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+
+The age of Earth is estimated to be 4.54 ± 0.05 billion years. This age represents the final stages of Earth's accretion and planetary differentiation. Age estimates are based on evidence from radiometric age-dating of meteoritic material—consistent with the radiometric ages of the oldest-known terrestrial material and lunar samples—and astrophysical accretion models consistent with observations of planet formation in protoplanetary disks.
+Following the development of radiometric dating in the early 20th century, measurements of lead in uranium-rich minerals showed that some were in excess of a billion years old. The oldest such minerals analyzed to date—small crystals of zircon from the Jack Hills of Western Australia—are at least 4.404 billion years old. Calcium–aluminium-rich inclusions—the oldest known solid constituents within meteorites that are formed within the Solar System—are 4.5673 ± 0.00016 billion years old giving a lower limit for the age of the Solar System.
+It is hypothesized that the accretion of Earth began soon after the formation of the calcium-aluminium-rich inclusions. Because the duration of this accretion process is not yet adequately constrained—predictions from different accretion models range from around 30 million to 100 million years—the difference between the age of Earth and of the oldest rocks is difficult to determine. It can also be difficult to determine the exact age of the oldest rocks on Earth, exposed at the surface, as they are aggregates of minerals of possibly different ages.
+
+== Development of modern geologic concepts ==
+
+Studies of strata—the layering of rocks and soil—gave naturalists an appreciation that Earth may have been through many changes during its existence. These layers often contained fossilized remains of unknown creatures, leading some to interpret a progression of organisms from layer to layer.
+Nicolas Steno in the 17th century was one of the first naturalists to appreciate the connection between fossil remains and strata. His observations led him to formulate important stratigraphic concepts (i.e., the "law of superposition" and the "principle of original horizontality"). In the 1790s, William Smith hypothesized that if two layers of rock at widely differing locations contained similar fossils, then it was very plausible that the layers were the same age. Smith's nephew and student, John Phillips, later calculated by such means that Earth was about 96 million years old.
+In the mid-18th century, the naturalist Mikhail Lomonosov suggested that Earth had been created separately from, and several hundred thousand years before, the rest of the universe. Lomonosov's ideas were mostly speculative. In 1779 the Comte de Buffon tried to obtain a value for the age of Earth using an experiment: he created a small globe that resembled Earth in composition and then measured its rate of cooling. This led him to estimate that Earth was about 75,000 years old. Even earlier, in 1687, in his Principia, the mathematician and physicist Isaac Newton was the first to calculate the age of the Earth by experiment, doing so by modeling its cooling from a red-hot state, theorizing a globe of red-hot iron the same size as Earth, ultimately coming to a conclusion of around 50,000 years, a method that Lord Kelvin would follow in his attempts to calculate the age of Earth.
+Other naturalists used these hypotheses to construct a history of Earth, though their timelines were inexact as they did not know how long it took to lay down stratigraphic layers. In 1830, geologist Charles Lyell, developing ideas found in James Hutton's works, popularized the concept that the features of Earth were in perpetual change, eroding and reforming continuously, and the rate of this change was roughly constant. This was a challenge to the traditional view, which saw the history of Earth as dominated by intermittent catastrophes. Many naturalists were influenced by Lyell to become "uniformitarians" who believed that changes were constant and uniform.
+
+== Early calculations ==
+
+In 1862, the physicist William Thomson, 1st Baron Kelvin published calculations that fixed the age of Earth at between 20 million and 400 million years. He assumed that Earth had formed as a completely molten object, and determined the amount of time it would take for the near-surface temperature gradient to decrease to its present value. His calculations did not account for heat produced via radioactive decay (a then unknown process) or, more significantly, convection inside Earth, which allows the temperature in the upper mantle to remain high much longer, maintaining a high thermal gradient in the crust much longer. Even more constraining were Thomson's estimates of the age of the Sun, which were based on estimates of its thermal output and a theory that the Sun obtains its energy from gravitational collapse; Thomson estimated that the Sun is about 20 million years old.

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+Geologists such as Lyell had difficulty accepting such a short age for Earth. For biologists, even 100 million years seemed much too short to be plausible. In Charles Darwin's theory of evolution, the process of random heritable variation with cumulative selection requires great durations of time, and Darwin stated that Thomson's estimates did not appear to provide enough time. According to modern biology, the total evolutionary history from the beginning of life to today has taken place since 3.5 to 3.8 billion years ago, the amount of time which passed since the last universal ancestor of all living organisms as shown by geological dating.
+In a lecture in 1869, Darwin's great advocate, Thomas Henry Huxley, attacked Thomson's calculations, suggesting they appeared precise in themselves but were based on faulty assumptions. The physicist Hermann von Helmholtz (in 1856) and astronomer Simon Newcomb (in 1892) contributed their own calculations of 22 and 18 million years, respectively, to the debate: they independently calculated the amount of time it would take for the Sun to condense down to its current diameter and brightness from the nebula of gas and dust from which it was born. Their values were consistent with Thomson's calculations. However, they assumed that the Sun was only glowing from the heat of its gravitational contraction. The process of solar nuclear fusion was not yet known to science.
+In 1892, Thomson was ennobled as Lord Kelvin in appreciation of his many scientific accomplishments. In 1895 John Perry challenged Kelvin's figure on the basis of his assumptions on conductivity, and Oliver Heaviside entered the dialogue, considering it "a vehicle to display the ability of his operator method to solve problems of astonishing complexity." Other scientists backed up Kelvin's figures. Darwin's son, the astronomer George H. Darwin, proposed that Earth and Moon had broken apart in their early days when they were both molten. He calculated the amount of time it would have taken for tidal friction to give Earth its current 24-hour day. His value of 56 million years was additional evidence that Thomson was on the right track. The last estimate Kelvin gave, in 1897, was: "that it was more than 20 and less than 40 million year old, and probably much nearer 20 than 40". In 1899 and 1900, John Joly calculated the rate at which the oceans should have accumulated salt from erosion processes and determined that the oceans were about 80 to 100 million years old.
+
+== Radiometric dating ==
+
+=== Overview ===
+By their chemical nature, rock minerals contain certain elements and not others; but in rocks containing radioactive isotopes, the process of radioactive decay generates exotic elements over time. By measuring the concentration of the stable end product of the decay, coupled with knowledge of the half life and initial concentration of the decaying element, the age of the rock can be calculated. Typical radioactive end products are argon from decay of potassium-40, and lead from decay of uranium and thorium. If the rock becomes molten, as happens in Earth's mantle, such nonradioactive end products typically escape or are redistributed. Thus the age of the oldest terrestrial rock gives a minimum for the age of Earth, assuming that no rock has been intact for longer than Earth itself.
+
+=== Convective mantle and radioactivity ===
+The discovery of radioactivity introduced another factor in the calculation. After Henri Becquerel's initial discovery in 1896, Marie and Pierre Curie discovered the radioactive elements polonium and radium in 1898; and in 1903, Pierre Curie and Albert Laborde announced that radium produces enough heat to melt its own weight in ice in less than an hour. Geologists quickly realized that this upset the assumptions underlying most calculations of the age of Earth. These had assumed that the original heat of Earth and the Sun had dissipated steadily into space, but radioactive decay meant that this heat had been continually replenished. George Darwin and John Joly were the first to point this out, in 1903.
+
+=== Invention of radiometric dating ===
+Radioactivity, which had overthrown the old calculations, yielded a bonus by providing a basis for new calculations, in the form of radiometric dating.

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+
+Ernest Rutherford and Frederick Soddy jointly had continued their work on radioactive materials and concluded that radioactivity was caused by a spontaneous transmutation of atomic elements. In radioactive decay, an element breaks down into another, lighter element, releasing alpha, beta, or gamma radiation in the process. They also determined that a particular isotope of a radioactive element decays into another element at a distinctive rate. This rate is given in terms of a "half-life", or the amount of time it takes half of a mass of that radioactive material to break down into its "decay product".
+Some radioactive materials have short half-lives; some have long half-lives. Uranium and thorium have long half-lives and so persist in Earth's crust, but radioactive elements with short half-lives have generally disappeared. This suggested that it might be possible to measure the age of Earth by determining the relative proportions of radioactive materials in geological samples. In reality, radioactive elements do not always decay into nonradioactive ("stable") elements directly, instead, decaying into other radioactive elements that have their own half-lives and so on, until they reach a stable element. These "decay chains", such as the uranium-radium and thorium series, were known within a few years of the discovery of radioactivity and provided a basis for constructing techniques of radiometric dating.
+The pioneers of radioactivity were chemist Bertram B. Boltwood and physicist Rutherford. Boltwood had conducted studies of radioactive materials as a consultant, and when Rutherford lectured at Yale in 1904, Boltwood was inspired to describe the relationships between elements in various decay series. Late in 1904, Rutherford took the first step toward radiometric dating by suggesting that the alpha particles released by radioactive decay could be trapped in a rocky material as helium atoms. At the time, Rutherford was only guessing at the relationship between alpha particles and helium atoms, but he would prove the connection four years later.
+Soddy and Sir William Ramsay had just determined the rate at which radium produces alpha particles, and Rutherford proposed that he could determine the age of a rock sample by measuring its concentration of helium. He dated a rock in his possession to an age of 40 million years by this technique. Rutherford wrote of addressing a meeting of the Royal Institution in 1904:
+
+I came into the room, which was half dark, and presently spotted Lord Kelvin in the audience and realized that I was in trouble at the last part of my speech dealing with the age of the Earth, where my views conflicted with his. To my relief, Kelvin fell fast asleep, but as I came to the important point, I saw the old bird sit up, open an eye, and cock a baleful glance at me! Then a sudden inspiration came, and I said, "Lord Kelvin had limited the age of the Earth, provided no new source was discovered. That prophetic utterance refers to what we are now considering tonight, radium!" Behold! the old boy beamed upon me.
+Rutherford assumed that the rate of decay of radium as determined by Ramsay and Soddy was accurate and that helium did not escape from the sample over time. Rutherford's scheme was inaccurate, but it was a useful first step. Boltwood focused on the end products of decay series. In 1905, he suggested that lead was the final stable product of the decay of radium. It was already known that radium was an intermediate product of the decay of uranium. Rutherford joined in, outlining a decay process in which radium emitted five alpha particles through various intermediate products to end up with lead, and speculated that the radium–lead decay chain could be used to date rock samples. Boltwood did the legwork and by the end of 1905 had provided dates for 26 separate rock samples, ranging from 92 to 570 million years. He did not publish these results, which was fortunate because they were flawed by measurement errors and poor estimates of the half-life of radium. Boltwood refined his work and finally published the results in 1907.
+Boltwood's paper pointed out that samples taken from comparable layers of strata had similar lead-to-uranium ratios, and that samples from older layers had a higher proportion of lead, except where there was evidence that lead had leached out of the sample. His studies were flawed by the fact that the decay series of thorium was not understood, which led to incorrect results for samples that contained both uranium and thorium. However, his calculations were far more accurate than any that had been performed to that time. Refinements in the technique would later give ages for Boltwood's 26 samples of 410 million to 2.2 billion years.

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+
+=== Arthur Holmes establishes radiometric dating ===
+Although Boltwood published his paper in a prominent geological journal, the geological community had little interest in radioactivity. Boltwood gave up work on radiometric dating and went on to investigate other decay series. Rutherford remained mildly curious about the issue of the age of Earth but did little work on it.
+Robert Strutt tinkered with Rutherford's helium method until 1910 and then ceased. However, Strutt's student Arthur Holmes became interested in radiometric dating and continued to work on it after everyone else had given up. Holmes focused on lead dating because he regarded the helium method as unpromising. He performed measurements on rock samples and concluded in 1911 that the oldest (a sample from Ceylon) was about 1.6 billion years old. These calculations were not particularly trustworthy. For example, he assumed that the samples had contained only uranium and no lead when they were formed.
+More important research was published in 1913. It showed that elements generally exist in multiple variants with different masses, or "isotopes". In the 1930s, isotopes would be shown to have nuclei with differing numbers of the neutral particles known as "neutrons". In that same year, other research was published establishing the rules for radioactive decay, allowing more precise identification of decay series.
+Many geologists felt these new discoveries made radiometric dating so complicated as to be worthless. Holmes felt that they gave him tools to improve his techniques, and he plodded ahead with his research, publishing before and after the First World War. His work was generally ignored until the 1920s, though in 1917 Joseph Barrell, a professor of geology at Yale, redrew geological history as it was understood at the time to conform to Holmes's findings in radiometric dating. Barrell's research determined that the layers of strata had not all been laid down at the same rate, and so current rates of geological change could not be used to provide accurate timelines of the history of Earth.
+Holmes' persistence finally began to pay off in 1921, when the speakers at the yearly meeting of the British Association for the Advancement of Science came to a rough consensus that Earth was a few billion years old and that radiometric dating was credible. Holmes published The Age of the Earth, an Introduction to Geological Ideas in 1927 in which he presented a range of 1.6 to 3.0 billion years. No great push to embrace radiometric dating followed, however, and the die-hards in the geological community stubbornly resisted. They had never cared for attempts by physicists to intrude in their domain, and had successfully ignored them so far. The growing weight of evidence finally tilted the balance in 1931, when the National Research Council of the US National Academy of Sciences decided to resolve the question of the age of Earth by appointing a committee to investigate.
+Holmes, being one of the few people who was trained in radiometric dating techniques, was a committee member and in fact wrote most of the final report. Thus, Holmes' report concluded that radioactive dating was the only reliable means of pinning down a geologic time scale. Questions of bias were deflected by the great and exacting detail of the report. It described the methods used, the care with which measurements were made, and their error bars and limitations.
+
+=== Modern radiometric dating ===
+Radiometric dating continues to be the predominant way scientists date geologic time scales. Techniques for radioactive dating have been tested and fine-tuned on an ongoing basis since the 1960s. Forty or so different dating techniques have been utilized to date, working on a wide variety of materials. Dates for the same sample using these different techniques are in very close agreement on the age of the material. Possible contamination problems do exist, but they have been studied and dealt with by careful investigation, leading to sample preparation procedures being minimized to limit the chance of contamination.
+
+==== Use of meteorites ====
+An age of 4.55 ± 0.07 billion years, very close to today's accepted age, was determined by Clair Cameron Patterson using uranium–lead isotope dating (specifically lead–lead dating) on several meteorites including the Canyon Diablo meteorite and published in 1956. The quoted age of Earth is derived, in part, from the Canyon Diablo meteorite for several important reasons and is built upon a modern understanding of cosmochemistry built up over decades of research.

