingford held in the Bodleian Library, Oxford. On display in St Albans Cathedral.
+York. The York Minster astronomical clock, an astronomical clock installed in 1955 as a memorial to airmen killed in World War II, shows the positions of the sun and stars from the perspective of a pilot flying over York. It was damaged by fire in 1984, and is not currently working.
+
+=== United States ===
+Cedar Rapids, Iowa: The clock tower outside the National Czech and Slovak Museum and Library features an exact replica of Prague's astronomical clock.
+
+== See also ==
+Astrolabe
+Astrarium
+Clock of the Long Now, also called the 10,000-year clock
+Orrery
+Solar System models
+Torquetum
+
+== Notes ==
+
+== References ==
+Needham, Joseph (1986). Physics and Physical Technology, Part 2, Mechanical Engineering. Science and Civilization in China. Vol. 4. Taipei: Caves Books Ltd.
+North, John (2005). God's Clockmaker, Richard of Wallingford and the invention of time. Hambledon and London.
+Sørnes, Tor (2008). The Clockmaker Rasmus Sørnes. Borgarsyssel Museum, Sarpsborg, 2003 Norwegian edition, and 2008 English edition (available from the museum).
+King, Henry (1978). Geared to the Stars: the evolution of planetariums, orreries, and astronomical clocks. University of Toronto Press. Bibcode:1978gtse.book.....K.
+
+== Further reading ==
+Needham, Joseph; Ling, Wang; deSolla Price, Derek J. (1986). Heavenly Clockwork: The Great Astronomical Clocks of Medieval China. Cambridge: Cambridge University Press. ISBN 978-0-521-32276-8.
+
+== External links ==
+
+The search for Rasmus Sørnes 4th clock
+Prague Astronomical Clock
+A modern, online astronomical clock
+Les Cadrans Solaires (Sundials), also showing European astronomical clocks (in French)
+MoonlightClock.com – Handmade Astronomical Clocks
+Festraets' astronomical clock

data/en.wikipedia.org/wiki/Astronomical_rings-0.md

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+---
+title: "Astronomical rings"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Astronomical_rings"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:29.975083+00:00"
+instance: "kb-cron"
+---
+
+Astronomical rings (Latin: annuli astronomici), also known as Gemma's rings, are an early astronomical instrument. The instrument consists of three rings, representing the celestial equator, declination, and the meridian.
+It can be used as a sun dial to tell time, if the approximate latitude and season is known, or to tell latitude, if the time is known or observed (at solar noon). It may be considered to be a simplified, portable armillary sphere, or a more complex form of astrolabe.
+
+
+== History ==
+Parts of the instrument go back to instruments made and used by ancient Greek astronomers. Gemma Frisius combined several of the instruments into a small, portable, astronomical-ring instrument. He first published the design in 1534, and in Petrus Apianus's  Cosmographia in 1539. These ring instruments combined terrestrial and celestial calculations.
+
+
+== Types ==
+
+
+=== Fixed astronomical rings ===
+
+Fixed astronomical rings are mounted on a plinth, like armillary spheres, and can be used as sundials.
+
+
+=== Traveller's sundial or universal equinoctal ring dial ===
+The dial is suspended from a cord or chain; the suspension point on the vertical meridian ring can be changed to match the local latitude. The time is read off on the equatorial ring; in the example below, the center bar is twisted until a sunray passes through a small hole and falls on the horizontal equatorial ring.
+
+
+=== Sun ring ===
+A sunring or farmer's ring is a latitude-specific simplification of astronomical rings. On one-piece sunrings, the time and month scale is marked on the inside of the ring; a sunbeam passing through a hole in the ring lights a point on this scale. Newer sunrings are often made in two parts, one of which slides to set the month; they are usually less accurate.
+
+
+=== Sea ring ===
+
+In 1610, Edward Wright created the sea ring, which mounted a universal ring dial over a magnetic compass.  This permitted mariners to determine the time and magnetic variation in a single step. These are also called "sundial compasses".
+
+
+== Structure and function ==
+The three rings are oriented with respect to the local meridian, the planet's equator, and a celestial object. The instrument itself can be used as a plumb bob to align it with the vertical. The instrument is then rotated until a single light beam passes through two points on the instrument. This fixes the orientation of the instrument in all three axes.
+The angle between the vertical and the light beam gives the solar elevation. The solar elevation is a function of latitude, time of day, and season. Any one of these variables can be determined using astronomical rings, if the other two are known.
+The altitude of the sun does not change much in a single day at the poles (where the sun rises and sets once a year), so rough measurements of solar altitude don't vary with time of day at high latitudes.
+
+
+=== Use as a calendar sundial ===
+When the solar time is exactly noon, or known from another clock, the instrument can be used to determine the time of year.
+The meridional ring can function as the gnomon, when the rings are used as a sundial. A horizontal line aligned on a meridian with a gnomon facing the noon-sun is termed a meridian line and does not indicate the time, but instead the day of the year. Historically they were used to accurately determine the length of the solar year. A fixed meridional ring on its own can be used as an analemma calendar sundial, which can be read only at noon.
+When the shadow of the rings are aligned so that they appear to be in the same, or nearly the same, place, the meridian identifies itself.
+
+
+=== Meridional ring ===
+The meridian ring is placed vertically, then rotated (relative to the celestial object) until it is parallel to the local north-south line. The whole ring is thus parallel to the circle of longitude passing through the place where the user is standing.
+Because the instrument is often supported by the meridional ring, it is often the outermost ring, as it is in the traveller's rings illustrated above. There, a sliding suspension shackle is attached to the top of the meridional ring, from which the whole device can be suspended. The meridional ring is marked in degrees of latitude (0–90, for each hemisphere). When properly used, the pointer on the support points to the latitude of the instrument's location. This tilts the equatorial ring so that it lies at the same angle to the vertical as the local equator.
+
+
+=== Equatorial ring ===
+The equatorial ring occupies a plane parallel to the celestial equator, at right angles to the meridian. It is aligned by
+
+being attached to the meridional ring at the marking for latitude zero (see above)
+being aligned to the declension ring, which is aligned to the celestial object.
+Often equipped with a graduated scale, it can be used to measure right ascension. On the traveller's sundial shown above, it is the inner ring.
+This ring is sometimes engraved with the months on one side and corresponding zodiac signs on the outside; very similar to an astrolabe. 
+Others have been found to be engraved with two twelve-hour time scales. Each twelve-hour scale is stretched over 180 degrees and numbered by hour with hashes every 20 minutes and smaller hashes every four minutes. The inside displays a calendrical scale with the names of the months indicated by their first letters, with a mark to show every 5 days and other marks to represent single days. On these, the outside of the ring is engraved with the corresponding symbols of the zodiac signs. The position of the symbol indicates the date of the entry of the sun into this particular sign. The vernal equinox is marked at March 15 and the autumnal equinox is marked at September 10.
+
+
+=== Declination ring ===
+
+The declination ring is moveable, and rotates on pivots set in the meridian ring. An imaginary line connecting these pivots is parallel to the Earth's axis. The declination "ring" of the traveller's sundial above is not a ring at all, but an oblong loop with a slider for setting the season.
+This ring is often equipped with vanes and pinholes for use as the alidade of a dioptra (see image). It can be used to measure declination.
+This ring is also often marked with the zodiac signs and twenty-five stars, similar to the astrolabe.
+
+
+== References ==
+
+
+== Bibliography ==
+
+Frisius, Gemma (1548). Usus annuli astronomici [The Use of the Astronomical Rings] (digital reprint) (in Latin). Antwerp. OCLC 166113158.

data/en.wikipedia.org/wiki/Atomic_Energy_Commission's_Historical_Advisory_Committee-0.md

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+---
+title: "Atomic Energy Commission's Historical Advisory Committee"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Atomic_Energy_Commission's_Historical_Advisory_Committee"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:34:52.283375+00:00"
+instance: "kb-cron"
+---
+
+The Atomic Energy Commission's Historical Advisory Committee was established in February 1958, when the United States Atomic Energy Commission was a decade old and continued until 1974 when the Energy Research and Development Administration (ERDA) and later the United States Department of Energy replaced the commission.
+
+
+== History ==
+In 1957, the United States Atomic Energy Commission appointed Dr Richard G. Hewlett to be the historian of the Atomic Energy Commission. Upon taking up this post, Hewlett proposed the creation of an historical advisory committee for the AEC. His proposal was referred to historians James Phinney Baxter III and Samuel Eliot Morison and Nobel Prize–winning physicist Isidor I. Rabi. These three men recommended the approval of Hewlett's proposal as a means of giving credibility of the AEC Historical Office's work and avoiding self-serving official history.
+
+
+== Chairman ==
+The following is a chronological list of chairmen, 1958–1974. In cases where a chairman also served as a regular member of the committee, his dates of such service are listed in the alphabetical listing of members. 
+
+James Phinney Baxter III, 1958-1967
+George E. Mowry, 1967-1969
+Alfred D. Chandler, Jr., 1969-1974
+
+
+== Members ==
+The following is an alphabetical listing of members who served on this committee:
+
+John Morton Blum, 1958-1962
+James L. Cate, 1958-1969
+Thomas C. Cochran, 1973-1974
+A. Hunter Dupree, 1968-1973
+Constance McL. Green, 1964-1969
+Ralph W. Hiddy, 1962-1969
+Thomas P. Hughes, 1973-1974
+Richard S. Kirkendall, 1973-1974
+Richard W. Leopold, 1973-1974
+Ernest R. May, 1969-1973
+George E. Mowry, 1962-1967
+Robert P. Multhauf, 1969-1973
+
+
+== Sources ==
+Richard W. Leopold, "Historians and the Federal Government: Historical Advisory Committees: State, Defense, and the Atomic Energy Commission," The Pacific Historical Review, vol. 44, No. 3. (Aug 1975), pp. 373–385.

data/en.wikipedia.org/wiki/Backstaff-0.md

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+---
+title: "Backstaff"
+chunk: 1/3
+source: "https://en.wikipedia.org/wiki/Backstaff"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:31.201916+00:00"
+instance: "kb-cron"
+---
+
+The backstaff is a navigational instrument that was used to measure the altitude of a celestial body, in particular the Sun or Moon. When observing the Sun, users kept the Sun to their back (hence the name) and observed the shadow cast by the upper vane on a horizon vane. It was invented by the English navigator John Davis, who described it in his book Seaman's Secrets in 1594.
+
+== Types of backstaffs ==
+Backstaff is the name given to any instrument that measures the altitude of the sun by the projection of a shadow.  It appears that the idea for measuring the sun's altitude using back observations originated with Thomas Harriot. Many types of instruments evolved from the cross-staff that can be classified as backstaffs.  Only the Davis quadrant remains dominant in the history of navigation instruments.  Indeed, the Davis quadrant is essentially synonymous with backstaff. However, Davis was neither the first nor the last to design such an instrument and others are considered here as well.
+
+== Davis quadrant ==
+
+Captain John Davis invented a version of the backstaff in 1594.  Davis was a navigator who was quite familiar with the instruments of the day such as the mariner's astrolabe, the quadrant and the cross-staff.  He recognized the inherent drawbacks of each and endeavoured to create a new instrument that could reduce those problems and increase the ease and accuracy of obtaining solar elevations.
+One early version of the quadrant staff is shown in Figure 1. It had an arc affixed to a staff so that it could slide along the staff (the shape is not critical, though the curved shape was chosen).  The arc (A) was placed so that it would cast its shadow on the horizon vane (B).  The navigator would look along the staff and observe the horizon through a slit in the horizon vane.  By sliding the arc so that the shadow aligned with the horizon, the angle of the sun could be read on the graduated staff.  This was a simple quadrant, but it was not as accurate as one might like.  The accuracy in the instrument is dependent on the length of the staff, but a long staff made the instrument more unwieldy.  The maximum altitude that could be measured with this instrument was 45°.
+The next version of his quadrant is shown in Figure 2. The arc on the top of the instrument in the previous version was replaced with a shadow vane placed on a transom.  This transom could be moved along a graduated scale to indicate the angle of the shadow above the staff.  Below the staff, a 30° arc was added.  The horizon, seen through the horizon vane on the left, is aligned with the shadow.  The sighting vane on the arc is moved until it aligns with the view of the horizon.  The angle measured is the sum of the angle indicated by the position of the transom and the angle measured on the scale on the arc.
+The instrument that is now identified with Davis is shown in Figure 3. This form evolved by the mid-17th century. The quadrant arc has been split into two parts.  The smaller radius arc, with a span of 60°, was mounted above the staff.  The longer radius arc, with a span of 30° was mounted below.  Both arcs have a common centre.  At the common centre, a slotted horizon vane was mounted (B).  A moveable shadow vane was placed on the upper arc so that its shadow was cast on the horizon vane.  A moveable sight vane was mounted on the lower arc (C).
+It is easier for a person to place a vane at a specific location than to read the arc at an arbitrary position.  This is due to Vernier acuity, the ability of a person to align two line segments accurately.  Thus an arc with a small radius, marked with relatively few graduations, can be used to place the shadow vane accurately at a specific angle.  On the other hand, moving the sight vane to the location where the line to the horizon meets the shadow requires a large arc.  This is because the position may be at a fraction of a degree and a large arc allows one to read smaller graduations with greater accuracy.  The large arc of the instrument, in later years, was marked with transversals to allow the arc to be read to greater accuracy than the main graduations allow.
+Thus Davis was able to optimize the construction of the quadrant to have both a small and a large arc, allowing the effective accuracy of a single arc quadrant of large radius without making the entire instrument so large.  This form of the instrument became synonymous with the backstaff.  It was one of the most widely used forms of the backstaff. Continental European navigators called it the English Quadrant.
+A later modification of the Davis quadrant was to use a Flamsteed glass in place of the shadow vane; this was suggested by John Flamsteed. This placed a lens on the vane that projected an image of the sun on the horizon vane instead of a shadow.  It was useful under conditions where the sky was hazy or lightly overcast; the dim image of the sun was shown more brightly on the horizon vane where a shadow could not be seen.

data/en.wikipedia.org/wiki/Backstaff-1.md

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+---
+title: "Backstaff"
+chunk: 2/3
+source: "https://en.wikipedia.org/wiki/Backstaff"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:31.201916+00:00"
+instance: "kb-cron"
+---
+
+=== Usage ===
+In order to use the instrument, the navigator would place the shadow vane at a location anticipating the altitude of the sun.  Holding the instrument in front of him, with the sun at his back, he holds the instrument so that the shadow cast by the shadow vane falls on the horizon vane at the side of the slit.  He then moves the sight vane so that he observes the horizon in a line from the sight vane through the horizon vane's slit while simultaneously maintaining the position of the shadow.  This permits him to measure the angle between the horizon and the sun as the sum of the angle read from the two arcs.
+Since the shadow's edge represents the limb of the sun, he must correct the value for the semidiameter of the sun.
+
+=== Instruments that derived from the Davis quadrant ===
+The Elton's quadrant derived from the Davis quadrant.  It added an index arm with spirit levels to provide an artificial horizon.
+
+== Demi-cross ==
+
+The demi-cross was an instrument that was contemporary with the Davis quadrant.  It was popular outside England.
+The vertical transom was like a half-transom on a cross-staff, hence the name demi-cross.  It supported a shadow vane (A in Figure 4) that could be set to one of several heights (three according to May, four according to de Hilster).  By setting the shadow vane height, the range of angles that could be measured was set.  The transom could be slid along the staff and the angle read from one of the graduated scales on the staff.
+The sight vane (C) and horizon vane (B) were aligned visually with the horizon.  With the shadow vane's shadow cast on the horizon vane and aligned with the horizon, the angle was determined.  In practice, the instrument was accurate but more unwieldy than the Davis quadrant.
+
+== Plough ==
+
+The plough was the name given to an unusual instrument that existed for a short time. It was part cross-staff and part backstaff. In Figure 5, A is the transom that casts its shadow on the horizon vane at B. It functions in the same manner as the staff in Figure 1. C is the sighting vane. The navigator uses the sighting vane and the horizon vane to align the instrument horizontally. The sighting vane can be moved left to right along the staff. D is a transom just as one finds on a cross-staff. This transom has two vanes on it that can be moved closer or farther from the staff to emulate different-length transoms. The transom can be moved on the staff and used to measure angles.
+
+== Almucantar staff ==
+
+The Almucantar staff is a device specifically used for measuring the altitude of the sun at low altitudes.
+
+== Cross-staff ==
+
+The cross-staff was normally a direct observation instrument.  However, in later years it was modified for use with back observations.
+
+== Quadrant ==
+There was a variation of the quadrant – the Back observation quadrant – that was used for measuring the sun's altitude by observing the shadow cast on a horizon vane.
+
+== Thomas Hood cross-staff ==
+
+Thomas Hood invented this cross-staff in 1590. It could be used for surveying, astronomy or other geometric problems.
+It consists of two components, a transom and a yard.  The transom is the vertical component and is graduated from 0° at the top to 45° at the bottom.  At the top of the transom, a vane is mounted to cast a shadow.  The yard is horizontal and is graduated from 45° to 90°.  The transom and yard are joined by a special fitting (the double socket in Figure 6) that permits independent adjustments of the transom vertically and the yard horizontally.
+It was possible to construct the instrument with the yard at the top of the transom rather than at the bottom.
+Initially, the transom and yard are set so that the two are joined at their respective 45° settings.  The instrument is held so that the yard is horizontal (the navigator can view the horizon along the yard to assist in this).  The socket is loosened so that the transom is moved vertically until the shadow of the vane is cast at the yard's 90° setting.  If the movement of just the transom can accomplish this, the altitude is given by the transom's graduations.  If the sun is too high for this, the yard horizontal opening in the socket is loosened and the yard is moved to allow the shadow to land on the 90° mark.  The yard then yields the altitude.
+It was a fairly accurate instrument, as the graduations were well spaced compared to a conventional cross-staff.  However, it was a bit unwieldy and difficult to handle in wind.

data/en.wikipedia.org/wiki/Backstaff-2.md

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+---
+title: "Backstaff"
+chunk: 3/3
+source: "https://en.wikipedia.org/wiki/Backstaff"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:31.201916+00:00"
+instance: "kb-cron"
+---
+
+== Benjamin Cole quadrant ==
+  
+A late addition to the collection of backstaves in the navigation world, this device was invented by Benjamin Cole in 1748.
+The instrument consists of a staff with a pivoting quadrant on one end.  The quadrant has a shadow vane, which can optionally take a lens like the Davis quadrant's Flamsteed glass, at the upper end of the graduated scale (A in Figure 7).  This casts a shadow or projects an image of the sun on the horizon vane (B).  The observer views the horizon through a hole in the sight vane (D) and a slit in the horizon vane to ensure the instrument is level.  The quadrant component is rotated until the horizon and the sun's image or shadow are aligned.  The altitude can then be read from the quadrant's scale.  In order to refine the reading, a circular vernier is mounted on the staff (C).
+The fact that such an instrument was introduced in the middle of the 18th century shows that the quadrant was still a viable instrument even in the presence of the octant.
+English scientist George Adams created a very similar backstaff at the same time. Adam's version ensured that the distance between the Flamsteed glass and horizon vane was the same as the distance from the vane to the sight vane.
+
+== Cross bow quadrant ==
+
+Edmund Gunter invented the cross bow quadrant, also called the mariner's bow, around 1623. It gets its name from the similarity to the archer's crossbow.
+This instrument is interesting in that the arc is 120° but is only graduated as a 90° arc. As such, the angular spacing of a degree on the arc is slightly greater than one degree.  Examples of the instrument can be found with a 0° to 90° graduation or with two mirrored 0° to 45° segments centred on the midpoint of the arc.
+The instrument has three vanes, a horizon vane (A in Figure 8) which has an opening in it to observe the horizon, a shadow vane (B) to cast a shadow on the horizon vane and a sighting vane (C) that the navigator uses to view the horizon and shadow at the horizon vane.  This serves to ensure the instrument is level while simultaneously measuring the altitude of the sun.  The altitude is the difference in the angular positions of the shadow and sighting vanes.
+With some versions of this instrument, the sun's declination for each day of the year was marked on the arc.  This permitted the navigator to set the shadow vane to the date and the instrument would read the altitude directly.
+
+== References ==
+Ephraim Chambers, Cyclopædia, The First Volume, 1728 explaining the use of a backstaff
+Maurice Daumas,  Scientific Instruments of the Seventeenth and Eighteenth Centuries and Their Makers, Portman Books, London 1989  ISBN 978-0-7134-0727-3
+Gerard L'Estrange Turner, Antique Scientific Instruments, Blandford Press Ltd. 1980 ISBN 0-7137-1068-3
+
+== Notes ==
+
+== External links ==
+"Backstaff" at answers.com – Good diagram of how a backstaff is held in use.
+Attribution
+ This article incorporates text from a publication now in the public domain: Chambers, Ephraim, ed. (1728). Cyclopædia, or an Universal Dictionary of Arts and Sciences (1st ed.). James and John Knapton, et al. {{cite encyclopedia}}: Missing or empty |title= (help)

data/en.wikipedia.org/wiki/Ballistic_galvanometer-0.md

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+---
+title: "Ballistic galvanometer"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Ballistic_galvanometer"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:32.373814+00:00"
+instance: "kb-cron"
+---
+
+A ballistic galvanometer is a type of sensitive galvanometer; commonly a mirror galvanometer. Unlike a current-measuring galvanometer, the moving part has a large moment of inertia, thus giving it a long oscillation period. It is really an integrator measuring the quantity of charge discharged through it. It can be either of the moving coil or moving magnet type.
+
+Before first use the ballistic constant of the galvanometer must be determined. This is usually done by connecting to the galvanometer a known capacitor, charged to a known voltage, and recording the deflection. The constant K is calculated from the capacitance C, the voltage V and the deflection d:
+
+  
+    
+      
+        K
+        =
+        C
+        V
+        
+          /
+        
+        d
+      
+    
+    {\displaystyle K=CV/d}
+  
+
+where K is expressed in coulombs per centimeter.
+In operation the unknown quantity of charge Q (in coulombs) is simply: 
+
+  
+    
+      
+        Q
+        =
+        k
+        d
+      
+    
+    {\displaystyle Q=kd}
+  
+.
+
+
+== Grassot Fluxmeter ==
+The Grassot Fluxmeter solves a particular problem encountered with regular galvanometers.
+For a regular galvanometer, the discharge time must be shorter than the natural period of oscillation of the mechanism.  In some applications, particularly those involving inductors, this condition cannot be met.  The Grassot fluxmeter resolves this problem, by operating without any restoring force, making the oscillation period effectively infinite and thereby longer than any discharge time.
+Its construction is similar to that of a ballistic galvanometer, but its coil is suspended without any restoring forces in the suspension thread or in the current leads. The core (bobbin) of the coil is of a non-conductive material. When an electric charge is connected to the instrument, the coil starts moving in the magnetic field of the galvanometer's magnet, generating an opposing electromotive force and coming to a stop regardless of the time of the current flow. The change in the coil position is proportional only to the quantity of charge. The coil is returned to the zero position manually or by reversing the direction of the current.
+
+
+== References ==
+
+Earle Terry, Advanced Laboratory Practice in Electricity and Magnetism. McGraw-Hill,   New York 1929 Page 24-34
+Electrical Instruments, "Tylor-Cambridge", Cambridge Scientific Instrument Company, Trade catalog, 1908 Page 34
+Bakshi, U.A. and Bakshi, L.A.V., Electronic Measurements and Instrumentation, Technical Publications, 2020, Chapter 2
+Bakshi, U.A. and Bakshi, L.A.V., Electric Measurements and Instrumentation, Technical Publications, 2020, Chapter 2

data/en.wikipedia.org/wiki/Barcelona_astrolabe-0.md

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+---
+title: "Barcelona astrolabe"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Barcelona_astrolabe"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:33.541647+00:00"
+instance: "kb-cron"
+---
+
+The Barcelona astrolabe is the oldest astrolabe with Carolingian characters that has survived in the Christian Occident.
+The French researcher Marcel Destombes founded the astrolabe, and left it as legacy to the Institute of the Arab World of Paris in 1983.
+The Academy of Sciences of Barcelona asked the astrolabe in loan to the Musée of l'Institut du Monde Arabe, to make a replica, today this replica is on display at the Academy of Sciences in the Ramblas.
+
+
+== Description ==
+This astrolabe presents some unusual characteristics. All the engraved characters are in Latin, this fact made the scholars think that the instrument was made in  Christian Europe. The pointers of his "spider" indicate eighteen stars: ten boreal stars and eight austral stars (that is to say, situated beneath of the equator). Eleven of them correspond to the date of 980 AD. Still like this, the names of the stars are not engraved on the brass. The words ROMA and FRANCIA are engraved in Latin characters in one of the eardrums. These characters are accompanied by the numbers 41-30 (in Arabic figures). The characters are identical to those used at the end of the 10th century in the Catalan Latin manuscripts, being Catalonia in that moment a mark of the Carolingian France. This would explain the presence of the word FRANCIA. The figures express in degrees and minutes: 41° 30′, which correspond exactly to the latitude of Barcelona.
+The fact of having engraved the date 980 AD. and the latitude of Barcelona (41–30), which archdeacon in those dates was Sunifred Llobet, to whom is attributed the authorship of the Ripoll manuscript: ms.225, which contains the description of an astrolabe, has led the scholars to attribute the paternity of the astrolabe to this famous astronomer.
+
+
+== Data ==
+Name: Astrolabe of Barcelona
+Place of manufacture: Barcelona, Principality of Catalonia
+Date / period: To the year 980
+Material and technical: Brass decorated with recorded
+Dimensions: 15,2 cm of diameter
+Conservation (city): Paris
+Conservation (place): Bequeathed by Marcel Destombes to the Musée of l'Institut du Monde Arabe (Paris)
+Number of inventory: AY 86-31
+
+
+== See also ==
+Gerbert of Aurillac
+
+
+== References ==
+
+
+== External links ==
+‘Carolingian' astrolabe. To Qantara – Mediterranean Heritage (English)

data/en.wikipedia.org/wiki/British_Society_for_the_History_of_Science-0.md

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+---
+title: "British Society for the History of Science"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/British_Society_for_the_History_of_Science"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:34:53.464500+00:00"
+instance: "kb-cron"
+---
+
+The British Society for the History of Science (BSHS) was founded in 1947 by Francis Butler, Joan Eyles and Victor Eyles.
+
+
+== Overview ==
+It is Britain's largest learned society devoted to the history of science, technology, and medicine. The society's aim is to bring together people with interests in all aspects of the field, and to publicise relevant ideas within the wider research and teaching communities and the media. Its mission statement states the society will strive "to foster the understanding of the history and social impact of science, technology and medicine in all their branches in the academic and the wider communities, and to provide a national focus for the discipline."
+Publications are a key feature of the society's professional activity. Print publications include:
+
+The British Journal for the History of Science (BJHS): a peer-reviewed quarterly academic journal, including articles and reviews of the latest books in the history of science, technology and medicine
+BJHS Themes: a peer-reviewed open access academic journal, an annual themed collection of articles
+Viewpoint: magazine of the society, published three times a year and featuring news and views from across the field
+BSHS Monographs: work of lasting scholarly value that might not otherwise be made available, and aids the dissemination of innovative projects advancing scholarship or education in the field
+Other publications are online, including the BSHS List of Theses, and the BSHS Guide to Institutions.
+The society also awards several prizes:
+
+The Singer Prize, awarded every two years for an unpublished research essay by new scholars
+The BSHS Hughes Prize, awarded every two years to the best history of science book written for a popular audience
+The BSHS Slade Prize, awarded between 1999 and 2009 for studies of conceptual innovation or scientific methodology
+The BSHS John Pickstone Prize, awarded every two years to the best scholarly history of science book written in English
+
+
+== Presidents ==
+Presidents from the Society's founding up to 1997 are reported by Janet Browne in a British Journal for the History of Science article.
+
+1946–48 Charles Joseph Singer
+1949–51 J. R. Partington
+1951–53 Frank Sherwood Taylor
+1953–55 H. Hamshaw Thomas
+1955–57 Herbert Dingle
+1957–62 E. Ashworth Underwood
+1962–64 Thomas Martin
+1964–66 Alistair Cameron Crombie
+1966–68 Alfred Rupert Hall
+1968–70 G. J. Whitrow
+1970–72 W. P. D. Wightman
+1972–74 John Anthony Chaldecott
+1974–76 Maurice P. Crosland
+1976–78 D. W. Waters
+1978–80 William Hodson Brock
+1980–82 Robert Fox (historian)
+1982–84 Jack B. Morrell
+1984–86 Gerard L'Estrange Turner
+1986–88 Colin A. Russell
+1988–90 Robert G. W. Anderson
+1990–92 Hugh S. Torrens
+1992–94 Geoffrey Cantor
+1994–96 D. M. Knight
+1996–98 John Hedley Brooke
+1998–2000 Ludmilla Jordanova
+2000–01 James Arthur Bennett
+2002–03 Janet Browne
+2004–06 Peter Bowler
+2006–08 Frank James
+2008–09 Jeff Hughes
+2010–12 Sally Horrocks
+2012–14 Hasok Chang
+2014‒16 Gregory Radick
+2016–18 Patricia Fara
+2018–20 Tim Boon
+2020–22 Charlotte Sleigh
+2022–24 James A. Secord
+2024–present Chiara Ambrosio
+
+
+== Wikipedia ==
+The society hosted an editathon at their annual conference in July 2015 at Swansea, which included wiki–skills training, and which resulted in better content on British scientists on Wikipedia.
+
+
+== References ==
+
+
+== External links ==
+Official website

data/en.wikipedia.org/wiki/Bygrave_slide_rule-0.md

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+---
+title: "Bygrave slide rule"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Bygrave_slide_rule"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:34.708068+00:00"
+instance: "kb-cron"
+---
+
+The Bygrave slide rule is a slide rule named for its inventor, Captain Leonard Charles Bygrave of the RAF.  It was used in celestial navigation, primarily in aviation. Officially, it was called the A. M. L. Position Line Slide Rule (A.M.L. for Air Ministry Laboratories).
+It was developed in 1920 at the Air Ministry Laboratories at Kensington in London and was produced by Henry Hughes & Son Ltd of London until the mid-1930s. It solved the so-called celestial triangle accurately to about one minute of arc and quickly enough for aerial navigation.  The solution of the celestial triangle used the John Napier rules for solution of square-angled spherical triangles.  The slide rule was constructed as two coaxial tubes with spiral scales, like the Fuller's cylindrical slide rules, with yet another tube on the outside carrying the cursors.
+During the Second World War, a closely related version was produced in Germany by Dennert & Pape as the HR1, MHR1 and HR2.
+
+
+== Famous users ==
+Sir Francis Chichester was a renowned aviator and yachtsman. He used a Bygrave Slide Rule as an aid to navigation during flights in the 1930s, one of which was the first solo flight from New Zealand to Australia in a Gipsy Moth biplane. He later completed a round the world cruise in his yacht Gipsy Moth IV. This was the first solo circumnavigation using the clipper route. Sir Francis Chichester wrote about these exploits in his autobiography, entitled The Lonely Sea and the Sky.
+
+
+== See also ==
+Otis King's Patent Calculator
+
+
+== References ==
+
+
+== External links ==
+
+LaPook, Gary. "Modern Bygrave Slide Rule".
+van Riet, Ronald W.M. "Position Line Slide Rules" (PDF).