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+
+Most geological samples from Earth are unable to give a direct date of the formation of Earth from the solar nebula because Earth has undergone differentiation into the core, mantle, and crust, and this has then undergone a long history of mixing and unmixing of these sample reservoirs by plate tectonics, weathering and hydrothermal circulation.
+All of these processes may adversely affect isotopic dating mechanisms because the sample cannot always be assumed to have remained as a closed system, by which it is meant that either the parent or daughter nuclide (a species of atom characterised by the number of neutrons and protons an atom contains) or an intermediate daughter nuclide may have been partially removed from the sample, which will skew the resulting isotopic date. To mitigate this effect it is usual to date several minerals in the same sample, to provide an isochron. Alternatively, more than one dating system may be used on a sample to check the date.
+Some meteorites are furthermore considered to represent the primitive material from which the accreting solar disk was formed. Some have behaved as closed systems (for some isotopic systems) soon after the solar disk and the planets formed. To date, these assumptions are supported by much scientific observation and repeated isotopic dates, and it is certainly a more robust hypothesis than that which assumes a terrestrial rock has retained its original composition.
+Nevertheless, ancient Archaean lead ores of galena have been used to date the formation of Earth as these represent the earliest formed lead-only minerals on the planet and record the earliest homogeneous lead–lead isotope systems on the planet. These have returned age dates of 4.54 billion years with a precision of as little as 1% margin for error.
+Statistics for several meteorites that have undergone isochron dating are as follows:
+
+==== Canyon Diablo meteorite ====
+
+The Canyon Diablo meteorite was used because it is both large and representative of a particularly rare type of meteorite that contains sulfide minerals (particularly troilite, FeS), metallic nickel-iron alloys, plus silicate minerals. This is important because the presence of the three mineral phases allows investigation of isotopic dates using samples that provide a great separation in concentrations between parent and daughter nuclides. This is particularly true of uranium and lead. Lead is strongly chalcophilic and is found in the sulfide at a much greater concentration than in the silicate, versus uranium. Because of this segregation in the parent and daughter nuclides during the formation of the meteorite, this allowed a much more precise date of the formation of the solar disk and hence the planets than ever before.
+
+The age determined from the Canyon Diablo meteorite has been confirmed by hundreds of other age determinations, from both terrestrial samples and other meteorites. The meteorite samples, however, show a spread from 4.53 to 4.58 billion years ago. This is interpreted as the duration of formation of the solar nebula and its collapse into the solar disk to form the Sun and the planets. This 50-million-year time span allows for accretion of the planets from the original solar dust and meteorites.
+The Moon, as another extraterrestrial body that has not undergone plate tectonics and that has no atmosphere, provides quite precise age dates from the samples returned from the Apollo missions. Rocks returned from the Moon have been dated at a maximum of 4.51 billion years old. Martian meteorites that have landed upon Earth have also been dated to around 4.5 billion years old by lead–lead dating. Lunar samples, since they have not been disturbed by weathering, plate tectonics or material moved by organisms, can also provide dating by direct electron microscope examination of cosmic ray tracks. The accumulation of dislocations generated by high energy cosmic ray particle impacts provides another confirmation of the isotopic dates. Cosmic ray dating is only useful on material that has not been melted, since melting erases the crystalline structure of the material, and wipes away the tracks left by the particles.
+
+== See also ==
+
+== References ==
+
+== Bibliography ==
+Dalrymple, G. Brent (1994-02-01). The Age of the Earth. Stanford University Press. ISBN 978-0-8047-2331-2.

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+title: "Age of Earth"
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+
+== Further reading ==
+Baadsgaard, H.; Lerbekmo, J. F.; Wijbrans, J. R.; Swisher III, C. C.; Fanning, M. (April 1993). "Multimethod radiometric age for a bentonite near the top of the Baculites reesidei Zone of southwestern Saskatchewan (Campanian–Maastrichtian stage boundary?)". Canadian Journal of Earth Sciences. 30 (4): 769–775. doi:10.1139/e93-063.
+Baadsgaard, H.; Lerbekmo, J. F.; McDougall, I. (July 1988). "A radiometric age for the Cretaceous–Tertiary boundary based upon K–Ar, Rb–Sr, and U–Pb ages of bentonites from Alberta, Saskatchewan, and Montana". Canadian Journal of Earth Sciences. 25 (7): 1088–1097. doi:10.1139/e88-106.
+Eberth, David A.; Braman, Dennis R.; Tokaryk, Tim T. (1990). "Stratigraphy, Sedimentology and Vertebrate Paleontology of the Judith River Formation (Campanian) Near Muddy Lake, West-Central Saskatchewan". Bulletin of Canadian Petroleum Geology. 38 (4): 387–406.
+Goodwin, Mark B.; Deino, Alan L. (July 1989). "The first radiometric ages from the Judith River Formation (Upper Cretaceous), Hill County, Montana". Canadian Journal of Earth Sciences. 26 (7): 1384–1391. doi:10.1139/e89-118.
+Gradstein, Felix M.; Agterberg, Frits P.; Ogg, James G.; Hardenbol, Jan; Veen, Paul Van; Thierry, Jacques; Huang, Zehui (1995). "A Triassic, Jurassic and Cretaceous Time Scale". Geochronology, Time Scales and Global Stratigraphic Correlation. doi:10.2110/pec.95.04.0095. ISBN 978-1-56576-091-2.
+Harland, W.B., Cox, A.V.; Llewellyn, P.G.; Pickton, C.A.G.; Smith, A.G.; and Walters, R., 1982. A Geologic Time Scale: 1982 edition. Cambridge University Press: Cambridge, 131p.
+Harland, W.B.; Armstrong, R.L.; Cox, A.V.; Craig, L.E.; Smith, A.G.; Smith, D.G., 1990. A Geologic Time Scale, 1989 edition. Cambridge University Press: Cambridge, p. 1–263. ISBN 0-521-38765-5
+Harper, C.W. Jr (1980). "Relative age inference in paleontology". Lethaia. 13 (3): 239–248. Bibcode:1980Letha..13..239H. doi:10.1111/j.1502-3931.1980.tb00638.x.
+Obradovich, J.D., 1993. A Cretaceous time scale. IN: Caldwell, W.G.E. and Kauffman, E.G. (eds.). Evolution of the Western Interior Basin. Geological Association of Canada, Special Paper 39, p. 379–396.
+Palmer, Allison R (1983). "The Decade of North American Geology 1983 Geologic Time Scale". Geology. 11 (9): 503–504. Bibcode:1983Geo....11..503P. doi:10.1130/0091-7613(1983)11<503:tdonag>2.0.co;2.
+Powell, James Lawrence, 2001, Mysteries of Terra Firma: the Age and Evolution of the Earth, Simon & Schuster, ISBN 0-684-87282-X
+
+== External links ==
+The Age of the Earth by Chris Stassen (TalkOrigins.org)
+USGS preface on the Age of the Earth
+NASA exposition on the age of Martian meteorites
+Ageing the Earth on In Our Time at the BBC
+Pre-1900 Non-Religious Estimates of the Age of the Earth

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+
+The andesite line is the most significant regional geologic distinction in the Pacific Ocean basin. It separates the mafic basaltic volcanic rocks of the Central Pacific Basin from the partially submerged continental areas of more felsic andesitic volcanic rock on its margins. The andesite line parallels the subduction zones and deep oceanic trenches around the Pacific basin. It is the surface expression of melting within and above the plunging subducting slab. It follows the western edge of the islands off California and passes south of the Aleutian Arc, along the eastern edge of the Kamchatka Peninsula, the Kuril Islands, Japan, the Mariana Islands, Yap, Palau, the Solomon Islands, Fiji, Tonga, and New Zealand's North Island. The dissimilarity continues northeastward along the western edge of the Andes mountains of South America to Mexico, returning then to the islands off California. Indonesia, the Philippines, Japan, New Guinea, and New Zealand lie outside the andesite line.
+Within the closed loop of the andesite line are most of the deep troughs, submerged volcanic mountains, and oceanic volcanic islands that characterize the Pacific basin. It is here that basaltic lavas gently flow out of rifts to build huge dome-shaped volcanic mountains whose eroded summits form island arcs, chains, and clusters. Outside the andesite line, volcanism is of the explosive type. The Pacific Ring of Fire runs parallel to the line and is the world's foremost belt of explosive volcanism.
+The term andesite line predates the geologic understanding of plate tectonics. The term was first used in 1912 by New Zealand geologist Patrick Marshall to describe the distinct structural and volcanologic boundary extending from east of New Zealand to Fiji and north of the New Hebrides and the Solomon Islands.
+
+
+== See also ==
+Ring of Fire
+Pacific Plate
+
+
+== References ==

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+
+Backlundtoppen  is a mountain in Olav V Land at Spitsbergen, Svalbard. It has a height of 1,068 m.a.s.l. and is located east of Billefjorden and west of Akademikarbreen. The mountain is named after Swedish-Russian astronomer Johan Oskar Backlund. It hosted a trigonometric station during the Swedish-Russian Arc-of-Meridian Expedition.
+
+
+== References ==

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+title: "Catastrophism"
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+
+In geology, catastrophism is the theory that the Earth has largely been shaped by sudden, short-lived, violent events, possibly worldwide in scope.
+This contrasts with uniformitarianism (sometimes called gradualism), according to which slow incremental changes, such as erosion, brought about all the Earth's  geological features. The proponents of uniformitarianism held that the present was "the key to the past", and that all geological processes (such as erosion) throughout the past resembled those that can be observed today. Since the 19th-century disputes between catastrophists and uniformitarians, a more inclusive and integrated view of geologic events has developed, in which the scientific consensus accepts that some catastrophic events occurred in the geologic past, but regards these as extreme examples of explicable natural processes.
+Proponents of catastrophism proposed that each geological epoch ended with violent and sudden natural catastrophes such as major floods and the rapid  formation of major mountain chains.  Plants and animals living in the parts of the world where such events occurred  became extinct, to be replaced abruptly by the new forms whose fossils defined the geological strata. Some catastrophists attempted to relate at least one such change to the Biblical account of Noah's flood.
+The French scientist Georges Cuvier (1769–1832) popularised the concept of catastrophism in the early 19th century; he proposed that new life-forms had moved in from other areas after local floods, and avoided religious or metaphysical speculation in his scientific writings.
+
+== History ==
+
+=== Geology and biblical beliefs ===
+
+In the early development of geology, efforts were made in a predominantly Christian western society to reconcile biblical narratives of Creation and the universal flood with new concepts about the processes which had formed the Earth. The discovery of other ancient flood myths was taken as explaining why the flood story was "stated in scientific methods with surprising frequency among the Greeks", an example being Plutarch's account of the Ogygian flood.
+
+=== Cuvier and the natural theologians ===
+
+The leading scientific proponent of catastrophism in the early nineteenth century was the French anatomist and paleontologist Georges Cuvier. His motivation was to explain the patterns of extinction and faunal succession that he and others were observing in the fossil record. While he did speculate that the catastrophe responsible for the most recent extinctions in Eurasia might have been the result of the inundation of low-lying areas by the sea, he did not make any reference to Noah's flood. Nor did he ever make any reference to divine creation as the mechanism by which repopulation occurred following the extinction event. In fact Cuvier, influenced by the ideas of the Enlightenment and the intellectual climate of the French Revolution, avoided religious or metaphysical speculation in his scientific writings. Cuvier also believed that the stratigraphic record indicated that there had been several of these revolutions, which he viewed as recurring natural events, amid long intervals of stability during the history of life on Earth. This led him to believe the Earth was several million years old.
+By contrast in Britain, where natural theology was influential during the early nineteenth century, a group of geologists including William Buckland and Robert Jameson interpreted Cuvier's work differently. Cuvier had written an introduction to a collection of his papers on fossil quadrupeds, discussing his ideas on catastrophic extinction. Jameson translated Cuvier's introduction into English, publishing it under the title Theory of the Earth. He added extensive editorial notes to the translation, explicitly linking the latest of Cuvier's revolutions with the biblical flood. The resulting essay was extremely influential in the English-speaking world. Buckland spent much of his early career trying to demonstrate the reality of the biblical flood using geological evidence. He frequently cited Cuvier's work, even though Cuvier had proposed an inundation of limited geographic extent and extended duration, whereas Buckland, to be consistent with the biblical account, was advocating a universal flood of short duration. Eventually, Buckland abandoned flood geology in favor of the glaciation theory advocated by Louis Agassiz, following a visit to the Alps where Agassiz demonstrated the effects of glaciation at first hand. As a result of the influence of Jameson, Buckland, and other advocates of natural theology, the nineteenth century debate over catastrophism took on much stronger religious overtones in Britain than elsewhere in Europe.

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+title: "Catastrophism"
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+---
+
+=== The rise of uniformitarianism in geology ===
+Uniformitarian explanations for the formation of sedimentary rock and an understanding of the immense stretch of geological time or, as the concept came to be known, deep time, were found in the writing of James Hutton, sometimes known as the father of geology, in the late 18th century. The geologist Charles Lyell built upon Hutton's ideas during the first half of 19th century and amassed observations in support of the uniformitarian idea that the Earth's features had been shaped by same geological processes that could be observed in the present acting gradually over an immense period of time. Lyell presented his ideas in the influential three volume work, Principles of Geology, published in the 1830s, which challenged theories about geological cataclysms proposed by proponents of catastrophism like Cuvier and Buckland. One of the key differences between catastrophism and uniformitarianism is that uniformitarianism requires vast timelines for continued processes, whereas catastrophism accepts that there appeared to have been abrupt changes. Today most geologists combine catastrophist and uniformitarianist standpoints, taking the view that Earth's history is a slow, gradual story punctuated by occasional natural catastrophic events that have affected Earth and its inhabitants.
+From around 1850 to 1980, most geologists endorsed uniformitarianism ("The present is the key to the past") and gradualism (geologic change occurs slowly over long periods of time) and rejected the idea that cataclysmic events such as earthquakes, volcanic eruptions, or floods of vastly greater power than those observed at the present time, played any significant role in the formation of the Earth's surface. Instead they believed that the Earth had been shaped by the long term action of forces such as volcanism, earthquakes, erosion, and sedimentation, that could still be observed in action today. In part, the geologists' rejection was fostered by their impression that the catastrophists of the early nineteenth century believed that God was directly involved in determining the history of Earth. Some of the theories about Catastrophism in the nineteenth and early twentieth centuries were connected with religion and catastrophic origins were sometimes considered miraculous rather than natural events.
+The rise in uniformitarianism made the introduction of a new catastrophe theory very difficult. In 1923 J Harlen Bretz published a paper on the channeled scablands formed by glacial Lake Missoula in Washington State, USA. Bretz encountered resistance to his theories from the geology establishment of the day, kicking off an acrimonious 40 year debate. Finally in 1979 Bretz received the Penrose Medal; the Geological Society of America's highest award.
+
+=== Immanuel Velikovsky's views ===
+
+In the 1950s, Immanuel Velikovsky propounded catastrophism in several popular books. He speculated that the planet Venus is a former "comet" which was ejected from Jupiter and subsequently 3,500 years ago made two catastrophic close passes by Earth, 52 years apart, and later interacted with Mars, which then had a series of near collisions with Earth which ended in 687 BCE, before settling into its current orbit. Velikovsky used this to explain the biblical plagues of Egypt, the biblical reference to the "Sun standing still" for a day (Joshua 10:12 & 13, explained by changes in Earth's rotation), and the sinking of Atlantis. Scientists vigorously rejected Velikovsky's conjectures.
+
+== Current application ==
+Neocatastrophism is the explanation of sudden extinctions in the palaeontological record by high magnitude, low frequency events (such as asteroid impacts, super-volcanic eruptions, supernova gamma ray bursts, etc.), as opposed to the more prevalent geomorphological thought which emphasises low magnitude, high frequency events.
+
+=== Luis Alvarez impact event hypothesis ===
+
+In 1980, Walter and Luis Alvarez published a paper suggesting that a 10 kilometres (6.2 mi) asteroid struck Earth 66 million years ago at the end of the Cretaceous period. The impact wiped out about 70% of all species, including the non-avian dinosaurs, leaving behind the Cretaceous–Paleogene boundary (K–T boundary). In 1990, a 180 kilometres (110 mi) candidate crater marking the impact was identified at Chicxulub in the Yucatán Peninsula of Mexico. These events sparked a wide acceptance of a scientifically based catastrophism with regard to certain events in the distant past. 
+Since then, the debate about the extinction of the dinosaurs and other mass extinction events has centered on whether the extinction mechanism was the asteroid impact, widespread volcanism (which occurred about the same time), or some other mechanism or combination. Most of the mechanisms suggested are catastrophic in nature.
+The observation of the Shoemaker-Levy 9 cometary collision with Jupiter illustrated that catastrophic events occur as natural events.
+
+=== Moon-formation ===
+
+Modern theories also suggest that Earth's anomalously large moon was formed catastrophically. In a paper published in Icarus in 1975, William K. Hartmann and Donald R. Davis proposed that a catastrophic near-miss by a large planetesimal early in Earth's formation approximately 4.5 billion years ago blew out rocky debris, remelted Earth and formed the Moon, thus explaining the Moon's lesser density and lack of an iron core. The impact theory does have some faults; some computer simulations show the formation of a ring or multiple moons post impact, and elements are not quite the same between the Earth and Moon.
+
+== See also ==
+
+== References ==
+
+== Sources ==
+King, Clarence (1877). "Catastrophism and Evolution". The American Naturalist. 11 (8): 449–470. Bibcode:1877ANat...11..449K. doi:10.1086/271929.
+Rudwick, Martin J. S. (1972). The Meaning of Fossils. Chicago, Illinois: University of Chicago Press. ISBN 0-226-73103-0.
+McGowan, Christopher (2001). The Dragon Seekers. Cambridge, Massachusetts: Perseus Publishing. ISBN 0-7382-0282-7.
+
+== Further reading ==
+Lewin, R.; Complexity, Dent, London, 1993, p. 75
+Palmer, T.; Catastrophism, Neocatastrophism and Evolution. Society for Interdisciplinary Studies in association with Nottingham Trent University, 1994, ISBN 0-9514307-1-8 (SIS) ISBN 0-905488-20-2 (Nottingham Trent University)
+
+== External links ==
+
+The Fall and Rise of Catastrophism
+Catastrophism! Man, Myth and Mayhem in Ancient History and the Sciences
+"Uniformitarianism and Catastrophism"  at the Dictionary of the History of Ideas

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+title: "Chiemgau impact hypothesis"
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+---
+
+Chiemgau impact hypothesis is an obsolete scientific theory that claimed the Tüttensee lake in southern Bavaria, Germany, to be the result of a Holocene meteorite impact. This claim has been refuted by geological research and the finding of a soil horizon of undisturbed peat and sedimentation since the end of the last glaciation period.  The lake is in fact one of many kettles under the foothills of the Bavarian alps.
+The claims of an impact crater had been raised by a team of hobby-archaeologists, calling themselves the CIRT (Chiemgau impact research team), and have resulted in some media reports in Germany and discussions in the local tourism industry, but are not accepted beyond the CIRT team today.
+
+
+== References ==

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+title: "Deep time"
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+---
+
+Deep time is the concept of geological time that spans billions of years, far beyond the scale of human experience. It provides the temporal framework for understanding the formation and evolution of Earth, the development of life, and the slow-moving processes that shape planetary change. First developed as a scientific idea in the 18th century and popularized in the 20th century by writers such as John McPhee, the concept of deep time has influenced fields ranging from geology and evolutionary biology to climate science, philosophy, education, and environmental ethics. Today, deep time is increasingly used in science communication and public engagement, offering a lens for understanding human impact during the Anthropocene.
+
+== Origins and definition ==
+The philosophical concept of geological time was developed in the 18th century by Scottish geologist James Hutton; his "system of the habitable Earth" was a deistic mechanism keeping the world eternally suitable for humans. The modern concept entails huge changes over the age of the Earth which has been determined to be, after a long and complex history of developments, around 4.55 billion years.
+James Hutton based his view of deep time on a form of geochemistry that had developed in Scotland and Scandinavia from the 1750s onward.  As mathematician John Playfair, one of Hutton's friends and colleagues in the Scottish Enlightenment, remarked upon seeing the strata of the angular unconformity at Siccar Point with Hutton and James Hall in June 1788, "the mind seemed to grow giddy by looking so far into the abyss of time".
+
+== Early theories ==
+Early geologists such as Nicolas Steno and Horace Bénédict de Saussure had developed ideas of geological strata forming from water through chemical processes, which Abraham Gottlob Werner developed into a theory known as Neptunism, envisaging the slow crystallisation of minerals in the ancient oceans of the Earth to form rock.  Hutton's innovative 1785 theory, based on Plutonism, visualised an endless cyclical process of rocks forming under the sea, being uplifted and tilted, then eroded to form new strata under the sea. In 1788 the sight of Hutton's Unconformity at Siccar Point convinced Playfair and Hall of this extremely slow cycle, and in that same year Hutton memorably wrote "we find no vestige of a beginning, no prospect of an end".
+
+== Developments in the 19th century ==
+The 19th century saw major expansion in how scientists conceptualized Earth's history, transforming deep time from a radical idea into a foundational principle of geology and evolutionary theory. Building on the foundations laid by James Hutton, several competing theories emerged that attempted to explain the formation of Earth's features over immense timescales.
+Georges Cuvier, a pioneer of paleontology, proposed that Earth's history was marked by a series of catastrophic events, each followed by the sudden appearance of new life forms. This theory of catastrophism suggested a segmented past, rather than a continuous one. Adam Sedgwick, who helped popularize catastrophism in Britain, introduced his student Charles Darwin to his way of thinking—prompting Darwin to later joke that Sedgwick was adept at "drawing large cheques upon the Bank of Time." 
+In a competing theory, Charles Lyell advanced a theory known as uniformitarianism, articulated in his Principles of Geology (1830–1833). Lyell proposed that slow, gradual processes such as erosion, sedimentation, and volcanic activity had shaped the Earth's surface over vast periods—implying an Earth far older than previously imagined. His view echoed and extended Hutton's original ideas, and positioned deep time as essential to understanding Earth's dynamic systems. 
+Darwin, deeply influenced by Lyell's thinking, read Principles of Geology during his voyage on HMS Beagle in the 1830s. Lyell's framing of deep time provided Darwin with the necessary timescale to support his own emerging theory of evolution by natural selection. Without a vast temporal backdrop, evolutionary change would have seemed implausible. Thus, the acceptance of deep time in geology directly enabled new theories of life's development and diversification.
+
+== Intellectual responses ==
+Throughout history, scholars and thinkers have attempted to make the vastness of deep time more intelligible. In The Science of Life (1929), H. G. Wells and Julian Huxley dismissed the difficulty of grasping geological time, arguing that "The use of different scales is simply a matter of practice." Like maps or microscopes, deep time requires training the imagination. 
+
+Modern authors have echoed this need for reframing. Physicist Gregory Benford's Deep Time: How Humanity Communicates Across Millennia (1999) and paleontologist Henry Gee's In Search of Deep Time: Beyond the Fossil Record to a New History of Life (2001)  both explore how science and storytelling intersect to help people comprehend timescales far beyond human experience. Stephen Jay Gould's Time's Arrow, Time's Cycle (1987) traces how scientific metaphors shape our temporal assumptions.
+11th century thinkers, like Avicenna in Persia and Shen Kuo in China, proposed timelines that stretched far beyond biblical frameworks. Meanwhile, Thomas Berry and Joanna Macy argue that experiencing deep time is essential to planetary stewardship, influencing movements like deep ecology and ecosophy.
+Together, these voices highlight a central challenge of deep time: not only measuring it, but making it meaningful.
+
+== Today's applications ==
+
+=== The Anthropocene ===
+The concept of deep time has taken on renewed urgency in discussions surrounding the Anthropocene—the proposed geological epoch defined by human impact on Earth's systems. In a landmark Science article, a multidisciplinary group of researchers argued that the Anthropocene is stratigraphically and functionally distinct from the Holocene marking a break in Earth's natural history that is visible in the geologic record.

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+title: "Deep time"
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+---
+
+=== Rethinking human time ===
+Anthropologists and philosophers have further explored the cultural and conceptual ramifications of this shift. The University of Vienna's Anthropocene Project promotes "deep time literacy" as a tool for understanding our species' geological footprint, while scholars such as Matt Edgeworth argue that archaeological traces from the modern world blur traditional boundaries between human time and geological time.
+Scholar Jakko Kemper argues that deep time offers a necessary counterbalance to the "microtime" of tech-driven economies, which prioritize short-term profits and optimization over long-term planetary care. By grounding human activity within geological time, he suggests, deep time thinking challenges anthropocentric timelines and encourages more reflective approaches to environmental and technological governance. 
+
+=== Science communication ===
+The concept of deep time has become a tool for science communication, especially in the context of climate change and environmental responsibility. The Smithsonian National Museum of Natural History opened the David H. Koch Hall of Fossils, a deep time exhibit contextualizing Earth's evolutionary past alongside present ecological challenges. This presentation encourages visitors to think beyond human lifespans and understand the long arc of planetary transformation.
+Media outlets have similarly leveraged the idea of deep time to encourage a shift in public perception. The BBC describes how contemplating deep time can foster patience, humility, and long-term thinking—qualities increasingly recognized as essential in the Anthropocene era. Podcasts are chiming in, as an episode of the Land and Climate Review podcast explored how nuclear waste repositories—designed to remain secure for tens of thousands of years—offer a real-world case study in communicating and planning across deep time scales.
+
+=== Legacy and the future ===
+Public-facing scholarship and exhibitions echo this view. The Smithsonian Human Origins Program describes deep time as a framework that helps us "understand how we arrived at our present moment and how our choices will shape the future"—placing current human behaviors in the context of long evolutionary arcs and environmental change. Popular science outlets like Discover Magazine also continue to amplify this discourse, helping readers grapple with the scale and implications of deep time in an age of accelerating change.
+
+== See also ==
+Timeline of human evolution
+History of life
+History of Earth
+Big History – Education strategy or academic discipline
+Chronology of the Universe – History and future of the universePages displaying short descriptions of redirect targets
+Clock of the Long Now – Clock designed to keep time for 10,000 years
+Deep history – Academic discipline that studies humanity's origins
+Formation of the Solar System
+Long-term nuclear waste warning messages – Messages to deter human intrusion at nuclear waste repositories in the far future
+The World Without Us – 2007 non-fiction book by Alan Weisman
+
+== Notes and references ==
+
+== Sources ==
+
+=== Web ===
+Campbell, Anthony (2001). "Book review: In Search of Deep Time". Archived from the original on 2007-01-02. Retrieved 2006-11-17.
+Colebrook, Michael (2014). "Thomas Berry". Archived from the original on 2014-12-08. Retrieved 2025-02-17.
+Darwin, C. R. (1831-07-09). "Darwin Correspondence Project – Letter 101 — Darwin, C. R. to Fox, W. D., (9 July 1831)". Archived from the original on 16 January 2009. Retrieved 26 March 2010.
+Korthof, Gert (2000). "A Revolution in Palaeontology: Review of Henry Gee's In Search of Deep Time". Archived from the original on 2014-05-29. Retrieved 2013-07-30.
+Montgomery, Keith (2003). "Siccar Point and Teaching the History of Geology" (PDF). University of Wisconsin. Archived (PDF) from the original on 2016-04-15. Retrieved 2008-03-26.
+Palmer, A. R.; Zen, E-an. Critical Issues Committee (ed.). "The Context of Humanity: Understanding Deep Time". Geological Society of America. Archived from the original on 2006-03-26. Retrieved 2005-10-16.
+Rance, Hugh (1999). "Hutton's unconformities" (PDF). Historical Geology: The Present is the Key to the Past. QCC Press. Archived from the original (PDF) on 2008-12-03. Retrieved 2008-10-20.
+
+=== Books ===
+Ialenti, Vincent (2020). Deep Time Reckoning: How Future Thinking Can Help Earth Now. Cambridge, Massachusetts: The MIT Press. Archived from the original on 2021-06-16. Retrieved 2020-07-31.
+McPhee, John (1998). Annals of the Former World. New York: Farrar, Straus and Giroux.
+Repcheck, Jack (2003). "Chapters 2 and 5". The Man Who Found Time: James Hutton and the Discovery of the Earth's Antiquity. Cambridge: Perseus Books. ISBN 0-7382-0692-X.
+Rossi, Paolo (1984). The Dark Abyss of Time: The History of the Earth and the History of Nations from Hooke to Vico, tr. by Lydia Cochrane, Chicago: University of Chicago Press, pp. 338, ISBN 0226728358.
+Sivin, Nathan (1995). Science in Ancient China: Researches and Reflections. Brookfield, Vermont: Ashgate Publishing Variorum series. pp. III, 23–24.
+Toulmin, Stephen; Goodfield, June (1965). The Ancestry of Science: The Discovery of Time. University of Chicago Press. p. 64.
+White, Andrew Dickson (1896). A History of the Warfare of Science with Theology in Christendom. New York: D. Appleton & Company. Archived from the original on 2007-10-05. Retrieved 2007-12-21.
+Winchester, Simon (2001). "Chapter 2". The Map That Changed the World: William Smith and the Birth of Modern Geology. New York: HarperCollins. ISBN 0-06-019361-1.
+
+=== Journals ===
+Ialenti, Vincent (2014). "Adjudicating Deep Time: Revisiting The United States' High-Level Nuclear Waste Repository Project At Yucca Mountain". Science & Technology Studies. 27 (2). doi:10.23987/sts.55323. SSRN 2457896.
+Kubicek, Robert (2008-03-01). "Ages in Chaos: James Hutton and the Discovery of Deep Time". The Historian. 70 (1): 142–143. ISBN 978-0-7653-1238-9.
+Playfair, John (1805). "Hutton's Unconformity". Transactions of the Royal Society of Edinburgh. V (III).
+
+== External links ==
+"The benefits of embracing 'deep time' in a year like 2020" (Vincent Ialenti) Archived 2022-08-07 at the Wayback Machine—BBC Future.
+ChronoZoom Archived 2017-05-08 at the Wayback Machine is a timeline for Big History being developed for the International Big History Association by Microsoft Research and University of California, Berkeley
+Deep Time Archived 2017-09-09 at the Wayback Machine in Evolution (TV series).  Note: This PBS/WGBH website advises Flash Player and Shockwave Player installation.
+Deep Time – A History of the Earth: Interactive Infographic Archived 2011-05-29 at the Wayback Machine
+Deep Time Walk App – A new story of the living Earth: Interactive Walking Experience
+"Embracing 'Deep Time' Thinking" (Vincent Ialenti) Archived 2019-07-06 at the Wayback Machine NPR Cosmos & Culture.
+"Pondering 'Deep Time' Could Inspire New Ways to View Climate Change" (Vincent Ialenti) Archived 2019-07-06 at the Wayback Machine NPR Cosmos & Culture.