data/en.wikipedia.org/wiki/C._H._Douglas-0.md

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+---
+title: "C. H. Douglas"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/C._H._Douglas"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:35:18.412919+00:00"
+instance: "kb-cron"
+---
+
+Major Clifford Hugh Douglas, MIMechE, MIEE (20 January 1879 – 29 September 1952), was a British engineer, economist and pioneer of the social credit economic reform movement.
+
+
+== Education and engineering career ==
+C. H. Douglas was born in either Edgeley or Manchester, the son of Hugh Douglas and his wife Louisa (Hordern) Douglas. Few details are known about his early life and training; he probably served an engineering apprenticeship before beginning an engineering career that brought him to locations throughout the British Empire in the employ of electric companies, railways and other institutions.  He taught at Stockport Grammar School. After a period in industry, he went up to Pembroke College, Cambridge, at the age of 31 but stayed only four terms and left without graduating. 
+He worked for the Westinghouse Electric Corporation of America and claimed to have been the Reconstruction Engineer for the British Westinghouse Company in India (the company has no record of him ever working there), Deputy Chief Engineer of the Buenos Aires and Pacific Railway Company, Railway Engineer of the London Post Office (Tube) Railway and Assistant Superintendent of the Royal Aircraft Factory Farnborough during World War I, with a temporary commission as captain in the Royal Flying Corps. His second wife was Edith Mary Douglas, President of the Women's Engineering Society.
+
+
+== Social credit ==
+While he was reorganising the work of the Royal Aircraft Establishment during World War I, Douglas noticed that the weekly total costs of goods produced was greater than the sums paid to workers for wages, salaries and dividends. This seemed to contradict the theory of classic Ricardian economics, saying that all costs are distributed simultaneously as purchasing power.
+Troubled by the seeming difference between the way money flowed and the objectives of industry ("delivery of goods and services", in his view), Douglas set out to apply engineering methods to the economic system.
+Douglas collected data from more than 100 large British businesses and found that all except those becoming bankrupt, spent less in salaries, wages and dividends than the value of goods and services produced each week: the workers were not paid enough to buy back what they had made.  He published his observations and conclusions in an article in the magazine English Review where he suggested: "That we are living under a system of accountancy which renders the delivery of the nation's goods and services to itself a technical impossibility."  The reason, Douglas concluded, was that the economic system was organized to maximize profits for those with economic power by creating unnecessary scarcity.  Between 1916 and 1920, he developed his economic ideas, publishing two books in 1920, Economic Democracy and Credit-Power and Democracy, followed in 1924 by Social Credit.
+The basis of Douglas's reform ideas was to free workers from this system by bringing purchasing power in line with production, which became known as social credit. His proposal had two main elements: a national dividend to distribute money (debt-free credit) equally to all citizens, over and above their earnings, to help bridge the gap between purchasing power and prices; also a price adjustment mechanism, called the "just price", to forestall inflation. The just price would effectively reduce retail prices by a percentage that reflected the physical efficiency of the production system. Douglas observed that the cost of production is consumption; meaning the exact physical cost of production is the total resources consumed in the production process. As the physical efficiency of production increases, the just price mechanism will reduce the price of products for the consumer. The consumers can then buy as much of what the producers produce that they want and automatically control what continues to be produced by their consumption of it. Individual freedom, primary economic freedom, was the central goal of Douglas's reform.
+At the end of World War I, Douglas retired from engineering to promote his reform ideas full-time, which he would do for the rest of his life. His ideas inspired the Canadian social credit movement (which obtained control of Alberta's provincial government in 1935), the short-lived Douglas Credit Party in Australia and the longer-lasting Social Credit Political League in New Zealand.  Douglas also lectured on social credit in the United States, the United Kingdom, Ireland, Canada, France, Germany, Italy, Japan, Australia, New Zealand and Norway.
+In 1923, he appeared as a witness before the Canadian Banking Inquiry, and in 1930 before the Macmillan Committee. In 1929 he made a lecture tour of Japan, where his ideas were enthusiastically received by industry and government. His 1933 edition of Social Credit made a reference to the Protocols of the Elders of Zion, which, while noting its dubious authenticity, wrote that what "is interesting about it, is the fidelity with which the methods by which such enslavement might be brought about can be seen reflected in the facts of everyday experience."
+
+
+== Death and legacy ==
+Douglas died in his home in Fearnan, Scotland.  Douglas and his theories are referred to several times (unsympathetically) in Lewis Grassic Gibbon's trilogy A Scots Quair. He is also mentioned, together with Karl Marx and Silvio Gesell, by John Maynard Keynes in The General Theory of Employment, Interest, and Money (1936, p. 32). Douglas's theories permeate the poetry and economic writings of Ezra Pound. Robert Heinlein's first novel For Us, The Living: A Comedy of Customs describes a near future United States operating according to the principles of social credit.
+
+
+== Publications ==
+Economic Democracy (1920) new edition:  December 1974; Bloomfield Books; ISBN 0-904656-06-3
+Credit-Power and Democracy (1920) new edition:  August 2011; BiblioLife; ISBN 978-1241274955
+The Control and Distribution of Production (1922)
+Social Credit (1924, Revised 1933) new edition:  December 1979; Institute of Economic Democracy, Canada; ISBN 0-920392-26-1
+Warning Democracy, C M Grieve, London; (1931)
+The Monopoly of Credit (1931) new edition:  1979; Bloomfield Books; ISBN 0-904656-02-0
+The Use of Money (1935)
+The Alberta Experiment: An Interim Survey (1937)
+The Brief for the Prosecution, Legion for the Survival of Freedom, Incorporated; (December 1986) ISBN 0-949667-80-3
+Whose Service is Perfect Freedom?, Canada; Veritas Publishing Company; (June 1986) ISBN 0-949667-64-1
+The Big Idea, Veritas Publishing Company, Canada; (June 1986) ISBN 0-88636-000-5
+The Grip of Death, Jon Carpenter, UK; (May 1998) ISBN 1-897766-40-8
+
+
+== See also ==
+
+Monetary reform
+Monetary reform in Britain
+
+
+== Notes ==
+
+
+== References ==
+Janet Martin-Nielsen, "An Engineer’s View of an Ideal Society: The Economic Reforms of C.H. Douglas, 1916-1920", Spontaneous Generations, Vol. 1, No. 1 (2007), pp. 95–109
+George Orwell, The Road to Wigan Pier, Chapter VI
+
+
+== Further reading ==
+Major Douglas and Alberta Social Credit by Bob Hesketh ISBN 0-8020-4148-5
+Clifford Hugh Douglas by Anthony Cooney ISBN 0-9535077-4-2
+Four monetary heretics by Hugh Gaitskell in What Everybody Wants To Know About Money Gollancz 1936
+
+
+== External links ==
+Works by or about C. H. Douglas at the Internet Archive
+Works by Clifford Hugh Douglas at Faded Page (Canada)
+Social Credit Secretariat
+Australian League of Rights online library
+Guido Giacomo Preparata – Major Douglas in the witness box

data/en.wikipedia.org/wiki/Cabinet_of_curiosities-0.md

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+---
+title: "Cabinet of curiosities"
+chunk: 1/5
+source: "https://en.wikipedia.org/wiki/Cabinet_of_curiosities"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:35.931697+00:00"
+instance: "kb-cron"
+---
+
+Cabinets of curiosities (German: Kunstkammer [ˈkʊnstˌkamɐ] and Kunstkabinett [ˈkʊnstkabiˌnɛt]), also known as wonder-rooms (German: Wunderkammer [ˈvʊndɐˌkamɐ] ), were encyclopedic collections of objects whose categorical boundaries were, in Renaissance Europe, yet to be defined.  Although more rudimentary collections had preceded them, the classic cabinets of curiosities emerged in the sixteenth century. The term cabinet originally described a room rather than a piece of furniture. Modern terminology would categorize the objects included as belonging to natural history (sometimes faked), geology, ethnography, archaeology, religious or historical relics, works of art (including cabinet paintings), and antiquities. In addition to the most famous and best documented cabinets of rulers and aristocrats, members of the merchant class and early practitioners of science in Europe formed collections that were precursors to museums.
+
+Cabinets of curiosities served not only as collections to reflect the particular interests of their curators but also as social devices to establish and uphold rank in society. There are said to be two main types of cabinets. As R. J. W. Evans notes, there could be "the princely cabinet, serving a largely representational function, and dominated by aesthetic concerns and a marked predilection for the exotic," or the less grandiose, "the more modest collection of the humanist scholar or virtuoso, which served more practical and scientific purposes." Evans goes on to explain that "no clear distinction existed between the two categories: all collecting was marked by curiosity, shading into credulity, and by some sort of universal underlying design".
+In addition to cabinets of curiosity serving as an establisher of socioeconomic status for its curator, these cabinets served as entertainment, as particularly illustrated by the proceedings of the Royal Society, whose early meetings were often a sort of open floor to any Fellow to exhibit the findings his curiosities led him to. However purely educational or investigative these exhibitions may sound, the Fellows in this period supported the idea of "learned entertainment," or the alignment of learning with entertainment. This was not unusual, as the Royal Society had an earlier history of a love of the marvellous. This love was often exploited by eighteenth-century natural philosophers to secure the attention of their audience during their exhibitions.
+
+== History ==
+
+=== To c. 1600 ===
+The earliest pictorial record of a natural history cabinet is the engraving in Ferrante Imperato's Dell'Historia Naturale (Naples 1599) (illustration). It serves to authenticate its author's credibility as a source of natural history information, by showing his open bookcases (at the right), in which many volumes are stored lying down and stacked, in the medieval fashion, or with their spines upward, to protect the pages from dust. Some of the volumes doubtless represent his herbarium. Every surface of the vaulted ceiling is occupied with preserved fishes, stuffed mammals and curious shells, with a stuffed crocodile suspended in the centre. Examples of corals stand on the bookcases. At the left, the room is fitted out like a studiolo with a range of built-in cabinets whose fronts can be unlocked and let down to reveal intricately fitted nests of pigeonholes forming architectural units, filled with small mineral specimens. Above them, stuffed birds stand against panels inlaid with square polished stone samples, doubtless marbles and jaspers or fitted with pigeonhole compartments for specimens. Below them, a range of cupboards contain specimen boxes and covered jars.
+
+In 1587 Gabriel Kaltemarckt advised Christian I of Saxony that three types of items were indispensable in forming a "Kunstkammer" or art collection: firstly sculptures and paintings; secondly "curious items from home or abroad"; and thirdly "antlers, horns, claws, feathers and other things belonging to strange and curious animals". When Albrecht Dürer visited the Netherlands in 1521, apart from artworks he sent back to Nuremberg various animal horns, a piece of coral, some large fish fins and a wooden weapon from the East Indies. 
+The highly characteristic range of interests represented in Frans II Francken's painting of 1636 (illustration, above) shows paintings on the wall that range from landscapes, including a moonlit scene—a genre in itself—to a portrait and a religious picture (the Adoration of the Magi) intermixed with preserved tropical marine fish and a string of carved beads, most likely amber, which is both precious and a natural curiosity. Sculptures both classical and secular (the sacrificing Libera, a Roman fertility goddess) on the one hand and modern and religious (Christ at the Column) are represented, while on the table are ranged, among the exotic shells (including some tropical ones and a shark's tooth): portrait miniatures, gem-stones mounted with pearls in a curious quatrefoil box, a set of sepia chiaroscuro woodcuts or drawings, and a small still-life painting leaning against a flower-piece, coins and medals—presumably Greek and Roman—and Roman terracotta oil-lamps, a Chinese-style brass lock, curious flasks, and a blue-and-white Ming porcelain bowl.
+
+The Kunstkammer of Rudolf II, Holy Roman Emperor (ruled 1576–1612), housed in the Hradschin at Prague, was unrivalled north of the Alps; it provided solace and retreat for contemplation that also served to demonstrate his imperial magnificence and power in the symbolic arrangement of their display, ceremoniously presented to visiting diplomats and magnates. 
+Rudolf's uncle, Ferdinand II, Archduke of Austria, also had a collection, organized by his treasurer, Leopold Heyperger, which put special emphasis on paintings of people with interesting deformities, which remains largely intact as the Chamber of Art and Curiosities at Ambras Castle in Austria. "The Kunstkammer was regarded as a microcosm or theater of the world, and a memory theater. The Kunstkammer conveyed symbolically the patron's control of the world through its indoor, microscopic reproduction." Of Charles I of England's collection, Peter Thomas states succinctly, "The Kunstkabinett itself was a form of propaganda."
+
+=== 17th century ===

data/en.wikipedia.org/wiki/Cabinet_of_curiosities-1.md

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+---
+title: "Cabinet of curiosities"
+chunk: 2/5
+source: "https://en.wikipedia.org/wiki/Cabinet_of_curiosities"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:35.931697+00:00"
+instance: "kb-cron"
+---
+
+Two of the most famously described seventeenth-century cabinets were those of Ole Worm, known as Olaus Wormius (1588–1654) (illustration, above right), and Athanasius Kircher (1602–1680). These seventeenth-century cabinets were filled with preserved animals, horns, tusks, skeletons, minerals, as well as other interesting man-made objects: sculptures wondrously old, wondrously fine or wondrously small; clockwork automata; ethnographic specimens from exotic locations. Often they would contain a mix of fact and fiction, including apparently mythical creatures. Worm's collection contained, for example, what he thought was a Scythian Lamb, a woolly fern thought to be a plant/sheep fabulous creature. However he was also responsible for identifying the narwhal's tusk as coming from a whale rather than a unicorn, as most owners of these believed. The specimens displayed were often collected during exploring expeditions and trading voyages.
+Cabinets of curiosities would often serve scientific advancement when images of their contents were published. The catalog of Worm's collection, published as the Museum Wormianum (1655), used the collection of artifacts as a starting point for Worm's speculations on philosophy, science, natural history, and more.
+Cabinets of curiosities were limited to those who could afford to create and maintain them. Many monarchs, in particular, developed large collections. A rather under-used example, stronger in art than other areas, was the Studiolo of Francesco I, the first Medici Grand-Duke of Tuscany. Frederick III of Denmark, who added Worm's collection to his own after Worm's death, was another such monarch. A third example is the Kunstkamera founded by Peter the Great in Saint Petersburg in 1714. Many items were bought in Amsterdam from Albertus Seba and Frederik Ruysch. The fabulous Habsburg Imperial collection included important Aztec artifacts, including the feather head-dress or crown of Montezuma now in the Museum of Ethnology, Vienna. 
+Similar collections on a smaller scale were the complex Kunstschränke produced in the early seventeenth century by the Augsburg merchant, diplomat and collector Philipp Hainhofer. These were cabinets in the sense of pieces of furniture, made from all imaginable exotic and expensive materials and filled with contents and ornamental details intended to reflect the entire cosmos on a miniature scale. The best preserved example is the one given by the city of Augsburg to King Gustavus Adolphus of Sweden in 1632, which is kept in the Museum Gustavianum in Uppsala. The curio cabinet, as a modern single piece of furniture, is a version of the grander historical examples.
+The juxtaposition of such disparate objects, according to Horst Bredekamp's analysis (Bredekamp 1995), encouraged comparisons, finding analogies and parallels and favoured the cultural change from a world viewed as static to a dynamic view of endlessly transforming natural history and a historical perspective that led in the seventeenth century to the germs of a scientific view of reality.
+
+=== 18th century and after ===
+
+In seventeenth-century parlance, both French and English, a cabinet came to signify a collection of works of art, which might still also include an assembly of objects of virtù or curiosities, such as a virtuoso would find intellectually stimulating. In 1714, Michael Bernhard Valentini published an early museological work, Museum Museorum, an account of the cabinets known to him with catalogues of their contents.
+
+In the second half of the eighteenth century, Belsazar Hacquet (c. 1735 – 1815) operated in Ljubljana, then the capital of Carniola, a natural history cabinet (German: Naturalienkabinet) that was appreciated throughout Europe and was visited by the highest nobility, including the Holy Roman Emperor, Joseph II, the Russian grand duke Paul and Pope Pius VI, as well as by famous naturalists, such as Francesco Griselini and Franz Benedikt Hermann. It included a number of minerals, including specimens of mercury from the Idrija mine, a herbarium vivum with over 4,000 specimens of Carniolan and foreign plants, a smaller number of animal specimens, a natural history and medical library, and an anatomical theatre.
+A late example of the juxtaposition of natural materials with richly worked artifice is provided by the "Green Vaults" formed by Augustus the Strong in Dresden to display his chamber of wonders. The "Enlightenment Gallery" in the British Museum, installed in the former "Kings Library" room in 2003 to celebrate the 250th anniversary of the museum, aims to recreate the abundance and diversity that still characterized museums in the mid-eighteenth century, mixing shells, rock samples and botanical specimens with a great variety of artworks and other man-made objects from all over the world.
+Some strands of the early universal collections, the bizarre or freakish biological specimens, whether genuine or fake, and the more exotic historical objects, could find a home in commercial freak shows and sideshows.
+
+=== England ===
+
+In 1671, when visiting Thomas Browne (1605–1682), the courtier John Evelyn remarked,
+
+His whole house and garden is a paradise and Cabinet of rarities and that of the best collection, amongst Medails, books, Plants, natural things.
+Late in his life Browne parodied the rising trend of collecting curiosities in his tract Musaeum Clausum, an inventory of dubious, rumoured and non-existent books, pictures and objects.
+
+Sir Hans Sloane (1660–1753) an English physician, member of the Royal Society and the Royal College of Physicians, and the founder of the British Museum in London, began sporadically collecting plants in England and France while studying medicine. In 1687, the Duke of Albemarle offered Sloane a position as personal physician to the West Indies fleet at Jamaica. He accepted and spent fifteen months collecting and cataloguing the native plants, animals, and artificial curiosities (e.g. cultural artifacts of native and enslaved African populations) of Jamaica. This became the basis for his two volume work, Natural History of Jamaica, published in 1707 and 1725. Sloane returned to England in 1689 with over eight hundred specimens of plants, which were live or mounted on heavy paper in an eight-volume herbarium. He also attempted to bring back live animals (e.g., snakes, an alligator, and an iguana) but they all died before reaching England.

data/en.wikipedia.org/wiki/Cabinet_of_curiosities-2.md

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+---
+title: "Cabinet of curiosities"
+chunk: 3/5
+source: "https://en.wikipedia.org/wiki/Cabinet_of_curiosities"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:35.931697+00:00"
+instance: "kb-cron"
+---
+
+Sloane meticulously cataloged and created extensive records for most of the specimens and objects in his collection. He also began to acquire other collections by gift or purchase. Herman Boerhaave gave him four volumes of plants from Boerhaave's gardens at Leiden. William Charleton, in a bequest in 1702, gave Sloane numerous books of birds, fish, flowers, and shells and his miscellaneous museum consisting of curiosities, miniatures, insects, medals, animals, minerals, precious stones and curiosities in amber. Sloane purchased Leonard Plukenet's collection in 1710. It consisted of twenty-three volumes with over 8,000 plants from Africa, India, Japan and China. Mary Somerset, Duchess of Beaufort (1630–1715), left him a twelve-volume herbarium from her gardens at Chelsea and Badminton upon her death in 1714. Reverend Adam Buddle gave Sloane thirteen volumes of British plants. In 1716, Sloane purchased Engelbert Kaempfer's volume of Japanese plants and James Petiver's virtual museum of approximately one hundred volumes of plants from Europe, North America, Africa, the Near East, India, and the Orient. Mark Catesby gave him plants from North America and the West Indies from an expedition funded by Sloane. Philip Miller gave him twelve volumes of plants grown from the Chelsea Physic Garden.
+Sloane acquired approximately three hundred and fifty artificial curiosities from North American Indians, Inuit, South America, Lapland, Siberia, East Indies, and the West Indies, including nine items from Jamaica.
+"These ethnological artifacts were important because they established a field of collection for the British Museum that was to increase greatly with the explorations of Captain James Cook in Oceania and Australia and the rapid expansion of the British Empire."
+Upon his death in 1753, Sloane bequeathed his sizable collection of 337 volumes to England for £20,000. In 1759, George II's royal library was added to Sloane's collection to form the foundation of the British Museum.
+John Tradescant the Elder (circa 1570s–1638) was a gardener, naturalist, and botanist in the employ of the Duke of Buckingham. He collected plants, bulbs, flowers, vines, berries, and fruit trees from Russia, the Levant, Algiers, France, Bermuda, the Caribbean, and the East Indies. His son, John Tradescant the Younger (1608–1662) traveled to Virginia in 1637 and collected flowers, plants, shells, an Indian deerskin mantle believed to have belonged to Powhatan, father of Pocahontas. Father and son, in addition to botanical specimens, collected zoological (e.g., the dodo from Mauritius, the upper jaw of a walrus, and armadillos), artificial curiosities (e.g., wampum belts, portraits, lathe turned ivory, weapons, costumes, Oriental footwear and carved alabaster panels) and rarities (e.g., a mermaid's hand, a dragon's egg, two feathers of a phoenix's tail, a piece of the True Cross, and a vial of blood that rained in the Isle of Wight). By the 1630s, the Tradescants displayed their eclectic collection at their residence in South Lambeth. Tradescant's Ark, as it came to be known, was the earliest major cabinet of curiosity in England and open to the public for a small entrance fee.
+Elias Ashmole (1617–1692) was a lawyer, chemist, antiquarian, Freemason, and a member of the Royal Society with a keen interest in astrology, alchemy, and botany. Ashmole was also a neighbor of the Tradescants in Lambeth. He financed the publication of Musaeum Tradescantianum, a catalogue of the Ark collection in 1656. Ashmole, a collector in his own right, acquired the Tradescant Ark in 1659 and added it to his collection of astrological, medical, and historical manuscripts. In 1675, he donated his library and collection and the Tradescant collection to the University of Oxford, provided that a suitable building be provided to house the collection. Ashmole's donation formed the foundation of the Ashmolean Museum at Oxford.
+Places of exhibitions of and places of new societies that promoted natural knowledge also seemed to culture the idea of perfect civility. Some scholars propose that this was "a reaction against the dogmatism and enthusiasm of the English Civil War and Interregum [sic]." This move to politeness put bars on how one should behave and interact socially, which enabled the distinguishing of the polite from the supposed common or more vulgar members of society. Exhibitions of curiosities (as they were typically odd and foreign marvels) attracted a wide, more general audience, which "[rendered] them more suitable subjects of polite discourse at the Society." 
+A subject was considered less suitable for polite discourse if the curiosity being displayed was accompanied by too much other material evidence, as it allowed for less conjecture and exploration of ideas regarding the displayed curiosity. Because of this, many displays simply included a concise description of the phenomena and avoided any mention of explanation for the phenomena. Quentin Skinner describes the early Royal Society as "something much more like a gentleman's club," an idea supported by John Evelyn, who depicts the Royal Society as "an Assembly of many honorable Gentlemen, who meete inoffensively together under his Majesty's Royal Cognizance; and to entertaine themselves ingenously, whilst their other domestique avocations or publique business deprives them of being always in the company of learned men and that they cannot dwell forever in the Universities."
+Cabinets of Curiosities can now be found at Snowshill Manor and Wallington Hall, and the Ashmolean Museum has a display of items from its disparate Ashmole and Tradescant founding collections.

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+---
+title: "Cabinet of curiosities"
+chunk: 4/5
+source: "https://en.wikipedia.org/wiki/Cabinet_of_curiosities"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:35.931697+00:00"
+instance: "kb-cron"
+---
+
+=== United States ===
+Thomas Dent Mutter (1811–1859) was an early American pioneer of reconstructive plastic surgery. His specialty was repairing congenital anomalies, cleft lip and palates, and club foot. He also collected medical oddities, tumors, anatomical and pathological specimens, wet and dry preparations, wax models, plaster casts, and illustrations of medical deformities. This collection began as a teaching tool for young physicians. Just prior to Mütter's death in 1859, he donated 1,344 items to the American College of Physicians in Philadelphia, along with a $30,000 endowment for the maintenance and expansion of his museum. Mütter's collection was added to ninety-two pathological specimens collected by Doctor Isaac Parrish between 1849 and 1852. The Mütter Museum began to collect antique medical equipment in 1871, including Benjamin Rush's medical chest and Florence Nightingale's sewing kit. In 1874 the museum acquired one hundred human skulls from Austrian anatomist and phrenologist, Joseph Hyrtl (1810–1894); a nineteenth-century corpse, dubbed the "soap lady"; the conjoined liver and death cast of Chang and Eng Bunker, the Siamese twins; and in 1893, Grover Cleveland's jaw tumor. The Mütter Museum is an excellent example of a nineteenth-century grotesque cabinet of medical curiosities.
+P. T. Barnum established Barnum's American Museum on five floors in New York, "perpetuating into the 1860s the Wunderkammer tradition of curiosities for gullible, often slow-moving throngs—Barnum's famously sly but effective method of crowd control was to post a sign, 'THIS WAY TO THE EGRESS!' at the exit door".
+In 1908, New York businessmen formed the Hobby Club, a dining club limited to 50 men, in order to showcase their "cabinets of wonder" and their selected collections. These included literary specimens and incunabula; antiquities such as ancient armour; precious stones and geological items of interest. Annual formal dinners would be used to open the various collections up to inspection for the other members of the club.
+
+== Declining influence ==
+By the early decades of the eighteenth century, curiosities and wondrous specimens had begun to lose their influence among European natural philosophers. As Enlightenment thinkers placed growing emphasis on patterns and systems within nature, anomalies and rarities came to be regarded as potentially misleading objects of study. Curiosities, previously interpreted as divine messages and expressions of nature's variety, were increasingly seen as vulgar exceptions to nature's overall uniformity.
+
+== Notable collections started in this way ==
+Ashmolean Museum Oxford – Ashmole and Tradescant collections
+Boerhaave Museum in Leiden
+British Museum in London – Sir Hans Sloane's and other collections
+Chamber of Art and Curiosities, Ambras Castle in Austria, remains largely intact
+Deyrolle in Paris
+Fondation Calvet, Avignon
+Grünes Gewölbe in Dresden
+Kunstkamera in Saint Petersburg, Russia
+Pitt Rivers Museum (Oxford, England) – former Ashmolean dodo
+Teylers Museum in Haarlem
+World Museum in Liverpool – 13th Earl of Derby's collection
+
+== In contemporary culture ==
+
+The Houston Museum of Natural Science houses a hands-on Cabinet of Curiosities, complete with taxidermied crocodile embedded in the ceiling a la Ferrante Imperato's Dell'Historia Naturale. In Los Angeles, the modern-day Museum of Jurassic Technology anachronistically seeks to recreate the sense of wonder that the old cabinets of curiosity once aroused. 
+In Spring Green, Wisconsin, the house and museum of Alex Jordan, known as House on the Rock, can also be interpreted as a modern day curiosity cabinet, especially in the collection and display of automatons. In Bristol, Rhode Island, Musée Patamécanique is presented as a hybrid between an automaton theater and a cabinet of curiosities and contains works representing the field of Patamechanics, an artistic practice and area of study chiefly inspired by Pataphysics. 
+The idea of a cabinet of curiosities has also appeared in recent publications and performances. For example, Cabinet magazine is a quarterly magazine that juxtaposes apparently unrelated cultural artifacts and phenomena to show their interconnectedness in ways that encourage curiosity about the world. The Italian cultural association Wunderkamern uses the theme of historical cabinets of curiosities to explore how "amazement" is manifested within today's artistic discourse. In May 2008, the University of Leeds Fine Art BA programme hosted a show called "Wunder Kammer", the culmination of research and practice from students, which allowed viewers to encounter work from across all disciplines, ranging from intimate installation to thought-provoking video and highly skilled drawing, punctuated by live performances.
+The concept has been reinterpreted at The Viktor Wynd Museum of Curiosities, Fine Art & Natural History. In July 2021 a new Cabinet of Curiosities room was opened at The Whitaker Museum & Art Gallery in Rawtenstall, Lancashire, curated by artist Bob Frith, founder of Horse and Bamboo Theatre.
+Several internet bloggers describe their sites as "wunderkammern" either because they are primarily links to interesting things, or inspire wonder similarly to the original wunderkammern (see External Links, below). Researcher Robert Gehl describes such internet video sites as YouTube as modern-day wunderkammern, although in danger of being refined into capitalist institutions "just as professionalized curators refined Wunderkammers into the modern museum in the 18th century."
+
+== See also ==
+Antiquarian
+Holophusikon
+Found objects
+Guillermo del Toro's Cabinet of Curiosities
+Imaginarium
+Maximalism
+Medical oddities
+Museum
+
+== References ==

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+---
+title: "Cabinet of curiosities"
+chunk: 5/5
+source: "https://en.wikipedia.org/wiki/Cabinet_of_curiosities"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:35.931697+00:00"
+instance: "kb-cron"
+---
+
+== Further reading ==
+Under the Sign: John Bargrave as Collector, Traveler, and Witness, Stephen Bann, Michigan, 1995
+Beßler, Gabriele, Chambers of Art and Wonders, EGO - European History Online, Mainz: Institute of European History, 2015, retrieved: March 8, 2021 (pdf).
+The Origins of Museums: The Cabinet of Curiosities in Sixteenth- and Seventeenth-Century Europe, ed. Oliver Impey and Arthur MacGregor, 2001, paperback, 431 pages, ISBN 1-84232-132-3
+Cabinets for the curious: looking back at early English museums, Ken Arnold, Ashgate, 2006, ISBN 0-7546-0506-X.
+Mr. Wilson's Cabinet Of Wonder: Pronged Ants, Horned Humans, Mice on Toast, and Other Marvels of Jurassic Technology, Lawrence Weschler, 1996, trade paperback, 192 pages, ISBN 0-679-76489-5 (see website link above)
+The Cabinet of Curiosities (novel), Douglas Preston and Lincoln Child, Warner Books, 2003, paperback, ISBN 0-446-61123-9.
+Helmar Schramm et al. (ed.). Collection, Laboratory, Theater. Scenes of Knowledge in the 17th Century, Berlin/New York 2005, ISBN 978-3-11-017736-7
+The Lure of Antiquity and the Cult of the Machine: The Kunstkammer and the Evolution of Nature, Art and Technology Horst Bredekamp (Allison Brown, translator) (Princeton: Marcus Weiner) 1995.
+Steven Lubar, "Cabinets of Curiosity: What they were, why they disappeared, and why they’re so popular now"
+
+== External links ==
+
+Historic cabinets
+
+J. Paul Getty Museum Augsburg Cabinet: 3-D model online interactive with high-resolution photography, description of subjects depicted, and mapping of exotic materials
+Ashmolean Museum: Powhatan's Mantle, pictures, full descriptions and history
+The Augsburg Art Cabinet, about the Uppsala art cabinet
+Dutch influence on 'wunderkammer' or 'rariteitenkabinet'
+The King's Kunstkammer, a Danish Internet exhibition on the idea behind renaissance art and curiosity chambers (text in English)
+Metropolitan Museum, New York: Collecting for the Kunstkammer exhibition
+Rijksmuseum Amsterdam: Presentation and very large and detailed image of the art cabinet made for Duke August of Brunswick-Lüneburg
+Smithsonian Institution: Crocodiles on the Ceiling exhibition
+Website with photos of remaining Germanic cabinets
+Wunderkammer Theorie High resolution images of two Wunderkammer
+Kunstkammer Image rich German site of Kunstkammer and Wunderkammer
+Idols of the Cave A history of science website devoted to Wunderkammern
+Salvadoriana History and current items of the Wunderkammer that the Salvador family started in the 17th century in Barcelona
+Modern "cabinets"
+
+Cabinets of Curiosities. Museum in Waco, Texas, with a Cabinets of Curiosities Room named for John K. Strecker, who was curator for 30 years, the museum was established in 1893 and was the oldest museum in Texas when it closed in 2003 to be incorporated into the Mayborn Museum Complex.
+A Small Wunderkammer. Web magazine issue dedicated to building a small, contemporary cabinet of curiosities.
+MuseumZeitraum Leipzig. Work and collections of the pioneering German modernist Johann Dieter Wassmann (1841–1898).
+The Renwick Gallery at the Smithsonian Institution includes a contemporary cabinet of curiosity entitled "Bureau of Bureaucracy" by Kim Schmahmann.
+Weblog modern equivalent of a Wunderkammer (anthropology essay)