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+title: "Discovery Investigations"
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+---
+
+The Discovery Investigations were a series of scientific cruises and shore-based investigations into the biology of whales in the Southern Ocean. They were funded by the British Colonial Office and organised by the Discovery Committee in London, which was formed in 1918. They were intended to provide the scientific background to stock management of the commercial Antarctic whale fishery.
+Discovery Investigations contributed greatly to knowledge of the whales, the krill they fed on and their habitat's oceanography, while charting the local topography, including Atherton Peak. They continued until 1951, with the final report published in 1980.
+Collected specimens are in the Discovery Collections.
+
+
+== Laboratory ==
+Shore-based work on South Georgia took place in the marine laboratory, Discovery House, built in 1925 at King Edward Point and occupied until 1931. The scientists lived and worked in the building, travelling half a mile or so across King Edward Cove to the whaling station at Grytviken to work on whales as they were brought ashore by commercial whaling ships.
+
+
+== Ships ==
+Vessels used were:
+
+RRS Discovery from 1924 to 1931
+RRS William Scoresby from 1927 to 1945 or later
+RRS Discovery II from 1929 to 1951
+
+
+== Reports ==
+Results of the investigations were printed in the Discovery Reports. This was a series of many small reports, published in 38 volumes by the Cambridge University Press, and latterly the Institute of Oceanographic Sciences. Many were printed as individual reports rather than in large volumes.
+
+
+=== List ===
+
+
+== Books ==
+The Discovery Investigations are described in the following books, all of which were out of print in 2008:
+
+Hardy, Alister Clavering, Sir (1968). Great Waters. New York: Harper & Row.{{cite book}}:  CS1 maint: multiple names: authors list (link)
+Ommanney, F. D. (1938). South Latitude. London: Longmans, Green and Co.
+Coleman-Cooke, John (1963). Discovery II In The Antarctic. London: Odhams Press.
+Saunders, Alfred (1950). A Camera in Antarctica. London: Winchester Publications.
+
+
+== References ==
+
+
+== External links ==
+Scanned copies of many of the reports are available at the Biodiversity Heritage Library.

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

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+---
+title: "French Geodesic Mission to Lapland"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/French_Geodesic_Mission_to_Lapland"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:47.308936+00:00"
+instance: "kb-cron"
+---
+
+The French Geodesic Mission to Lapland was one of the two geodesic missions carried out in 1736–1737 by the French Academy of Sciences for measuring the shape of the Earth.
+One expedition was sent to Ecuador to perform measurements near the Equator; the other was sent to Torne Valley to perform measurements near the Arctic Circle.
+The expedition to Torne Valley was led by Pierre Louis Maupertuis. As Swedish representative, professor Anders Celsius joined the team. The expedition arrived in Tornio on June 19, 1736, spent the rest of 1736 making measurements, and returned to France on June 10, 1737. By measuring the length of the arc, Maupertuis's team was able to prove that the Earth is, indeed, flattened at the poles as Sir Isaac Newton had predicted.
+The books describing this trip, written by Maupertuis and Réginald Outhier, have given us much information about the nature and culture of 18th-century Lapland, and the books have inspired many travellers to head to Torne Valley.
+
+
+== Results ==
+The team measured the length of a meridian arc of approximately one degree's length – about 111 km. The south end of the arc was at the tower of the church of Tornio (Torneå), the north end was at the hill of Kittisvaara. 
+After arriving in Tornio in summer, the team moved north along the Torne Valley, making precise angle measurements between reference points to lay down a system of triangulations. They also performed astronomical observations to determine their latitude. After reaching Kittisvaara, they turned back and reached Tornio in winter. They then laid out a 8.4-mile baseline and used wooden rods to measure its length to an accuracy of 4 inches.
+
+After analyzing their data, they found that the length of 1 degree of latitude to be 57,422 toise in Lapland. The other expedition to Ecuador found it to be 56,734 toise in Ecuador. Jean Picard had surveyed the Paris-Amiens region in 1669, finding a figure of 57,060 toise. Together, these figures showed the shape of the Earth to be oblate. Thus, Sir, You See the Earth is Oblate, according to the Actual Measurements, as it has been already found by the Law of Staticks: and this flatness appears even more considerable than Sir Isaac Newton thought it.
+Maupertuis' Letter to James Bradley, third Astronomer Royal of Great Britain.Later, Euler used figures from these expeditions, as well as later data, to compute the shape of the Earth.
+
+
+== References ==

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

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+---
+title: "French Geodesic Mission to the Equator"
+chunk: 1/2
+source: "https://en.wikipedia.org/wiki/French_Geodesic_Mission_to_the_Equator"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:48.770857+00:00"
+instance: "kb-cron"
+---
+
+The Spanish-French Geodesic Mission (French: Expédition géodésique française en Équateur), also called the French Geodesic Mission to Peru, was an 18th-century expedition to what is now Ecuador carried out for the purpose of performing an arc measurement, measuring the length of a degree of latitude near the Equator, by which the Earth's radius can be inferred. The mission was one of the first geodesic (or geodetic) missions carried out under modern scientific principles, and the first major international scientific expedition. 
+
+== Background ==
+In the 18th century, there was significant debate in the scientific community, specifically in the French Academy of Sciences (Académie des sciences), as to whether the circumference of the Earth was greater around the Equator or around the poles. French astronomer Jacques Cassini held to the view that the polar circumference was greater. King Louis XV and the academy sent two expeditions to determine the answer: a northern expedition was sent to Meänmaa in Lapland, close to the Arctic Circle, with the Swedish physicist Anders Celsius and under the guidance of the French mathematician Pierre Louis Maupertuis. The other mission was sent to Ecuador, at the Equator. Previous accurate measurements had been taken in Paris by Cassini and others.
+
+== Expedition ==
+
+The equatorial mission was led by French astronomers Charles Marie de La Condamine, Pierre Bouguer, Louis Godin and Spanish geographers Jorge Juan and Antonio de Ulloa.  They were accompanied by several assistants, including the naturalist Joseph de Jussieu and Louis's cousin Jean Godin. La Condamine was joined in his journey down the Amazon by Ecuadoran geographer and topographer Pedro Maldonado. (Maldonado later traveled to Europe to continue his scientific work.)
+The Ecuadoran expedition 
+left France in May 1735. They landed on the Caribbean coast in Colombia, sailed to Panama where they traveled overland to the Pacific, and continued by sail to Ecuador, then called the Territory of Quito by Spain. In Ecuador, they split into two groups, traveling overland through rain forests, arriving in Quito in June 1736.
+Pierre Bouguer established the length of a pendulum beating seconds on the Equator at Quito, near Quito at the top of Pinchincha, and at sea level to determine gravity of Earth. La Condamine had a marble plaque prepared, with a bronze exemplar (varilla metalica) of the length of such a pendulum set into it, which he presented to the Jesuit College of San Francisco in Quito in 1742, engraved with an inscription reading: Penduli simplicis aequinoctialis, unius minuti secundi temporis medii, in altitudine Soli Quitensis, archetypus (mensurae naturalis exemplar, utinam et universalis) ["Archetype of the equinoctial simple pendulum, of one second of a minute of mean time at the latitude of Quito (a natural and, may it be, a universal model of measure)"]. The plaque is now in the Observatorio Astronómico in the Parque La Alameda.
+Bouguer, La Condamine, Godin and their colleagues measured arcs of the Earth's curvature on the Equator from the plains near Quito to the southern city of Cuenca. These measurements enabled the first accurate determination of the shape of the Earth, eventually leading to the establishment of the international metric system of measurement. When an International Commission for Weights and Measures was convened in Paris to settle the true length of the metre, it adopted on 22 June 1799 a standard metre based on the length of the half meridian connecting the North Pole with the Equator. The French Academy of Sciences had commissioned an expedition led by Jean Baptiste Joseph Delambre and Pierre Méchain, lasting from 1792 to 1799, which attempted to accurately measure the distance between a belfry in Dunkerque and Montjuïc castle in Barcelona at the longitude of Paris Panthéon. This portion of the Paris meridian was to serve as the basis for the length of the half meridian connecting the North Pole with the Equator. The metre was defined as the ten-millionth of the half meridian's length extrapolated from an Earth's flattening of 1/334 obtained from the results of the survey by Delambre and Méchain combined with those of the Peru meridian arc as established by La Condamine and his colleagues.
+They completed their survey measurements by 1739, measuring the length of a meridian arc of three degrees at the Equator. They did this in spite of earlier news that the expedition to Lapland led by Maupertuis had already finished their work and had proven that the Earth is oblate; i.e., flattened at the poles.  However, problems with astronomical observations kept them in Ecuador several more years.
+Bouguer returned first from the expedition, going overland to the Caribbean and then to France.  La Condamine, along with Maldonado, returned by way of the Amazon River. Louis Godin took a position as professor in Lima, where he helped rebuild the city after the devastating 1746 earthquake, and returned to Europe in 1751. Bouguer, La Condamine and the Spanish officers each wrote separate accounts of the expedition, which opened up European eyes to the exotic landscapes, flora and fauna of South America and led directly to the great naturalist expeditions by Alexander von Humboldt and others.
+La Condamine tried in vain to promote the length of the seconds pendulum measured at the Equator as a universal measure of length. He was more successful with his proposal to adopt the geodetic standard used in Peru as the official standard of the toise of Paris. The toise of Peru became the royal standard of the toise in 1766 under the name Toise de l'Académie.
+
+== Observations during the mission ==

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+---
+title: "French Geodesic Mission to the Equator"
+chunk: 2/2
+source: "https://en.wikipedia.org/wiki/French_Geodesic_Mission_to_the_Equator"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:48.770857+00:00"
+instance: "kb-cron"
+---
+
+Ulloa and Juan visited the architectural Inca complex in San Agustin de Callo and subsequently wrote a descriptive document of what they observed at the ruins. Ulloa made a drawing of the ruins.
+In 1739, Charles Marie de La Condamine became the first European to make a scientific description of Ingapirca.
+The scientists witnessed two eruptions of the Cotopaxi volcano in 1743 and 1744.
+Expedition members, through talking to local inhabitants, became the first Europeans to discover and scientifically document rubber tapping (and thus rubber), and identify the correct type of cinchona tree that produces the active form of quinine (an important anti-malarial agent).
+Charles Marie de La Condamine developed the concept of the metre as a universal unit of measure based on the dimensions of the Earth (rather than local standards that differed and hindered trade).
+
+== Subsequent mission ==
+In the late 19th century, the Academy of Sciences sent another mission to Ecuador at the behest of the International Association of Geodesy to confirm the results of the First Geodesic Mission and commemorate the relationship between the two republics. This second mission was led by Captain E. Maurain and several other military personnel during its tenure in Ecuador from 1901 to 1906.  The only two members of the French mission to spend the entire time in Ecuador were Lieutenant (later General) Georges Perrier and medical officer Paul Rivet, later an important anthropologist and founder of the Musée de l'Homme in Paris.
+
+== Monument ==
+A reproduction of the pyramids that marked the baseline for measurement at Yaruqui (which was destroyed by Quito authorities in the 1740s) was erected in 1836, the centennial of the expedition, by the Rocafuerte administration of the nascent republic of Ecuador. This monument fell into disrepair over the next century but was rebuilt in 1936, minus its original French inscription, for the bicentennial of the first geodesic expedition, along with a second pyramid at San Antonio de Pichincha on the Equator. These monuments still exist today. The new Quito International Airport opened in the Yaruqui Valley. Though talks of having a mural celebrating the Geodesic Mission took place during planning stages, no acknowledgement of the scientific importance of this site currently exists.
+
+In 1936, the French American Committee of Ecuador sponsored the idea of the Ecuadoran geographer Dr. Luis Tufiño and raised a monument commemorating the bicentennial of the arrival of the First Geodesic Mission. They raised a 10-meter-high monument at Ciudad Mitad del Mundo in San Antonio de Pichincha, in Pichincha Province of Ecuador. However, there is no record that the Mission ever visited the area.
+There was a project to build a new pyramid exactly on the Equator, to be designed by the famed architect Rafael Viñoly (d. 2023).
+
+== Publications ==
+Relación histórica del viaje a la América meridional, Jorge Juan and Ulloa, 1748
+Figure de la terre determine, Bouguer, 1749
+Mesure des trois premiers degrés du méridien dans l'hémisphère austral, La Condamine, 1751
+Journal du voyage, La Condamine, 1751
+Le procès des étoiles, 1735–1771, ISBN 978-2-232-10176-2, ISBN 978-2-232-11862-3
+
+== See also ==
+French Geodesic Mission to Lapland
+Geodesy
+History of geodesy
+History of the metre
+Seconds pendulum
+De Lacaille's arc measurement
+Charles Marie de La Condamine#In South America
+Jorge Juan y Santacilia#Sojourn in South America
+Antonio de Ulloa#South American expedition
+
+== Footnotes ==
+
+== References ==
+
+== Further reading ==
+"Figure of the Earth". Voyages of Discovery. Episode 4. July–August 2008. BBC. Archived from the original on December 5, 2006.
+"Mitad del Mundo Half of the World". Ecuadorsbest.com. Archived from the original on 20 May 2012. Retrieved 18 November 2011.
+Ferreiro, Larrie D. (2011). Measure of the Earth: The Enlightenment Expedition that Reshaped Our World. New York: Basic Books. ISBN 978-0-465-01723-2. OCLC 657595545. Retrieved 18 November 2011.
+Crane, Nicholas (2021). Latitude: The True Story of the World's Very First International Scientific Expedition. Michael Joseph. ISBN 978-0-241-47834-9. Retrieved 13 November 2021.
+"Historical Brief Description of the Middle of the World and Its Monument". Mitad del Mundo. c. 2002. Archived from the original on 23 January 2010. Retrieved 18 November 2011.
+Mockler, Terry (February 2005). "Historic Cultural and Scientific Expeditions to Equator and Ecuador". Retrieved 18 November 2011.(registration required)
+Neill, David A. "Geography". Catalogue of the Vascular Plants of Ecuador. Missouri Botanical Garden. Retrieved 18 November 2011.
+O'Connor, J. J.; Robertson, E. F. (April 2003). "Jacques Cassini". Scotland: School of Mathematics and Statistics, University of St Andrews. Retrieved 18 November 2011.