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+---
+title: "Carl Gunnar Engström"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Carl_Gunnar_Engström"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:35:52.416806+00:00"
+instance: "kb-cron"
+---
+
+Carl Gunnar David Engström (1 September 1912 – 9 January 1987) was a Swedish physician and innovator. He is the inventor of the first intermittent positive pressure mechanical ventilator that could deliver breaths of controllable volume and frequency and  also deliver inhalation anesthetics.
+The Engström150 Respirator (EngströmUniversal Respirator) began series production in 1954. The basic principle of the mechanical ventilator is still the same today, but a technological leap was made with the Siemens-Elema servo fan in the 1970s.
+
+
+== Life ==
+Engström was born on 1 September 1912 in Oskarshamn to Carl Johan Engström and Judith Ringberg. He obtained is degree in medicine in 1941. He worked from 1941 at Stockholm Hospital for Infectious Diseases and started to work in the Swedish Air Force in 1956. He got his PhD in medicine at Uppsala University in 1963 with a thesis entitled The clinical application of prolonged controlled ventilation: with special reference to a method developed by the author.
+Before the invention of Engström, the only available respirator was the iron lung. It is a negative pressure ventilator, a mechanical respirator which encloses most of a person's body, and varies the air pressure in the enclosed space, to stimulate breathing. It assists breathing when muscle control is lost, or the work of breathing exceeds the person's ability suffering from polio and botulism and certain poisons (for example, barbiturates, tubocurarine).
+Rows of iron lungs filled hospital wards at the height of the polio outbreaks of the 1940s and 1950s helping children, and some adults, with bulbar polio and bulbospinal polio. A polio patient with a paralyzed diaphragm would typically spend two weeks inside an iron lung while recovering. This machine kept the patient breathing, with the help of underpressure and overpressure. The whole body, except the head, was placed in a pressure chamber, where it was not possible to regulate how much air the patient received. Engstrom found that the iron lungs did not adequately ventilate patients with severe poliomyelitis.
+This problem solved Engström with his respirator, by blowing air into the patient's lungs via a simple tube through the trachea. The respirator had a cylinder and a pump to determine the amount of air. A tube was inserted into the patient's trachea, a small balloon was inflated as a seal around the tube, and then the respirator pumped air into the lungs. The amount of air and the amount per unit of time was set with a knob.
+Engström patented the respirator in 1950. Engstrom's respirators were used for the first time in Blegdams Hospital, Copenhagen, Denmark, during a polio outbreak in 1952. Engström respirators were also tested in the 1953 Swedish polio epidemic.
+The Engstrom 150 Respirator (Engstrom Universal Respirator) began series production in 1954. Mivab, the company that first manufactured Engström's respirator, is today a part of the Datex / Ohmeda division of General Electric Health Care.
+Positive pressure ventilation systems are now more common than negative pressure systems like the iron lungs. It proved to be lifesaving in other conditions including respiratory insufficiency and soon superseded the iron lung throughout Europe.
+
+
+== References ==
+
+
+== External links ==
+Image of the 1954 Engstrom 150 respirator at www.woodlibrarymuseum.org
+Picture of Carl-Gunnar Engström, page 12

data/en.wikipedia.org/wiki/Cavallo's_multiplier-0.md

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+---
+title: "Cavallo's multiplier"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Cavallo's_multiplier"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:37.078596+00:00"
+instance: "kb-cron"
+---
+
+Cavallo's multiplier was an early electrostatic influence machine, invented in 1795 by the Anglo-Italian natural philosopher Tiberius Cavallo. Its purpose was to multiply, or amplify, a small electric charge to a level where it was detectable by the insensitive electroscopes of the day. Repeated operation of the device could produce voltages high enough to generate sparks.
+
+
+== Description ==
+Cavallo described his machine in his 1795 Treatise on Electricity. He had examined Bennet's charge doubler of 1787 and found it wanting in several regards, notably in its inconsistent operation and tendency to retain the charge from an earlier experiment. Cavallo resolved to build a better device. His machine consisted of four metal plates supported on a wooden board by posts, of which three were insulating and one conducting.
+The charge to be multiplied was applied to the first of these (plate A), which stood on an insulating post. A moveable insulated metal plate (B) was brought close to A (though not permitted to touch it), and then grounded. The charge on A caused charge separation on B due to electrostatic induction. Plate B was then moved away, breaking its earth connection. Since B was insulated, it acquired and retained a small charge opposite in sign to the charge on A. Plate B was transferred by means of an insulating rod to be brought into electrical contact with the third metal plate C which was insulated. Since both B and C were conducting, B would transfer a portion of its charge to C. To maximise the transferred charge, C was placed in close proximity to a final metal plate D, which was earthed.
+The experimenter would move Plate B repeatedly back and forth, placing it near to A and earthed at one end of its motion, and then into contact with C at the other. With each cycle, charge was drawn from the Earth and added to C. After a suitable number of cycles, the grounded plate D would be removed, and the electrostatic potential on C would rise to approximately the potential of A multiplied by the number of operations.
+Cavallo termed his device a multiplier, though 'addition' was perhaps a more accurate description of its operation, as the charge on C was accumulated by successive additions.
+
+
+== Wilson's machine ==
+Wilson's machine, described by its inventor in Nicholson's Journal in August 1804, was a development on this concept which simultaneously operated two Cavallo's multipliers by means of a pair of reciprocating levers. One side would accumulate the charge of the other, and since the two accumulating plates were connected together by means of a wire, Wilson's machine was a true multiplier, rather than an addition machine. The charge would thus accumulate more rapidly than Cavallo's multiplier and the machine could generate high voltages in a short period of time. It moreover was self-exciting, needing no initial charge to operate, as the small initial charge acquired from contact electrification was enough to start the accumulation process.
+
+
+== References ==
+
+
+== External links ==
+Video of reproduction Wilson's machine

data/en.wikipedia.org/wiki/Celestial_Sphere_Woodrow_Wilson_Memorial-0.md

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+---
+title: "Celestial Sphere Woodrow Wilson Memorial"
+chunk: 1/2
+source: "https://en.wikipedia.org/wiki/Celestial_Sphere_Woodrow_Wilson_Memorial"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:38.333218+00:00"
+instance: "kb-cron"
+---
+
+The Celestial Sphere (also known as the Woodrow Wilson Memorial Sphere) is an armillary sphere artpiece situated in the Palais des Nations in Geneva, Switzerland, one of the four headquarters of the United Nations. It was donated in 1939 by the Woodrow Wilson Foundation to what was then the League of Nations building. It is today a symbol of Geneva International and of Geneva as the centre of dialogue and peace.
+The grounds of the Palais des Nations (seat of the United Nations Office at Geneva) contain many fine objects donated by member states of the United Nations, private sponsors and artists. One of them is the huge—over four-meter-diameter—Celestial Sphere is the chef d'oeuvre of the American sculptor Paul Manship (1885–1966) located in the Ariana Park of the Palais des Nations.
+
+== History ==
+Contacted in late 1935 by the Board of the Woodrow Wilson Foundation, Manship was asked to provide an idea for a memorial to President of the United States Woodrow Wilson as the founding father of the League of Nations. At that time the Palais des Nations was still under construction.
+
+The first idea for Manship's contribution to the new buildings was to have him design two doors to the Assembly Hall from the Halle des Pas Perdus. Both the artist and the donor, the Woodrow Wilson Foundation, rejected this idea because doors would not be suitable for a memorial.  Manship then proposed a large-scale version of the present celestial sphere, which he had developed after years of study.  It is based upon several earlier versions, including the Aero Memorial in Philadelphia, Pennsylvania. It differs from these in that the Sphere is supported upon the backs of four tortoises, taken from his models for the gates to the New York Bronx Zoo, which in turn rest upon a stepped socle bearing a cast representation of the Chinese "celestial sea" (Hai Shui Jiang Ya). The tortoises may therefore be thought to represent the Chinese tortoise of immortality (Ao) - an auspicious symbol from Tang times on. Other zodiac signs come from the world's major civilizations, both past and present.
+Manship described this sphere in the following words:
+
+The representation of the heavenly constellations is derived from Babylonia and Assyria: the Greeks and Latins added their names and gave the constellations a local significance in some cases and I have adhered as closely as possible to the ancient forms.  Thus the star, Aldebaran, which represents the eye of Taurus, dictates the character of the design, as is also the case of Regulus, Leo's Heart, and so with all the constellations. The forms and attitudes of the figures have been made to correspond firstly with the positions and the meanings of the emblems themselves.   After that the inter-relationship of the constellations was designed to create a harmonious ensemble.
+In a letter written by Ham Armstrong to Arthus Sweetser dated 30 June 1935, we read that the building committee considered the Celestial Sphere, which they had seen in Paris, superb, not only in originality of conception, but in delicacy of execution and in spirituality of meaning. However, two obstacles were foreseen; first, that it would cost more than the budget available and, second, that it would be difficult to obtain the approval of committee in New York and Geneva on anything so novel and non-utilitarian. Nonetheless, Manship's proposal for a monumental celestial sphere was accepted and a commission for the project was awarded to him in April 1936.
+
+== Process ==
+In spring of 1936, immediately after the approval by the committee, Manship began working on a large-scale model in wax. At his atelier, he gathered a team of sculptors and other artists to work on the various aspects of the design. The team included such famous names as Angelo Colombo, Giuseppe Massari, and Richard Pousette-Dart, the renowned painter who collaborated with Herbert Kammerer on the sphere's lettering.
+The original plaster moulds, executed by Flitzer, were ready in 1938 and were sent to the Bruno Bearzi Atelier in Florence for casting. Bearzi cast the sphere's elements from these plaster moulds using a cire-perdu process from a bronze/zinc high-tin alloy with added lead. The constellations were originally gilded, with chrome-silvered starts. The meridians and architectural elements of the composition have been variously nielloed.
+The Celestial Sphere measures 410 cm. in diameter and weighs some 5,800 kg. The spherical frame is adorned with constellations and stars. The Sphere represents 85 constellations of the universe and shows four stars of the first four magnitudes. The constellations are gilded and the 840 stars are silvered. As his signature, it bears Manship's self-portrait with his tools, in profile, hidden among the constellations.
+
+== A place for the Celestial Sphere ==
+One of the main difficulties was to find a location for the sphere. Even though Manship designed it for the Court of Honour in front of the Assembly Hall, the question was raised in 1937 whether this space should be left completely open for a full panorama. When neither the Woodrow Wilson Foundation nor the artist wanted to hear of a change in 1938, it was decided to put the sphere in the middle of the Park, not too close to the building and not too close to the trees. The sphere was placed in a small reservoir that would reflect the image of the sphere and the building in the water. The sphere was installed in its present location, in the Court d'Honneur of the Ariana park of the Palais des Nations by the Bearzi Atelier in August 1939. The official inauguration of what has become a United Nations symbol took place in September 1939.
+The sphere is equipped with a motor. In the words of the artist it was designed "so that it would rotate slowly" around an axis turned to the Pole star, and it was intended to be illuminated at night.
+
+== Concerns ==

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+---
+title: "Celestial Sphere Woodrow Wilson Memorial"
+chunk: 2/2
+source: "https://en.wikipedia.org/wiki/Celestial_Sphere_Woodrow_Wilson_Memorial"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:38.333218+00:00"
+instance: "kb-cron"
+---
+
+=== Dysfunctional rotation system and illumination ===
+Due to the outbreak of the Second World War the rotation motor of the Celestial Sphere was used for several months only.   In the files of the Woodrow Wilson Foundation, the following brief description was found: "A complex silence and solitude reigned; the great ceremony of dedication, with the 30th Assembly in session, had become impossible: only an occasional chance visitor and a few especially interested Americans watched the Italians putting the great sphere, representative of universal comity, into its place of high honour."  The rotation motor of the Celestial Sphere was not used during 1940–1945 and ceased to function in the early 1960s.
+
+=== Deteriorating conditions ===
+The sphere began to have significant problems as early as 1942. The alloy used by the Bearzi Atelier contracted so sharply during the winter that a considerable amount of water could and did enter the hollow constellations. The freezing of that water caused the metal to crack. Already several of the constellations had to be repaired in 1942–43 and at least one cover of a meridian had to be replaced after falling off. "Weep holes" were drilled in all the constellations at that time to allow the water to drain out. The socle, which bears the whole of the 5,800 kg weight, has cracked. Large areas of corrosion and uneven natural patina are seen. The 840 chrome-plated stars, once present in four sizes, have been widely lost. The sphere cage is at the limit of its weight bearing load. Metal fatigue, cracks and corrosion have increasingly added to its deterioration.
+
+=== Restorations ===
+A restoration of the monument was first undertaken in 1983, qualified as "clumsy" for using materials such as concrete in filling parts of the shallow pieces.
+In 2003, some elements of the sphere were regilded towards a start of, restoration although it had to be delated for more than a decade. Finally, in the late 2010s, thanks to the funding by "an anonymous donation," the sculpture was newly restored in Italy by the Ferdinando Marinelli Artistic Foundry.
+
+== Symbol of Peace "Pax Universalis" ==
+Today the Celestial Sphere stands in the Court d’Honneur of the Palais des Nations, itself an important landmark of the City of Geneva.  It serves as a vivid reminder that despite all cultural and religious differences we are inhabitants of one and the same planet of the galaxy, the Earth. The time has come to think in terms of Pax Universalis rather than of other Paxes, and one of the contributors to a Pax Universalis is an action-oriented dialogue, based on common human values and the ideals of the United Nations.
+
+== Gallery ==
+
+== References ==
+
+Jean-Claude Pallas (2001). Histoire et architecture des Palais des Nations, 1924-2001: l'art déco au service des relations internationales, Nations Unies, pp. 48, 65, 100, 111, 354.
+Franklin Delano Roosevelt, Edgar Burkhardt Nixon, Donald B. Schewe (1979)Franklin D. Roosevelt and foreign affairs, second series, January 1937-August 1939.
+Ernest Willian Watson, Arthur Leighton Guptill (1951), American artist, Watson-Guptil Publications.
+Janis C. Conner, Joel Rosenkranz, David Finn (1989). Rediscoveries in American sculpture: studio works, 1893-1939.
+(2006).Encyclopedia Americana, Scholastic Library Publishing, p. 264.
+I.Dembinski (2009). International Geneva Yearbook 2008, Dominique Dembinski-Goumard, p. 341.
+Harry Rand (1989). Paul Manship Smithsonian Institution Press, p. 124-126.
+(1949). United Nations world, UN World Inc., p. 63.
+Albert Picot (1965). Le rayonnement international de Genève, Editions du Griffon.
+Laure De Gonneville (2009). Suisse 2009 Edition Petite Futé.
+(2006). Geneva - centre for new dialogue among civilizations, UN Special Magazine, No. 652 (www.unspecial.org)
+(2008). Pax Universalis Aeternaque, UN Special Magazine, No. 671 (www.unspecial.org)
+Christian David and Evelina Rioukhina (2010). The Celestial Sphere Woodrow Wilson Memorial, UN Special (magazine), No. 699
+Tom Armstrong (1976). 200 years of American sculpture, Whitney Museum of American Art
+(1985) Paul Manship: changing taste in America: 19 May to 18 August 1985, Minnesota Museum of Art, Landmark Center.
+(2000). Booklet “The Dutch 17th Century in Etchings” for the exhibition of Rembrandt at the United Nations by Museum Geelvinck Hinlopen Huis (with the project proposals by Maecenas World Patrimony Foundation (www.maecenasworldpatrimony.org) “Contribute to the Cycle of Life – the restoration of the Armillary Sphere”, Geneva.
+Alastair Duncan (1986). American art deco, Abrams.
+Carol Hynning Smith (1987). Drawings by Paul Manship: the Minnesota Museum of Art collection, Minnesota Museum of Art.
+
+== External links ==
+
+Genève tourisme Archived 2005-03-18 at the Wayback Machine
+La Genève internationale
+Peace monuments in Switzerland
+UN Special magazine
+Maecenas World Patrimony Foundation

data/en.wikipedia.org/wiki/Centre_for_History_and_Philosophy_of_Science,_University_of_Leeds-0.md

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+---
+title: "Centre for History and Philosophy of Science, University of Leeds"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Centre_for_History_and_Philosophy_of_Science,_University_of_Leeds"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:34:54.673496+00:00"
+instance: "kb-cron"
+---
+
+The Centre for History and Philosophy of Science is a research centre devoted to the historical and philosophical study of science, technology and medicine, based in the School of Philosophy, Religion and History of Science, at the University of Leeds in West Yorkshire, England. The Centre – previously known as the Division of History and Philosophy of Science, which was founded in 1956 – is one of the oldest units of its kind in the world. Throughout its history, the Centre has been home to many of the leading historians and philosophers of science who have deepened our understanding of scientific activity and how it shapes and is shaped by wider society.
+
+
+== History ==
+The key figure in establishing history and philosophy of science (HPS) as a discipline at Leeds was the philosopher of science Stephen Toulmin, who was appointed Professor of Philosophy at Leeds in 1954 and head of department in 1956. Whilst Thomas Kuhn is often seen as the founder of the modern field of history and philosophy of science, Toulmin had argued for an integration of philosophy of science and history of science some nine years before Kuhn published his famous work, The Structure of Scientific Revolutions. The distinguished philosophy of science, Mary Hesse, who was based at Leeds from 1951-55 as a lecturer in mathematics, was also instrumental in establishing what became the Division of History and Philosophy of Science. One of the earliest PhD students in the division was the historian and author June Goodfield, who graduated in 1959 before a varied career spanning appointments at Wellesley College, Michigan State University, and George Washington University.
+The 1970s saw a period of further expansion of the Division, with the appointments of John Christie, Jonathan Hodge (recipient in 2019 of the distinguished Hull Prize awarded by the ISHPSSB), and Geoffrey Cantor following the arrival of Robert Olby. Olby in particular became a leading figure in the Division, not least through his ground-breaking book, Path to the Double Helix, which showed how the 1953 discoveries of Crick and Watson were rooted in the work of two University of Leeds scientists: the creator of molecular biology, William Astbury, and the Nobel prizewinning inventor of X-ray crystallography, William Henry Bragg. Cantor, Christie, Hodge, and Olby formed the core of the Division for the following decade, culminating in the joint publication of the major reference text, Companion to the History of Modern Science (1989), known locally simply as the Leeds Companion. This cemented the reputation of the Division, which made regular further appointments over the following years, before becoming incorporated as a Centre within the School of Philosophy, Religion and History of Science in 2013.
+Since its inception the Centre, now a core part of the broader School of Philosophy, Religion and History of Science, has fostered the development of significant figures in history and philosophy of science, including  Jerry Ravetz, who wrote in Leeds one of the foundational works of Post-normal science. Major research projects, especially Science in the Nineteenth Century Periodical, Owning and Disowning Invention, the Leeds Genetics Pedagogies Project, and Scientific Realism and the Quantum, have been based in the Centre, with significant collaboration across other research institutions within and beyond the UK.
+
+
+== Degree Programmes ==
+The Centre has a long history of innovation in teaching the history and philosophy of science, particularly in conjunction with other subject areas in both the sciences and the arts and humanities. At undergraduate level the suite# includes Joint Honours degree programmes in history and philosophy of science with history, biology, physics, or philosophy, and a unique programme in Philosophy, Psychology and Scientific Thought. At Masters level the MA History of Science, Technology and Medicine is the Centre's flagship programme, and prepares students for a wide range of careers as well as further historical research. The Centre maintains a sizeable cohort of doctoral researchers, and has since 2007 received the largest number of AHRC Collaborative Doctoral Awards of any academic unit in the UK.
+
+
+== Activities ==
+The Centre runs two major seminar series during the academic year, each of which cuts across the broad field of history and philosophy of science. The fortnightly HPS Seminar Series features a diverse range of field-leading speakers from within the UK and internationally. Meanwhile the weekly HPS Work-in-progress Seminar Series serves as a testing ground for postgraduate researchers and academic members of the Centre, who showcase their research at various stages of development, from inception of ideas to preparing for publication. Other focal points include regular reading groups, particularly in history and philosophy of biology and the history of technology, and stand-alone conferences.
+Research in the Centre has been supported by a range of funding bodies, including the AHRC, UK Research and Innovation, Wellcome Trust, National Science Foundation, British Academy, and Leverhulme Trust. The Centre has been involved in significant partnership work with science and heritage organisations, including the Leeds-based Thackray Museum of Medicine, Science Museum Group, Leeds Museums & Galleries, Action on Hearing Loss, BT Archives, Women's Engineering Society, British Library, and National Institute of Agricultural Botany.
+
+
+== Museum and "HPS in 20" ==
+The Museum of the History of Science, Technology and Medicine is a major focal point of research, teaching, and engagement activities. The Museum was formed in 2007 by staff and students in the Centre, and works to preserve and promote the use of scientific artefacts in teaching, research and public engagement. Led by its director, the Museum maintains and catalogues objects in storage, develops exhibitions and digital materials, runs public events and school visits, and plays a key role in teaching activities for both undergraduate and postgraduate students. With over 20,000 objects and specimens in storage or on display in various locations across campus, the collections are broad-ranging and reflect the historic scientific strengths of the University of Leeds in textiles and colour chemistry, as well as in science education. Particular highlights from within the collection include the Newlyn-Phillips Machine (the only extant prototype of MONIAC, the hugely influential early computation device), an example of the very early 'Laennec' stethoscope (), Irene Manton's microscope, and William Astbury's camera.
+Across 2016 and 2017 the collections formed the basis of a major series of twenty lectures charting the History and Philosophy of Science in 20 Objects. The lectures featured academic members of staff, postdoctoral and visiting researchers, and postgraduate researchers and provided a synoptic overview of the history and philosophy of science. It has since been reimagined as an online resource for pre-university students with interests in both history and science, technology, and medicine.
+
+
+== Further information ==
+Graeme Gooday, 'History and Philosophy of Science at Leeds', Notes and Records of the Royal Society 60 (2006), 183–192.
+
+
+== References ==
+
+
+== External links ==
+Centre website
+HPS Research at Leeds
+Current staff and research students within the broader School of Philosophy, Religion and History of Science
+Undergraduate degree programmes
+Postgraduate degree programmes
+Research degree programmes

data/en.wikipedia.org/wiki/Christian_Boyling-0.md

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+---
+title: "Christian Boyling"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Christian_Boyling"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:35:48.883715+00:00"
+instance: "kb-cron"
+---
+
+Christian Boyling (flourished in 1669) was a scientific instrument maker.
+All that is known for certain about this craftsman is that he was serving as "Mechanic" to the Duke of Saxony in 1669.
+He designed and built a perpetual calendar held by the Museo Galileo in Florence, consisting of two overlapping brass plates sandwiching a revolving disk containing twelve enameled disks representing the months (eleven are extant) which show through a window on the front plate.  The finely perforated front plate is decorated with the arms of the House of Saxony.  At its center is a circle showing the hours and containing three-time disks: a  moon phase night clock, a perpetual calendar, and a zodiacal calendar showing lengths of the diurnal cycle over the year.
+
+
+== See also ==
+Duke of Saxony
+
+
+== References ==
+
+
+== External links ==

data/en.wikipedia.org/wiki/Computer_Conservation_Society-0.md

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+---
+title: "Computer Conservation Society"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Computer_Conservation_Society"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:34:55.853249+00:00"
+instance: "kb-cron"
+---
+
+The Computer Conservation Society (CCS) is a British organisation, founded in 1989. It is under the joint umbrella of the British Computer Society (BCS), the London Science Museum and the Manchester Museum of Science and Industry.
+
+
+== Overview ==
+The CCS is interested in the history of computing in general and the conservation and preservation of early British historical computers in particular.
+The society runs a series of monthly public lectures between September and May each year in both London and Manchester.  The events are detailed on the society's website.
+The CCS publishes a quarterly journal, Resurrection.
+The society celebrated its 25th anniversary in 2014.
+Dr Doron Swade, formerly the curator of the computing collection at the London Science Museum, was a founding committee member and As of 2021 is the current chair of the society. David Morriss, Rachel Burnett, and Roger Johnson are previous chairs, also all previous presidents of the BCS.
+
+
+== Projects ==
+The society organises a number of projects to reconstruct and maintain early computers and to conserve early software. For example:
+
+Restorations
+Elliott 401
+Elliott 803
+Elliott 903 and 905
+DEC Systems
+Ferranti Pegasus
+ICT 1301 Project
+Harwell Dekatron Computer
+Differential analyser
+HEC 1
+Reconstructions
+Colossus Rebuild
+Manchester Baby
+Bombe Rebuild
+EDSAC Replica Project
+Babbage's Analytical Engine
+Other projects
+Software preservation
+"Our Computer Heritage" website
+Tony Sale Award for computer conservation and restoration
+
+
+== Locations ==
+London Science Museum:
+
+Ferranti Pegasus (Not currently being displayed working)
+Museum of Science and Industry, Manchester:
+
+Manchester Baby
+Hartree Differential Analyser
+The National Museum of Computing:
+
+Colossus
+Harwell Dekatron or WITCH
+ICL 2966
+Elliot 803
+Elliott 905
+EDSAC Replica
+Bletchley Park Trust:
+
+Bombe
+Currently not on public display:
+
+ICT 1301 (Currently in storage at The National Museum of Computing)
+Elliott 401
+
+
+== References ==
+
+
+== External links ==
+Official Website
+Our Computer Heritage – a project led by the CCS

data/en.wikipedia.org/wiki/Corbett's_electrostatic_machine-0.md

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+---
+title: "Corbett's electrostatic machine"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Corbett's_electrostatic_machine"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:40.611013+00:00"
+instance: "kb-cron"
+---
+
+Corbett's electrostatic machine is a static electricity generating device that was made by the Shaker physician Thomas Corbett in 1810. Intended to treat rheumatism, the device built up a static charge and stored it in a Leyden jar, an early type of capacitor.
+
+
+== Description ==
+
+Corbett was a medical physician for the Shakers, a religious group of colonial America. He was a botanist and preferred herbal medicines to bloodletting. His machine was hand-operated. Rotating a glass cylinder in contact with a silk pad caused a static charge to accumulate on the cylinder. A metal comb collected this charge, which was then stored in a Leyden jar. From the jar, the electrical charge could then be released into the patient, producing a shock akin to "touching a doorknob after walking across carpet in dry weather".
+
+
+== See also ==
+Franklin's electrostatic machine
+
+
+== References ==

data/en.wikipedia.org/wiki/Crookes_tube-0.md

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+---
+title: "Crookes tube"
+chunk: 1/4
+source: "https://en.wikipedia.org/wiki/Crookes_tube"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:41.769217+00:00"
+instance: "kb-cron"
+---
+
+A Crookes tube (also Crookes–Hittorf tube) is an early experimental discharge tube with partial vacuum invented by English physicist William Crookes and others around 1869–1875, in which cathode rays, streams of electrons, were discovered. 
+Developed from the earlier Geissler tube, the Crookes tube consists of a partially evacuated glass bulb of various shapes, with two metal electrodes, the cathode and the anode, one at either end. When a high voltage is applied between the electrodes, cathode rays (electrons) are projected in straight lines from the cathode. It was used by Crookes, Johann Hittorf, Julius Plücker, Eugen Goldstein, Heinrich Hertz, Philipp Lenard, Kristian Birkeland and others to discover the properties of cathode rays, culminating in J. J. Thomson's 1897 identification of cathode rays as negatively charged particles, which were later named electrons. Crookes tubes are now used only for demonstrating cathode rays.
+Wilhelm Röntgen discovered X-rays using the Crookes tube in 1895. The term Crookes tube is also used for the first generation, cold cathode X-ray tubes, which evolved from the experimental Crookes tubes and were used until about 1920.
+
+== History ==
+
+=== Invention ===
+
+Crookes tubes evolved from the earlier Geissler tubes invented by the German physicist and glassblower Heinrich Geissler in 1857, experimental tubes which are similar to modern neon tube lights. Geissler tubes had only a low vacuum, around 10−3 atm (100 Pa), and the electrons in them could only travel a short distance before hitting a gas molecule. So the current of electrons moved in a slow diffusion process, constantly colliding with gas molecules, never gaining much energy. These tubes did not create beams of cathode rays, only a colorful glow discharge that filled the tube as the electrons struck the gas molecules and excited them, producing light.
+By the 1870s, William Crookes (among other researchers) was able to evacuate his tubes to a lower pressure, 10−6 to 5×10−8 atm, using an improved Sprengel mercury vacuum pump invented by his coworker Charles A. Gimingham. He found that as he pumped more air out of his tubes, a dark area in the glowing gas formed next to the cathode. As the pressure got lower, the dark area, now called the Faraday dark space or Crookes dark space, spread down the tube, until the inside of the tube was totally dark. However, the glass envelope of the tube began to glow at the anode end.  What was happening was that as more air was pumped out of the tube, there were fewer gas molecules to obstruct the motion of the electrons from the cathode, so they could travel a longer distance, on average, before they struck one. By the time the inside of the tube became dark, they were able to travel in straight lines from the cathode to the anode, without a collision. They were accelerated to a high velocity by the electric field between the electrodes, both because they did not lose energy to collisions, and also because Crookes tubes were operated at a higher voltage. By the time they reached the anode end of the tube, they were going so fast that many flew past the anode and hit the glass wall. The electrons themselves were invisible, but when they hit the glass walls of the tube they excited the atoms in the glass, making them give off light or fluoresce, usually yellow-green. Later experimenters painted the back wall of Crookes tubes with fluorescent paint, to make the beams more visible.
+This accidental fluorescence allowed researchers to notice that objects in the tube, such as the anode, cast a sharp-edged shadow on the tube wall. Johann Hittorf was first to recognise in 1869 that something must be travelling in straight lines from the cathode to cast the shadow. In 1876, Eugen Goldstein proved that they came from the cathode, and named them cathode rays (Kathodenstrahlen).
+At the time, atoms were the smallest particles known and were believed to be indivisible, the electron was unknown, and what carried electric currents was a mystery. During the last quarter of the 19th century, many ingenious types of Crookes tubes were invented and used in historic experiments to determine what cathode rays were. There were two theories: Crookes believed they were 'radiant matter'; that is, electrically charged atoms, while German scientists Hertz and Goldstein believed they were 'aether vibrations'; some new form of electromagnetic waves.  The debate was resolved in 1897 when J. J. Thomson measured the mass to charge ratio of the cathode rays, showing they were made of particles, but were around 1800 times lighter than the lightest atom, hydrogen. Therefore, they were not atoms, but a new particle, the first subatomic particle to be discovered, which was later named the electron.
+The colorful glowing tubes were also popular in public lectures to demonstrate the mysteries of the new science of electricity.  Decorative tubes were made with fluorescent minerals, or butterfly figures painted with fluorescent paint, sealed inside. When power was applied, the fluorescent materials lit up with many glowing colors.
+In 1895, Wilhelm Röntgen discovered X-rays emanating from Crookes tubes. The many uses for X-rays were immediately apparent, the first practical application for Crookes tubes. Medical manufacturers began to produce specialized Crookes tubes to generate X-rays, the first X-ray tubes. 
+Crookes tubes were unreliable and temperamental. Both the energy and the quantity of cathode rays produced depended on the pressure of residual gas in the tube. Over time the gas was absorbed by the walls of the tube, reducing the pressure. This reduced the amount of cathode rays produced and caused the voltage across the tube to increase, creating more energetic cathode rays. In Crookes X-ray tubes this phenomenon was called "hardening" because the higher voltage produced "harder", more penetrating X-rays; a tube with a higher vacuum was called a "hard" tube, while one with lower vacuum was a "soft" tube. Eventually the pressure got so low the tube stopped working entirely. To prevent this, in heavily used tubes such as X-ray tubes various "softener" devices were incorporated that released a small amount of gas, restoring the tube's function.
+The electronic vacuum tubes invented later around 1904 superseded the Crookes tube. These operate at a still lower pressure, around 10−9 atm (10−4 Pa), at which there are so few gas molecules that they do not conduct by ionization. Instead, they use a more reliable and controllable source of electrons, a heated filament or hot cathode which releases electrons by thermionic emission. The ionization method of creating cathode rays used in Crookes tubes is today only used in a few specialized gas discharge tubes such as thyratrons.
+The technology of manipulating electron beams pioneered in Crookes tubes was applied practically in the design of vacuum tubes, and particularly in the invention of the cathode-ray tube by Ferdinand Braun in 1897 and is now used in sophisticated processes such as electron microscopes and electron beam lithography.