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

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+---
+title: "Geological Exploration of the Fortieth Parallel"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Geological_Exploration_of_the_Fortieth_Parallel"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:50.083375+00:00"
+instance: "kb-cron"
+---
+
+The Geological Exploration of the Fortieth Parallel was a geological survey made by order of the Secretary of War according to acts of Congress of March 2, 1867, and March 3, 1869, under the direction of Brig. and Bvt. Major General A. A. Humphreys, Chief of Engineers, by Clarence King, U. S. geologist. More commonly known as the Fortieth Parallel Survey, the survey conducted field work from 1867 to 1872, exploring the area along the fortieth parallel north from northeastern California, through Nevada, to eastern Wyoming.
+
+
+== Results ==
+The results of the survey were published in eight volumes of the Fortieth Parallel Survey:
+
+Vol. I. Systematic geology, by Clarence King, U. S. Geologist. 1878. xii, 803 pp., and atlas of 12 sheets.
+Vol. II. Descriptive geology, by Arnold Hague and S. F. Emmons. 1877. xiii, 890 pp.
+Vol. III. Mining industry, by James Duncan Hague, with geological contributions by Clarence King. 1870. xv, 647 pp. and atlas of 14 sheets.
+Vol. IV. Part I, Palaeontology. by F. B. Meek. Part II, Palaeontology, by James Hall and R. P. Whitfield. Part III, Ornithology, by Robert Ridgway. 1877. xii, 669 pp.
+Vol. V. Botany, by Sereno Watson, aided by Prof. Daniel C. Eaton and others. 1871. liii, 525 pp.
+Vol. VI. Microscopical petrography, by Ferdinand Zirkel. 1876. xv, 297 pp.
+Vol. VII. Odontornithes, A monograph on the extinct toothed birds of North America, by Othniel Charles Marsh. 1880. xv, 201 pp.
+Special Publication: List of plants collected in Nevada and Utah, 1867-69; numbered as distributed. Sereno Watson, collector.
+Atlases:
+
+Atlas accompanying the report of the Geological Exploration of the Fortieth Parallel. by Clarence King, U. S. geologist-in-charge. 1876. Julius Bien, Lithographer. Folio, 2 11., (title and legend), 1 single and 11 double folio sheets (1 single folio map, 10 double folio maps, 1 double folio section).
+Atlas accompanying Volume III on Mining Industry. [List of plates.] Engraved and printed by Julius Bien, New York. Folio, 11. (title page), 14 plates.
+
+
+== References ==
+
+
+=== Additional Sources ===
+USGS Historical Photography Library - Collection of photographs from the 40th Parallel Survey.
+Photos of volumes - held at the American Geographical Society Library, UW Milwaukee.

data/en.wikipedia.org/wiki/Geometrical_crystallography_before_X-rays-0.md

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+---
+title: "Geometrical crystallography before X-rays"
+chunk: 1/4
+source: "https://en.wikipedia.org/wiki/Geometrical_crystallography_before_X-rays"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:27.087973+00:00"
+instance: "kb-cron"
+---
+
+Geometrical crystallography before X-rays describes how geometrical crystallography developed as a science up to the discovery of X-rays by Wilhelm Conrad Röntgen in 1895. In the period before X-rays, crystallography can be divided into three broad areas: geometric crystallography culminating in the discovery of the 230 space groups in 1891–1894, physical crystallography and chemical crystallography.
+Geometrical crystallography before X-rays covers the study of crystal form and the mathematical representation of crystal structure. It includes the atomism and dynamism theories of crystal structure, the invention of the Miller indices, and the discovery of the 7 crystal systems, the 32 crystal classes, the 14 Bravais lattices, and the 230 space groups.
+
+== 16th century ==
+
+The study of the geometrical properties of crystals began in the 16th century. In 1546 Georgius Agricola published a study of mineralogy in which morphology, or geometrical shape, was one of the characteristics used to classify minerals such as quartz. In 1550 Gerolamo Cardano made an early attempt to explain the shape of crystals as the result of a close packing of spheres. In 1591 Thomas Harriot studied the close packing of cannonballs (spheres). In 1597 Andreas Libavius recognized the geometrical characteristics of crystals and identified salts from their crystal shape.
+
+== 17th century ==
+
+In 1611 Johannes Kepler published Strena Seu de Nive Sexangula (A New Year's Gift of Hexagonal Snow) which is considered the first treatise on geometrical and atomistic crystallography. Kepler studied the packing of spheres, in order to explain the hexagonal symmetry of snow crystals. Kepler demonstrated that in a compact packing each sphere has six neighbours in the same plane, three in the plane above, and three in the plane below, for a total of twelve touching spheres. Kepler concluded that π/(3√2) = 0.74084 is the maximum possible density amongst any arrangement of spheres — this became known as the Kepler conjecture. The conjecture was finally proved by Thomas Hales in 1998.
+In 1665 Robert Hooke attempted to explain crystal morphology based on the stacking of atoms. In his work Micrographia he reported on the regularity of quartz crystals observed with the recently invented microscope, and proposed that they are formed by spherules.
+Nicolas Steno rejected Paracelsus's proposed organic origin for crystals. Steno first observed the law of constancy of interfacial angles when studying quartz crystals (De solido intra solidum naturaliter contento, Florence, 1669), and noted that, although the crystals of a substance differed in appearance from one to another, the angles between corresponding faces were always the same. Steno's work can be considered as the beginning of crystallography as an independent discipline.
+
+In 1678 Christiaan Huygens proposed a structural explanation of the double refraction of calcite based on ellipsoidal atoms. Huygens discovered the polarization of light by Iceland spar, a transparent form of calcite, and published his results in his Traité de la Lumière.
+A geometrical theory of crystal structure based on polyhedra was proposed by Domenico Guglielmini. Guglielmini's publications of 1688 (Riflessioni filosofiche dedotte dalle figure de Sali) and 1705 (De salibus dissertatio epistolaris physico-medico-mechanica) concluded that basic forms (cube, rhombohedron, hexagonal prism, and octahedron) of various salt crystals are characteristic of each substance, are identical in form, indivisible, and have faces with identical inclinations to each other.
+
+== 18th century ==
+In 1723 Moritz Anton Cappeller published Prodromus Crystallographiae, the first treatise on crystal shapes. The introduction of the term crystallography is attributed to Cappeller. In 1758 Roger Joseph Boscovich published his atomic theory which stated that particles of matter were linked by attractive and repulsive forces and that the solid so formed was compressible rather than rigid; this would become relevant in the 19th century when Haüy theorised that crystals were constructed from identical units stacked up without spaces.
+Carl Linnaeus promoted a morphological, as opposed to a physical or chemical, approach to the study of crystals. Linneaus published many accurate and detailed drawings of crystals, and identified the forms which were related by truncation.
+
+In 1749 Mikhail Lomonosov postulated spherical atoms to study the structure of niter and rediscovered cubic close packing. However, his work was not influential at the time.
+In 1773 Torbern Bergman, a leader in the field of chemical analysis, described the crystal forms of calcite and stated that all the forms could be built up from the cleavage rhombohedron. Bergman, building on the previous work of Linnaeus, developed a classification of minerals based on chemical characteristics, with subclasses organized by their external shapes, and defined seven primary crystal forms. In 1774 Abraham Gottlob Werner published his classification of minerals. Werner's postulated seven primary forms, and showed that some geometrical forms could be derived from one another by truncation.
+With Jean-Baptiste L. Romé de l'Isle's Essai de cristallographie published in 1772 and Cristallographie published in 1783 the scientific approach to crystal structure began. Romé de l'Isle described over 500 crystal forms and accurately measured the interfacial angles of a great variety of crystals, using the goniometer designed by his student Arnould Carangeot. Romé de l'Isle noted that the angles are characteristic of a substance, thus generalizing the law of constancy of angles postulated by Steno. Romé de l'Isle considered that the shape of a crystal is a consequence of the packing of elemental particles, and defined six primitive forms. However, Romé de l'Isle criticized René Just Haüy and Torbern Bergman for speculation on the internal structure of crystals without sufficient observational data.

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+title: "Geometrical crystallography before X-rays"
+chunk: 2/4
+source: "https://en.wikipedia.org/wiki/Geometrical_crystallography_before_X-rays"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:27.087973+00:00"
+instance: "kb-cron"
+---
+
+In 1781 René Just Haüy (often termed the "Father of crystallography") discovered that crystals always cleave along crystallographic planes. Based on this observation, and the fact that the inter-facial angles in each crystal species always have the same value, Haüy concluded that crystals must be periodic and composed of regularly arranged layers of tiny polyhedra (molécules intégrantes). This theory explained why all crystal planes are related by small rational numbers (the law of rational indices). In 1784 René-Just Haüy published Essai d'une théorie sur la structure des cristaux, appliquée à plusieurs genres de substances cristallisées in which he stated his law of decrements (décroissement): a crystal is composed of molecules arranged periodically in three dimensions without leaving any gaps. Haüy's molecular crystal structure theory assumed that molécules intégrantes were specific in shape and composition for every compound. Haüy developed his mathematical theory of crystal structure over many years. Haüy's theory turned out to be remarkably accurate, and gave crystallography a legitimate place among the sciences.
+Haüy's crystal structure theory was criticised as over-simplistic by William Hyde Wollaston in 1813 and by Henry James Brooke in 1819. Haüy also tended to ignore experimental results that contradicted his structural theory, such as those achieved with the more accurate reflection goniometer invented by Wollaston in 1809. In 1819 Eilhard Mitscherlich discovered the law of isomorphism which states that compounds which contain the same number of atoms, and have similar structures, tend to exhibit similar crystal forms. The discovery of the phenomena of isomorphism and polymorphism dealt a clear blow to Haüy's crystal structure theory.
+
+== Atomism versus Dynamism ==
+
+Christian Samuel Weiss became familiar with Haüy's theory by translating the 4-volume Traité de mineralogie (1801). Weiss added an appendix to volume 1 of the translation in which he first outlined his dynamical theory of crystals. In contrast to Haüy, Weiss took a purely geometric approach to external crystal morphology, completely disregarding any attempt at modelling the internal structure of crystals. Weiss has been termed "the founder of geometric crystallography".
+Weiss rejected Haüy's static "atomistic" theory of crystals instead using a "dynamic" approach that was typical of the German natural philosophers of the early 19th century. Weiss understood the external forms of crystals as a consequence of internal attractions and repulsions, and that generative forces were expressed in definite directions which could be observed as one or more axes of rotation. Weiss used crystallographic axes as the basis of his systematic classification of crystals.
+Weiss and his followers Moritz Ludwig Frankenheim and Johann F. C. Hessel studied the symmetry of crystals. Up until 1800 the concept of symmetry had a variety of meanings, however during the 19th century crystallography was progressively transformed into an empirical and mathematical science by the adoption of symmetry concepts. "In the first half of the 19th century the paramount symmetry problem was that of point symmetry: to enumerate all possible combinations of symmetry elements which pass through a common point, the origin, and therefore leave this point single. The crystallographic symmetry elements were observed to be exclusively 2, 3, 4 and 6-fold axes, mirror planes, and centres of inversion."
+In 1829 Justus Günther Graßmann published a study of the symmetries of the crystal systems using an algebra of linear combinations. In 1832 Franz Ernst Neumann used symmetry considerations when studying double refraction in crystals. By the second half of the 19th century the study of crystals was focused more on their geometry and mathematical analysis than their physical properties.
+Gabriel Delafosse continued Haüy's work in France. He was the first to use the terms lattice (réseau) and unit cell (maille). He stated that the orientation of the axes in a substance is constant, which implies symmetry of translation (a defining feature of a lattice), and that the external symmetry of a crystal reflects its inner symmetry, namely the symmetry of the constituent atoms and their arrangement. In other words, the law of symmetry applies to both the inside and the outside of a crystal.
+French scientists did not adopt the dynamic crystallographic theory, but they did attempt to learn from it. Delafosse built on Haüy's crystallographic approach by stating that the structure and physical properties of crystals should exhibit the same symmetry. Delafosse aimed to resolve the apparent counter-examples to Haüy's law of symmetry by explaining that the symmetry of the physical phenomena revealed the inner structure of crystals. This structure is sometimes more complex than the external morphology. Crystals, in these cases, are of lower symmetry than the lattice. This substructure explained the behaviour of hemihedral crystals, which were not adequately accounted for by Haüy. Delafosse argued that Haüy's molécules intégrante did not necessarily have a physical reality, but rather that its polyhedral form should be regarded instead as the space surrounding a lattice point.
+
+== Crystal systems ==
+
+Christian Samuel Weiss introduced the concept of crystal systems in 1815. Weiss defined seven crystal systems: five based on three orthogonal axes (cubic, tetragonal, orthorhombic, monoclinic and triclinic), and two (trigonal and hexagonal) based on three axes in a plane at 60° to each other and a fourth axis orthogonal to the plane. The number and type of the crystal systems of Weiss correspond to the modern systems apart from the triclinic and monoclinic cases which have non-orthogonal axes.
+Friedrich Mohs established a classification system for minerals based solely on their external shape. Mohs distinguished four crystal systems rather than the seven identified by Weiss. In 1822 Weiss and Mohs engaged in a priority dispute on who had first discovered the crystal systems.
+
+In 1824 Carl Friedrich Naumann confirmed Mohs' observation that the triclinic and monoclinic systems required inclined rather than orthogonal axes. Naumann attempted a synthesis of the Weiss and Mohs systems by considering four different configuration of axes: orthogonal (three right angles), monoclinic (two right angles and one oblique one), diclinic (one right angle and two oblique ones), and triclinic (three oblique ones). The diclinic system has not survived.
+
+== Crystal classes ==