data/en.wikipedia.org/wiki/Crookes_tube-1.md

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+---
+title: "Crookes tube"
+chunk: 2/4
+source: "https://en.wikipedia.org/wiki/Crookes_tube"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:41.769217+00:00"
+instance: "kb-cron"
+---
+
+=== Discovery of X-rays ===
+
+When the voltage applied to a Crookes tube is high enough, around 5,000 volts or greater, it can accelerate the electrons to a high enough velocity to create X-rays when they hit the anode or the glass wall of the tube. The fast electrons emit X-rays when their path is bent sharply as they pass near the high electric charge of an atom's nucleus, a process called bremsstrahlung, or they knock an atom's inner electrons into a higher energy level, and these in turn emit X-rays as they return to their former energy level, a process called X-ray fluorescence. Many early Crookes tubes undoubtedly generated X-rays, because early researchers such as Ivan Pulyui had noticed that they could make foggy marks on nearby unexposed photographic plates. 
+On November 8, 1895, Wilhelm Röntgen was operating a Crookes tube covered with black cardboard when he noticed that a nearby fluorescent screen glowed faintly. He realized that some unknown invisible rays from the tube were able to pass through the cardboard and make the screen fluoresce. He found that they could pass through books and papers on his desk. Röntgen began to investigate the rays full-time, and on December 28, 1895, published the first scientific research paper on X-rays. Röntgen
+was awarded the first Nobel Prize in Physics (in 1901) for his discoveries.
+The many applications of X-rays created the first practical use for Crookes tubes, and workshops began manufacturing specialized Crookes tubes to generate X-rays, the first X-ray tubes. The anode was made of a heavy metal, usually platinum, which generated more X-rays, and was tilted at an angle to the cathode, so the X-rays would radiate through the side of the tube. The cathode had a concave spherical surface which focused the electrons into a small spot around 1 mm in diameter on the anode, in order to approximate a point source of X-rays, which gave the sharpest radiographs. These cold cathode type X-ray tubes were used until about 1920, when they were superseded by the hot cathode Coolidge X-ray tube.
+
+== Operation ==
+
+Crookes tubes are cold cathode tubes, meaning that they do not have a heated filament in them that releases electrons as the later electronic vacuum tubes usually do. Instead, electrons are generated by the ionization of the residual air by a high DC voltage (from a few kilovolts to about 100 kilovolts) applied between the cathode and anode electrodes in the tube, usually by an induction coil (a "Ruhmkorff coil").  The Crookes tubes require a small amount of air in them to function, from about 10−6 to 5×10−8 atmosphere (7×10−4 - 4×10−5 torr or 0.1-0.006 pascal).
+When high voltage is applied to the tube, the electric field accelerates the small number of electrically charged ions and free electrons always present in the gas, created by natural processes like photoionization and radioactivity. The electrons collide with other gas molecules, knocking electrons off them and creating more positive ions. The electrons go on to create more ions and electrons in a chain reaction called a Townsend discharge. All the positive ions are attracted to the cathode or negative electrode. When they strike it, they knock large numbers of electrons out of the surface of the metal, which in turn are repelled by the cathode and attracted to the anode or positive electrode. These are the cathode rays.
+Enough of the air has been removed from the tube that most of the electrons can travel the length of the tube without striking a gas molecule. The high voltage accelerates these low-mass particles to a high velocity (about 37,000 miles per second, or 59,000 km/s, about 20 percent of the speed of light, for a typical tube voltage of 10 kV). When they get to the anode end of the tube, they have so much momentum that, although they are attracted to the anode, many fly past it and strike the end wall of the tube. When they strike atoms in the glass, they knock their orbital electrons into a higher energy level. When the electrons fall back to their original energy level, they emit light. This process, called cathodoluminescence, causes the glass to glow, usually yellow-green. The electrons themselves are invisible, but the glow reveals where the beam of electrons strikes the glass. Later on, researchers painted the inside back wall of the tube with a phosphor, a fluorescent chemical such as zinc sulfide, in order to make the glow more visible. After striking the wall, the electrons eventually make their way to the anode, flow through the anode wire, the power supply, and back to the cathode.
+The full details of the action in a Crookes tube are complicated, because it contains a nonequilibrium plasma of positively charged ions, electrons, and neutral atoms which are constantly interacting. At higher gas pressures, above 10−6 atm (0.1 Pa), this creates a glow discharge; a pattern of different colored glowing regions in the gas, depending on the pressure in the tube (see diagram). The details were not fully understood until the development of plasma physics in the early 20th century.
+
+== Experiments ==
+During the last quarter of the 19th century Crookes tubes were used in dozens of historic experiments to try to find out what cathode rays were. There were two theories: British scientists Crookes and Cromwell Varley believed they were particles of 'radiant matter', that is, electrically charged atoms. German researchers E. Wiedemann, Heinrich Hertz, and Eugen Goldstein believed they were 'aether vibrations', some new form of electromagnetic waves, and were separate from what carried the current through the tube. The debate continued until J. J. Thomson measured cathode ray’s mass, proving they were a previously unknown negatively charged particle in an atom, the first subatomic particle, which he called a 'corpuscle' but was later renamed the 'electron'.

data/en.wikipedia.org/wiki/Crookes_tube-2.md

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+---
+title: "Crookes tube"
+chunk: 3/4
+source: "https://en.wikipedia.org/wiki/Crookes_tube"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:41.769217+00:00"
+instance: "kb-cron"
+---
+
+=== Cathode rays move in parallel lines ===
+Julius Plücker in 1869 built a tube with an anode shaped like a Maltese Cross facing the cathode. It was hinged, so it could fold down against the floor of the tube. When the tube was turned on, the cathode rays cast a sharp cross-shaped shadow on the fluorescence on the back face of the tube, showing that the rays moved in straight lines. This fluorescence was used as an argument that cathode rays were electromagnetic waves, since the only thing known to cause fluorescence at the time was ultraviolet light. After a while the fluorescence would get 'tired' and the glow would decrease. If the cross was folded down out of the path of the rays, it no longer cast a shadow, and the previously shadowed area would fluoresce more strongly than the area around it.
+
+=== Perpendicular emission ===
+
+Eugen Goldstein in 1876 found that cathode rays were always emitted perpendicular to the cathode's surface. If the cathode was a flat plate, the rays were shot out in straight lines perpendicular to the plane of the plate. This was evidence that they were particles, because a luminous object, like a red hot metal plate, emits light in all directions, while a charged particle will be repelled by the cathode in a perpendicular direction.  Cathode rays heat matter which they strike.  If the electrode was made in the form of a concave spherical dish, the cathode rays would be focused to a spot in front of the dish.  This could be used to heat samples to a high temperature.
+
+=== Electrostatic deflection ===
+ 
+Heinrich Hertz built a tube with a second pair of metal plates to either side of the cathode ray beam, a crude CRT. If the cathode rays were charged particles, their path should be bent by the electric field created when a voltage was applied to the plates, causing the spot of light where the rays hit to move sideways. He did not find any bending, but it was later determined that his tube was insufficiently evacuated, causing accumulations of surface charge which masked the electric field. Later Arthur Schuster repeated the experiment with a higher vacuum. He found that the rays were attracted toward a positively charged plate and repelled by a negative one, bending the beam. This was evidence they were negatively charged, and therefore not electromagnetic waves.
+
+=== Magnetic deflection ===
+
+Crookes put a magnet across the neck of the tube, so that the North pole was on one side of the beam and the South pole was on the other, and the beam travelled through the magnetic field between them. The beam was bent down, perpendicular to the magnetic field. To reveal the path of the beam, Crookes invented a tube (see pictures) with a cardboard screen with a phosphor coating down the length of the tube, at a slight angle so the electrons would strike the phosphor along its length, making a glowing line on the screen. The line could be seen to bend up or down in a transverse magnetic field. This effect (now called the Lorentz force) was similar to the behavior of electric currents in an electric motor and showed that the cathode rays obeyed Faraday's law of induction like currents in wires. Both electric and magnetic deflection were evidence for the particle theory, because static electric and magnetic fields have no effect on a beam of light waves in vacuum.
+
+=== Paddlewheel ===
+
+Crookes put a tiny vaned turbine or paddlewheel in the path of the cathode rays, and found that it rotated when the rays hit it. The paddlewheel turned in a direction away from the cathode side of the tube, suggesting that the force of the cathode rays striking the paddles was causing the rotation. Crookes concluded at the time that this showed that cathode rays had momentum, so the rays were likely matter particles. However, later it was concluded that the paddle wheel turned not due to the momentum of the particles (or electrons) hitting the paddle wheel but due to the radiometric effect.  When the rays hit the paddle surface they heated it, and the heat caused the gas next to it to expand, pushing the paddle. This was proven in 1903 by J. J. Thomson who calculated that the momentum of the electrons hitting the paddle wheel would only be sufficient to turn the wheel one revolution per minute. All this experiment really showed was that cathode rays were able to heat surfaces.
+
+=== Electric charge ===
+Jean-Baptiste Perrin wanted to determine whether cathode rays actually carried negative charge, or whether they just accompanied the charge carriers, as the Germans thought. In 1895 he constructed a tube with a 'catcher', a closed aluminum cylinder with a small hole in the end facing the cathode, to collect the cathode rays. The catcher was attached to an electroscope to measure its charge. The electroscope showed a negative charge, proving that cathode rays really carry negative electricity.
+
+=== Anode rays ===
+
+Goldstein found in 1886 that if the cathode is made with small holes in it, streams of a faint luminous glow will be seen issuing from the holes on the back side of the cathode, facing away from the anode. It was found that in an electric field these anode rays bend in the opposite direction from cathode rays, toward a negatively charged plate, indicating that they carry a positive charge. These were the positive ions which were attracted to the cathode, and created the cathode rays. They were named canal rays (Kanalstrahlen) by Goldstein.

data/en.wikipedia.org/wiki/Crookes_tube-3.md

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+---
+title: "Crookes tube"
+chunk: 4/4
+source: "https://en.wikipedia.org/wiki/Crookes_tube"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:41.769217+00:00"
+instance: "kb-cron"
+---
+
+=== Spectral shift ===
+Eugen Goldstein thought he had figured out a method of measuring the speed of cathode rays. If the glow discharge seen in the gas of Crookes tubes was produced by the moving cathode rays, the light radiated from them in the direction they were moving, down the tube, would be shifted in frequency due to the Doppler effect. This could be detected with a spectroscope because the emission line spectrum would be shifted. He built a tube shaped like an "L", with a spectroscope pointed through the glass of the elbow down one of the arms. He measured the spectrum of the glow when the spectroscope was pointed toward the cathode end, then switched the power supply connections so the cathode became the anode and the electrons were moving in the other direction, and again observed the spectrum looking for a shift. He did not find one, which he calculated meant that the rays were traveling very slowly. It was later recognized that the glow in Crookes tubes is emitted from gas atoms hit by the electrons, not the electrons themselves. Since the atoms are thousands of times more massive than the electrons, they move much slower, accounting for the lack of Doppler shift.
+
+=== Lenard window ===
+
+Philipp Lenard wanted to see if cathode rays could pass out of the Crookes tube into the air. See diagram. He built a tube with a "window" (W) in the glass envelope made of aluminum foil just thick enough to hold the atmospheric pressure out (later called a "Lenard window") facing the cathode (C) so the cathode rays would hit it.  He found that something did come through. Holding a fluorescent screen up to the window caused it to fluoresce, even though no light reached it. A photographic plate held up to it would be darkened, even though it was not exposed to light. The effect had a very short range of about 2.5 centimetres (0.98 in). He measured the ability of cathode rays to penetrate sheets of material, and found they could penetrate much farther than moving atoms could. Since atoms were the smallest particles known at the time, this was first taken as evidence that cathode rays were waves. Later it was realized that electrons were much smaller than atoms, accounting for their greater penetration ability.
+
+== See also ==
+Crookes radiometer – 1873 device that rotates when exposed to light
+
+== References ==
+
+== External links ==
+
+An illustration of a "maltese cross" Crookes tube.
+The Cathode Ray Tube site
+Crookes and Geissler tubes shown working
+Java animation of a Crookes tube
+"The Cathode Rays". Library. Oracle Thinkquest Education Foundation. Archived from the original on 2008-05-06. Retrieved 2008-04-28. History of d
+Jenkins, John. "Crookes and Geissler tubes". Spark Museum. Retrieved 2008-04-29.

data/en.wikipedia.org/wiki/Cyanometer-0.md

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+---
+title: "Cyanometer"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Cyanometer"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:45.088006+00:00"
+instance: "kb-cron"
+---
+
+A cyanometer (from cyan and -meter) is an instrument for measuring "blueness", specifically the colour intensity of blue sky. It is attributed to Horace-Bénédict de Saussure and Alexander von Humboldt. It consists of squares of paper dyed in graduated shades of blue and arranged in a color circle or square that can be held up and compared to the color of the sky.
+
+
+== History ==
+
+Horace-Bénédict de Saussure, a Swiss physicist and mountain climber, is credited with inventing the cyanometer in the 1760s. De Saussure's cyanometer was divided into colored, numbered sections, ranging from white to gradually darker shades of blue, dyed with Prussian blue and arranged in a circle. The cyanometers were manually produced with a predefined recipe of watercolor concentration for each section, and then distributed to friends and fellow naturalists to gather more observations.
+In an article from 1790, de Saussure presents an illustration of a wheel with 40 stops, though clarifies that it serves merely to give the reader "an idea of its form"; the actual cyanometer had 53 stops (or "degrees"), starting with white as 0 and black as 52.
+De Saussure believed that the color of the sky was dependent on the amount of particles suspended in the atmosphere, and that these particles had an opaque color blue (thought to be 34 degrees on the scale). If this were true, then one could estimate the concentration of such particles using the cyanometer.
+The tool was meant to be used outside, by holding it up to the sky and finding the closest color to the sky's. Additionally, in an attempt to standardize testing, de Saussure gives a few pointers on how observations should be made. For example:
+
+[...] si on faisoit son observation à la fenêtre ou sur le seuil d'une porte, ces couleurs ne seroient éclairées que par la lumière qui viendroit de l'intérieur de la maison & ainsi elles paroîtroient plus obscures qu'en rase campagne où elles sont éclairées par une grande partie du Ciel.
+[(...) if one were to make an observation at the window or at a door, the colors would only be illuminated by the light coming from inside the house, and thus they would appear darker than in the open countryside where they are illuminated by a large part of the Sky.]
+
+De Saussure used the device to measure the color of the sky at Geneva, Chamonix, and Mont Blanc (Col du Géant): 
+
+Alexander von Humboldt (1769–1859) was an eager user of the cyanometer on his voyages and explorations: during his trip across the Atlantic Ocean, he observed 23.5 degrees at noon; at the summit of Teide, a record 41 degrees; and, while climbing to the summit of Chimborazo, on 23 June 1802, Humboldt broke both the record of highest altitude ever reached by humans, but also of observed darkness of the sky, with 46 degrees on the cyanometer.
+In his satirical verse epic Don Juan (Canto IV, 112), Lord Byron alludes to this device as an ironical means of measuring the blue of bluestocking ladies, crediting Humboldt for its invention.
+
+
+== Theory ==
+
+The blueness of clear air in Earth's atmosphere is due to Rayleigh scattering by nitrogen and oxygen molecules. Dry air is 78% nitrogen and 21% oxygen. Atmospheric water content ranges from 0% to 5%.
+When looking through clear air toward the horizon, distant sunlight of all wavelengths (colors) will generally undergo Mie scattering from spherical suspended particles. In an unpolluted sky, these spherical particles will primarily be liquid water condensed onto natural atmospheric dust grains. This is known as "wet haze". Therefore, in an unpolluted clear sky, wet haze adds white sunlight to blue Rayleigh-scattered light. More wet haze in the observer's line of sight results in a brighter and paler blue sky color.
+When looking toward the horizon, an observer looks through up to 40 times as much atmosphere compared to looking overhead. Therefore, more Mie scattering is seen when viewing parts of the sky closer to the horizon. A darker blue sky will be observed if less wet haze is in the observer's line of sight. This occurs when looking directly overhead and at a higher altitude.
+
+
+== See also ==
+Diffuse sky radiation
+
+
+== Notes ==
+
+
+== References ==
+
+
+== Bibliography ==
+Heubner (1840). "Über das Cyanometer". Zeitschrift für Physik und verwandte Wissenschaften. 6: 201.
+Hermann von Schlagintweit, Adolf Schlagintweit (1850). Untersuchungen über die physicalische Geographie der Alpen in ihren Beziehungen zu den Phaenomenen der Gletscher, zur Geologie, Meteorologie und PflanzengeographieBarth. p. 441.
+
+
+== External links ==
+The Cyanometer Is a 225-Year-Old Tool for Measuring the Blueness of the Sky (9 May 2014), an article by Christopher Jobson for Colossal.

data/en.wikipedia.org/wiki/Dark_Romanticism-0.md

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+---
+title: "Dark Romanticism"
+chunk: 1/2
+source: "https://en.wikipedia.org/wiki/Dark_Romanticism"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:35:17.269786+00:00"
+instance: "kb-cron"
+---
+
+Dark Romanticism is a literary sub-genre of Romanticism, reflecting popular fascination with the irrational, the demonic and the grotesque. Often conflated with Gothic fiction, it has shadowed the euphoric Romantic movement ever since its 18th-century beginnings. Edgar Allan Poe is often celebrated as one of the supreme exponents of the tradition. Dark Romanticism focuses on human fallibility, self-destruction, judgement, punishment, as well as the psychological effects of guilt and sin.
+
+== Historical context ==
+The term "Romanticism" comes from Old French "romanz," meaning stories written in the vernacular (local) "Roman" tongue (not Latin), which evolved from Latin "romanice" ("in the Roman manner"). Not only has it become an iconic style of art, but also had an effect on literature and music. It was driven by emotions and imagination rather than science and rationality. The Romantic Movement began in Europe at the end of the 18th century and migrated to America in the early 19th century. American Romanticism authors were most productive between 1830 and 1865. Within Romanticism, two conflicting sub-genres arose: optimists who believed in human virtue and spirituality formed the Transcendentalism Movement, while pessimists who accepted human fallibility and our proclivity for sin formed the Dark Romantic Movement.  
+
+== Definitions ==
+Romanticism's celebration of euphoria and sublimity has always been dogged by an equally intense fascination with melancholia, insanity, crime and shady atmosphere; with the options of ghosts and ghouls, the grotesque, and the irrational. The name "Dark Romanticism" was given to this form by the literary theorist Mario Praz in his lengthy study of the genre published in 1930, The Romantic Agony.
+According to the critic G. R. Thompson, "the Dark Romantics adapted images of anthropomorphized evil in the form of Satan, devils, ghosts, werewolves, vampires, and ghouls" as emblematic of human nature. Thompson sums up the characteristics of the sub-genre, writing:
+
+Fallen man's inability fully to comprehend haunting reminders of another, supernatural realm that yet seemed not to exist, the constant perplexity of inexplicable and vastly metaphysical phenomena, a propensity for seemingly perverse or evil moral choices that had no firm or fixed measure or rule, and a sense of nameless guilt combined with a suspicion the external world was a delusive projection of the mind—these were major elements in the vision of man the Dark Romantics opposed to the mainstream of Romantic thought.
+
+=== Example quote ===
+"Cannibals? Who is not a cannibal? I tell you it will be more tolerable for the Fejee that salted down a lean missionary in his cellar against a coming famine; it will be more tolerable for that provident Fejee, I say, in the day of judgement, than for thee, civilized and enlightened gourmand, who nailest geese to the ground and feastest on their bloated livers in thy pate de fois gras.” – Herman Melville's Moby Dick: or The Whale
+
+== Characteristics ==
+To fully grasp the idea of dark romanticism, we must recognize the attributes that come with the artwork so we can identify them. The characteristics that define dark romanticism are questioning the natural perfection of man, believing that man cannot ever be perfect, that man will never have perfection. People began to have a less conventional perspective of religion, to pay greater attention to catastrophes, and to let the investigation into terrible realities into their daily life.
+Furthermore, the most popular notions are that humans are naturally subject to sin and destruction, that people cannot ever escape sin or be rescued from it, and that people may destroy society, religions, and themselves.
+
+== Artists' impact ==
+Loneliness and sadness, desire and death, the obsession with horror, and the absurdity of dreams are all themes explored in the artwork. Artists like Salvador Dalí, René Magritte, Paul Klee, and Max Ernst continued to think in this spirit throughout the twentieth century. Dark Romanticism arose as a reaction to the Enlightenment, the Industrial Revolution, and widespread rationalization, emphasizing raw emotion, pure aesthetic experiences, and other types of extreme emotion.
+
+=== Artists ===
+
+==== Johann Heinrich Fuseli ====
+
+In Switzerland, Johann Heinrich Fuseli had studied to be an evangelical preacher. He produced an emblem of Dark Romanticism with his artwork. This piece leads off the exhibit, which spans two levels of the temporary exhibition space. The appearance of the incubus and the lecherous horse in a scenario situated in the present, shocked Fuseli's contemporaries greatly. Furthermore, the voyeur's requirements were met by the erotic-compulsive and daemonic material, as well as the sad environment.
+
+==== William Blake ====
+
+This painting reflects the conflict between good and evil, misery and lust, light and darkness, and other aspects of his work. Fuseli's unique pictorial language impacted a number of painters, including William Blake, whose famous watercolor The Great Red Dragon is on display at the Brooklyn Museum.
+
+==== Francisco Goya ====
+
+One of the most significant individuals in Spanish painting was Francisco Goya. He was also a precursor of Romanticism in the creation of contemporary artistic appreciation, both in terms of the substance of his paintings, with their in-depth examination of reality and references to the dream realm, and in terms of his innovative technique. His art expresses his own innovative views, opposing academicism and established topics. Goya characterized himself as a student of Velazquez, Rembrandt, and nature, gaining a taste for delicately shaded color applied in layers from Velazquez, a preference for dark and enigmatic backdrop settings from Rembrandt, and an unending diversity of shapes from nature; some beautiful, others ugly.
+
+==== John Constable ====
+
+The goal of John Constable's landscape paintings was to represent nature with honesty, to convey its beauty and simplicity without becoming pretentious. He is not the personification of nature's passion, poetry, or sorrow. He thought his life and art were in ruins, so he looked for a glimpse of his own spirit in nature, which he discovered in a bleak landscape of Hadleigh Castle in Essex.
+
+==== Eugène Delacroix ====

data/en.wikipedia.org/wiki/Dark_Romanticism-1.md

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+---
+title: "Dark Romanticism"
+chunk: 2/2
+source: "https://en.wikipedia.org/wiki/Dark_Romanticism"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:35:17.269786+00:00"
+instance: "kb-cron"
+---
+
+Delacroix is usually considered as the founder of the Romantic movement in French painting throughout the nineteenth century. His painting technique – full of rich, agitated brushwork and throbbing with vibrant color – expressed the movement's concern for emotion, exoticism, and the sublime, and his life and work embodied the movement's concern for passion, exoticism, and the sublime.
+
+== Timeline ==
+The American Renaissance (literature) was between 1840 and 1860. This included Dark Romanticism and Transcendentalism.
+Since it allowed for the study of gloomy ideas, writing, and topics, Dark Romanticism had a huge effect on American literature.
+Dark Romanticism began as a response to the Transcendental movement of the mid-nineteenth century. This was a mental shift in thinking from rigid religious Puritan thought to a dark, immoral point of view. People were disinterested in optimism when they considered their sin and human nature.
+Authors and artists were not afraid to express their sinister side. Authors began to investigate man's wicked nature even before 1840.
+1809 – Edgar Allan Poe was born in Boston, Massachusetts. Poe is probably one of the most influential writers of this time. His themes focused on human sin and the evil in man.
+Herman Melville – another influential writer, but he is completely different in his writing from Poe and Hawthorne. His themes focus on "the truths of ragged edges"
+From 1840 to the late 1870s, Dark Romanticism dominated literature and art.
+The primary element employed was symbolism. They would symbolize man's bad side and "study human nature's difficulties." Artists sought to show how evil, rather than virtue, consumes people, and how individual acts lead to self-destruction.
+
+== 18th-/19th-century movements in national literatures ==
+Elements of Dark Romanticism were a perennial possibility within the broader international movement of Romanticism, in both literature and art.
+
+=== Germany ===
+Dark Romanticism arguably began in Germany, with writers such as E. T. A. Hoffmann, and Ludwig Tieck, and also pre-Romantic figure of Christian Heinrich Spiess, — though their emphasis on existential alienation, the demonic in sex, and the uncanny, was offset at the same time by the more homely cult of Biedermeier.
+Like the Gothic novel, Schwarze Romantik is a genre based on the terrifying side of the Middle Ages, and frequently feature the same elements (castles, ghost, monster, etc.). However, Schauerroman's key elements are necromancy and secret societies, and it is remarkably more pessimistic than the English Gothic novel. All those elements are the basis for Friedrich Schiller's unfinished novel The Ghost-Seer (1786–1789). The motive of secret societies is also present in Karl Grosse's Horrid Mysteries (1791–1794) and Christian August Vulpius' The History of Rinaldo Rinaldini (1798). Benedikte Naubert's novel Hermann of Unna (1788) is seen as being very close to the Schauerroman genre.
+Other early authors and works included Christian Heinrich Spiess, with his works Das Petermännchen (1793), Der alte Überall und Nirgends (1792), Die Löwenritter (1794), and Hans Heiling, vierter und letzter Regent der Erd- Luft- Feuer- und Wasser-Geister (1798); Heinrich von Kleist's short story "Das Bettelweib von Locarno" (1797); and Ludwig Tieck's Der blonde Eckbert (1797) and Der Runenberg (1804).
+
+==== Jüngere Romantik ====
+For two decades, the most famous author of Gothic literature in Germany was the polymath E. T. A. Hoffmann. His novel The Devil's Elixirs (1815) was influenced by Lewis's The Monk and even mentions it. The novel also explores the motive of Doppelgänger, the term coined by another German author and supporter of Hoffmann, Jean Paul, in his humorous novel Siebenkäs (1796–1797).  Aside from Hoffmann and de la Motte Fouqué, three other important authors from the era were Joseph Freiherr von Eichendorff (The Marble Statue, 1818), Ludwig Achim von Arnim (Die Majoratsherren, 1819), and Adelbert von Chamisso (Peter Schlemihls wundersame Geschichte, 1814). After them, Wilhelm Meinhold wrote The Amber Witch (1838) and Sidonia von Bork (1847). The last work from the German writer Theodor Storm, The Rider on the White Horse (1888), uses Gothic motives and themes.
+
+=== Britain ===
+British authors such as Lord Byron, Samuel Taylor Coleridge, Mary Shelley, and John William Polidori, who are frequently linked to Gothic fiction, are also sometimes referred to as Dark Romantics. Dark Romanticism is characterized by stories of personal torment, social outcasts, and usually offers commentary on whether the nature of man will save or destroy him. Some authors of English and Irish horror fiction, such as Bram Stoker and Daphne du Maurier, follow in this lineage.
+
+=== American ===
+The American form of this sensibility centered on the writers Edgar Allan Poe, Nathaniel Hawthorne and Herman Melville, with Charles Brockden Brown being a predecessor. As opposed to the perfectionist beliefs of Transcendentalism, these darker contemporaries emphasized human fallibility and proneness to sin and self-destruction, as well as the difficulties inherent in attempts at social reform.
+
+=== France ===
+
+The 19th-century fantastique literature after 1830 was dominated by the influence of E. T. A. Hoffmann, and then by that of Edgar Allan Poe. French authors such as Jules Barbey d'Aurevilly, Charles Baudelaire, Paul Verlaine and Arthur Rimbaud echoed the dark themes found in the German and English literature. Baudelaire was one of the first French writers to admire Edgar Allan Poe, but this admiration or even adulation of Poe became widespread in French literary circles in the late 19th century.
+
+== See also ==
+
+== References ==
+
+== Further reading ==
+Galens, David, ed. (2002) Literary Movements for Students Vol. 1.
+Levin, Harry. The Power of Blackness (1958)
+Praz, Mario. The Romantic Agony (1933)
+Mullane, Janet and Robert T. Wilson, eds. (1989) Nineteenth Century Literature Criticism Vols. 1, 16, 24.
+
+== External links ==
+
+Poe Studies/Dark Romanticism Journal
+The Gothic as an Aspect of American Romanticism

data/en.wikipedia.org/wiki/Dioptra-0.md

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+---
+title: "Dioptra"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Dioptra"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:48.449658+00:00"
+instance: "kb-cron"
+---
+
+A dioptra (sometimes also named dioptre or diopter, from Greek: διόπτρα) is a classical astronomical and surveying instrument, dating from the 3rd century BC. The dioptra was a sighting tube or, alternatively, a rod with a sight at both ends, attached to a stand. If fitted with protractors, it could be used to measure angles.
+
+
+== Use ==
+Greek astronomers used the dioptra to measure the positions of stars; both Euclid and Geminus refer to the dioptra in their astronomical works.
+It continued in use as an effective surveying tool. Adapted to surveying, the dioptra is similar to the theodolite, or surveyor's transit, which dates to the sixteenth century. It is a more accurate version of the groma.
+There is some speculation that it may have been used to build the Eupalinian aqueduct. Called "one of the greatest engineering achievements of ancient times," it is a tunnel 1,036 metres (3,399 ft) long, excavated through a mountain on the Greek island of Samos during the reign of Polycrates in the sixth century BC.  Scholars disagree, however, whether the dioptra was available that early.
+An entire book about the construction and surveying usage of the dioptra is credited to Hero of Alexandria (also known as Heron; a brief description of the book is available online; see Lahanas link, below). Hero was "one of history’s most ingenious engineers and applied mathematicians."
+The dioptra was used extensively on aqueduct building projects. Screw turns on several different parts of the instrument made it easy to calibrate for very precise measurements.
+The dioptra was replaced as a surveying instrument by the theodolite.
+
+
+== How it works ==
+The dioptra consists of a sighting tube or rod fitted with sights at both ends and mounted on a stable stand. The stand usually includes adjustable screw turns that allow the instrument to be precisely calibrated. When used for astronomical purposes, the user would align the sights with a specific star or celestial object, and then measure the angle using protractors attached to the instrument. In surveying, the dioptra was used to measure angles and distances by sighting along the rod and taking readings from graduated scales.
+
+
+== Advantages and disadvantages ==
+The dioptra offered several advantages over other contemporary instruments. Its ability to measure both vertical and horizontal angles with high precision made it a versatile tool for both astronomy and surveying. The screw turns allowed for fine adjustments, improving accuracy. The instrument's simplicity and robustness made it reliable and easy to use in the field.
+However, the dioptra also had its limitations. The accuracy of measurements depended on the user's skill and the quality of the instrument's construction. The sighting tube or rod could be affected by environmental factors such as wind or temperature changes, which could introduce errors. Additionally, the dioptra required careful calibration before each use, which could be time-consuming.
+Compared to later instruments like the theodolite, the dioptra was less advanced and lacked some of the refinements and improvements that made theodolites more accurate and easier to use. The theodolite eventually replaced the dioptra as the primary instrument for surveying due to its superior performance and reliability.
+
+
+== History and development ==
+The dioptra's origins trace back to the Hellenistic period when Greek scientists and engineers sought to improve observational accuracy in astronomy and surveying. Over time, the instrument underwent several modifications, incorporating advancements in material science and geometric principles. Notably, Hero of Alexandria's detailed work on the dioptra exemplifies the pinnacle of Hellenistic engineering prowess, showcasing the instrument's versatility and precision.
+
+
+== Applications in ancient engineering ==
+Beyond its use in astronomy, the dioptra played a crucial role in various engineering projects in ancient Greece and Rome. It was instrumental in constructing aqueducts, roads, and buildings. The instrument's ability to measure angles with high precision allowed engineers to plan and execute large-scale infrastructure projects with greater accuracy and efficiency. For example, its use in the Eupalinian aqueduct's construction demonstrated the dioptra's significance in solving complex engineering challenges of the time.
+
+
+== Comparison with other instruments ==
+The dioptra's design and functionality can be compared to other contemporary instruments such as the groma, the alidade, and the later theodolite. While the groma was primarily used for laying out straight lines and right angles, the dioptra offered greater versatility in measuring angles in both vertical and horizontal planes. The alidade, another important surveying instrument, was used to measure angles and determine directions. It typically consisted of a straightedge with sights at either end. The alidade was often mounted on a plane table, which allowed for direct plotting of survey data. The theodolite, which emerged in the sixteenth century, eventually surpassed the dioptra in accuracy and ease of use due to technological advancements and refinements in optical and mechanical components.
+
+
+== See also ==
+Alidade
+Groma
+Theodolite
+
+
+== References ==
+
+
+== Further reading ==
+Isaac Moreno Gallo (2006) The Dioptra Tesis and reconstruction of the Dioptra.
+Michael Jonathan Taunton Lewis (2001), Surveying Instruments of Greece and Rome, Cambridge University Press, ISBN 0-521-79297-5
+Lucio Russo (2004), The Forgotten Revolution: How Science Was Born in 300 BC and Why It Had To Be Reborn, Berlin: Springer. ISBN 3-540-20396-6.
+Evans, J., (1998) The History and Practice of Ancient Astronomy, pages 34–35. Oxford University Press.
+
+
+== External links ==
+Michael Lahanas, Heron of Alexandria, Inventions, Biography, Science
+Nathan Sidoli (2005), Heron's Dioptra 35 and Analemma Methods: An Astronomical Determination of the Distance between Two Cities, Centaurus, 47(3), 236-258
+Bamber Gascoigne, History of Measurement, historyworld.net
+Tom M. Apostol (2004), The Tunnel of Samos, Engineering and Science, 64(4), 30-40
+Olshausen, Eckart and Sauer, Werner (2002), "Dioptra", in: Brill’s New Pauly, Antiquity volumes edited by: Hubert Cancik and Helmuth Schneider, English Edition by: Christine F. Salazar, Classical Tradition volumes edited by: Manfred Landfester, English Edition by: Francis G. Gentry.

data/en.wikipedia.org/wiki/Dividing_engine-0.md

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+---
+title: "Dividing engine"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Dividing_engine"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:49.621289+00:00"
+instance: "kb-cron"
+---
+
+A dividing engine is a device employed to mark graduations on measuring instruments.
+
+
+== History ==
+
+There has always been a need for accurate measuring instruments. Whether it is a linear device such as a ruler or vernier or a circular device such as a protractor, astrolabe, sextant, theodolite, or setting circles for astronomical telescopes, the desire for ever greater precision has always existed. For every improvement in the measuring instruments, such as better alidades or the introduction of telescopic sights, the need for more exact graduations immediately followed.
+In early instruments, graduations were typically etched or scribed lines in wood, ivory or brass. Instrument makers devised various devices to perform such tasks. Early Islamic instrument makers must have had techniques for the fine division of their instruments, as this accuracy is reflected in the accuracy of the readings they made. This skill and knowledge seems to have been lost, given that small quadrants and astrolabes in the 15th and 16th centuries did not show fine graduations and were relatively roughly made.
+In the 16th century, European instrument makers were hampered by the materials available. Brass was in hammered sheets with rough surfaces and iron graving tools were poor quality. There were not enough makers to have created a long tradition of practice and few were trained by masters.
+Transversals set a standard in the early 14th century. Tycho Brahe used transversals on his instruments and made the method better known.  Transversals based on straight lines do not provide correct subdivisions on an arc, so other methods, such as those based on the use of circular arcs as developed by Philippe de La Hire, were also used.
+Another system was created in the 16th century by Pedro Nunes and was called nonius after him. It consisted of tracing a certain number of concentric circles on an instrument and dividing each successive one with  one fewer divisions than the adjacent outer circle. Thus the outermost quadrant would have 90° in 90 equal divisions, the next inner would have 89 divisions, the next 88 and so on. When an angle was measured, the circle and the division on which the alidade fell was noted. A table was then consulted to provide the exact measure.  However, this system was difficult to construct and used by few. Tycho Brahe was one exception.
+Some improvements to Nunes' system were developed by Christopher Clavius and Jacob Curtius. Curtius' work led directly to that of Pierre Vernier, published in 1631. Vernier refined this process and gave us the vernier scale. However, though these various techniques improved the reading of graduations, they did not contribute directly to the accuracy of their construction. Further improvements came slowly, and a new development was required: the dividing engine.
+Prior work on the development of gear cutting machines had prepared the way. Such devices were required to cut a circular plate with uniform gear teeth. Clockmakers were familiar with these methods and they were important in developing dividing engines. George Graham devised a process of using geometric methods to divide the limb of an instrument. He developed a sophisticated beam compass to aid marking of the graduations. John Bird and Jeremiah Sisson followed on with these techniques. These beam compass techniques were used into the 19th century, as the dividing engines that followed did not scale up to the largest instruments being constructed.
+
+The first true circular dividing engine was probably constructed by Henry Hindley, a clockmaker, around 1739. This was reported to the Royal Society by John Smeaton in 1785. It was based directly on a gear cutting machine for clockworks. It used a toothed index plate and a worm gear to advance the mechanism. Duc de Chaulnes created two dividing engines between 1765 and 1768 for dividing circular arcs and linear scales. He desired to improve on the graduation of instruments by removing the skill of the maker from the technique where possible. While beam compass use was critically dependent on the skill of the user, his machine produced more regular divisions by virtue of its design. His machines were also inspired by the prior work of the clockmakers.
+Jesse Ramsden followed duc de Chaulnes by five years in the production of his dividing engine.  As with the prior inventions, Ramsden's used a tangent screw mechanism to advance the machine from one position to another. However, he had developed a screw-cutting lathe that was particularly advanced and produced a superior product. This engine was developed with funding from the Board of Longitude on condition that it be described in detail (along with the related screw-cutting lathe) and not be protected by patent. This allowed others to freely copy the device and improve on it. In fact, the Board required that he teach others to construct their own copies and make his dividing engine available to graduate instruments made by others.
+
+
+== Refinements ==
+Edward Troughton was the first to build a copy of the Ramsden design. He enhanced the design and produced his own version. This permitted an improvement in the accuracy of the dividing engine.
+Samuel Rhee developed his own endless screw cutting machine and was able to sell machines to others. His screws were considered the finest available at the time.
+In France, Étienne Lenoir created a dividing engine of greater accuracy than the English version. Mégnié, Richer, Fortin and Jecker had also built dividing engines of considerable quality.
+By the beginning of the 19th century, it was possible to make instruments such as the sextant that remained fully serviceable and of sufficient accuracy to be in use for a half century or more.
+The dividing engine was unique among developments in the manufacture of scientific instruments, as it was immediately accepted by all makers. There was no uncertainty in the value of this development.
+Bryan Donkin designed and built a screw cutting and dividing engine lathe in 1826, which set new standards of precision for the creation of accurate leadscrews, a necessary precursor to the development of precision machining in the Industrial Revolution.
+
+
+== See also ==
+Henry Joseph Grayson - an Australian inventor who developed an engine (~1900) for making diffraction gratings that ruled 120,000 lines to the inch (approximately 4,700 per mm).
+
+
+== References ==
+
+
+== External links ==
+
+Palmer, Christopher (2020). Diffraction Grating Handbook (8th ed.). MKS Newport.

data/en.wikipedia.org/wiki/Eise_Eisinga_Planetarium-0.md

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+---
+title: "Eise Eisinga Planetarium"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Eise_Eisinga_Planetarium"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:50.802517+00:00"
+instance: "kb-cron"
+---
+
+The Royal Eise Eisinga Planetarium (Dutch: Koninklijk Eise Eisinga Planetarium) is an 18th-century orrery in Franeker, Friesland, Netherlands. It is currently a museum and open to the public. The orrery has been on the top 100 Dutch heritage sites list since 1990. In September 2023, it received the status of UNESCO World Heritage Site. It is the oldest working orrery in the world.
+
+
+== History ==
+The orrery was built from 1774 to 1781 by Eise Eisinga, a wool carder and amateur astronomer.
+Eise Eisinga’s mechanical planetarium is built into the timber roof of the living room ceiling of his historic canal house. William I, Prince of Orange and the first King of the Netherlands, was so impressed with the planetarium, he purchased the house and it became a royal planetarium.
+The museum consists of the planetarium room, a screening room where documentaries are shown, and special exhibits based on modern astronomy.  Other parts on permanent display are Eisinga’s former wool combing establishments and a collection of historical astronomical instruments.  Those instruments in the collection include Georgian telescopes, 18th century octants and a tellurium, an educational model of the Sun, Earth and Moon.
+The museum has a Planetarium Café and Brasserie De Stadstuin located in the former Van Balen coffee-roasting house.
+In 2018, the Planetarium celebrated the 250th anniversary of Eisinga’s move to the city of Franeker in 1768, six years before he began work on his Planetarium.
+It is listed as a Rijksmonument, number 15668.
+The orrery was nominated on 12 December 2011 by the Dutch government for UNESCO World Heritage status, based on its long history as a working planetarium open to the public and its continued efforts to preserve its heritage. In December 2018, it was announced that the Dutch minister of Education, Culture and Science will be sending an application to UNESCO to request a formal nomination of the orrery, bringing heritage status one step closer.
+
+
+== Orrery ==
+
+An orrery is a planetarium, a working model of the Solar System.  The orrery is painted with royal blue glimmer and outlined in shiny gold paint. The Sun is painted at the center of the ceiling.  The Earth is represented by a golden orb dangling on a wire.  The zodiac is also depicted.  The clockwork-like mechanical planetarium moves as it does in reality at a reduced scale. The planetarium is very exact, but is not perfect. The pendulum, for instance, is made of a single type of metal so it is influenced by temperature fluctuations.
+The "face" of the model looks down from the ceiling of what used to be his living room, with most of the mechanical works in the space above the ceiling. It is driven by a pendulum clock, which has 9 weights or ponds. The planets move around the model in real time, automatically. (A slight "re-setting" must be done by hand every four years to compensate for the February 29th of a leap year.) The planetarium includes a display for the current time and date. The plank that has the year numbers written on it has to be replaced every 22 years.
+The Eise Eisinga Planetarium is the oldest still working planetarium in the world.
+To create the gears for the model, 10,000 handmade nails were used.
+In addition to the basic orrery, there are displays of the phase of the moon and other astronomical phenomena.
+The orrery was constructed to a scale of 1:1,000,000,000,000 (1 millimetre: 1 million kilometres).
+
+
+== References ==
+
+
+== External links ==
+
+Official website
+Eisinga Planetarium at Atlas Obscura
+Eise Eisinga Planetarium Archived 2011-07-24 at the Wayback Machine at Jusonline.nl
+UNESCO inscription at UNESCO

data/en.wikipedia.org/wiki/Electric_bath_(electrotherapy)-0.md

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+---
+title: "Electric bath (electrotherapy)"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Electric_bath_(electrotherapy)"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:52.142335+00:00"
+instance: "kb-cron"
+---
+
+An electric bath is a 19th-century medical treatment in which high-voltage electrical apparatus was used for electrifying patients by causing an electric charge to build up on their bodies. In the US this process was known as Franklinization after Benjamin Franklin. The process became widely known after Franklin described it in the mid-18th century, but after that it was mostly practiced by quacks. Golding Bird brought it into the mainstream at Guy's Hospital in the mid-19th century and it fell into disuse in the early 20th century.
+
+
+== Description ==
+
+The source of electricity for an electric bath was usually a frictional electrical machine. The patient was seated on a wooden stool, and both the patient and the stool insulated from ground by a platform on glass legs or some other insulator. In some arrangements, the patient was lying down rather than seated. The patient was then charged with static electricity either by direct connection to one electrode of the generator (usually the positive), or else through electrostatic induction by holding a large electrode close to the patient's body. The electric tension applied was around 30–50 kV. Treatment could take several hours. Following charging the patient was "bathed" in electricity, hence the name of the procedure. This can be observed in a darkened room as a luminous discharge around the patient, especially at the hair and extremeties.
+The electric bath treatment was painless, but it caused the patient to warm and sweat, and the heart rate to increase. It also caused the hair to stand on end. The electric bath could form a treatment in itself. It could also be the first stage in further treatment. A common procedure was to draw sparks from the patient after charging, especially from the spine.
+
+
+== History ==
+Electricity had been in use for medical treatment since the mid-18th century. However, this was mainly at the hands of quacks and charlatans, often promoting the treatment as a universal panacea. One notorious fringe practitioner using the electric bath was James Graham. It was brought into the mainstream by Golding Bird at Guy's Hospital who ran the "electrifying room" there from 1836. This was not the first time electricity had been used as a treatment in a hospital, but Bird was the first to study its efficacy with scientific rigour. According to Thomas Addison, past hospital use had been "vague and indiscriminate". Bird was well aware of the need to overcome this bad reputation and convince his colleagues. In a series of Guy's Hospital Reports, Bird identified specific treatments for specific conditions based on case studies. He was quick to highlight conditions that could not be treated so that his work was distinguished from the charlatans. Nevertheless, electrotherapy was usually considered a treatment of last resort when all else had failed.
+Bird's most common use of the electric bath was to use the electric charge on the patient to draw off sparks by placing another electrode near the point of treatment. He used this method on the spine of chorea sufferers with some success. Another condition for which Bird used this treatment was wrist drop caused by lead poisoning. Bird found that there were some conditions for which this treatment did not work, mostly conditions where the brain or nervous system had been damaged such as epilepsy.
+The process of charging up a patient with static electricity was called Franklinization after Benjamin Franklin briefly experimented in this field. He attempted to treat a number of paralytics, first with electric shocks, and then with static charging, but without much success. He described these procedures in a letter of 1757. Franklinization could also be applied locally to a wound or specific patch of skin with a hand-held array of needle electrodes. The intention was often to generate a "static breeze", a wind of ionized air over the skin. Alternatively, the intention could be to breathe in the ionized air as a form of ozone therapy.
+Electric bath apparatus for medical use were still for sale as late as 1908.
+
+
+== References ==
+
+
+== Bibliography ==
+Bird, Golding (1841). "Report on the value of electricity, as a remedial agent in the treatment of diseases". Guy's Hospital Reports. Vol. 6. Guy's Hospital. pp. 84–120.
+Chalovich, Joseph (January 23, 2012). "Franklinization: Early Therapeutic Use of Static Electricity". The ScholarShip, East Carolina University. Retrieved May 28, 2024.
+Coley, N. G. (October 1969). "The collateral sciences in the work of Golding Bird (1814–1854)". Medical History. 13 (4): 363–376. doi:10.1017/S0025727300014794. ISSN 2048-8343. PMC 1033981. PMID 4899816.
+Knight, James (1874). Orthopædia. New York: GP Putnam's Sons. British Library 018207409
+Morus, Iwan Rhys (1998). Frankenstein's Children: Electricity, Exhibition, and Experiment in Early-nineteenth-century London. Princeton University Press. ISBN 978-0-691-05952-5.
+Pinchuk, LS; Nikolaev, VI; Tsetkova, EA; Goldade, VA (2005-12-02). Tribology and Biophysics of Artificial Joints. Elsevier. ISBN 978-0-08-045808-3.
+Schiffer, Michael Brian (2001). "The explanation of long-term technological change". Anthropological Perspectives on Technology. UNM Press. ISBN 978-0-8263-2369-9.
+Schiffer, Michael Brian (2006-03-02). Draw the Lightning Down: Benjamin Franklin and Electrical Technology in the Age of Enlightenment. University of California Press. ISBN 978-0-520-24829-8.

data/en.wikipedia.org/wiki/Electrophorus-0.md

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+---
+title: "Electrophorus"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Electrophorus"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:53.319583+00:00"
+instance: "kb-cron"
+---
+
+In electromagnetism, an electrophorus or electrophore is a simple, manual, capacitive, electrostatic generator used to produce charge via the process of electrostatic induction. A first version of it was invented in 1762 by Swedish professor Johan Carl Wilcke. Italian scientist Alessandro Volta improved and popularized the device in 1775, and is sometimes erroneously credited with its invention. The word electrophorus was coined by Volta from the Greek ήλεκτρον, elektron, and φορεύς, phoreus, meaning 'electricity bearer'.
+
+
+== Description and operation ==
+
+The electrophorus consists of a dielectric plate (originally a 'cake' of resinous material such as pitch or wax, but in modern versions plastic is used) and a metal plate with an insulating handle. The dielectric plate is first charged through the triboelectric effect by rubbing it with fur or cloth. For this discussion, imagine the dielectric gains negative charge by rubbing, as in the illustration below. The metal plate is then placed onto the dielectric plate. The dielectric does not transfer a significant fraction of its surface charge to the metal because the microscopic contact is poor. Instead the electrostatic field of the charged dielectric causes the charges in the metal plate to separate. It develops two regions of charge – the positive charges in the plate are attracted to the side facing down toward the dielectric, charging it positively, while the negative charges are repelled to the side facing up, charging it negatively,  with the plate remaining electrically neutral as a whole. Then, the side facing up is momentarily grounded (which can be done by touching it with a finger), draining off the negative charge. Finally, the metal plate, now carrying only one sign of charge (positive in our example), is lifted.
+Since the charge on the dielectric is not depleted in this process, the charge on the metal plate can be used for experiments, for example by touching it to metal conductors allowing the charge to drain away, and the uncharged metal plate can be placed back on the dielectric and the process repeated to get another charge. This can be repeated as often as desired, so in principle an unlimited amount of induced charge can be obtained from a single charge on the dielectric. For this reason Volta called it elettroforo perpetuo (the perpetual electricity bearer). In actual use the charge on the dielectric will eventually (within a few days at most) leak through the surface of the cake or the atmosphere to recombine with opposite charges around to restore neutrality.
+One of the largest examples of an electrophorus was built in 1777 by German scientist Georg Christoph Lichtenberg. It was 6 feet (approximately 183 centimeters) in diameter, with the metal plate raised and lowered using a pulley system. It could reportedly produce 15-inch (38 cm) sparks. Lichtenberg used its discharges to create the strange treelike marks known as Lichtenberg figures.
+
+
+== The source of the charge ==
+
+Charge in the universe is conserved. The electrophorus simply separates positive and negative charges. A positive or negative charge ends up on the metal plate (or other storage conductor), and the opposite charge is stored in another object after grounding (in the earth or the person touching the metal plate). This separation takes work since the lowest energy state implies uncharged objects. Work is done by raising the charged metal plate away from the oppositely charged resinous plate. This additional energy put into the system is converted to potential energy in the form of charge separation (opposite charges that were originally on the plate), so raising the metal plate actually increases its voltage relative to the dielectric plate.
+The electrophorus is thus actually a manually operated electrostatic generator, using the same principle of electrostatic induction as electrostatic machines such as the Wimshurst machine and the Van de Graaff generator.
+
+
+== See also ==
+Electret
+
+
+== Notes ==
+
+
+== References ==
+Pancaldi, Giuliano (2003). Volta, Science and Culture in the Age of Enlightenment. Princeton University Press. ISBN 0-691-12226-1., pp. 73–105  Volta's 'invention' of the electrophorus
+Jones, Thomas B. (July 2007). "Electrophorus and accessories". Thomas B. Jones website. University of Rochester. Archived from the original on 16 December 2007. Retrieved 27 December 2007.
+Schiffer, Michael Brian (2003). Draw the Lightning Down:Benjamin Franklin and electrical technology in the Age of Enlightenment. University of California Press. ISBN 0-520-23802-8.  pp. 55–57.  Place of electrophorus in history of electrostatics, although the author does not mention Wilcke's contribution.
+Fleming, John Ambrose (1911). "Electrophorus" . In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 09 (11th ed.). Cambridge University Press. p. 237.

data/en.wikipedia.org/wiki/Electroscope-0.md

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+---
+title: "Electroscope"
+chunk: 1/2
+source: "https://en.wikipedia.org/wiki/Electroscope"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:54.498121+00:00"
+instance: "kb-cron"
+---
+
+The  electroscope is an early scientific instrument used to detect the presence of electric charge on a body.  It detects  this by the movement of a test charge due to the Coulomb electrostatic force on it.  The amount of charge on an object is proportional to its voltage.  The accumulation of enough charge to detect with an electroscope requires hundreds or thousands of volts, so electroscopes are used with high voltage sources such as static electricity and electrostatic machines.  An electroscope can only give a rough indication of the quantity of charge; an instrument that measures electric charge quantitatively is called an electrometer.
+The electroscope was the first electrical measuring instrument. The first electroscope was a pivoted needle (called the versorium), invented by British physician William Gilbert around 1600.   The pith-ball electroscope and the gold-leaf electroscope are two classical types of electroscope that are still used in physics education to demonstrate the principles of electrostatics.  A type of electroscope is also used in the quartz fiber radiation dosimeter. Electroscopes were used by the Austrian scientist
+Victor Hess in the discovery of cosmic rays.
+
+== Pith-ball electroscope ==
+
+In 1731, Stephen Gray used a simple hanging thread, which would be attracted to any nearby charged object.  This was the first improvement on Gilbert's versorium from 1600.
+The pith-ball electroscope, invented by British schoolmaster and physicist John Canton in 1754, consists of one or two small balls of a lightweight nonconductive substance, originally a spongy plant material called pith, suspended by silk or linen thread from the hook of an insulated stand. Tiberius Cavallo made an electroscope in 1770 with pith balls at the end of silver wires. Modern electroscopes usually use balls made of plastic. In order to test the presence of a charge on an object, the object is brought near to the uncharged pith ball. If the object is charged, the ball will be attracted to it and move toward it.
+The attraction occurs because of induced polarization of the atoms inside the pith ball.  All matter consists of electrically charged particles located close together; each atom consists of a positively charged nucleus with a cloud of negatively charged electrons surrounding it.   The pith is an insulator, so the electrons in the ball are bound to atoms of the pith and are not free to leave the atoms and move about in the ball, but they can move a little within the atoms. See diagram. If, for example, a positively charged object (B) is brought near the pith ball (A), the negative electrons (blue minus signs) in each atom (yellow ovals) will be attracted and move slightly toward the side of the atom nearer the object.  The positively charged nuclei (red plus signs) will be repelled and will move slightly away.  Since the negative charges in the pith ball are now nearer to the object than the positive charges (C), their attraction is greater than the repulsion of the positive charges, resulting in a net attractive force.  This separation of charge is microscopic, but since there are so many atoms, the tiny forces add up to a large enough force to move a light pith ball.
+If the external object (B) instead has a negative charge, the positive nuclei of each atom will be attracted toward it while the electrons will be repelled away from it.  Again, this causes opposite charges to be closer to the external object than charges of the same polarity, resulting in a net attractive force.
+The pith ball can be charged by touching it to a charged object, so some of the charges on the surface of the charged object move to the surface of the ball.  Then the ball can be used to distinguish the polarity of charge on other objects because it will be repelled by objects charged with the same polarity or sign it has, but attracted to charges of the opposite polarity.
+Often the electroscope will have a pair of suspended pith balls.  This allows one to tell at a glance whether the pith balls are charged. If one of the pith balls is touched to a charged object, charging it, the second one will be attracted and touch it, communicating some of the charge to the surface of the second ball.  Now both balls have the same polarity charge, so they repel each other.  They hang in an inverted 'V' shape with the balls spread apart.  The distance between the balls will give a rough idea of the magnitude of the charge.
+
+== Gold-leaf electroscope ==

data/en.wikipedia.org/wiki/Electroscope-1.md

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+---
+title: "Electroscope"
+chunk: 2/2
+source: "https://en.wikipedia.org/wiki/Electroscope"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:54.498121+00:00"
+instance: "kb-cron"
+---
+
+The gold-leaf electroscope was developed in 1787 by British clergyman and physicist Abraham Bennet, as a more sensitive instrument than  pith ball or straw blade electroscopes then in use. It consists of a vertical metal rod, usually brass, from the end of which hang two parallel strips of thin flexible gold leaf.  A disk or ball terminal is attached to the top of the rod, where the charge to be tested is applied. To protect the gold leaves from drafts of air they are enclosed in a glass bottle, usually open at the bottom and mounted over a conductive base. Often there are grounded metal plates or foil strips in the bottle flanking the gold leaves on either side.   These are a safety measure; if an excessive charge is applied to the delicate gold leaves, they will touch the grounding plates and discharge before tearing.  They also capture charge leaking through the air that  accumulates on the glass walls, increasing the sensitivity of the instrument.  In the precision instruments the inside of the bottle was occasionally evacuated, to prevent the charge on the terminal from leaking off through the ionization of the air.
+When the metal terminal is touched with a charged object, the gold leaves spread apart in an inverted 'V'. This is because some of the charge from the object is conducted through the terminal and metal rod to the leaves. Since the leaves receive the same sign charge they repel each other and thus diverge. If the terminal is grounded by touching it with a finger, the charge is transferred through the human body into the earth and the gold leaves close together.
+The electroscope leaves can also be charged without touching a charged object to the terminal, by electrostatic induction. As the charged object is brought near the electroscope terminal, the leaves spread apart, because the electric field from the object induces a charge in the conductive electroscope rod and leaves, and the charged leaves repel each other. The opposite-sign charge is attracted to the nearby object and collects on the terminal disk, while the same-sign charge is repelled from the object and collects on the leaves (but only as much as left the terminal), so the leaves repel each other.  If the electroscope is grounded while the charged object is nearby, by touching it momentarily with a finger, the repelled same-sign charges travel through the contact to ground, leaving the electroscope with a net charge having the opposite sign as the object.  The leaves initially hang down free because the net charge is concentrated at the terminal end.  When the charged object is moved away, the charge at the terminal spreads into the leaves, causing them to spread apart again.
+
+The Bohnenberger electroscope was developed in the early 19th century by the German physicist Johann Gottlieb Friedrich von Bohnenberger as an improvement on earlier gold-leaf electroscopes. The instrument employed a single gold leaf suspended between two oppositely charge plates,  increasing sensitivity and allowing clearer detection of both the presence and sign of an electric charge.
+Bohnenberger electroscopes were widely used in 19th-century experimental physics and appear in university laboratories, teaching collections, and scientific manuals throughout Europe. The design influenced later high-sensitivity electroscopic instruments.
+Eberbach & Son electroscope instruments were designed primarily for educational and laboratory use, following classical electroscope principles while emphasizing robustness and standardized construction for teaching environments.
+
+While they did not introduce new electroscopic principles, they played a role in the standardization of electrostatics instruction in North America.
+
+== See also ==
+
+== Footnotes ==
+
+== External links ==
+"Pith-ball electroscope". Physics demonstration resource. St. Mary's University. Retrieved 2015-05-28.
+"Computer simulation of electroscopes". Molecular Workbench. Concord Consortium. Archived from the original on 2022-07-03. Retrieved 2008-02-03.
+"Pith Ball and Charged Rod Video". St. Mary's Physics YouTube Channel. St. Mary's Physics Online. Archived from the original on 2021-12-22.

data/en.wikipedia.org/wiki/Electrostatic_generator-0.md

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+---
+title: "Electrostatic generator"
+chunk: 1/5
+source: "https://en.wikipedia.org/wiki/Electrostatic_generator"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:55.653201+00:00"
+instance: "kb-cron"
+---
+
+An electrostatic generator, or electrostatic machine, is an electrical generator that produces static electricity, or electricity at high voltage and low continuous current. The knowledge of static electricity dates back to the earliest civilizations, but for millennia it remained merely an interesting and mystifying phenomenon, without a theory to explain its behavior and often confused with magnetism. By the end of the 17th century, researchers had developed practical means of generating electricity by friction, but the development of electrostatic machines did not begin in earnest until the 18th century, when they became fundamental instruments in the studies about the new science of electricity.
+Electrostatic generators operate by using manual (or other) power to transform mechanical work into electric energy, or using electric currents. Manual electrostatic generators develop electrostatic charges of opposite signs rendered to two conductors, using only electric forces, and work by using moving plates, drums, or belts to carry electric charge to a high potential electrode.
+
+== Description ==
+Electrostatic machines are typically used in science classrooms to safely demonstrate electrical forces and high voltage phenomena. The elevated potential differences achieved have also been used for a variety of practical applications, such as operating X-ray tubes, particle accelerators, spectroscopy, medical applications, sterilization of food, and nuclear physics experiments. Electrostatic generators such as the Van de Graaff generator, and variations as the Pelletron, also find use in physics research.
+Electrostatic generators can be divided into categories depending on how the charge is generated:
+
+Friction machines use the triboelectric effect (electricity generated by contact or friction)
+Influence machines use electrostatic induction
+Others
+
+=== Friction machines ===
+
+==== History ====
+
+The first electrostatic generators are called friction machines because of the friction in the generation process. A primitive form of frictional machine was invented around 1663 by Otto von Guericke, using a sulphur globe that could be rotated and rubbed by hand. It may not actually have been rotated during use and was not intended to produce electricity (rather cosmic virtues), but inspired many later machines that used rotating globes. Isaac Newton constructed his own primitive electrostatic generator, being the first to use a glass globe instead of a sulphur one. In about 1706 Francis Hauksbee improved the basic design, with his frictional electrical machine that enabled a glass sphere to be rotated rapidly against a woollen cloth.
+Generators were further advanced when, about 1730, Prof. Georg Matthias Bose of Wittenberg added a collecting conductor (an insulated tube or cylinder supported on silk strings). Bose was the first to employ the "prime conductor" in such machines, this consisting of an iron rod held in the hand of a person whose body was insulated by standing on a block of resin.
+In 1746, William Watson's machine had a large wheel turning several glass globes, with a sword and a gun barrel suspended from silk cords for its prime conductors. Johann Heinrich Winckler, professor of physics at Leipzig, substituted a leather cushion for the hand. During 1746, Jan Ingenhousz invented electric machines made of plate glass. Experiments with the electric machine were largely aided by the invention of the Leyden Jar. This early form of the capacitor, with conductive coatings on either side of the glass, can accumulate a charge of electricity when connected with a source of electromotive force.
+The electric machine was soon further improved by Andrew (Andreas) Gordon, a Scotsman and professor at Erfurt, who substituted a glass cylinder in place of a glass globe; and by Giessing of Leipzig who added a "rubber" consisting of a cushion of woollen material. The collector, consisting of a series of metal points, was added to the machine by Benjamin Wilson about 1746, and in 1762, John Canton of England (also the inventor of the first pith-ball electroscope) improved the efficiency of electric machines by sprinkling an amalgam of tin over the surface of the rubber. In 1768, Jesse Ramsden constructed a widely used version of a plate electrical generator.
+In 1783, Dutch scientist Martin van Marum of Haarlem designed a large electrostatic machine of high quality with glass disks 1.65 meters in diameter for his experiments. Capable of producing voltage with either polarity, it was built under his supervision by John Cuthbertson of Amsterdam the following year. The generator is currently on display at the Teylers Museum in Haarlem.
+In 1785, N. Rouland constructed a silk-belted machine that rubbed two grounded tubes covered with hare fur. Edward Nairne developed an electrostatic generator for medical purposes in 1787 that had the ability to generate either positive or negative electricity, the first of these being collected from the prime conductor carrying the collecting points and the second from another prime conductor carrying the friction pad. The Winter machine possessed higher efficiency than earlier friction machines.
+In the 1830s, Georg Ohm possessed a machine similar to the Van Marum machine for his research (which is now at the Deutsches Museum, Munich, Germany). In 1840, the Woodward machine was developed by improving the 1768 Ramsden machine, placing the prime conductor above the disk(s). Also in 1840, the Armstrong hydroelectric machine was developed, using steam as a charge carrier.