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+title: "Geometrical crystallography before X-rays"
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+---
+
+In 1826 Moritz Ludwig Frankenheim published the first derivation of the 32 crystal classes, but his work was forgotten for many decades. In 1830, Johann Hessel proved that, as a consequence of the law of rational indices, morphological forms can combine to give exactly 32 kinds of crystal symmetry in Euclidean space, since only two-, three-, four-, and six-fold rotation axes can occur (the crystallographic restriction). However, Hessel's work remained practically unknown for over 60 years and, in 1867, Axel Gadolin independently rediscovered his results. Gadolin, who was unaware of the work of his predecessors, found the crystal classes using stereographic projection to represent the symmetry elements of the 32 groups. Gadolin's work had a clarity that attracted widespread attention, and caused Hessel's earlier work to be neglected.
+In 1884 Bernhard Minnigerode recognized the relationship with crystallography, and analyzed the 32 possible crystal classes in terms of group theory. It was not recognized until later that it is precisely the mathematical group properties that make symmetry significant for crystals.
+
+== Miller indices ==
+
+The first to introduce indices to denote crystal planes was Christian Samuel Weiss. In the Weiss system a face is denoted by its three intercepts, ma, nb, pc, with three orthogonal axes, where a, b and c are unit lengths along these axes (in modern notation (⁠1/m⁠ ⁠1/n⁠ ⁠1/p⁠)). In 1823 Franz Ernst Neumann suggested that the inverse of the Weiss indices (m n p) were simpler and easier to use. In 1825 William Whewell, independently from Neumann, proposed essentially the same indices although he used the letters p, q and r.
+William Hallowes Miller, a student of Whewell and subsequently his successor in the Chair of Mineralogy at Cambridge University, introduced the Miller indices in his book A Treatise on Crystallography (1839). The Miller indices are essentially the same as those of Neumann and Whewell but Miller used the letters h, k and l (h k l). Miller's indices were accepted by his contemporaries because of their algebraic convenience, and it is his notation that is currently used in crystallography.
+
+== Bravais lattices ==
+
+In 1835 Moritz Ludwig Frankenheim introduced the notion of lattice, independently of Ludwig August Seeber, and derived 15 lattice types; these correspond to the 14 Bravais lattices, but Frankenheim double-counted one of the monoclinic lattices.
+In 1848 Auguste Bravais presented his work in deriving the 14 Bravais lattices. The work was published in 1850, and translated into English in 1949. Bravais's work can be considered as drawing on a combination of the approaches of Haüy and Weiss. Bravais constructed his mathematical lattices as finite sets of points in space, thus avoiding the need for the packing of spheres or polyhedra to represent physical atoms or molecules. He defined axes, planes and centres of inversion as symmetry elements, and identified all of their possible combinations. Bravais assumed that every atom or molecule in the lattice had the same orientation; in 1879 Leonhard Sohncke removed this restriction to derive his "Sohncke groups". Camille Jordan acknowledged Bravais' work on the combination of symmetry elements in his group theory paper Mémoire sur les groupes des mouvements published in 1868–9.
+In 1851 Bravais showed that crystals preferentially cleaved parallel to lattice planes of high density. This is sometimes referred to as Bravais's law or the law of reticular  density and is an equivalent statement to the law of rational indices.
+
+== Space groups ==
+
+The identification of the 230 space groups has been extensively documented and is now regarded as a major achievement of 19th century science. The space groups became important in the 20th century after the discovery of X-ray diffraction and the founding of the field of X-ray crystallography.
+Ludwig August Seeber first put forward the concept of the space lattice in 1824. He proposed that crystals were assembled from minute particles represented by spheres rather than stacked parallelepipeds without any gaps as Haüy had theorised (compare the scalenohedron diagrams of Haüy and Seeber). Seeber attempted to reconcile the atomistic and dynamic approaches by the regular arrangement of particles with attractive and repulsive forces between them; the gaps between the particles allow for expansion or contraction in response to external physical forces.
+In 1879 Leonhard Sohncke combined the 14 Bravais lattices with the rotation axes and the screw axes to arrive at his 65 spatial arrangements of points in which chiral crystal structures form. Sohncke enumerated the space groups containing only the translations and rotations. Sohncke credited previous researchers, especially Auguste Bravais and Camille Jordan. He also rediscovered Seeber's 1824 paper on space lattices, and arranged an 1891 republication of Johann F. C. Hessel's 1830 work on the 32 crystal classes which had been previously overlooked.
+Rotoinversions and glide reflections were introduced by Evgraf Fedorov and Arthur Moritz Schoenflies to derive the 230 space groups. Fedorov and Schoenflies used different methods, but collaborated to reach the final list of space groups in 1891. William Barlow also derived the 230 space groups in 1894 using a method based on patterns of oriented motifs.
+Schoenflies work was more influential than Fedorov's because he published his work in German rather than Russian, and Schoenflies' notation was more convenient and became widely adopted. An English synthesis of the work of Fedorov, Schoenflies and Barlow was made available by Harold Hilton in 1903. Fedorov went on to derive the 17 plane groups in 1891 and to study space-filling polyhedra.
+The discovery of the space groups was not universally recognized as an important scientific breakthrough at the time, but after the invention of X-ray crystallography their physical significance was fully appreciated.
+
+By the beginning of the 20th century Paul Groth defined the geometric structure of a crystal as follows: "A crystal—considered as indefinitely extended—consists of n interpenetrating regular-point systems; each of which is formed from similar atoms; each of these point systems is built up from a number of interpenetrating space lattices, each of the latter being formed from similar atoms occupying parallel positions."
+
+== Crystal structure prediction ==

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+---
+title: "Geometrical crystallography before X-rays"
+chunk: 4/4
+source: "https://en.wikipedia.org/wiki/Geometrical_crystallography_before_X-rays"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:27.087973+00:00"
+instance: "kb-cron"
+---
+
+Until the use of X-rays there was no way to determine the actual crystal structure of even the simplest substances such as salt (NaCl). For example, in the 1880s, William Barlow proposed several crystal structures based on close-packing of spheres some of which were validated later by X-ray crystallography; however the available data were too scarce in the 1880s to accept his models as conclusive.
+In the period between the discovery of X-rays (1895) and X-ray diffraction (1912) Barlow and William Jackson Pope developed the principles of packing, and showed how to deduce the structures of some simple compounds. William Johnson Sollas emphasised the importance of different atomic sizes in constructing simple crystals, and correctly concluded that the sodium and chlorine atoms in salt would be of different sizes.
+
+== Research community ==
+
+Before the 20th century crystallography was not a well-established academic discipline. There were no academic positions specifically in crystallography. Workers in the field normally carried out their crystallographic research as an ancillary to other employment(s), or had independent means.  The leading workers in the field of geometrical crystallography were employed as follows:
+
+Professors
+Mathematics or science: Bergman, Bravais, Fedorov, Frankenheim, Guglielmini, Kepler, Schoenflies, Seeber, Sohncke,
+Mineralogy: Delafosse, Groth, Haüy, Hessel, Miller, Mohs, Naumann, Neumann, Weiss, Whewell
+Physicians: Cappeller, Hessel, Steno, Wollaston
+Clerics: Haüy, Steno
+Officials:
+Military officers: Bravais, Gadolin,
+Municipal officials: Hooke,
+Other employment:  Carangeot (business manager), Romé de l'Isle (cataloguer), Sohncke (meteorological service)
+Independently wealthy: Barlow, Huygens
+In the nineteenth century there were informal schools of geometrical crystallography researchers in France (Haüy, Delafosse, Bravais), Germany (Weiss, Mohs, Frankenheim, Hessel, Seeber, Naumann, Neumann, Sohncke, Groth, Schoenflies) and England (Wollaston, Whewell, Miller, Barlow).
+Until the founding of Zeitschrift für Krystallographie und Mineralogie by Paul Groth in 1877 there was no lead journal for the publication of crystallographic papers. The majority of crystallographic research was published in the journals of national scientific societies, or in mineralogical journals. The inauguration of Groth's  journal marked the emergence of crystallography as a mature science independent of geology.
+
+== See also ==
+History of crystallography before X-rays
+Chemical crystallography before X-rays
+Physical crystallography before X-rays
+Timeline of crystallography
+
+== Citations ==
+
+== Works cited ==

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+---
+title: "Geomythology"
+chunk: 1/2
+source: "https://en.wikipedia.org/wiki/Geomythology"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:51.372327+00:00"
+instance: "kb-cron"
+---
+
+Geomythology (also called “legends of the earth," "landscape mythology," “myths of observation,” “natural knowledge") is the study of oral and written traditions created
+by pre-scientific cultures to account for, often in poetic or mythological imagery, geological events and phenomena such as earthquakes, volcanoes, floods, tsunamis, land formation, fossils, and natural features of the landscape. Dorothy Vitaliano, a geologist at Indiana University, coined the term in 1968.
+
+Geomythology indicates every case in which the origin of myths and legends can be shown to contain references to geological phenomena and aspects, in a broad sense including astronomical ones (comets, eclipses, meteor impacts, etc.). As indicated by Vitaliano (1973) 'primarily, there are two kinds of geologic folklore, that in which some geologic feature or the occurrence of some geologic phenomenon has inspired a folklore explanation, and that which is the garbled explanation of some actual geologic event, usually a natural catastrophe'. 
+Oral traditions about nature are often expressed in mythological language and may contain genuine and perceptive natural knowledge based on careful observation of physical evidence over generations. In some instances, geomyths can provide valuable information about past earthquakes, tsunamis, floods, impact events, fossil discoveries, and other events.
+Geomyths include folk explanations of conspicuous geological features, and sometimes garbled or metaphorical descriptions of catastrophic geological events that were witnessed in antiquity. In the case of massive geomorphic events in the pre-human past, such as mountain formation, observations and imagination combined in mythic explanations that were handed down orally over millennia. In the case of natural catastrophes within living human memory, descriptions were handed down over generations. Both types of geomyth often include supernatural details. Because the descriptive narratives were expressed in mythological language, scientists and historians have not been aware of the real events and rational concepts embedded in geomythological stories. One type of geomyth includes tales arising from imagination or popular misconceptions, for example, beings magically transformed into stone to account for landforms. As more studies are done in geomythology, however, scientists and historians are finding accurate insights about geological processes. And datable events such as tsunamis, earthquakes, and volcanic eruptions have been found to be recorded by eyewitness accounts, some from thousands of years ago.
+Some myths transmitted real information about real events and observations, preserving geological data over millennia within non-literate cultures. A well-documented example of a datable geological event recorded in myth is the creation of Crater Lake in Oregon when Mount Mazama collapsed. Geologists’ scientific interpretation of how the volcanic cataclysm long ago resulted in Crater Lake, is echoed point for point in a local myth of its origin, told by members of the Klamath Indian tribe who saw it happen almost 8,000 years ago.
+In August 2004 the 32nd International Geological Congress held a session on "Myth and Geology", which resulted in the first peer-reviewed collection of papers on the subject (2007).
+
+== Examples ==
+
+=== Fimbulwinter ===
+The Norse mythological tale of the unending winter - the Fimbulwinter - has been posited to be an example of geomythology. Here the Fimbulwinter is seen as a Viking folk memory of a much earlier time when an eruption in Central America at Lake Ilopango caused a long winter throughout the world. The eruption spewed 87 cubic kilometres of ejecta into the atmosphere, blocking out the sunlight. Trees withered for lack of sun and crops failed. In Scandinavia, a region already low on agricultural land, many people starved to death: as many as half the population of Scandinavia died during the long winter, according to one estimate, and the effects went on for at least three years. Archaeologist Neil Price has argued that the Fimbulwinter myth is likely a folk memory of this time, although he is careful to point out that "Geomythology is by its very nature an inexact concept: inherently unproveable, prone to confirmation bias, and hampered by a lack of precise dating in both textual and archaeological sources." Price gives several examples as to why the Fimbulwinter myth is an example of geomythology. One example is from Snorri's poem the Poetic Edda:
+
+First of all that a winter will come called Fimbulwinter.
+Then snow will drift from all directions.
+There will then be great frosts and keen winds.
+The sun will do no good.
+There will be three of these winters together
+
+and no summer in between.
+"The description of this terrible distortion of the seasons," writes Price, "is remarkably similar to the cycle scientists postulate for the immediate effects of the eruptions."
+
+=== South African Horned Serpent ===
+A horned serpent cave art is known from the La Belle France cave in South Africa, often conflated with the Dingonek. It may be based on dicynodont fossils.
+
+=== American West Coast deluge ===
+According to J. G Swan (1868), the Makah American Indian people, who occupied the tip of the Olympic Peninsula in Washington State, USA, have an old story of a deluge. A long time ago, but not at a very remote period, Swan was informed, a rise of water flowed over fields and meadows, making an island of Cape Flattery. The waters receded over a four-day period, leaving Neah Bay dry. The waters then returned, and are said to have submerged the entire area, killing many and the rest escaping in canoes, and receding to its normal level in four days.
+
+=== The Lowland Hundred (Cantre'r Gwaelod) ===
+
+A mythological ancient sunken kingdom that, according to oral tradition, existed between Ramsey Island and Bardsey Island in what is now Cardigan Bay to the west of Wales. Further research revealed that this tract of land was indeed inhabited, with there being a submerged forest and evidence of ancient settlements present.
+
+== See also ==
+Landscape mythology
+Euhemerus
+
+== References ==
+
+=== Bibliography ===
+Price, Neil (2022). The Children of Ash and Elm: A History of the Vikings. London: Penguin.