data/en.wikipedia.org/wiki/Electrostatic_generator-1.md

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+---
+title: "Electrostatic generator"
+chunk: 2/5
+source: "https://en.wikipedia.org/wiki/Electrostatic_generator"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:55.653201+00:00"
+instance: "kb-cron"
+---
+
+==== Friction operation ====
+The presence of surface charge imbalance means that the objects will exhibit attractive or repulsive forces. This surface charge imbalance, which leads to static electricity, can be generated by touching two differing surfaces together and then separating them due to the phenomenon of the triboelectric effect. Rubbing two non-conductive objects can generate a great amount of static electricity. This is not the result of friction; two non-conductive surfaces can become charged by just being placed one on top of the other. Since most surfaces have a rough texture, it takes longer to achieve charging through contact than through rubbing. Rubbing objects together increases amount of adhesive contact between the two surfaces. Usually insulators, e.g., substances that do not conduct electricity, are good at both generating, and holding, a surface charge. Some examples of these substances are rubber, plastic, glass, and pith. Conductive objects in contact generate charge imbalance too, but retain the charges only if insulated. The charge that is transferred during contact electrification is stored on the surface of each object. Note that the presence of electric current does not detract from the electrostatic forces nor from the sparking, from the corona discharge, or other phenomena. Both phenomena can exist simultaneously in the same system.
+
+=== Influence machines ===
+
+==== History ====
+Frictional machines were, in time, gradually superseded by the second class of instrument mentioned above, namely, influence machines. These operate by electrostatic induction and convert mechanical work into electrostatic energy by the aid of a small initial charge which is continually being replenished and reinforced. The first suggestion of an influence machine appears to have grown out of the invention of Volta's electrophorus. The electrophorus is a single-plate capacitor used to produce imbalances of electric charge via the process of electrostatic induction.
+The next step was when Abraham Bennet, the inventor of the gold leaf electroscope, described a "doubler of electricity" (Phil. Trans., 1787), as a device similar to the electrophorus, but that could amplify a small charge by means of repeated manual operations with three insulated plates, in order to make it observable in an electroscope. In 1788, William Nicholson proposed his rotating doubler, which can be considered as the first rotating influence machine. His instrument was described as "an instrument which by turning a winch produces the two states of electricity without friction or communication with the earth". (Phil. Trans., 1788, p. 403) Nicholson later described a "spinning condenser" apparatus, as a better instrument for measurements.
+Erasmus Darwin, W. Wilson, G. C. Bohnenberger, and (later, 1841) J. C. E. Péclet developed various modifications of Bennet's 1787 device. Francis Ronalds automated the generation process in 1816 by adapting a pendulum bob as one of the plates, driven by clockwork or a steam engine – he created the device to power his electric telegraph.
+Others, including T. Cavallo (who developed the "Cavallo multiplier", a charge multiplier using simple addition, in 1795), John Read, Charles Bernard Desormes, and Jean Nicolas Pierre Hachette, developed further various forms of rotating doublers. In 1798, The German scientist and preacher Gottlieb Christoph Bohnenberger, described the Bohnenberger machine, along with several other doublers of Bennet and Nicholson types in a book. The most interesting of these were described in the "Annalen der Physik" (1801). Giuseppe Belli, in 1831, developed a simple symmetrical doubler which consisted of two curved metal plates between which revolved a pair of plates carried on an insulating stem. It was the first symmetrical influence machine, with identical structures for both terminals. This apparatus was reinvented several times, by C. F. Varley, that patented a high power version in 1860, by Lord Kelvin (the "replenisher") 1868, and by A. D. Moore (the "dirod"), more recently. Lord Kelvin also devised a combined influence machine and electromagnetic machine, commonly called a mouse mill, for electrifying the ink in connection with his siphon recorder, and a water-drop electrostatic generator (1867), which he called the "water-dropping condenser".
+
+===== Holtz machine =====
+
+Between 1864 and 1880, W. T. B. Holtz constructed and described a large number of influence machines which were considered the most advanced developments of the time. In one form, the Holtz machine consisted of a glass disk mounted on a horizontal axis which could be made to rotate at a considerable speed by a multiplying gear, interacting with induction plates mounted in a fixed disk close to it. In 1865, August J. I. Toepler developed an influence machine that consisted of two disks fixed on the same shaft and rotating in the same direction. In 1868, the Schwedoff machine had a curious structure to increase the output current. Also in 1868, several mixed friction-influence machine were developed, including the Kundt machine and the Carré machine. In 1866, the Piche machine (or Bertsch machine) was developed. In 1869, H. Julius Smith received the American patent for a portable and airtight device that was designed to ignite powder. Also in 1869, sectorless machines in Germany were investigated by Poggendorff.
+The action and efficiency of influence machines were further investigated by F. Rossetti, A. Righi, and Friedrich Kohlrausch. E. E. N. Mascart, A. Roiti, and E. Bouchotte also examined the efficiency and current producing power of influence machines. In 1871, sectorless machines were investigated by Musaeus. In 1872, Righi's electrometer was developed and was one of the first antecedents of the Van de Graaff generator. In 1873, Leyser developed the Leyser machine, a variation of the Holtz machine. In 1880, Robert Voss (a Berlin instrument maker) devised a form of machine in which he claimed that the principles of Toepler and Holtz were combined. The same structure become also known as the Toepler–Holtz machine.
+
+===== Wimshurst machine =====

data/en.wikipedia.org/wiki/Electrostatic_generator-2.md

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+---
+title: "Electrostatic generator"
+chunk: 3/5
+source: "https://en.wikipedia.org/wiki/Electrostatic_generator"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:55.653201+00:00"
+instance: "kb-cron"
+---
+
+In 1878, the British inventor James Wimshurst started his studies about electrostatic generators, improving the Holtz machine, in a powerful version with multiple disks. The classical Wimshurst machine, that became the most popular form of influence machine, was reported to the scientific community by 1883, although previous machines with very similar structures were previously described by Holtz and Musaeus. In 1885, one of the largest-ever Wimshurst machines was built in England (it is now at the Chicago Museum of Science and Industry). The Wimshurst machine is a considerably simple machine; it works, as all influence machines, with electrostatic induction of charges, which means that it uses even the slightest existing charge to create and accumulate more charges, and repeats this process for as long as the machine is in action. Wimshurst machines are composed of: two insulated disks attached to pulleys of opposite rotation, the disks have small conductive (usually metal) plates on their outward-facing sides; two double-ended brushes that serve as charge stabilizers and are also the place where induction happens, creating the new charges to be collected; two pairs of collecting combs, which are, as the name implies, the collectors of electrical charge produced by the machine; two Leyden Jars, the capacitors of the machine; a pair of electrodes, for the transfer of charges once they have been sufficiently accumulated. The simple structure and components of the Wimshurst Machine make it a common choice for a homemade electrostatic experiment or demonstration, these characteristics were factors that contributed to its popularity, as previously mentioned.
+In 1887, Weinhold modified the Leyser machine with a system of vertical metal bar inductors with wooden cylinders close to the disk for avoiding polarity reversals. M. L. Lebiez described the Lebiez machine, that was essentially a simplified Voss machine (L'Électricien, April 1895, pp. 225–227). In 1893, Louis Bonetti patented a machine with the structure of the Wimshurst machine, but without metal sectors in the disks. This machine is significantly more powerful than the sectored version, but it must usually be started with an externally applied charge.
+
+===== Pidgeon machine =====
+In 1898, the Pidgeon machine was developed with a unique setup by W. R. Pidgeon. On October 28 that year, Pidgeon presented this machine to the Physical Society after several years of investigation into influence machines (beginning at the start of the decade). The device was later reported in the Philosophical Magazine (December 1898, pg. 564) and the Electrical Review (Vol. XLV, pg. 748). A Pidgeon machine possesses fixed electrostatic inductors arranged in a manner that increases the electrostatic induction effect (and its electrical output is at least double that of typical machines of this type [except when it is overtaxed]). The essential features of the Pidgeon machine are, one, the combination of the rotating support and the fixed support for inducing charge, and, two, the improved insulation of all parts of the machine (but more especially of the generator's carriers). Pidgeon machines are a combination of a Wimshurst Machine and Voss Machine, with special features adapted to reduce the amount of charge leakage. Pidgeon machines excite themselves more readily than the best of these types of machines. In addition, Pidgeon investigated higher current "triplex" section machines (or "double machines with a single central disk") with enclosed sectors (and went on to receive British Patent 22517 (1899) for this type of machine).
+Multiple disk machines and "triplex" electrostatic machines (generators with three disks) were also developed extensively around the turn of the 20th century. In 1900, F. Tudsbury discovered that enclosing a generator in a metallic chamber containing compressed air, or better, carbon dioxide, the insulating properties of compressed gases enabled a greatly improved effect to be obtained owing to the increase in the breakdown voltage of the compressed gas, and reduction of the leakage across the plates and insulating supports. In 1903, Alfred Wehrsen patented an ebonite rotating disk possessing embedded sectors with button contacts at the disk surface. In 1907, Heinrich Wommelsdorf reported a variation of the Holtz machine using this disk and inductors embedded in celluloid plates (DE154175; "Wehrsen machine"). Wommelsdorf also developed several high-performance electrostatic generators, of which the best known were his "Condenser machines" (1920). These were single disk machines, using disks with embedded sectors that were accessed at the edges.
+
+==== Van de Graaff ====

data/en.wikipedia.org/wiki/Electrostatic_generator-3.md

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+---
+title: "Electrostatic generator"
+chunk: 4/5
+source: "https://en.wikipedia.org/wiki/Electrostatic_generator"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:55.653201+00:00"
+instance: "kb-cron"
+---
+
+The Van de Graaff generator was invented by American physicist Robert J. Van de Graaff in 1929 at MIT as a particle accelerator. The first model was demonstrated in October 1929. In the Van de Graaff machine, an insulating belt transports electric charge to the interior of an insulated hollow metal high voltage terminal, where it is transferred to the terminal by a "comb" of metal points. The advantage of the design was that since there was no electric field in the interior of the terminal, the charge on the belt could continue to be discharged onto the terminal regardless of how high the voltage on the terminal was. Thus the only limit to the voltage on the machine is ionization of the air next to the terminal. This occurs when the electric field at the terminal exceeds the dielectric strength of air, about 30 kV per centimeter. Since the highest electric field is produced at sharp points and edges, the terminal is made in the form of a smooth hollow sphere; the larger the diameter the higher the voltage attained. The first machine used a silk ribbon bought at a five and dime store as the charge transport belt. In 1931 a version able to produce 1,000,000 volts was described in a patent disclosure.
+The Van de Graaff generator was a successful particle accelerator, producing the highest energies until the late 1930s when the cyclotron superseded it. The voltage on open air Van de Graaff machines is limited to a few million volts by air breakdown. Higher voltages, up to about 25 megavolts, were achieved by enclosing the generator inside a tank of pressurized insulating gas. This type of Van de Graaff particle accelerator is still used in medicine and research. Other variations were also invented for physics research, such as the Pelletron, that uses a chain with alternating insulating and conducting links for charge transport.
+Small Van de Graaff generators are commonly used in science museums and science education to demonstrate the principles of static electricity. A popular demonstration is to have a person touch the high voltage terminal while standing on an insulated support; the high voltage charges the person's hair, causing the strands to stand out from the head.
+
+=== Others ===
+
+Not all electrostatic generators use the triboelectric effect or electrostatic induction. Electric charges can be generated by electric currents directly. Examples are ionizers and ESD guns.
+
+== Applications ==
+
+=== Gridded ion thruster ===
+
+=== EWICON ===
+An electrostatic vaneless ion wind generator, the EWICON, has been developed by The School of Electrical Engineering, Mathematics and Computer Science at Delft University of Technology (TU Delft). Its stands near Mecanoo, an architecture firm. The main developers were Johan Smit and Dhiradj Djairam. Other than the wind, it has no moving parts. It is powered by the wind carrying away charged particles from its collector. The design suffers from poor efficiency.
+
+=== Dutch Windwheel ===
+The technology developed for EWICON has been reused in the Dutch Windwheel.
+
+=== Air ioniser ===
+
+== Fringe science and devices ==
+These generators have been used, sometimes inappropriately and with some controversy, to support various fringe science investigations. In 1911, George Samuel Piggott received a patent for a compact double machine enclosed within a pressurized box for his experiments concerning radiotelegraphy and "antigravity". Much later (in the 1960s), a machine known as "Testatika" was built by German engineer, Paul Suisse Bauman, and promoted by a Swiss community, the Methernithans. Testatika is an electromagnetic generator based on the 1898 Pidgeon electrostatic machine, said to produce "free energy" available directly from the environment.
+
+== See also ==
+Electrostatic motor
+Electrometer (also known as the "electroscope")
+Electret
+Static electricity
+
+== References ==

data/en.wikipedia.org/wiki/Electrostatic_generator-4.md

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+---
+title: "Electrostatic generator"
+chunk: 5/5
+source: "https://en.wikipedia.org/wiki/Electrostatic_generator"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:55.653201+00:00"
+instance: "kb-cron"
+---
+
+== Further reading ==
+Gottlieb Christoph Bohnenberger: Beschreibung unterschiedlicher Elektrizitätsverdoppler von einer neuen Einrichtung nebst einer Anzahl von Versuchen üb. verschiedene Gegenstände d. Elektrizitätslehre [Description of different electricity-doubler of a new device, along with a number of experiments on various subjects of electricity] Tübingen 1798.
+Holtz, W. (1865). "Ueber eine neue Elektrisirmaschine" [On a new electrical machine]. Annalen der Physik und Chemie (in German). 202 (9). Wiley: 157–171. Bibcode:1865AnP...202..157H. doi:10.1002/andp.18652020911. ISSN 0003-3804.
+Wilhelm Holtz: the higher charge on insulating surfaces by side pull and the transfer of this principle to the construction of induction machines .. In: Johann Poggendorff, CG Barth (eds): Annals of physics and chemistry. 130, Leipzig 1867, pp. 128–136
+Wilhelm Holtz: The influence machine. In: F. Poske (Eds.): Annals of physics and chemistry. Julius Springer, Berlin 1904 (seventeenth year, the fourth issue).
+O. Lehmann: Dr. J. Frick's physical technique. 2, Friedrich Vieweg und Sohn, Braunschweig 1909, p. 797 (Section 2).
+F. Poske: New forms of influence machines. In: F. Poske (eds) for the physical and chemical education. journal Julius Springer, Berlin 1893 (seventh year, second issue).
+C. L. Stong, "Electrostatic motors are powered by electric field of the Earth". October, 1974. (PDF)
+Oleg D. Jefimenko, "Electrostatic Motors: Their History, Types, and Principles of Operation". Electret Scientific, Star City, 1973.
+G. W. Francis (author) and Oleg D. Jefimenko (editor), "Electrostatic Experiments: An Encyclopedia of Early Electrostatic Experiments, Demonstrations, Devices, and Apparatus". Electret Scientific, Star City, 2005.
+V. E. Johnson, "Modern High-Speed Influence Machines; Their principles, construction and applications to radiography, radio-telegraphy, spark photography, electro-culture, electro-therapeutics, high-tension gas ignition, and the testing of materials". ISBN B0000EFPCO
+Simon, Alfred W. (1 November 1924). "Quantitative Theory of the Influence Electrostatic Generator". Physical Review. 24 (6). American Physical Society (APS): 690–696. Bibcode:1924PhRv...24..690S. doi:10.1103/physrev.24.690. ISSN 0031-899X. PMC 1085669. PMID 16576822.
+J. Clerk Maxwell, Treatise on Electricity and Magnetism (2nd ed., Oxford, 1881), vol. i. p. 294
+Joseph David Everett, Electricity (expansion of part iii. of Augustin Privat-Deschanel's "Natural Philosophy") (London, 1901), ch. iv. p. 20
+A. Winkelmann, Handbuch der Physik (Breslau, 1905), vol. iv. pp. 50–58 (contains a large number of references to original papers)
+J. Gray, "Electrical Influence Machines, Their Historical Development and Modern Forms [with instruction on making them]" (London, I903). (J. A. F.)
+Silvanus P. Thompson, The Influence Machine from Nicholson – 1788 to 1888, Journ. Soc. Tel. Eng., 1888, 17, p. 569
+John Munro, The Story Of Electricity (The Project Gutenberg Etext)
+A. D. Moore (Editor), "Electrostatics and its Applications". Wiley, New York, 1973.
+Oleg D. Jefimenko (with D. K. Walker), "Electrostatic motors". Phys. Teach. 9, 121–129 (1971).
+Pidgeon, W R (1892). "An Influence-Machine". Proceedings of the Physical Society of London. 12 (1). IOP Publishing: 406–411. Bibcode:1892PPSL...12..406P. doi:10.1088/1478-7814/12/1/327. ISSN 1478-7814.
+Pidgeon, W R (1897). "An Influence-Machine". Proceedings of the Physical Society of London. 16 (1). IOP Publishing: 253–257. Bibcode:1897PPSL...16..253P. doi:10.1088/1478-7814/16/1/330. ISSN 1478-7814.
+
+== External links ==
+
+Electrostatic Generator – Interactive Java Tutorial National High Magnetic Field Laboratory
+Fleming, John Ambrose (1911). "Electrical Machine" . In Chisholm, Hugh (ed.). Encyclopædia Britannica. Vol. 9 (11th ed.). Cambridge University Press. pp. 176–179.
+"How it works : Electricity". triquartz.co.uk.

data/en.wikipedia.org/wiki/Elton's_quadrant-0.md

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+---
+title: "Elton's quadrant"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Elton's_quadrant"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:56.867994+00:00"
+instance: "kb-cron"
+---
+
+An Elton's quadrant is a derivative of the Davis quadrant. It adds an index arm and artificial horizon to the instrument, and was invented by English sea captain John Elton, who patented his design in 1728 and published details of the instrument in the Philosophical Transactions of the Royal Society in 1732.
+
+
+== Construction ==
+
+This instrument clearly reflects the shape and features of the Davis quadrant.  The significant differences are the change in the upper arc to a simple triangular frame and the addition of an index arm.  The triangular frame at the top spans 60° as did the arc on the backstaff.  The main graduated arc subtends 30° as in the backstaff.  The 30° arc is graduated in degrees and sixths of a degree, that is, at ten-minute intervals.
+The sighting vane of the backstaff is replaced with a sight (called an eye vane) mounted on the end of the index arm.
+The index arm includes a nonius to allow reading the large scale with ten divisions between the graduations on the scale.  This provides the navigator with the ability to read the scale to the nearest minute of arc.  The index arm has a spirit level to allow the navigator to ensure that the index is horizontal even when he cannot see the horizon.  
+The instrument has a horizon vane like a Davis quadrant, but Elton refers to it as the shield or ray vane.   The shield is attached to the label.   The label is an arm that extends from the centre of the arc to the outside of the upper triangle and can be set to one of the three positions in the triangle (in the diagram, it appears to bisect the triangle as it is set to the centre or 30° position).  At the upper end of the label is a Flamsteed glass or lens.
+The three set positions allow the instrument to read 0° to 30°, 30° to 60° or 60° to 90°.  The lens projects an image of the Sun rather than a shadow of the Sun on the shield.  This provides an image even when the sky is hazy or lightly overcast.  In addition, at the mid-span of the label there is a mounting point for a lantern to be used during nocturnal observations.
+There are two spirit levels on the shield.  One, called the azimuth tube, ensures that the plane of the instrument is vertical.  The other is perpendicular to the shield and will indicate when the plane of the shield is vertical and the label is horizontal.
+
+
+== Usage ==
+
+
+=== Solar altitude by backsight ===
+For measuring the altitude of the Sun, the Elton's quadrant can be used in the same manner as a Davis quadrant.  However, with the artificial horizon, the eye vane is not required to be used.
+Hold the instrument in a comfortable manner with the arc towards the Sun.  Set the label so that the Sun's image is projected on the shield at the hole with the index arm roughly horizontal.  Move the index arm so that the index's spirit level shows the arm is precisely horizontal.  This sets the instrument and the angle can be read with the scale and nonius.
+
+
+=== Stellar altitude by foresight ===
+This is a means of measuring altitude of a celestial object that is very different from what can be done with a Davis quadrant.  It reveals one of the significant improvements of the Elton's quadrant over the former instrument.
+Set the label to a position that will put the object to be measured within the range of the instrument.  Observe the object through the eye vane so that the object touches the upper edge of the shield while using the azimuth tube to ensure that the frame is vertical.  Move the index arm so that the shield's horizontal tube indicates that the shield is precisely vertical.  This sets the instrument and the angle can be read on the arc.
+
+
+== Significance to navigation ==
+The Elton's quadrant is not very well known as a navigation instrument.  It was used, though to what degree is not known.  Elton had the misfortune to invent his instrument in the same period of time as the octant.  In fact, John Hadley published details on his octant prior to Elton's article in the same volume of the Philosophical Transactions (article 37 vs 48).
+Given that Elton's quadrant was roughly as complex as an octant in construction, there would not likely be a significant advantage in price.  The octant was an easier instrument to use and Hadley had supported the use of artificial horizons on the octant in the form of spirit levels.  This would have given no advantage to Elton's instrument.  In addition, there were many other instruments competing for the attention of navigators in this period.  In the end, the Hadley octant and later sextant took precedence as instruments for navigators.
+
+
+== References ==
+
+
+== External links ==
+Maritime Art Greenwich, at the National Maritime Museum, London Painting of a captain holding an Elton's Quadrant.

data/en.wikipedia.org/wiki/Equatorial_ring-0.md

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+---
+title: "Equatorial ring"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Equatorial_ring"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:58.041980+00:00"
+instance: "kb-cron"
+---
+
+An equatorial ring was an astronomical instrument used in the Hellenistic world to determine the exact moment of the spring and autumn equinoxes. Equatorial rings were placed before the temples in Alexandria, in Rhodes, and perhaps in other places, for calendar purposes. 
+The easiest way to understand the use of an equatorial ring is to imagine a ring placed vertically in the east-west plane at the Earth's equator. At the time of the equinoxes, the Sun will rise precisely in the east, move across the zenith, and set precisely in the west. Throughout the day, the bottom half of the ring will be in the shadow cast by the top half of the ring. On other days of the year, the Sun passes to the north or south of the ring, and will illuminate the bottom half. For latitudes away from the equator, the ring merely needs to be placed at the correct angle to the equatorial plane. At the Earth's poles, the ring would be horizontal.
+The equatorial ring was about one to two cubits (45cm–90cm) in diameter. Because the Sun is not a point source of light, the width of the shadow on the bottom half of the ring is slightly less than the width of the ring. By waiting until the shadow was centered on the ring, the time of the equinox could be fixed to within an hour or so. If the equinox happened at night, or if the sky was cloudy, an interpolation could be made between two days' measurements.
+The main disadvantage with the equatorial ring is that it needed to be aligned very precisely or false measurements could occur. Ptolemy mentions in the Almagest that one of the equatorial rings in use in Alexandria had shifted slightly, which meant that the instrument showed the equinox occurring twice on the same day. False readings can also be produced by atmospheric refraction of the Sun when it is close to the horizon.
+Equatorial rings can also be found on armillary spheres and equatorial sundials.
+
+
+== References ==
+Anton Pannekoek, (1989), A History of Astronomy, page 124. Courier Dover Publications
+James Evans, (1998), The History and Practice of Ancient Astronomy, pages 206-7. Oxford University Press.

data/en.wikipedia.org/wiki/Equatorium-0.md

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+---
+title: "Equatorium"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Equatorium"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:59.223473+00:00"
+instance: "kb-cron"
+---
+
+An equatorium (plural, equatoria) is an astronomical calculating instrument. It can be used for finding the positions of the Moon, Sun, and planets without arithmetic operations, using a geometrical model to represent the position of a given celestial body.
+
+
+== History ==
+In his comment on Ptolemy's Handy Tables, 4th century mathematician Theon of Alexandria introduced some diagrams to geometrically compute the position of the planets based on Ptolemy's epicyclical theory. The first description of the construction of a solar equatorium (as opposed to planetary) is contained in Proclus's fifth-century work Hypotyposis, where he gives instructions on how to construct one in wood or bronze.
+The earliest known descriptions of planetary equatoria are in the Latin translation of an early eleventh century text by Ibn al‐Samḥ and a 1080/1081 treatise by al-Zarqālī, contained in the Libros del saber de astronomia (Books of the knowledge of astronomy), a Castilian compilation of astronomical works collected under the patronage of Alfonso X of Castile in the thirteenth century.
+The Theorica Planetarum (c. 1261–1264) by Campanus of Novara is the earliest extant description of the construction of an equatorium in Latin Europe. Campanus' instrument resembled an astrolabe, with several interchangeable plates within a mater. The best manuscripts of Campanus' treatise contain paper and parchment equatoria with moveable parts.
+Early in 1393, the English Benedictine monk John Westwyk completed his Equatorie de Planetis, a manuscript containing original designs for a large equatorium, along with directions for its construction and a long series of astronomical tables calibrated for use with the device. If built according to his instructions, Westwyk's equatorium would have measured 6 feet in diameter, allowing astronomers a much greater degree of precision in their calculations, but a full-scale model made to Westwyk's ideal specifications would have been prohibitively expensive during his lifetime, making it unlikely that his ideal iteration of the device was ever constructed. 
+
+
+== Variations ==
+
+The history of the equatorium does not just end after the 11th century, but it inspired a more diverse invention called “The Albion”. The Albion is an astronomical instrument invented by Richard of Wallingford at the beginning of the 14th century. It has various functional uses such as that of the equatorium for planetary and conjunction computations. It can calculate when eclipses will occur. The Albion is made up of 18 different scales which makes it extremely complex in comparison to the equatorium. The history of this instrument is still disputed to this day, as the only Albion from the past is both unnamed and unmarked.
+
+
+== Astrolabe compared with equatorium ==
+The roots of the equatorium lie in the astrolabe. The history of the astrolabe dates back to roughly 220 BC in the works of Hipparchus. The difference between the two instruments is that the astrolabe measures the time and position of the sun and stars at a specific location in time. In contrast, the equatorium is used to calculate the past or future positions of the planets and celestial bodies according to the planetary theory of Ptolemy.
+
+
+== Uses ==
+The equatorium can further be specialized depending on the epicycle. There are three possible epicycles that can be adjusted to serve for planetary positions in three groups: the Moon, the stars, and the Sun. The Sun was considered a planet in the Ptolemaic system, hence why the equatorium could be used to determine its position. Through the use of Ptolemy's model, astronomers were able to make a single instrument with various capabilities that catered to the belief that the Solar System had the Earth at the center. In fact, specialized equatoriums had astrological aspects of medicine, as the orientation of planets gave insight to zodiac signs which helped some doctors cater medical treatments to patients.
+At least 15 minutes was needed to calculate the planetary position with the use of a table for each celestial body. A horoscope of that era would have required the positions of seven astronomical objects, requiring nearly two hours of manual calculation time.
+
+
+== See also ==
+
+Antikythera mechanism
+Armillary sphere
+Astrarium
+Astrolabe
+Astronomical clock
+Orrery
+Planetarium
+The Equatorie of the Planetis
+Torquetum
+
+
+== References ==
+
+
+== Further reading ==
+Seb Falk's blog: making a planetary equatorium

data/en.wikipedia.org/wiki/F._J._Duarte-0.md

@@ -0,0 +1,273 @@
+---
+title: "F. J. Duarte"
+chunk: 1/2
+source: "https://en.wikipedia.org/wiki/F._J._Duarte"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:35:50.108359+00:00"
+instance: "kb-cron"
+---
+
+Francisco Javier "Frank" Duarte (born c. 1954) is a laser physicist and author/editor of several books on tunable lasers.
+His research on physical optics and laser development has won several awards, including an Engineering Excellence Award in 1995 for the invention of the N-slit laser interferometer.
+
+== Research ==
+
+=== Laser oscillators ===
+Duarte and Piper introduced multiple-prism near-grazing-incidence grating cavities which originally were disclosed as copper-laser-pumped narrow-linewidth tunable laser oscillators. Subsequently, he developed narrow-linewidth multiple-prism grating configurations for high-power CO2 laser oscillators and solid-state tunable organic laser oscillators.
+
+=== Intracavity dispersion theory ===
+Duarte also conceived the multiple-prism dispersion theories for tunable narrow-linewidth laser oscillators, and multiple-prism laser pulse compression, which are summarized in several of his books.  The introduction to this theory is the generalized multiple-prism dispersion equation
+
+  
+    
+      
+        
+          ∇
+          
+            λ
+          
+        
+        
+          ϕ
+          
+            2
+            ,
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+            (
+            m
+            −
+            1
+            )
+          
+        
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+          
+            )
+          
+        
+      
+    
+    {\displaystyle \nabla _{\lambda }\phi _{2,m}=H_{2,m}\nabla _{\lambda }n_{m}+(k_{1,m}k_{2,m})^{-1}{\bigg (}H_{1,m}\nabla _{\lambda }n_{m}\pm \nabla _{\lambda }\phi _{2,(m-1)}{\bigg )}}
+  
+
+which has found a variety of applications.
+
+=== Tunable lasers for isotope separation ===
+His tunable narrow-linewidth laser oscillator configurations have been adopted by various research groups working  on uranium atomic vapor laser isotope separation (AVLIS).   This work was supported by the Australian Atomic Energy Commission. During the course of this research, Duarte writes that he did approach the then federal minister for energy, Sir John Carrick, to advocate for the introduction of an AVLIS facility in Australia. In 2002, he participated in research that led to the isotope separation of lithium using narrow-linewidth tunable diode lasers.
+
+=== Solid state organic dye lasers ===
+From the mid-1980s to early 1990s Duarte and scientists from the US
+Army Missile Command developed ruggedized narrow-linewidth laser oscillators tunable directly in the visible spectrum.  This constituted the first disclosure, in the open literature, of a tunable narrow-linewidth laser tested on a rugged terrain.  This research led to experimentation with polymer gain media and in 1994 Duarte reported on the first narrow-linewidth tunable solid state dye laser oscillators.   These dispersive oscillator architectures were then refined to yield single-longitudinal-mode emission limited only by Heisenberg's uncertainty principle.
+
+=== Organic gain media ===
+Joint research, with R. O. James, on solid-state organic-inorganic materials, led to the discovery of polymer-nanoparticle gain media and to the emission of tunable low-divergence homogeneous laser beams from this class of media. In 2005, Duarte and colleagues were the first to demonstrate    directional coherent emission from an electrically excited organic semiconductor.   These experiments utilized a tandem OLED within an integrated interferometric configuration.
+Duarte's work in this area began with the demonstration of narrow-linewidth laser emission using coumarin-tetramethyl dyes which offer high conversion efficiency and wide tunability in the green region of the electromagnetic spectrum.
+
+=== Interferometry and quantum optics ===
+
+In the late 1980s, he invented the digital N-slit laser interferometer for applications in imaging and microscopy. Concurrently, he applied Dirac's notation to describe quantum mechanically its interferometric and propagation characteristics. A further innovation in this interferometer was the use of extremely elongated Gaussian beams, width to height ratios of up to 2000:1, for 
+sample illumination.
+This research  also led to the generalized N-slit interferometric equation that was then applied to describe classical optics phenomena such as interference, diffraction, refraction, and reflection, in a generalized and unified quantum approach that includes positive and negative refraction.  He also derived the cavity linewidth equation, for dispersive laser oscillators, using quantum mechanical principles.
+Further developments include very large N-slit laser interferometers to generate and propagate interferometric characters for secure free-space optical communications.  Interferometric characters is a term coined in 2002 to link interefometric signals to alphanumerical characters (see figure's legend). 
+These experiments provided the first observation of diffraction patterns superimposed over propagating interference signals, thus demonstrating non-destructive (or soft) interception of propagating interferograms.
+A spin-off of this research, with applications to the aviation industry, resulted from the discovery that N-slit laser interferometers are very sensitive detectors of clear air turbulence.
+Duarte provides a description of quantum optics, almost entirely via Dirac's notation, in his book Quantum Optics for Engineers.  In this book he derives the probability amplitude for quantum entanglement,
+
+  
+    
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+            |
+            x
+            ⟩
+          
+          
+            2
+          
+        
+        )
+      
+    
+    {\displaystyle \left|\psi \right\rangle ={1 \over {\sqrt {2}}}(\left|x\right\rangle _{1}\left|y\right\rangle _{2}-\left|y\right\rangle _{1}\left|x\right\rangle _{2})}
+  
+
+which he calls the Pryce-Ward probability amplitude, from an N-slit interferometric perspective.  It is this 
+  
+    
+      
+        
+          |
+          ψ
+          ⟩
+        
+      
+    
+    {\displaystyle \left|\psi \right\rangle }
+  
+ that becomes the probability 
+  
+    
+      
+        
+          |
+          ψ
+          ⟩
+        
+        
+          
+            |
+            ψ
+            ⟩
+          
+          
+            ∗
+          
+        
+      
+    
+    {\displaystyle \left|\psi \right\rangle \left|\psi \right\rangle ^{*}}
+  
+ disclosed by Pryce and Ward.  Duarte also emphasizes a pragmatic non-interpretational approach to quantum mechanics.
+
+== Career ==
+
+=== Macquarie University ===
+At Macquarie University, Duarte studied quantum physics under John Clive Ward and semiconductor physics under Ronald Ernest Aitchison.  His PhD research was on laser physics and his supervisor was James A. Piper.
+In the area of university politics, he established and led the Macquarie science reform movement, that transformed the degree structure of the university.  Macquarie's science reform, was widely supported by local scientists including physicists R. E. Aitchison, R. E. B. Makinson, A. W. Pryor, and J. C. Ward.
+In 1980, Duarte was elected as one of the Macquarie representatives to the Australian Union of Students from where he was expelled, and then reinstated, for "running over the tables."
+Following completion of his PhD work, Duarte did post doctoral research, with B. J. Orr at the University of New South Wales, and then back at Macquarie University.

data/en.wikipedia.org/wiki/F._J._Duarte-1.md

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+---
+title: "F. J. Duarte"
+chunk: 2/2
+source: "https://en.wikipedia.org/wiki/F._J._Duarte"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:35:50.108359+00:00"
+instance: "kb-cron"
+---
+
+=== American phase ===
+In 1983, Duarte traveled to the United States to assume a physics professorship at the University of Alabama.  In 1985 he joined the Imaging Research Laboratories, at the Eastman Kodak Company, where he remained until 2006.  While at Kodak he was chairman of Lasers '87 and subsequent conferences in this series.  Duarte has had a long association with the US Army Missile Command and the US Army Aviation and Missile Command, where he has participated (with R. W. Conrad and T. S. Taylor) in directed energy research.
+He was elected Fellow of the Australian Institute of Physics in 1987) and a Fellow of the Optical Society of America in 1993.
+In 1995, he received the Engineering Excellence Award for "the invention of an electrooptic coherent interferometer for direct applications to imaging diagnostics of  transparent surfaces, such as photographic film and film substrates. and in 2016, he was awarded the David Richardson Medal for "seminal contributions to the physics and technology of multiple-prism arrays for narrow-linewidth tunable laser oscillators and laser pulse compression," from the Optical Society.
+
+=== Personal ===
+
+Duarte was born in Santiago, Chile, and traveled to Sydney, Australia, as a teenager.  There, he lived first in Strathfield and then in the northern small town of Cowan.  In the  United States he resided for a brief period in Tuscaloosa, Alabama, and then moved to Western New York.
+
+=== Books ===
+Dye Laser Principles (1990)
+Tunable Laser Optics, 2nd Ed. (2015, Second edition)
+Tunable Laser Applications, 3rd Ed (1996, 2009, 2016)
+Fundamentals of Quantum Entanglement (2019)
+Quantum Entanglement Engineering and Applications (2021)
+
+== See also ==
+Heat equation
+Laser space communications
+Multiple-prism beam expanders
+Organic laser
+Polarization rotator
+
+== References ==
+
+== External links ==
+
+Duarte's home page
+United States Patents by F. J. Duarte, at Patent Genius

data/en.wikipedia.org/wiki/Filar_micrometer-0.md

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+date_saved: "2026-05-05T09:37:01.632726+00:00"
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data/en.wikipedia.org/wiki/Franklin's_electrostatic_machine-0.md

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+---
+title: "Franklin's electrostatic machine"
+chunk: 1/3
+source: "https://en.wikipedia.org/wiki/Franklin's_electrostatic_machine"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:37:04.008946+00:00"
+instance: "kb-cron"
+---
+
+Franklin's electrostatic machine is a high-voltage static electricity-generating device used by Benjamin Franklin in the mid-18th century for research into electrical phenomena. Its key components are a glass globe which turned on an axis via a crank, a cloth pad in contact with the spinning globe, a set of metal needles to conduct away the charge developed on the globe by its friction with the pad, and a Leyden jar – a high-voltage capacitor – to accumulate the charge. Franklin's experiments with the machine eventually led to new theories about electricity and inventing the lightning rod.
+
+== Background ==
+
+Franklin was not the first to build an electrostatic generator. European scientists developed machines to generate static electricity decades earlier. In 1663, Otto von Guericke generated static electricity with a device that used a sphere of sulfur. Francis Hauksbee developed a more advanced electrostatic generator around 1704 using a glass bulb that had a vacuum. He later replaced the globe with a glass tube of about 2.5 feet (0.76 m) emptied of air. The glass tube was a less effective static generator than the globe, but it became more popular because it was easier to use.
+Machines that generated static electricity with a glass disc were popular and widespread in Europe by 1740. In 1745, German cleric Ewald Georg von Kleist and Dutch scientist Pieter van Musschenbroek discovered independently that the electric charge from these machines could be stored in a Leyden jar, named after the city of Leiden in the Netherlands.
+In 1745, Peter Collinson, a businessman from London who corresponded with American and European scientists, donated a German "glass tube" along with instructions how to make static electricity, to Franklin's Library Company of Philadelphia. Collinson was the library's London agent and provided the latest technology news from Europe. Franklin wrote a letter to Collinson on March 28, 1747, thanking him, and saying the tube and instructions had motivated  several colleagues and him to begin serious experiments with electricity.
+
+In 1746, Franklin began working on electrical experiments with Ebenezer Kinnersley after he bought all of Archibald Spencer's electrical equipment that he used in his lectures. Later, he was also associated with Thomas Hopkinson and Philip Syng in experimentation with electricity. In the summer of 1747 they had received an electrical system from Thomas Penn. While no records exists to tell exactly what parts were included in the system, historian J. A. Leo LeMay believes it was a combination of an electricity generating machine, a Leyden jar, a glass tube, and a stool that was electrically insulated from the ground. This gave Franklin a complete system to experiment with generating and storing electricity.
+When amber, sulfur, or glass are rubbed with certain materials, they produce electrical effects. Franklin theorized this "electrical fire" was collected from this other material somehow, and not produced by the friction on the object. He decided to retire early from his printing business, still in his early forties, to spend more time studying electricity. In 1748, Franklin turned over his entire printing business to his partner David Hall. He moved into a new Philadelphia home with his wife, where he built a laboratory to conduct experiments and research new electrical theories. Franklin experimented not only with the electrostatic machine with the glass globe, but also with the Leyden jar. He kept a detailed journal of his research in a diary called "Electrical Minutes" that has since been lost. Franklin's machine was given to Library Company of Philadelphia by Franklin's grandson in 1792, and is currently on display at the Franklin Institute.
+
+== Description ==
+Franklin's machine used a belt and pulley system that could be operated by one person turning a crank. A large pulley was attached to the crank handle, and a much smaller pulley was attached to a large glass globe. An iron axle passed through the globe. This allowed the globe to be rotated at high speed. When the crank was turned, the glass globe rubbed against a leather pad, which generated a large static charge, similar to the electrical charge that could be created by rubbing a glass tube with wool cloth by hand. The machine was unique improvement over others made in Europe at the time, as the glass globe could be spun faster with much less labor. A few revolutions of the handle were all that were needed to charge a Leyden jar.
+The electricity produced by the machine, in the form of sparks, passed through a set of metal needles positioned close to the spinning globe. The electric charge continued passing through a beaded iron chain, which acted as a conductor, to a Leyden jar that received the electricity. Franklin called the sparks produced by the machine "electrical fire".
+The glass globes, known as "electerizing globes", were made of glass that was scientifically designed to produce static electricity effectively. Franklin specified the materials to be used in the glass formula, and the globes were manufactured by Caspar Wistar, a close associate of Franklin. Wistarburgh Glass Works also made scientific glass for the Leyden jars Franklin used in the 1750s.

data/en.wikipedia.org/wiki/Franklin's_electrostatic_machine-1.md

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+---
+title: "Franklin's electrostatic machine"
+chunk: 2/3
+source: "https://en.wikipedia.org/wiki/Franklin's_electrostatic_machine"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:37:04.008946+00:00"
+instance: "kb-cron"
+---
+
+== Electrical principles ==
+Franklin's experiments with Leyden jars progressed to connecting several Leyden jars together in a series, with "one hanging on the tail of the other". All of the jars in the series could be charged simultaneously, which multiplied the electrical effect. A similar apparatus had been created earlier by Daniel Gralath. Franklin called this device an "electrical battery", but that term later came to have a different meaning, referring instead to a set of one or more galvanic cells. At that time, the word "battery" was a military term for a group of cannons. Franklin was the first to apply the terms "positive" and "negative" to electricity.
+Through his research, Franklin was among first to prove the electrical principal of conservation of charge in 1747: a similar discovery was made independently in 1746 by William Watson. Franklin wrote detailed letters and documents about his experiments with the electrostatic machine and Leyden jars. In 1749, Franklin made a list of several ways in which lightning was similar to electricity. He concluded that lightning was essentially nothing more than giant electric sparks, similar to the sparks from the static charges produced by his electrostatic machine. He referred to static electricity as "electric fire", "electric matter", or "electric fluid". The term "electric fluid" was based on the idea that a jar could be filled and refilled when it became empty. That led to the revolutionary idea of "electrical fire" as a type of motion or current flow rather than a type of explosion.
+Several 18th-century electric terms were derived from his name. For example, static electricity was known as "Franklin current", and "Franklinization" is a form of electrotherapy where Franklin shocked patients with strong static charges, to treat patients with various illnesses.
+
+== Lightning rod invention ==
+
+Franklin invented the lightning rod based on what he learned from experiments with his electrostatic machine.  Franklin and his associates observed that pointed objects were more effective than blunt objects at "drawing off" and "throwing off" sparks from static electricity. This discovery was first reported by Hopkinson. Franklin wondered if this discovery could be used in a practical invention.  He thought something could be made to attract the electricity out of storm clouds, but first he had to verify that lightning bolts really are giant electric sparks. He wrote Collinson and Cadwallader Colden letters about this theory, and he described the kite experiment in the October 19, 1752 issue of the Pennsylvania Gazette. (Tom Tucker of the Isothermal Community College doubts the account, however, because of ambiguities in the account and points that out in his book Bolt of Fate: Benjamin Franklin and his Electric Kite Hoax. Others disagree with this view, arguing that Franklin would not make up such a fake story because he valued the integrity of the scientific community.)
+
+To test his theory, Franklin proposed a potentially deadly experiment, to be performed during an electrical storm, where a person would stand on an insulated stool inside a sentry box, and hold out a long, pointed iron rod to attract a lightning bolt. A similar but less dangerous version of this experiment was first performed successfully in France On May 10, 1752, and later repeated several more times throughout Europe, though after a fatality in 1753 it was less frequently tried. Franklin declared that this "sentry-box experiment" showed that lightning and electricity were one and the same.
+Franklin realized that wooden buildings could be protected from lightning strikes, and the deadly fires that often resulted, by placing a pointed iron on a rooftop, with the other end of the rod placed deep into the ground. The sharp point of the lightning rod would attract the electrical discharge from the cloud, and the lightning bolt would hit the iron rod instead of the wooden building. The electric charge from the lightning would flow through the rod directly into the earth, bypassing the structure, and preventing a fire.
+Franklin's friend Kinnersley traveled throughout the eastern United States in the 1750s demonstrating man-made "lightning" on model thunder houses to show a how an iron rod placed into the ground would protect a wooden structure. He explained that lightning followed the same principles as the sparks from Franklin's electrostatic machine. These lectures by Kinnersley were widely advertised, and were one of the ways Franklin's lightning rod was demonstrated to the general public.
+
+== Legacy ==

data/en.wikipedia.org/wiki/Franklin's_electrostatic_machine-2.md

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+---
+title: "Franklin's electrostatic machine"
+chunk: 3/3
+source: "https://en.wikipedia.org/wiki/Franklin's_electrostatic_machine"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:37:04.008946+00:00"
+instance: "kb-cron"
+---
+
+Franklin distributed copies of the electrostatic machine to many of his close associates to encourage them to study electricity. Between 1747 and 1750, Franklin sent many letters to his friend Collinson in London about his experiments with the electrostatic machine and the Leyden jar, including his observations and theories on the principles of electricity. These letters were collected and published in 1751 in a book entitled Experiments and Observations on Electricity.
+While Joseph Priestley was writing about the history of electricity, Franklin encouraged him to use an electrostatic machine to perform the experiments he was writing about. Priestly designed and used his own variations of Franklin's machine. While replicating the electrical experiments, some unanswered questions prompted Priestly to design additional experiments, leading to additional discoveries. In 1767, he published a 700-page book on his findings called The History and Present State of Electricity.
+Eighteenth-century scientific laboratories usually contained some form of hand-operated electrostatic machine. Italian scientist Luigi Galvani had an electrostatic generator in his laboratory, where experiments with frog legs led him to conclude that animals generated a vital force, an animal electricity. Another Italian scientist, Alessandro Volta, disagreed with Galvani's claim that the electrical effects were due to something peculiar to living matter, and he demonstrated that electricity can be generated merely by placing wet, salty material in between two different metals. This led directly to the invention of the first practical electric battery, the voltaic pile.
+After Franklin's death, two iconic artifacts from his research, the original "battery" of Leyden jars, and the "glass tube" that was a gift from Collinson in 1747, were given to the Royal Society in 1836 by Thomas Hopkinson's grandson Joseph Hopkinson, in accordance with Franklin's will.
+
+== See also ==
+Wistarburgh Glass Works
+Corbett's electrostatic machine
+Van de Graaff generator
+
+== References ==
+
+=== Citations ===
+
+=== Sources ===
+Avery, John Scales (2016). Science and Society. World Scientific. ISBN 978-981-3147-73-7.
+Boese, Alex (2015). "The Electric Kite Hoax". The Museum of Hoaxes. Retrieved February 6, 2017.
+Bridenbaugh, Carl (2012). The Colonial Craftsman. Courier Corporation. ISBN 978-0-486-14473-3.
+Cohen, I. Bernard (1956). Franklin and Newton: An Inquiry Into Speculative Newtonian Experimental Science and Franklin's Work in Electricity as an Example Thereof. Harvard University Press.
+Cohen, I. Bernard (1990). Benjamin Franklin's Science. Harvard University Press. p. 61. ISBN 978-0-674-06659-5. Peter Collinson glass tube Franklin gift.
+Coulson, Thomas (1950). Joseph Henry: His Life and Work. Princeton University Press. The atmosphere of Philadelphia gave him and his associates exceptional opportunity to exercise their skill with the electrostatic machine. As a result, many of their experiments were of an original character. The famous kite experiment enabled the Philadelphia group to established what had been surmised by others, that lightning was identical to the mild charge of electricity produced by the friction of the electrostatic machine. Franklin invented the lightning rod, which goes down in history as the first practical electrical invention.
+Crane, Verner Winslow (1954). Benjamin Franklin and a Rising People. Little, Brown and Company.
+Finger, Stanley (2012). Doctor Franklin's Medicine. University of Pennsylvania Press. ISBN 978-0-8122-0191-8.
+Franklin, Benjamin (1751). "Experiments and Observations on Electricity". E. Cave. Retrieved 28 October 2016 – via Smithsonian Libraries.
+Garche, Jürgen (2013). Encyclopedia of Electrochemical Power Sources. Newnes. ISBN 978-0-444-52745-5.
+Gregory, George (1822). A Dictionary of Arts and Sciences. Collins and Company.
+Grimnes, Sverre (2014). Bioimpedance and Bioelectricity Basics. Academic Press. ISBN 978-0-12-411533-0.
+Isaacson, Walter (2004). Benjamin Franklin: An American Life. Simon and Schuster. ISBN 978-0-7432-5807-4.
+Jackson, Joe (2005). World on Fire. Viking. ISBN 978-0-670-03434-5.
+LeMay, J. A. Leo (1987). Benjamin Franklin: Writings. Penguin Group USA. ISBN 978-0-940450-29-5.
+Lemay, J. A. Leo (2009). The Life of Benjamin Franklin, Volume 3: Soldier, Scientist, and Politician, 1748–1757. University of Pennsylvania Press. ISBN 978-0-8122-4121-1.
+Lynn, Barry C. (2009). Cornered: The New Monopoly Capitalism and the Economics of Destruction. John Wiley & Sons. ISBN 978-0-470-55703-7.
+Maclean, John (1877). History of the College of New Jersey: From Its Origin in 1746 to the Commencement of 1854. Lippincott.
+Matthews, Robert (June 1, 2003). "Benjamin Franklin 'faked kite experiment'". The Telegraph. Retrieved February 6, 2017.
+McGrath, Kimberley A. (2001). The Gale Encyclopedia of Science: Catastrophism-Eukaryotae. Gale Group. ISBN 978-0-7876-4372-0.
+McNichol, Tom (2006). AC/DC: The Savage Tale of the First Standards War. John Wiley & Sons. ISBN 978-1-118-04702-6.
+Morgan, Edmund Sears (2003). Benjamin Franklin. Yale University Press. ISBN 978-0-300-10162-1.
+Malmivuo, Jaakko; Plonsey, Robert (1995). Bioelectromagnetism: Principles and Applications of Bioelectric and Biomagnetic Fields. Oxford University Press. ISBN 978-0-19-505823-9.
+Pasles, Paul C. (2008). Benjamin Franklin's Numbers: An Unsung Mathematical Odyssey. Princeton University Press. ISBN 978-0-691-12956-3.
+Pyenson, Lewis; Gauvin, Jean-François (2002). Art of Teaching Physics. Les Éditions du Septentrion. ISBN 978-2-89448-320-6.
+Schafer, Larry E. (1992). Taking Charge: An Introduction to Electricity. NSTA Press. ISBN 978-0-87355-110-6.
+Schiffer, Michael B. (2003). Draw the Lightning Down. University of California Press. ISBN 0-520-23802-8.
+Schiffer, Michael B. (2004). "Bolt of Fate: Benjamin Franklin and His Electric Kite Hoax (review)". Technology and Culture. 45 (4): 839–840. doi:10.1353/tech.2004.0202. S2CID 109344397.
+Schofield, Robert E. (1997). Enlightenment of Joseph Priestley. Penn State Press. ISBN 0-271-04083-1.
+Secor, Robert (1975). Pennsylvania: 1776. Pennsylvania State University Press. ISBN 978-0-271-01217-9.
+Talbott, Page (2005). Search of a Better World. Yale University Press. ISBN 978-1-4379-6732-6.
+Tucker, Tom (2005). Bolt of Fate. PublicAffairs. ISBN 978-0-7867-3942-4.
+Waldstreicher, David (2005). Runaway America. Farrar, Straus and Giroux. ISBN 978-0-8090-8315-2.
+
+== External links ==
+Benjamin Franklin's electrical apparatus (electrostatic machine) at Smithsonian National Museum of American History
+The Amazing Adventures of Ben Franklin – Scientist & Inventor / Opposites Attract with picture of glass globe on top
+Franklin's Electrostatic Generator information and picture from University of Maryland Electrical and Computer Engineering Dept. Archived 2016-12-06 at the Wayback Machine

data/en.wikipedia.org/wiki/Franklin_bells-0.md

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+---
+title: "Franklin bells"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Franklin_bells"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:37:02.808625+00:00"
+instance: "kb-cron"
+---
+
+Franklin bells (also known as lightning bells) are an early demonstration of electric charge designed to work with a Leyden jar or a lightning rod. Franklin bells are only a qualitative indicator of electric charge and were used for simple demonstrations rather than research. The bells are an adaptation to the first device that converted electrical energy into mechanical energy in the form of continuous mechanical motion: in this case, the moving of a bell clapper back and forth between two oppositely charged bells.
+
+
+== History ==
+Scientific investigation of the phenomena of lightning originates with Benjamin Franklin. He accumulated analogical evidence favoring the supposition that lightning must be an electrical discharge on a large scale. In the mid-18th century, lightning strikes were a serious problem for buildings and structures, causing damage and sometimes even fires. Franklin set out to understand the nature of lightning and to find ways to protect buildings from its destructive effects. He began his investigations by observing how lightning strikes affected various types of buildings. He noticed that some buildings were more vulnerable to lightning strikes than others and that buildings with sharp pointed roofs were more likely to be struck than those with flat roofs. He also observed that lightning seemed to follow conductive paths, such as metal rods or wires, and that these paths could be used to divert lightning strikes away from buildings.
+Based on these observations, Franklin developed the idea of the lightning rod. The lightning rod consists of a metal rod or conductor, typically made of copper or aluminum, that is mounted on the roof of a building and connected to the ground by means of a conductive wire. When lightning strikes, the rod provides a path of least resistance for the electrical charge, allowing it to be safely conducted to the ground rather than passing through the building and causing damage. The invention of the lightning rod was a significant breakthrough in the field of electrical engineering, and has saved countless buildings and lives from the destructive effects of lightning strikes.
+The Franklin bells were named for Benjamin Franklin, an early adopter who used it during his experimentation with electricity. Its predecessor was invented by the Scottish inventor Andrew Gordon, Professor of Natural Philosophy at the University of Erfurt, Germany. In 1742 he invented a device known as the "electric chimes", which was widely described in textbooks of electricity. Franklin made use of Gordon's idea by connecting one bell to his pointed lightning rod, attached to a chimney, and a second bell to the ground. One of his papers contains the following description:
+
+In September 1752, I erected an iron rod to draw the lightning down into my house, in order to make some experiments on it, with two bells to give notice when the rod should be electrified.
+I found the bells rang sometimes when there was no lightning or thunder, but only a dark cloud over the rod; that sometimes after a flash of lightning they would suddenly stop; and at other times, when they had not rang before, they would, after a flash, suddenly begin to ring; that the electricity was sometimes very faint, so that when a small spark was obtained, another could not be got for sometime after; at other times the sparks would follow extremely quick, and once I had a continual stream from bell to bell, the size of a crow-quill. Even during the same gust there were considerable variations.
+Through this experiment, Franklin was able to demonstrate that electricity behaves like a fluid, flowing through conductive materials and causing effects along the way. Franklin's experiment with the bells and the lightning rod was groundbreaking in its time, as it provided a clear demonstration of the nature of electricity and its properties and provided a foundation for further experiments and discoveries in the field.
+Franklin's experimentation with the bell setup was pivotal to discovering that electricity exists outside of lightning and thunderstorms. The bells' odd properties intrigued Franklin and fueled further hypotheses.
+
+
+== Design and operation ==
+The bells consist of a metal stand with a crossbar, from which hang three bells. The outer two bells hang from conductive metal chains, while the central bell hangs from a nonconductive thread. In the spaces between these bells hang two metal clappers, small pendulums, on nonconductive threads. A short metal chain hangs from the central bell.
+
+The system of operation of the Franklin clock considers that the electrostatic force generated by an electric field is used to move the pendulums that strike two metal bells. The Franklin bells uses a metal rod as a lightning rod to attract current. One bell is connected to the lightning rod and the other bell is connected to the ground. A metal battering ram is suspended between the two bells by an insulated wire. The negatively charged clouds before the thunderstorm make the lightning rod negatively charged, and also make the bell connected to it negatively charged. The metal ball is attracted and crashes into the fully charged bell. When the ball hits the first bell, it will be charged with the same potential and will therefore be repelled again. Since the opposite bell is reversely charged, this will also attract the ball to it. When the ball hits the second bell, the charge is transferred and the process is repeated until the charges are balanced again. Before the storm, the device would ring to remind Franklin, who had been obsessed with the study of lightning, urging him to chase the lightning.
+
+
+== Modern Impact ==
+Benjamin Franklin's experiment with bells and a lightning rod has remained a popular example of electric phenomena in modern times. The experiment has been adapted and updated, and is now commonly used in classrooms and demonstrations to illustrate a variety of concepts related to electricity.
+For instance, the experiment can be used to demonstrate the concept of electric current and how it flows through a conductor. By connecting the bells with metal wires and charging the lightning rod, students can see the flow of electric charges through the wires and observe the resulting electromagnetic effects that cause the bells to ring.
+The experiment can also be used to illustrate the properties of static electricity, and how it can be conducted through metal wires to create an electric current. By rubbing a balloon or other object to create a static charge, and then using the charge to activate the bells, students can see the effects of static electricity and learn how it can be harnessed and utilized. The Franklin Bell is now a common electrical experiment demonstration in high school and introductory college physics courses.
+
+
+== See also ==
+Oxford Electric Bell, a set of electrostatic bells in the University of Oxford, has been ringing continuously since 1840.
+Lightning-prediction system
+
+
+== References ==
+
+
+== External links ==
+Ben Franklin's Lightning Bells(Franklin Institute)
+Franklin’s Bells (Gordon’s Bells) Archived 2013-08-09 at the Wayback Machine (PV Scientific Instruments)
+"Franklin’s Bells" and charge transport as an undergraduate lab (American Journal of Physics)
+Franklin's Bells (Research Media & Cybernetics)

data/en.wikipedia.org/wiki/François-Antoine_Jecker-0.md

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+---
+title: "François-Antoine Jecker"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/François-Antoine_Jecker"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:35:59.288765+00:00"
+instance: "kb-cron"
+---
+
+François-Antoine Jecker (November 14, 1765 – September 30, 1834) was a French scientific-instrument maker. Trained in London under Jesse Ramsden, he established a workshop in Paris that produced astronomical, optical, and measuring instruments.
+
+
+== Life and work ==
+Jecker was born in Hirtzfelden near Colmar, Haut-Rhin, the son of a farmer. His brother Laurenz Jecker (1769–1834) became a needle manufacturer. He apprenticed with a watchmaker in Besançon where two uncles worked as musicians. He went to London in 1786 and trained with Jesse Ramsden and returned to Paris in 1792 where he started a workshop to manufacture astronomical instruments and precision measuring instruments. He was joined by his brothers Gervais and Protais and by 1800 he had nearly 40 employees.
+
+
+== References ==
+
+
+== External links ==
+Jecker Museum in Hirtzfelden
+Drum microscopes made by Jecker

data/en.wikipedia.org/wiki/Friedrich_Adolph_Nobert-0.md

@@ -0,0 +1,19 @@
+---
+title: "Friedrich Adolph Nobert"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Friedrich_Adolph_Nobert"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:36:05.169864+00:00"
+instance: "kb-cron"
+---
+
+Friedrich Adolph Nobert (17 January 1806 – 21 February 1881) was a Pomeranian microscope designer who pioneered the use of diamond-ruled microscope slide gratings for accurate measurements. This extended further to diffraction gratings for use in spectrometers and the measurement of the solar spectrum by Anders Jonas Ångström which was published in 1868 made use of gratings made by Nobert. The finest lines were found to be at a distance of 0.1128 μm.
+
+
+== Biography ==
+
+Nobert was born in Barth on the Baltic coast, where his father Johann Friedrich Nobert was a clockmaker. He was known as Fritz, and being the eldest son, he was expected to receive a technical education and continue as a clockmaker. A younger brother studied theology and became a pastor. He found his schooling insufficient for the clockmaking work and tried to study arithmetic, geometry and trigonometry on his own. He made a watch that could measure seconds, and corrected for temperature and sent it for an exhibition in Berlin in 1827. This was examined by astronomer Johann Franz Encke who wrote to Nobert and encouraged him to check its accuracy with astronomical measurements. This required a telescope and not able to purchase one, he began to construct one on his own. In 1829 he measure several star positions using a 2 foot quadrant and was able to tell that the accuracy of his chronometer was close to those made by  Breguet in Paris and Kessels in Altona. He then applied for a bursary to support his education and received 300 Thalers to join the Technical Institute in Berlin from October 1833 after which he would receive the post of technician at the University of Greifswald. Nobert maintained a diary of his studies and it included lessons in astronomy and the circle-dividing engine. Nobert was appointed to Universitatsmechaniker at Greifswald in 1835, and married the same year. One of his first works was in determining the resolution of a microscope. He began to develop methods to create fine ruling on glass. Nobert's ultra-fine micrometric standards created by Nobert began in 1840 with ten lines cut between a specific distance which then extended to 20 division in 1851 and thirty in 1855. These test gratings were sold along with microscopes or separately for about 5 Thalers in 1846. Nobert also made microscopes, although he made them alone and took as long as a year to deliver one. These had a micrometer stage holding the grating measurement slide and a mechanism for slow and controlled movement. After the death of his father, Nobert returned to Barth in 1846 and worked there until his death.
+
+
+== References ==

data/en.wikipedia.org/wiki/Galvanometer-0.md

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+---
+title: "Galvanometer"
+chunk: 1/4
+source: "https://en.wikipedia.org/wiki/Galvanometer"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:37:05.190184+00:00"
+instance: "kb-cron"
+---
+
+A galvanometer is an electromechanical measuring instrument for electric current. Early galvanometers were uncalibrated, but improved versions, called ammeters, were calibrated and could measure the flow of current more precisely.  Galvanometers work by deflecting a pointer in response to an electric current flowing through a coil in a constant magnetic field.  The mechanism is also used as an actuator in applications such as hard disks.
+Galvanometers came from the observation, first noted by Hans Christian Ørsted in 1820, that a magnetic compass's needle deflects when near a wire having electric current. They were the first instruments used to detect and measure small amounts of current. André-Marie Ampère, who gave mathematical expression to Ørsted's discovery, named the instrument after the Italian electricity researcher Luigi Galvani, who in 1791 discovered the principle of the frog galvanoscope – that electric current would make the legs of a dead frog jerk.
+Galvanometers have been essential for the development of science and technology in many fields. For example, in the 1800s they enabled long-range communication through submarine cables, such as the earliest transatlantic telegraph cables, and were essential to discovering the electrical activity of the heart and brain, by their fine measurements of current.
+Galvanometers have also been used as the display components of other kinds of analog meters (e.g., light meters and VU meters), capturing the outputs of these meters' sensors. Today, the main type of galvanometer still in use is the D'Arsonval/Weston type.
+
+== Operation ==
+
+Modern galvanometers, of the D'Arsonval/Weston type, are constructed with a small pivoting coil of wire, called a spindle, in the field of a permanent magnet. The coil is attached to a thin pointer that traverses a calibrated scale. A tiny torsion spring pulls the coil and pointer to the zero position.
+
+When a direct current (DC) flows through the coil, the coil generates a magnetic field. This field acts against the permanent magnet. The coil twists, pushing against the spring, and moves the pointer. The hand points at a scale indicating the electric current. Careful design of the pole pieces ensures that the magnetic field is uniform so that the angular deflection of the pointer is proportional to the current. A useful meter generally contains a provision for damping the mechanical resonance of the moving coil and pointer, so that the pointer settles quickly to its position without oscillation.
+The basic sensitivity of a meter might be, for instance, 100 microamperes full scale (with a voltage drop of, say, 50 millivolts at full current). Such meters are often calibrated to read some other quantity that can be converted to a current of that magnitude. The use of current dividers, often called shunts, allows a meter to be calibrated to measure larger currents. A meter can be calibrated as a DC voltmeter if the resistance of the coil is known by calculating the voltage required to generate a full-scale current. A meter can be configured to read other voltages by putting it in a voltage divider circuit. This is generally done by placing a resistor in series with the meter coil. A meter can be used to read resistance by placing it in series with a known voltage (a battery) and an adjustable resistor. In a preparatory step, the circuit is completed and the resistor adjusted to produce full-scale deflection. When an unknown resistor is placed in series in the circuit the current will be less than full scale and an appropriately calibrated scale can display the value of the previously unknown resistor.
+These capabilities to translate different kinds of electric quantities into pointer movements make the galvanometer ideal for turning the output of other sensors that output electricity (in some form or another), into something that can be read by a human.
+Because the pointer of the meter is usually a small distance above the scale of the meter, parallax error can occur when the operator attempts to read the scale line that "lines up" with the pointer. To counter this, some meters include a mirror along with the markings of the principal scale. The accuracy of the reading from a mirrored scale is improved by positioning one's head while reading the scale so that the pointer and the reflection of the pointer are aligned; at this point, the operator's eye must be directly above the pointer and any parallax error has been minimized.
+
+== Uses ==
+
+Probably the largest use of galvanometers was of the D'Arsonval/Weston type used in analog meters in electronic equipment. Since the 1980s, galvanometer-type analog meter movements have been displaced by analog-to-digital converters (ADCs) for many uses. A digital panel meter (DPM) contains an ADC and numeric display. The advantages of a digital instrument are higher precision and accuracy, but factors such as power consumption or cost may still favor the application of analog meter movements.