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+---
+title: "Geomythology"
+chunk: 2/2
+source: "https://en.wikipedia.org/wiki/Geomythology"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:51.372327+00:00"
+instance: "kb-cron"
+---
+
+== Further reading ==
+Burbery T. (2021). Geomythology: How Common Stories Reflect Earth Events. Routledge.
+Hamacher, D.W. (2014). Geomythology and Cosmic Impacts in Australia. West Australian Geologist, No. 505, pp. 11–14.
+Hamacher, D.W. and Goldsmith, J. (2013). Aboriginal oral traditions of Australian impact craters Archived 2018-08-20 at the Wayback Machine. Journal of Astronomical History and Heritage, Vol. 16(3), pp. 295–311.
+Hamacher, D.W. and Norris, R.P., (2009). Australian Aboriginal Geomythology: eyewitness accounts of cosmic impacts? Archaeoastronomy, Vol. 22, pp. 60–93.
+Mayor, A., (2011). The First Fossil Hunters: Dinosaurs, Mammoths, and Myth in Greek and Roman Times. Princeton University Press.
+Mayor, A. (2005). Fossil Legends of the First Americans. Princeton University Press.
+Piccardi, L. (2000). Active faulting at Delphi: seismotectonic remarks and a hypothesis for the geological environment of a myth. Geology, Vol. 28 (7), pp. 651–654. doi:10.1130/0091-7613(2000)28<651:AFADGS>2.0.CO;2
+Piccardi, L. (2001). Fault-related sanctuaries. EOS Transactions, American Geophysical Union, 52 (47), U52B-03. https://www.researchgate.net/publication/234424583_Fault-Related_Sanctuaries
+Piccardi, L. (2005). Paleoseismic evidence of legendary earthquakes: the apparition of Archangel Michael at Monte Sant’Angelo (Italy). Tectonophysics, Vol. 408, pp. 113–128. doi:10.1016/j.tecto.2005.05.041
+Piccardi, L. (2005). The head of the Hydra of Lerna (Greece). Archaeopress, British Archaeological Reports, International Series, Vol. 1337/2005, pp. 179–186.
+Piccardi, L. (2007). The AD 60 Denizli Basin earthquake and the apparition of Archangel Michael at Colossae (Aegean Turkey). in Piccardi, L. and Masse, W.B. (eds) (2007). Myth and Geology. Geological Society, London, Special Publications No. 273, pp. 95–105. doi:10.1144/GSL.SP.2007.273.01.08
+Piccardi, L., Monti, C., Vaselli, O., Tassi, F., Gaki-Papanastassiou, K., Papanastassiou, D. (2008). Scent of a myth: tectonics, geochemistry and geomythology at Delphi (Greece). Journal of the Geological Society, London, Vol. 165, pp. 5–18. doi:10.1144/0016-76492007-055
+Piccardi, L. (2014). Post-glacial activity and earthquakes of the Great Glen Fault (Scotland). Memorie Descrittive della Carta Geologica d’Italia, vol. XCVI, pp. 432–446. https://www.isprambiente.gov.it/it/pubblicazioni/periodici-tecnici/memorie-descrittive-della-carta-geologica-ditalia/memdes_96_piccardi2.pdf
+Stewart, I.S., Piccardi, L. (2017). Seismic faults and sacred sanctuaries in Aegean antiquity. Proceedings of the Geologists Association, vol. 128, pp. 711–721. https://core.ac.uk/download/pdf/151192491.pdf
+Vitaliano, D. B. (1968). Geomythology. Journal of the Folklore Institute, Vol. 5, No. 1 (June 1968), p. 11.
+Vitaliano, D. B. (2007). “Geomythology: Geological Origins of Myths and Legends”. In: Myth and Geology. Piccardi, L., Masse, W. B (ed). GSL, Special Publications. 273: 1–7.

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+title: "Highlands controversy of Northwest Scotland"
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+---
+
+The Highlands controversy was a scientific controversy which started between British geologists in the middle of the nineteenth century concerning the nature of the rock strata in the Northwest Highlands of Scotland. The disagreement stemmed from the apparent ages of the strata, particularly the existence, now confirmed, of older rock above younger rock as well as duplicated and inverted strata, which could not be satisfactorily explained by contemporary geology.  This rock formation and surrounding controversy were the impetus for Albert Heim's theory of thrust faulting, which, in conjunction with anticlines and imbrication, are now commonly accepted as the primary geological mechanisms that created the Northwest Highlands rock strata.
+At the time, the debate became contentious, even acrimonious, because of some of the personalities involved and because it pitted professional geologists of the Geological Survey against academic and amateur geologists. An initial resolution was achieved by about 1886 but the great complexity and scientific importance of the discovery of the Moine Thrust Belt and the geological processes involved in its creation led to field work continuing for a further twenty years culminating in the 1907 publication by the Geological Survey of a book of fundamental geological significance: The Geological Structure of the North-West Highlands of Scotland.
+The acrimony was an important factor in the political decision to set up the Wharton Committee of 1899 to review the state-funded Geological Survey. The committee's report probably precipitated the retiral of Archibald Geikie, the Survey's director-general, who had been slow to accept the new geological paradigm. However, in retirement Geikie's status flourished as he went on to become president both of the Geological Society and the Royal Society and to receive the Order of Merit.
+The northwest highlands region of Scotland is now known to be where part of the Iapetus Ocean closed with the collision of the continents of Laurentia and Baltica about 400 million years ago. The consequent Caledonian Orogeny produced intense folding and compression of rocks – at thrust faults older rock strata slid for miles over younger rocks and, at nappes, the sequences of rock strata became inverted and duplicated at overturned anticlines.
+
+== Background ==
+
+=== Geological science in the mid nineteenth century ===
+
+From around 1830 geologists were beginning to date rocks according to the embedded fossils. The law of superposition whereby younger rocks lie above older ones was very well established and it was recognised that some layers may be missing because they had been eroded away.  Folding and faulting of strata were recognised and in 1841 Arnold Escher von der Linth discovered that sometimes older rocks lay above younger ones. However his explanation involved such large horizontal movements of rock and folding on such a massive scale that he was afraid to publish his results because his theory would seem ridiculous. It was not until after his death that his pupil Albert Heim published the findings in 1878.
+Thrust faulting, where there is a considerable horizontal movement of younger strata over older, had not yet been identified.
+Roderick Murchison's expedition to Wales in 1831 led to his identification of the Silurian period and he came to regard the Silurian geological system as being his own territory. He went on to decide that Silurian rocks extended into parts of England and southern Scotland and this caused bitter arguments with his friend Adam Sedgwick who had previously identified the rocks as Cambrian − the intervening Ordovician period was yet to be characterised. Murchison identified the Silurian on the basis of the types of fossils the rocks contained whereas earlier geologists had studied the type of rock. The strength of Murchison's views became buttressed by his knighthood in 1846 and when he was appointed director-general of the Geological Survey in 1855 he decided to turn his researches to the little-known and even less understood Northwest Highlands of Scotland expecting to extend his Silurian domain up there.
+
+=== Northwest Highlands of Scotland ===
+
+The Northwest Highlands were, and still are, remote and difficult to access. Along a coastal strip some 200 kilometres (120 mi) long and 15–25 kilometres (10–15 mi) wide the terrain is austere with isolated mountains rising above barren lower ground where knolls of  bare rock lie among lochans and peat bogs. This geological region runs from the Sleat peninsula of Skye northward through Kyle of Lochalsh, Ullapool and Assynt to Cape Wrath and Loch Eriboll.
+
+For the geologist Assynt provides some of the best formations of rock and the finest scenery. The low-lying hummocky ground to the west is of hard metamorphic rock – Lewisian gneiss, the oldest rock in Britain. Above this basement are less-disturbed sandstones, quartzite and some Durness limestone. No fossils are to be found in the sandstone; the quartzite contained "Pipe Rock" but at the time this was not recognised as containing fossils; and the fossils in the limestone could not be unambiguously dated at the time. Away to the east of the coastal strip are the strongly metamorphosed Moine rocks which in places lie above non-metamorphosed strata.
+
+For nineteenth-century geologists, this was a major puzzle because younger rocks are expected to lie above older ones and so non-metamorphosed should lie above metamorphosed – what were the ages of the rocks and why did they seem to be in the wrong order?  Why had seemingly upper and lower layers of quartzite apparently been discovered both above and below basement gneiss?
+
+== Murchison and Nicol in the Northwest Highlands ==

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+In 1827 Murchison had made a cursory survey of the area from the sea but in 1855, hearing news of the discovery of fossils in the limestone at Durness, he visited again with James Nicol, professor of geology at Aberdeen University. The fossils were thought to be Devonian and the limestone was clearly more recent than the underlying sandstone. This was a problem because the sandstone, later to be called Torridonian sandstone, was thought to be equivalent to the Old Red Sandstone on the east coast of Scotland which certainly contained Devonian fossils. Because of the conditions on the ground they were unable to conduct a thorough geological survey but Murchison considered there was an ascending series (becoming younger) of strata exposed on the surface as one moved west to east. He concluded that this exemplified the stratigraphic column of Britain. The strata must dip down from west to east, he thought, so at any particular elevation the rocks towards the east were younger than those to the west and so, he assumed, the schist and gneiss of the north of Scotland were Silurian sediments above a basement.
+
+James Nicol, professor of geology at Aberdeen University disagreed. Following a separate visit in 1856 he claimed that a geological fault ran right down along the northwest coast and that the seemingly younger rocks were in reality far older having been shifted upwards compared with those to the west. A matter that was to become especially difficult was that Murchison considered that there were two quartzite layers of different age at two stratigraphic levels whereas Nicol claimed there was one layer but vertically displaced along the fault. However both geologists had to gloss over the difficulty that the quartzite was greatly folded and in some places seemed to fold over itself.
+In 1859, following another tour of the highlands when he was accompanied by his second-in-command at the Geological Survey, Andrew Ramsay, Murchison addressed a British Association in Aberdeen where he explained what he considered was the essential simplicity of the geology of the north of Scotland. It seems his lecture was regarded as a triumph by the attendees and by The Times and the Scottish press. John Phillips spoke of the high estimation in which Murchison was held as "master of the Silurian". Nicol, meanwhile, had been preoccupied organising the geology section of the meeting – his paper hardly got a mention in the press and seems to have received little support at the meeting.
+
+== Murchison involves Geikie ==
+
+In 1860 Nicol returned to the Northwest Highlands to investigate further and Murchison, after hearing of Nicol's travels, made a quite separate journey taking along with him a junior but very ambitious member of the Survey, Archibald Geikie. Murchison confirmed in his own mind what he had already observed and Geikie, anxious to please, became a strong supporter of Murchison's views. However, in his posthumous biography of Murchison he was to say of the expedition that Murchison "stuck to his leading principle, from which no amount of contradictory detail would make him swerve".
+When Nicol announced the results of his latest investigations to the Geological Society in December 1860 he refuted Murchison's findings and rejected the presence of Silurian sediments. He considered igneous rock was to be found along a "zone of complication" from Durness to Skye and faulting was responsible for the perplexing strata. He utterly rejected Murchison's idea that metamorphic rock could lie with no unconformity (with no intervening period of erosion) over unaltered sedimentary layers. There was no evidence that the highlands were of Silurian age. Murchison was enraged and wrote to his protegé Archibald Geikie "we have a fight in which our reputation and veracity are at stake". In February 1861 he and Geikie delivered their paper to the Geological Society and this and Nicol's papers were published in the same volume of the Quarterly Journal of the Geological Society.
+
+At that time the geological community in Britain had not formed a definite opinion on these matters but Murchison's view was the one that was to prevail at least for a time. Murchison held great prestige and Geikie was a persuasive writer and speaker who was well able to place the best possible gloss on Murchison's views, sometimes by writing favourable anonymous reviews of the two geologists' own publications. For example, Geike wrote a seemingly independent review of his and Murchison's 1861 map. So, the Murchison–Geikie view became orthodox.
+Nicol and Murchison never resolved their differences and Nicol, after making little progress persuading the geological community of his theory, ceased publishing on the matter after 1866 although he continued to make geological field studies in the north of Scotland throughout his career. He died in 1879.
+Geikie was appointed director of the Scottish Geological Survey in 1867 and, in 1871, the year of Murchison's death, he was appointed to the newly created chair of Murchison professor of geology at Edinburgh University, endowed by Murchison himself. He continued to promulgate Murchison's Silurian theories and carried the professional geological establishment with him.
+
+== Rising dissent in the 1880s ==