data/en.wikipedia.org/wiki/Galvanometer-1.md

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+---
+title: "Galvanometer"
+chunk: 2/4
+source: "https://en.wikipedia.org/wiki/Galvanometer"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:37:05.190184+00:00"
+instance: "kb-cron"
+---
+
+=== Modern uses ===
+Most modern uses for the galvanometer mechanism are in positioning and control systems. Galvanometer mechanisms are divided into moving magnet and moving coil galvanometers; in addition, they are divided into closed-loop and open-loop - or resonant - types.
+Mirror galvanometer systems are used as beam positioning or beam steering elements in laser scanning systems. For example, for material processing with high-power lasers, closed loop mirror galvanometer mechanisms are used with servo control systems. These are typically high power galvanometers and the newest galvanometers designed for beam steering applications can have frequency responses over 10 kHz with appropriate servo technology. Closed-loop mirror galvanometers are also used in similar ways in stereolithography, laser sintering, laser engraving, laser beam welding, laser TVs, laser displays and in imaging applications such as retinal scanning with Optical Coherence Tomography (OCT) and Scanning Laser Ophthalmoscopy (SLO). Almost all of these galvanometers are of the moving magnet type. The closed loop is obtained measuring the position of the rotating axis with an infrared emitter and 2 photodiodes. This feedback is an analog signal.
+Open loop, or resonant mirror galvanometers, are mainly used in some types of laser-based bar-code scanners, printing machines, imaging applications, military applications and space systems. Their non-lubricated bearings are especially of interest in applications that require functioning in a high vacuum.
+
+Moving coil type galvanometer mechanisms (called 'voice coils' by hard disk manufacturers) are used for controlling the head positioning servos in hard disk drives and CD/DVD players, in order to keep mass (and thus access times), as low as possible.
+
+=== Past uses ===
+A major early use for galvanometers was for finding faults in telecommunications cables. They were superseded in this application late in the 20th century by time-domain reflectometers.
+Galvanometer mechanisms were also used to get readings from photoresistors in the metering mechanisms of film cameras (as seen in the adjacent image).
+In analog strip chart recorders such as used in electrocardiographs, electroencephalographs and polygraphs, galvanometer mechanisms were used to position the pen. Strip chart recorders with galvanometer driven pens may have a full-scale frequency response of 100 Hz and several centimeters of deflection.
+
+== History ==
+
+=== Hans Christian Ørsted ===
+The deflection of a magnetic compass needle by the current in a wire was first described by Hans Christian Ørsted in 1820. The phenomenon was studied both for its own sake and as a means of measuring electric current.
+
+=== Schweigger and Ampère ===
+The earliest galvanometer was reported by Johann Schweigger at the University of Halle on 16 September 1820. André-Marie Ampère also contributed to its development. Early designs increased the effect of the magnetic field generated by the current by using multiple turns of wire. The instruments were at first called "multipliers" due to this common design feature. The term "galvanometer," in common use by 1836, was derived from the surname of Italian electricity researcher Luigi Galvani, who in 1791 discovered that electric current would make a dead frog's leg jerk.
+
+=== Poggendorff and Thomson ===
+
+Originally, the instruments relied on the Earth's magnetic field to provide the restoring force for the compass needle. These were called "tangent" galvanometers and had to be oriented before use. Later instruments of the "astatic" type used opposing magnets to become independent of the Earth's field and would operate in any orientation.
+An early mirror galvanometer was invented in 1826 by Johann Christian Poggendorff. An astatic galvanometer was invented by Hermann von Helmholtz in 1849; a more sensitive version of that device, the Thomson mirror galvanometer, was patented in 1858 by William Thomson (Lord Kelvin). Thomson's design was able to detect very rapid current changes by using small magnets attached to a lightweight mirror, suspended by a thread, instead of a compass needle. The deflection of a light beam on the mirror greatly magnified the deflection induced by small currents. Alternatively, the deflection of the suspended magnets could be observed directly through a microscope.
+
+=== Georg Ohm ===
+The ability to measure voltage and current quantitatively allowed Georg Ohm, in 1827, to formulate Ohm's law – that the voltage across a conductor is directly proportional to the current through it.
+
+=== D'Arsonval and Deprez ===
+
+The early moving-magnet form of galvanometer had the disadvantage that it was affected by any magnets or iron masses near it, and its deflection was not linearly proportional to the current. In 1882 Jacques-Arsène d'Arsonval and Marcel Deprez developed a form with a stationary permanent magnet and a moving coil of wire, suspended by fine wires which provided both an electrical connection to the coil and the restoring torque to return to the zero position. An iron tube between the magnet's pole pieces defined a circular gap through which the coil rotated. This gap produced a consistent, radial magnetic field across the coil, giving a linear response throughout the instrument's range. A mirror attached to the coil deflected a beam of light to indicate the coil position. The concentrated magnetic field and delicate suspension made these instruments sensitive; d'Arsonval's initial instrument could detect ten microamperes.
+
+=== Edward Weston ===

data/en.wikipedia.org/wiki/Galvanometer-2.md

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+---
+title: "Galvanometer"
+chunk: 3/4
+source: "https://en.wikipedia.org/wiki/Galvanometer"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:37:05.190184+00:00"
+instance: "kb-cron"
+---
+
+Edward Weston extensively improved the design of the galvanometer. He substituted the fine wire suspension with a pivot and provided restoring torque and electrical connections through spiral springs rather than through the traditional wristwatch balance wheel hairspring. He developed a method of stabilizing the magnetic field of the permanent magnet, so the instrument would have consistent accuracy over time. He replaced the light beam and mirror with a knife-edge pointer that could be read directly. A mirror under the pointer, in the same plane as the scale, eliminated parallax observation error. To maintain the field strength, Weston's design used a very narrow circumferential slot through which the coil moved, with a minimal air-gap. This improved linearity of pointer deflection with respect to coil current. Finally, the coil was wound on a lightweight form made of conductive metal, which acted as a damper. By 1888, Edward Weston had patented and brought out a commercial form of this instrument, which became a standard electrical equipment component. It was known as a "portable" instrument because it was affected very little by mounting position or by transporting it from place to place. This design is almost universally used in moving-coil meters today.
+Initially, laboratory instruments relying on the Earth's own magnetic field to provide restoring force for the pointer, galvanometers were developed into compact, rugged, sensitive portable instruments essential to the development of electro-technology.
+
+=== Taut-band movement ===
+The taut-band movement is a modern development of the D'Arsonval-Weston movement.  The jewel pivots and hairsprings are replaced by tiny strips of metal under tension. Such a meter is more rugged for field use.
+
+== Types ==
+There are broadly two types of galvanometers. Some galvanometers use a solid pointer on a scale to show measurements; other very sensitive types use a miniature mirror and a beam of light to provide mechanical amplification of low-level signals.
+
+=== Tangent galvanometer ===
+A tangent galvanometer is an early measuring instrument used for the measurement of electric current. It works by using a compass needle to compare a magnetic field generated by the unknown current to the magnetic field of the Earth. It gets its name from its operating principle, the tangent law of magnetism, which states that the tangent of the angle a compass needle makes is proportional to the ratio of the strengths of the two perpendicular magnetic fields. It was first described by Johan Jakob Nervander in 1834.
+A tangent galvanometer consists of a coil of insulated copper wire wound on a circular non-magnetic frame. The frame is mounted vertically on a horizontal base provided with levelling screws. The coil can be rotated on a vertical axis passing through its centre. A compass box is mounted horizontally at the centre of a circular scale. It consists of a tiny, powerful magnetic needle pivoted at the centre of the coil. The magnetic needle is free to rotate in the horizontal plane. The circular scale is divided into four quadrants. Each quadrant is graduated from 0° to 90°. A long thin aluminium pointer is attached to the needle at its centre and at right angle to it. To avoid errors due to parallax, a plane mirror is mounted below the compass needle.
+In operation, the instrument is first rotated until the magnetic field of the Earth, indicated by the compass needle, is parallel with the plane of the coil. Then the unknown current is applied to the coil. This creates a second magnetic field on the axis of the coil, perpendicular to the Earth's magnetic field. The compass needle responds to the vector sum of the two fields and deflects to an angle equal to the tangent of the ratio of the two fields. From the angle read from the compass's scale, the current could be found from a table. The current supply wires have to be wound in a small helix, like a pig's tail, otherwise the field due to the wire will affect the compass needle and an incorrect reading will be obtained.
+
+==== Theory ====
+The galvanometer is oriented so that the plane of the coil is vertical and aligned along parallel to the horizontal component BH of the Earth's magnetic field (i.e. parallel to the local "magnetic meridian"). When an electric current flows through the galvanometer coil, a second magnetic field B is created. At the center of the coil, where the compass needle is located, the coil's field is perpendicular to the plane of the coil. The magnitude of the coil's field is:
+
+  
+    
+      
+        B
+        =
+        
+          
+            
+              
+                μ
+                
+                  0
+                
+              
+              n
+              I
+            
+            
+              2
+              r
+            
+          
+        
+        
+      
+    
+    {\displaystyle B={\mu _{0}nI \over 2r}\,}
+  
+
+where I is the current in amperes, n is the number of turns of the coil and r is the radius of the coil. These two perpendicular magnetic fields add vectorially, and the compass needle points along the direction of their resultant BH+B. The current in the coil causes the compass needle to rotate by an angle θ:
+
+  
+    
+      
+        θ
+        =
+        
+          tan
+          
+            −
+            1
+          
+        
+        ⁡
+        
+          
+            B
+            
+              B
+              
+                H
+              
+            
+          
+        
+        
+      
+    
+    {\displaystyle \theta =\tan ^{-1}{\frac {B}{B_{H}}}\,}
+  
+
+From tangent law, B = BH tan θ, i.e.
+
+  
+    
+      
+        
+          
+            
+              
+                μ
+                
+                  0
+                
+              
+              n
+              I
+            
+            
+              2
+              r
+            
+          
+        
+        =
+        
+          B
+          
+            H
+          
+        
+        tan
+        ⁡
+        θ
+        
+      
+    
+    {\displaystyle {\mu _{0}nI \over 2r}=B_{H}\tan \theta \,}
+  
+
+or
+
+  
+    
+      
+        I
+        =
+        
+          (
+          
+            
+              
+                2
+                r
+                
+                  B
+                  
+                    H
+                  
+                
+              
+              
+                
+                  μ
+                  
+                    0
+                  
+                
+                n
+              
+            
+          
+          )
+        
+        tan
+        ⁡
+        θ
+        
+      
+    
+    {\displaystyle I=\left({\frac {2rB_{H}}{\mu _{0}n}}\right)\tan \theta \,}
+  
+
+or I = K tan θ, where K is called the Reduction Factor of the tangent galvanometer.
+One problem with the tangent galvanometer is that its resolution degrades at both high currents and low currents.  The maximum resolution is obtained when the value of θ is 45°. When the value of θ is close to 0° or 90°, a large percentage change in the current will only move the needle a few degrees.

data/en.wikipedia.org/wiki/Galvanometer-3.md

@@ -0,0 +1,38 @@
+---
+title: "Galvanometer"
+chunk: 4/4
+source: "https://en.wikipedia.org/wiki/Galvanometer"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:37:05.190184+00:00"
+instance: "kb-cron"
+---
+
+==== Geomagnetic field measurement ====
+A tangent galvanometer can also be used to measure the magnitude of the horizontal component of the geomagnetic field. When used in this way, a low-voltage power source, such as a battery, is connected in series with a rheostat, the galvanometer, and an ammeter. The galvanometer is first aligned so that the coil is parallel to the geomagnetic field, whose direction is indicated by the compass when there is no current through the coils. The battery is then connected and the rheostat is adjusted until the compass needle deflects 45 degrees from the geomagnetic field, indicating that the magnitude of the magnetic field at the center of the coil is the same as that of the horizontal component of the geomagnetic field. This field strength can be calculated from the current as measured by the ammeter, the number of turns of the coil, and the radius of the coils.
+
+=== Astatic galvanometer ===
+Unlike the tangent galvanometer, the astatic galvanometer does not use the Earth's magnetic field for measurement, so it does not need to be oriented with respect to the Earth's field, making it easier to use. Developed by Leopoldo Nobili in 1825, it consists of two magnetized needles parallel to each other but with the magnetic poles reversed. These needles are suspended by a single silk thread. The lower needle is inside a vertical current sensing coil of wire and is deflected by the magnetic field created by the passing current, as in the tangent galvanometer above.  The purpose of the second needle is to cancel the dipole moment of the first needle, so the suspended armature has no net magnetic dipole moment, and thus is not affected by the earth's magnetic field.  The needle's rotation is opposed by the torsional elasticity of the suspension thread, which is proportional to the angle.
+
+=== Mirror galvanometer ===
+
+To achieve higher sensitivity to detect extremely small currents, the mirror galvanometer substitutes a lightweight mirror for the pointer.  It consists of horizontal magnets suspended from a fine fiber, inside a vertical coil of wire, with a mirror attached to the magnets.  A beam of light reflected from the mirror falls on a graduated scale across the room, acting as a long mass-less pointer. The mirror galvanometer was used as the receiver in the first trans-Atlantic submarine telegraph cables in the 1850s, to detect the extremely faint pulses of current after their thousand-mile journey under the Atlantic. In a device called an oscillograph, the moving beam of light is used, to produce graphs of current versus time, by recording measurements on photographic film. The string galvanometer is a type of mirror galvanometer so sensitive that it was used to make the first electrocardiogram of the electrical activity of the human heart.
+
+=== Ballistic galvanometer ===
+
+A ballistic galvanometer is a type of sensitive galvanometer for measuring the quantity of charge discharged through it. It is an integrator, by virtue of the long time constant of its response, unlike a current-measuring galvanometer. The moving part has a large moment of inertia that gives it an oscillation period long enough to make the integrated measurement. It can be either of the moving coil or moving magnet type; commonly it is a mirror galvanometer.
+
+== See also ==
+Vibration galvanometer
+Thermo galvanometer
+String galvanometer
+History of electrochemistry
+
+== References ==
+
+== External links ==
+
+Galvanometer - Interactive Java Tutorial National High Magnetic Field Laboratory
+Selection of historic galvanometer in the Virtual Laboratory of the Max Planck Institute for the History of Science
+The History Corner: The Galvanometer by Nick Joyce and David Baker, April 1, 2008, Ass. of Physological Science. Retrieved February 26, 2022.
+Moving Coil Galvanometer

data/en.wikipedia.org/wiki/Globe_of_Matelica-0.md

@@ -0,0 +1,24 @@
+---
+title: "Globe of Matelica"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Globe_of_Matelica"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:37:06.372345+00:00"
+instance: "kb-cron"
+---
+
+The Globe of Matelica (Globo of Matelica) is an Ancient Greek sundial sculpted on a marble ball. The artifact was found during the 1985 reconstruction of the medieval Palazzo Pretorio, presently Museo Civico Archeologico, of Matelica in the Marches, region of Italy.
+
+
+== Description ==
+The globe measures nearly 29 cm in diameter and appears to be sculpted from a crystalline marble originating near Ephesus in present-day Turkey. It is thought to date from the first two centuries CE. There is one similar item, identified in 1939 by Carl William Blegen in a Museum in Nafplio, Greece.
+All that remains is the stone component, which is engraved with a variety of inscribed lines and letters. The sphere is bisected by a center line, while on its top are three concentric circles of various diameters, intersected by an arc of a circle and on which words in ancient Greek alphabet are still visible. Additionally it features 13 holes, each marked by a Greek letter. In these holes there were - probably - metallic insertions that delineated the hour.
+In the lower part there is a large conical depression which ends with a big rectangular hole, likely made to secure the base. Other theories for the sphere are that it was used for astronomical calculations, thus as an armillary sphere or for use in spherical astronomy.
+
+
+== See also ==
+Farnese Atlas
+
+
+== References ==

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data/en.wikipedia.org/wiki/Groma_(surveying)-0.md

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+---
+title: "Groma (surveying)"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Groma_(surveying)"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:37:08.672050+00:00"
+instance: "kb-cron"
+---
+
+The groma (as standardized in the imperial Latin, sometimes croma, or gruma in the literature of the republican times) was a surveying instrument used in the Roman Empire. The groma allowed projecting right angles and straight lines and thus enabling the centuriation (setting up of a rectangular grid). It is the only Roman surveying tool with examples that survive to the present day.
+
+
+== History ==
+The name "groma" came to Latin from the Greek gnoma via the Etruscan language. It is unclear which of the many meanings of the Ancient Greek: γνώμων gnomon (cf. Liddell & Scott, "gnoma" is a form) was used, although in multiple sources the Greek term is used to designate the central point of a camp or town.  
+Dividing the land into rectangular plots was used by the Ancient Greeks, Egyptians and even Mesopotamians. However, the sheer scale of Roman centuriation from the 2nd century BC, when the new colonies were formed mostly to provide for veterans and landless citizens, was unprecedented, so it is not clear to what extent  Greek practices influenced the Roman surveyors. The peculiarities of the Roman surveying methods and terminology suggest independence of Roman measurement tradition. 
+The groma may have originated in Mesopotamia or Greece before the 4th century BC. Subsequently, it was brought to Rome by the Etruscans and named cranema. There were apparently no improvements to groma introduced in Roman times: all writers on the subject clearly assumed the perfect familiarity of a reader with the tool.
+
+
+== Construction ==
+
+The tool utilizes a rotating horizontal cross with plumb bobs hanging down from all four ends.  The center of the cross represents the umbilicus soli (reference point). The cross is mounted on a  vertical Jacob's staff, or ferramentum. The umbilicus is offset with respect to the ferramentum by using a bracket pivoting on the top of the staff (frequently ferramentum is used to describe the whole tool). The purpose of offsetting the reference point from the Jacob's staff (vertical pole) is twofold: it enables sighting of lines on the ground through a pair of strings (used to suspend an opposite pair of plumbs from the cross) without the staff obscuring the view and allows placing the reference point over a sturdy object (like a boundary stone), where the staff cannot be inserted.
+The pivoting bracket on the top of the staff was suggested in the 1912 reconstruction by Adolf Schulten and confirmed by Matteo Della Corte soon afterwards. However, as asserted by Thorkild Schiöler in 1994, the 5-kilogram cross found in Pompeii is too heavy to be supported in this way, thus the bracket had never existed. Furthermore, there is no archeological evidence of the bracket, and the images of gromas on tombstones do not show it. The archeologists rejecting the bracket suggest that the staff was slightly angled to permit sighting without the pole obscuring the view.
+
+
+== Use ==
+
+Despite a great deal of surviving information about the groma (and the simplicity of the tool itself), the details of its operation are not entirely clear. The general idea is straightforward: the staff was inserted into the ground a bracket length away from the marker, and the bracket was then swung so that the umbilicus soli was directly on top of the center of the marker. The cross was then turned to align with the desired directions and the surveyor's assistant would step back and place a pole as directed by the surveyor (a gromaticus). The surveyor could then view the pole through two strings on the opposite ends of the cross.
+The distances were measured using rods. The setup works on the level ground or gentle slopes; the details of a survey crossing a steep-sided valley are not clear.
+The alignment of the plumb-lines of the groma is quite susceptible to wind. This compares unfavorably with dioptra. Also, the far plumb-line on the cross is optically thinner than the closer one, introducing the angle error calculated by the archeologists to be about 1.5 promille (linear error of about 1 meter per the side of centuria, 710 meters).
+
+
+== Notes ==
+
+
+== Sources ==
+Lewis, M. J. T. (2001-04-23). "The groma". Surveying Instruments of Greece and Rome. Cambridge University Press. pp. 120–133. doi:10.1017/cbo9780511483035.008. ISBN 978-0-521-79297-4.
+Stone, Edward Noble (1928). "Roman Surveying Instruments". A Bibliography of Chaucer 1908–1924. University of Washington Publications: Language and Literature. Vol. 4. University of Washington Press. pp. 215–242. Retrieved 2023-09-27.
+Russo, Flavio; Rossi, Cesare; Ceccarelli, Marco; Russo, Ferruccio (2009). "Devices for Distance and Time Measurement at the Time of the Roman Empire". International Symposium on History of Machines and Mechanisms: Proceedings of HMM 2008. History of Mechanism and Machine Science. Springer Netherlands. p. 107. ISBN 978-1-4020-9485-9. Retrieved 2023-09-30.
+Kelsey, Francis W. (July 1926). "Groma by Matteo della Corte". Classical Philology. 21 (3). The University of Chicago Press: 259–262. doi:10.1086/360795. JSTOR 263160.
+Liddell, Henry George; Scott, Robert (1889). "γνώμων". An Intermediate Greek-English Lexicon. Oxford: Clarendon Press.
+
+
+== External links ==
+ Media related to Groma at Wikimedia Commons

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+---
+title: "Gualterus Arsenius"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Gualterus_Arsenius"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:35:53.579060+00:00"
+instance: "kb-cron"
+---
+
+Gualterus Arsenius (c. 1530 – c. 1580), also known as Gualterius Arsenius, Gautier Arsens, and Walter Arsenius, was a Flemish scientific instrument maker.
+He was the nephew of the mathematician and cosmographer Gemma Frisius (1508–1555), and he worked in Louvain from 1555 to about 1570 (his presence there is still documented in 1579). The most prominent member of a family of scientific instrument makers, Arsenius produced exquisitely crafted and highly accurate devices such as armillary spheres, astrolabes, astronomical annuli (rings) and sundials, whose designs reveal the influence of his uncle and Gerard Mercator (1512–1594).
+
+
+== References ==
+
+
+== External links ==
+"Museo Galileo - object description".

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+---
+title: "Hipparchus"
+chunk: 1/10
+source: "https://en.wikipedia.org/wiki/Hipparchus"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:35:58.068622+00:00"
+instance: "kb-cron"
+---
+
+Hipparchus (; Greek: Ἵππαρχος, Hípparkhos; c. 190 – c. 120 BC) was a Greek astronomer, geographer, and mathematician. He is considered the founder of trigonometry, but is most famous for his incidental discovery of the precession of the equinoxes. Hipparchus was born in Nicaea, Bithynia, and probably died on the island of Rhodes, Greece. He is known to have been a working astronomer between 162 and 127 BC.
+Hipparchus is considered the greatest ancient astronomical observer and, by some, the greatest overall astronomer of antiquity. He was the first whose quantitative and accurate models for the motion of the Sun and Moon survive. For this he certainly made use of the observations and perhaps the mathematical techniques accumulated over centuries by the Babylonians and by Meton of Athens (fifth century BC), Timocharis, Aristyllus, Aristarchus of Samos, and Eratosthenes, among others.
+He developed trigonometry and constructed trigonometric tables, and he solved several problems of spherical trigonometry. His other reputed achievements include the discovery and measurement of Earth's precession, the compilation of the first known comprehensive star catalog from the western world, and possibly the invention of the astrolabe, as well as of the armillary sphere that he may have used in creating the star catalogue. He contributed to optics, developing an atomist theory of light. He is often called the "father of astronomy", a title conferred on him by Jean Baptiste Joseph Delambre in 1817.
+
+== Life and work ==
+Hipparchus was born in Nicaea (Ancient Greek: Νίκαια), in Bithynia. The exact dates of his life are not known, but Ptolemy attributes astronomical observations to him in the period from 147 to 127 BC, and some of these are stated as made in Rhodes; earlier observations since 162 BC might also have been made by him. His birth date (c. 190 BC) was calculated by Delambre based on clues in his work. Hipparchus must have lived some time after 127 BC because he analyzed and published his observations from that year. Hipparchus obtained information from Alexandria as well as Babylon, but it is not known when or if he visited these places. He is believed to have died on the island of Rhodes, where he seems to have spent most of his later life.
+In the second and third centuries, coins were made in his honour in Bithynia that bear his name and show him with a globe.
+Relatively little of Hipparchus's direct work survives into modern times. Although he wrote at least fourteen books, only his commentary on the popular astronomical poem by Aratus was preserved by later copyists. Most of what is known about Hipparchus comes from Strabo's Geography and Pliny's Natural History in the first century; Ptolemy's second-century Almagest; and additional references to him in the fourth century by Pappus and Theon of Alexandria in their commentaries on the Almagest.
+Hipparchus's only preserved work is Commentary on the Phaenomena of Eudoxus and Aratus (Ancient Greek: Τῶν Ἀράτου καὶ Εὐδόξου φαινομένων ἐξήγησις). This is a highly critical commentary in the form of two books on a popular poem by Aratus based on the work by Eudoxus. Hipparchus also made a list of his major works that apparently mentioned about fourteen books, but which is only known from references by later authors. His famous star catalog was incorporated into the one by Ptolemy and may be almost perfectly reconstructed by subtraction of two and two-thirds degrees from the longitudes of Ptolemy's stars . The first trigonometric table was apparently compiled by Hipparchus, who is consequently now known as "the father of trigonometry".
+
+== Babylonian sources ==
+
+Earlier Greek astronomers and mathematicians were influenced by Babylonian astronomy to some extent, for instance the period relations of the Metonic cycle and Saros cycle may have come from Babylonian sources (see "Babylonian astronomical diaries"). Hipparchus seems to have been the first to exploit Babylonian astronomical knowledge and techniques systematically. Eudoxus in the 4th century BC and Timocharis and Aristillus in the 3rd century BC already divided the ecliptic in 360 parts (our degrees, Greek: moira) of 60 arcminutes and Hipparchus continued this tradition. It was only in Hipparchus's time (2nd century BC) when this division was introduced (probably by Hipparchus's contemporary Hypsicles) for all circles in mathematics. Eratosthenes (3rd century BC), in contrast, used a simpler sexagesimal system dividing a circle into 60 parts. Hipparchus also adopted the Babylonian astronomical cubit unit (Akkadian ammatu, Greek πῆχυς pēchys) that was equivalent to 2° or 2.5° ('large cubit').
+Hipparchus probably compiled a list of Babylonian astronomical observations; Gerald J. Toomer, a historian of astronomy, has suggested that Ptolemy's knowledge of eclipse records and other Babylonian observations in the Almagest came from a list made by Hipparchus. Hipparchus's use of Babylonian sources has always been known in a general way, because of Ptolemy's statements, but the only text by Hipparchus that survives does not provide sufficient information to decide whether Hipparchus's knowledge (such as his usage of the units cubit and finger, degrees and minutes, or the concept of hour stars) was based on Babylonian practice. However, Franz Xaver Kugler demonstrated that the synodic and anomalistic periods that Ptolemy attributes to Hipparchus had already been used in Babylonian ephemerides, specifically the collection of texts nowadays called "System B" (sometimes attributed to Kidinnu).
+Hipparchus's long draconitic lunar period (5,458 months = 5,923 lunar nodal periods) also appears a few times in Babylonian records. But the only such tablet explicitly dated is post-Hipparchus, so the direction of transmission is not settled by the tablets.

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+---
+title: "Hipparchus"
+chunk: 2/10
+source: "https://en.wikipedia.org/wiki/Hipparchus"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:35:58.068622+00:00"
+instance: "kb-cron"
+---
+
+== Geometry, trigonometry and other mathematical techniques ==
+Hipparchus was recognized as the first mathematician known to have possessed a trigonometric table, which he needed when computing the eccentricity of the orbits of the Moon and Sun. He tabulated values for the chord function, which for a central angle in a circle gives the length of the straight line segment between the points where the angle intersects the circle. He may have computed this for a circle with a circumference of 21,600 units and a radius (rounded) of 3,438 units; this circle has a unit length for each arcminute along its perimeter. (This was “proven” by Toomer, but he later “cast doubt“ upon his earlier affirmation. Other authors have argued that a circle of radius 3,600 units may instead have been used by Hipparchus.) He tabulated the chords for angles with increments of 7.5°. In modern terms, the chord subtended by a central angle in a circle of given radius R equals R times twice the sine of half of the angle, i.e.:
+
+  
+    
+      
+        chord
+        ⁡
+        θ
+        =
+        2
+        R
+        ⋅
+        sin
+        ⁡
+        
+          
+            
+              1
+              2
+            
+          
+        
+        θ
+      
+    
+    {\displaystyle \operatorname {chord} \theta =2R\cdot \sin {\tfrac {1}{2}}\theta }
+  
+
+The now-lost work in which Hipparchus is said to have developed his chord table, is called Tōn en kuklōi eutheiōn (Of Lines Inside a Circle) in Theon of Alexandria's fourth-century commentary on section I.10 of the Almagest. Some claim the table of Hipparchus may have survived in astronomical treatises in India, such as the Surya Siddhanta. Trigonometry was a significant innovation, because it allowed Greek astronomers to solve any triangle, and made it possible to make quantitative astronomical models and predictions using their preferred geometric techniques.
+Hipparchus must have used a better approximation for π than the one given by Archimedes of between 3+10⁄71 (≈ 3.1408) and 3+1⁄7 (≈ 3.1429). Perhaps he had the approximation later used by Ptolemy, sexagesimal 3;08,30 (≈ 3.1417) (Almagest VI.7).
+Hipparchus could have constructed his chord table using the Pythagorean theorem and a theorem known to Archimedes. He also might have used the relationship between sides and diagonals of a cyclic quadrilateral, today called Ptolemy's theorem because its earliest extant source is a proof in the Almagest (I.10).
+The stereographic projection was ambiguously attributed to Hipparchus by Synesius (c. 400 AD), and on that basis Hipparchus is often credited with inventing it or at least knowing of it. However, some scholars believe this conclusion to be unjustified by available evidence. The oldest extant description of the stereographic projection is found in Ptolemy's Planisphere (2nd century AD).
+Besides geometry, Hipparchus also used arithmetic techniques developed by the Chaldeans. He was one of the first Greek mathematicians to do this and, in this way, expanded the techniques available to astronomers and geographers.
+There are several indications that Hipparchus knew spherical trigonometry, but the first surviving text discussing it is by Menelaus of Alexandria in the first century, who now, on that basis, commonly is credited with its discovery. (Previous to the finding of the proofs of Menelaus a century ago, Ptolemy was credited with the invention of spherical trigonometry.) Ptolemy later used spherical trigonometry to compute things such as the rising and setting points of the ecliptic, or to take account of the lunar parallax. If he did not use spherical trigonometry, Hipparchus may have used a globe for these tasks, reading values off coordinate grids drawn on it, or he may have made approximations from planar geometry, or perhaps used arithmetical approximations developed by the Chaldeans.
+
+== Lunar and solar theory ==
+
+=== Motion of the Moon ===
+
+Hipparchus also studied the motion of the Moon and confirmed the accurate values for two periods of its motion that Chaldean astronomers are widely presumed to have possessed before him. The traditional value (from Babylonian System B) for the mean synodic month is 29 days; 31,50,8,20 (sexagesimal) = 29.5305941... days. Expressed as 29 days + 12 hours + ⁠793/1080⁠ hours this value has been used later in the Hebrew calendar. The Chaldeans also knew that 251 synodic months ≈ 269 anomalistic months. Hipparchus used the multiple of this period by a factor of 17, because that interval is also an eclipse period, and is also close to an integer number of years (4,267 moons : 4,573 anomalistic periods : 4,630.53 nodal periods : 4,611.98 lunar orbits : 344.996 years : 344.982 solar orbits : 126,007.003 days : 126,351.985 rotations). What was so exceptional and useful about the cycle was that all 345-year-interval eclipse pairs occur slightly more than 126,007 days apart within a tight range of only approximately ±1⁄2 hour, guaranteeing (after division by 4,267) an estimate of the synodic month correct to one part in order of magnitude 10 million.
+Hipparchus could confirm his computations by comparing eclipses from his own time (presumably 27 January 141 BC and 26 November 139 BC according to Toomer) with eclipses from Babylonian records 345 years earlier (Almagest IV.2).
+Later al-Biruni (Qanun VII.2.II) and Copernicus (de revolutionibus IV.4) noted that the period of 4,267 moons is approximately five minutes longer than the value for the eclipse period that Ptolemy attributes to Hipparchus. However, the timing methods of the Babylonians had an error of no fewer than eight minutes. Modern scholars agree that Hipparchus rounded the eclipse period to the nearest hour, and used it to confirm the validity of the traditional values, rather than to try to derive an improved value from his own observations. From modern ephemerides and taking account of the change in the length of the day (see ΔT) we estimate that the error in the assumed length of the synodic month was less than 0.2 second in the fourth century BC and less than 0.1 second in Hipparchus's time.

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+---
+title: "Hipparchus"
+chunk: 3/10
+source: "https://en.wikipedia.org/wiki/Hipparchus"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T09:35:58.068622+00:00"
+instance: "kb-cron"
+---
+
+=== Orbit of the Moon ===
+It had been known for a long time that the motion of the Moon is not uniform: its speed varies. This is called its anomaly and it repeats with its own period; the anomalistic month. The Chaldeans took account of this arithmetically, and used a table giving the daily motion of the Moon according to the date within a long period. However, the Greeks preferred to think in geometrical models of the sky. At the end of the third century BC, Apollonius of Perga had proposed two models for lunar and planetary motion:
+
+In the first, the Moon would move uniformly along a circle, but the Earth would be eccentric, i.e., at some distance of the center of the circle. So the apparent angular speed of the Moon (and its distance) would vary.
+The Moon would move uniformly (with some mean motion in anomaly) on a secondary circular orbit, called an epicycle that would move uniformly (with some mean motion in longitude) over the main circular orbit around the Earth, called deferent; see deferent and epicycle.
+Apollonius demonstrated that these two models were in fact mathematically equivalent. However, all this was theory and had not been put to practice. Hipparchus is the first astronomer known to attempt to determine the relative proportions and actual sizes of these orbits. Hipparchus devised a geometrical method to find the parameters from three positions of the Moon at particular phases of its anomaly. In fact, he did this separately for the eccentric and the epicycle model. Ptolemy describes the details in the Almagest IV.11. Hipparchus used two sets of three lunar eclipse observations that he carefully selected to satisfy the requirements. The eccentric model he fitted to these eclipses from his Babylonian eclipse list: 22/23 December 383 BC, 18/19 June 382 BC, and 12/13 December 382 BC. The epicycle model he fitted to lunar eclipse observations made in Alexandria at 22 September 201 BC, 19 March 200 BC, and 11 September 200 BC.
+
+For the eccentric model, Hipparchus found for the ratio between the radius of the eccenter and the distance between the center of the eccenter and the center of the ecliptic (i.e., the observer on Earth): 3144 : 327+2⁄3;
+and for the epicycle model, the ratio between the radius of the deferent and the epicycle: 3122+1⁄2 : 247+1⁄2 .
+These figures are due to the cumbersome unit he used in his chord table and may partly be due to some sloppy rounding and calculation errors by Hipparchus, for which Ptolemy criticised him while also making rounding errors. A simpler alternate reconstruction agrees with all four numbers. Hipparchus found inconsistent results; he later used the ratio of the epicycle model (3122+1⁄2 : 247+1⁄2), which is too small (60 : 4;45 sexagesimal). Ptolemy established a ratio of 60 : 5+1⁄4. (The maximum angular deviation producible by this geometry is the arcsin of 5+1⁄4 divided by 60, or approximately 5° 1′, five degrees and one arc minute, a figure that is sometimes therefore quoted as the equivalent of the Moon's equation of the center in the Hipparchan model.)
+
+=== Apparent motion of the Sun ===