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+title: "Highlands controversy of Northwest Scotland"
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+
+At this time the Geological Society's members were academic geologists and amateurs, some of them becoming very knowledgeable and well respected. There were often differences of approach and opinion between, on the one hand, members of the Society and, on the other, senior spokesmen and managers of the "professionals" employed in the Geological Survey who carried out most of the actual fieldwork. The Survey's directors considered themselves better informed than amateurs and academics (who they regarded also as amateurs). From around 1878 papers by members of the Society started to appear, sometimes supporting Nicol and at other times just drawing attention to the inconsistencies in both contemporary theories and the incompatibility of the various field observations.
+Murchison retired as director-general in 1867 to be succeeded by Andrew Ramsay. In 1880 an anonymous letter to The Times was highly critical of the state-funded Survey remarking that it had been set up to be, and should be, a temporary organisation, that it was prolonging its own existence and that the surveyors, rather than being peripatetic, were settling down in particular regions, hence exacerbating the problem. The matter was debated in both Commons and Lords leading to inquiries by the Science and Art Department. Ramsay, by now in poor health, was not well able to defend his organisation – he had suggested it would take 22 years to complete the Scottish survey. This led to his retirement in 1882 and a reduction in the staff and scope of the Survey's work.
+Geikie made further field trips in 1880 and 1881 and, although he noted several, or many, anomalies, he stuck with the Murchison paradigm of Silurian simplicity. In 1882 Wilfred Hudleston wrote of a ubiquitous but unidentified type of rock, which was then being called "Logan rock" and is now known to be Lewisian gneiss, saying "this monster will, in most places, have to be dealt with on the basis of a fold over of some of the lower beds". From about 1880 the first Ordnance Survey maps of northwest Scotland started to be published and these eased the work of the geologists. A few six-inch-maps came first, followed shortly by a one-inch series with contour lines.
+
+In 1881 an amateur geologist Charles Callaway surveyed in detail the Durness and Inchnadamph regions and presented a paper to the Geological Society saying the overlying gneiss could not have been formed more recently than the unmetamorphosed limestone below it. His paper generated considerable interest but little agreement except to say that the geological structure of the region was not currently understood. Not deterred by a Geological Survey letter to Nature assuring that Murchison's interpretation would "never be invalidated", the following year Callaway ventured north again equipping him in 1883 to write, according to Oldroyd, "one of the most important documents pertaining to the Highlands controversy". Indeed, in 1882 there was almost a score of geologists busy in the Highlands, knowing something was there to be discovered but not knowing what it was.
+Callaway now proposed a particular stratigraphic sequence of rocks (in order of the time they were originally deposited) and compared this with the sequence of strata he observed in vertical sections taken along lines at different locations and in different directions. He found that he could generally work out that some sequences were the right way up and that others were inverted. Where a particular type of rock had seemed to be at more than one position in the stratigraphic column it now appeared it was one layer folded over on itself. For Loch Eriboll Callaway claimed that over-hastiness had led earlier geologists to misread the geological situation. Only Nicol had seen the real structure and, Callaway said, he was pleased "however humbly, to vindicate his reputation". At the meeting where Callaway presented his paper it was well received and no one from the Geological Survey rose to make any objections.
+Underlying the debate about geological thrusts and faults at this time was a developing world view of the earth's geology. It was theorised that, because the earth was cooling, it was shrinking and, therefore, wrinkling and this was the cause of mountain building. Faults formed at areas of weakness as the land collapsed into the shrinking interior. In particular, faults developed beside the rigid Lewisian gneiss at the coastal region of northwest Scotland.
+
+== Lapworth's discoveries ==
+
+=== Southern Uplands ===

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+title: "Highlands controversy of Northwest Scotland"
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+
+From about 1869, Charles Lapworth, then a schoolteacher, had been quietly surveying the geology of the Southern Uplands of Scotland as a hobby. There are few fossils except in some dark shale bands which are packed with the fossils of graptolites. Previously geologists, if they considered graptolites at all, had considered them as an unreliable indicator of age whereas Lapworth identified different species at different levels. Because these free-floating creatures had turned to fossils in sedimentation on the sea bed this gave a good indication of the era in which each species had lived and died, regardless of the prior geological stratification of the ground on which they were deposited. Between about 1872 and 1877 Lapworth studied the locality known as Dob's Linn where an anticline makes it likely the five layers of dark shale have not been inverted in the immediate vicinity so, knowing the order of ages of rock, he could work out the order of ages of the different species.
+By applying this knowledge over the Southern Uplands as a whole he could tell that, after the fossils had been laid down, the land had often been severely folded sometimes to the extent of being overturned with a single geological layer being duplicated. This showed that the Geological Survey's maps of the area were in error in showing the rock to be Silurian and so the Survey was forced to map the area all over again using Lapworth's detailed techniques. In 1872 Lapworth had been elected as a fellow of the Geological Society – he went on to become a world authority on graptolites and was appointed professor of geology and metallurgy in 1881.
+
+=== Northwest Highlands ===
+The Silurian theory received another setback when Lapworth examined the Northwest Highlands in 1882 and 1883. In 1882 Lapworth had made an inch by inch inspection and discovered that the "upper" and "lower" quartz layers were in reality part of a single layer folded over on itself and by the following year he was able to demonstrate this convincingly to colleagues. At Durness and Eriboll where the layers of rock were most pronounced he could not find fossils sufficiently indicative for his purposes so he had to turn to lithostratigraphy rather than continue with the biostratigraphy he had used so successfully in the Southern Highlands. Detailed examination of the lithological characteristics enabled him to build up a finely divided geological sequence and place it in the correct stratigraphical order. At Eriboll he recognised that it was foliation that could be observed, not sedimentary bedding planes, and the foliation was the result of large lateral forces from the southeast forcing older rocks to slide over younger ones.
+What Murchison had identified as bedding planes – adjacent layers of different types and ages of rock – were actually thrust planes – dislocations in a layer caused by sideways thrusting having occurred. 
+
+"For many years the Highland controversy has appeared to outsiders, and to those geologists who were unaware of the difficulties attending the stratigraphy of the older rocks, as a trivial dispute between the Geological Survey on the one hand and a few misguided amateurs on the other."
+
+== Peach and Horne ==
+
+Geikie, who had been appointed director-general of the Geological Survey in 1882, arranged for his colleagues Ben Peach and John Horne to make a detailed survey of the Northwest Highlands starting in 1883 with the intention of confirming Murchison's hypothesis. After only one season they were able to report that Lapworth had again been correct at least in the northern Durness-Eriboll region although Geikie still saw the evidence as favouring Murchison. However, by the following year, after a more southerly survey, Geikie became convinced when he was shown Torridonian sandstone metamorphosed to schist and he wrote in support of the new theory in his preface to Peach and Horne's 1884 report where he made first use of the term "thrust plane".
+There had been no great differences of opinion between the officers of the Geological Survey out in the field and the amateur and academic geologists likewise engaged. Rather it was the successive directors of the Survey, Murchison, Ramsay and Geikie, who had been unwilling to accept that the official position was unsatisfactory. By 1884, with the stratigraphy less contentious, Geikie extended the remit of the survey to include the petrology of the metamorphic rocks – what they had been made from in the first place. Recognising that his organisation was not strong in petrology or petrography compared with the work elsewhere in Europe, particularly Germany, in 1884 Geikie started approaching Jethro Teall to join the Survey and at last persuaded him in 1888, the year Teall's book British Petrography was published. By the time of  Peach and Horne's 1888 paper they were able to extend their analysis of the complex stratigraphy to many more locations along the fault and by 1891 all ideas of Silurian rocks in northwest Scotland had been abandoned. So, confirming Lapworth's view, what Murchison had considered to be Silurian was now identified on the basis of the Durness fossils to be Cambrian and the Torridonian sandstone was placed in the later stages of the Precambrian. A series of geological maps was produced in this period at scales of one inch and six inches to the mile.

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+title: "Highlands controversy of Northwest Scotland"
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+tags: "science, encyclopedia"
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+---
+
+== Wharton Committee ==
+In a series of articles on "scientific worthies", in December 1892 Nature published an adulatory article about Geikie, written by his close friend and eminent French geologist Albert Auguste de Lapparent. Dealing with the Highlands Controversy, it said that Murchison's theory had never "quite satisfied" Geikie who, for his "love of truth", had delegated to Peach and Horne the task of making a new survey of the region without any preconceptions. No mention was made of any involvement by geologists outside the Geological Survey. Soon after this an editorial article appeared in the Daily Chronicle condemning the state-funded system in England that allowed eminent establishment scientists to "blunder with impunity". The article continued that Murchison's "absurd theory" had been strongly supported by Geikie who had then instituted a second survey of the whole region, both carried out at the taxpayers' expense. Letter writing extended onto The Times and broadened  to discuss the whole British scientific establishment, particularly the Royal Society, with suggestions of corruption.
+Geologists regarded the work in northwest Scotland as being of considerable scientific importance but the Scottish work (which held little commercial significance) lagged far behind that in England, Wales and Ireland. Politicians, under pressure from both commercial and tax-saving lobbies, started questioning the work of the Geological Survey and there was a proposal to transfer it from the Department of Science and Art to the Ordnance Survey. In 1900 a committee under John Wharton started to inquire into these matters. The committee found in favour of the Survey's continuance, recommended improved staff pay and working conditions, and a transfer to the Board of Education. There was no explicit criticism of Geikie but the committee's report was likely to have led to his retirement the next year. Horne was interviewed by the committee and was promoted to become deputy director to Teall, taking responsibility for Scotland. Peach wrote an extremely generous letter on the occasion of Geikie's retirement which Geikie published in his 1924 autobiography.
+
+== Geological Structure of the North-West Highlands of Scotland ==
+
+Peach and Horne continued their work and published The Geological Structure of the North-West Highlands of Scotland in 1907 with Geikie, in his retirement, making the final editing. Their research was into one of the most geologically complex regions of Britain, and they introduced the term "Moine Thrust". In his preface to the memoir, Geikie refers the area of the Moine Thrust as being a place to study "some of the more stupendous kinds of movement by which the crust of the earth has been affected".
+The introduction to the memoir, written by Horne, provides an accessible description of geological structure that had been uncovered. Horne describes four groups of rocks, dealing with them from oldest to youngest, west to east. First, along the west coast, the Lewisian complex of gneiss stretches from Cape Wrath to Loch Torridon and then out to the Hebridean islands South Rona and Raasay. The topology is low, rounded and hollowed, only occasionally forming peaks such as at Ben Stack. The rock is ancient and highly metamorphosed of igneous and occasionally sedimentary origin, with many igneous dykes and sills intruding. Before this was overlaid by Torridonian sandstone it was subject to immense stress towards west-northwest deforming the intrusions and the heat generated produced further metamorphosis. There was then a long period of erosion of what was then a land surface before the much later Torridonian sandstone sedimentation.
+Secondly. the overlying Torridonian sandstones show gently inclined sedimentary strata with minor faults and joints that have eroded away to form the buttresses of high mountains. No definite fossils could be found. After a long period of marine erosion, the rock that was laid down on top, white over dark red, could be dated as Cambrian, indicating that the Torridonian sandstone was Precambrian. Where later earth movements thrust into and over the sandstone it became metamorphosed into schist.
+
+Thirdly is a series of marine sedimentary layers – quartzite, dolomite and limestone – within which was discovered Cambrian age trace trilobite fossils. Peach and Horne remarked that the fauna are "identical" to those in the corresponding geological strata in North America. Occasionally the sedimentary rock rests on the basement gneiss when the Torridonian sandstone had been completely eroded away, such as just south of Loch Assynt. These layers are separated from the underlying sandstone by an unconformity during which time interval the sandstone was folded and greatly eroded away, sometimes completely. The Cambrian sediment became intersected with sills and dykes, particularly near Inchnadamph.
+Fourthly, and what became the most interesting feature for the geologists, was the immense horizontal movement of rock over all these layers that occurred subsequently towards the west-northwest. The underlying rock became broken up into slices that became piled up (imbricated) between thrust planes that also became folded. Basement Lewisian gneiss could be thrust up to the surface and rock strata could be shifted around to the extent that they could become inverted in their sequence – for example gneiss could overlay limestone. The main thrust, the Moine Thrust, moved schist from the east towards and over the pre-existing rock on the west while the effect of shearing at the thrust itself was to metamorphose the material at the interface into a mylonite structure. In "pipe rock" the deformation had the effect of bending over fossilised vertical worm casts so they become flattened horizontally. At one time this material extended much further to the west but it, and the underlying rocks, have been eroded, so exposing the underlying rocks and their geological history.

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+title: "Highlands controversy of Northwest Scotland"
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+
+The work has been described as "one of the most notable geological memoirs ever published in the English language". According to Butler, the memoir has provided a "startling synthesis" describing, for the first time, the folds within imbricate slices and thrust sheets and the thrusts that delimit them. So definitive was the work that it was not until 1980 that the structural evolution of the region again started being reinvestigated including with deep seismic profiling techniques. Imbricate faulting was proposed to explain the asymmetrical pattern of the stratigraphy that could not be explained by folding. The 1907 memoir and its accompanying 1-inch (1:63360) geological maps have been inspiring to geologists and have given what was arguably the start of thrust belt research worldwide and showed the importance of field mapping for tectonic research.
+
+== Afterwards ==
+
+The region of the Moine Thrust is now known to be where part of the Iapetus Ocean closed with the collision of the continents of Laurentia and Baltica about 400 million years ago. The consequent Caledonian Orogeny produced intense folding and rocks of what is now called the Moine Supergroup were thrust a distance of some 100 km (60 miles) over the strata at the northwest coast. There is a particularly good exposure of the strata at Knockan Crag, now the site of the Knockan Crag National Nature Reserve, within the North West Highlands Geopark.
+
+On the centenary of the publication of The Geological Structure, the Geological Society published an article by Rob Butler discussing the book's continuing significance. Butler says the memoir was considered to be "an instant classic" and a "masterpiece of regional geoscience" leading to generations of geology students visiting the area, now marked by a memorial, to learn about "the golden years of NW Highland geology". Much of the discussion of the geology of the Lewisian complex in the memoir is now taken for granted and it correctly identified the deformation of the intruding dykes and sills and the association between deformation and metamorphism.
+As well as the 1930 memorial at Inchnadamph, a statue of the two geologists was erected at Knockan Crag in 2001.
+
+== See also ==
+The Great Devonian Controversy
+
+== Notes ==
+
+== References ==
+
+=== Citations ===

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+title: "Highlands controversy of Northwest Scotland"
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+---
+
+=== Works cited ===
+Anon (Geikie) (1861). "Art VI: Recent Discoveries in Scottish Geology". The North British Review. 35: 125–156.
+Butler, Rob (2007). "Peach and Horne - the memoir at 100". Geoscientist. 17 (1). The Geological Society of London.
+Callaway, Charles (1883). "The Age of the Newer Gneissic Rocks of the Northern Highlands". The Quarterly Journal of the Geological Society of London. 39 (1–4): 355–422. doi:10.1144/GSL.JGS.1883.039.01-04.24. S2CID 140678182.
+with a brief preemptive paper: Callaway, Charles. (1883). "The Highland Problem". Geological Magazine. 10 (3): 139–140. Bibcode:1883GeoM...10..139C. doi:10.1017/S0016756800164362. ISSN 1469-5081. S2CID 129021620.
+Dalziel, Ian W. D. (2010). "The North-West Highlands memoir: a century-old legacy for understanding Earth before Pangaea". Geological Society, London, Special Publications. 335 (1): 189–205. Bibcode:2010GSLSP.335..189D. doi:10.1144/sp335.9. S2CID 129235161.
+Dryburgh, P.M.; Ross, S.M.; Thompson, C.L. (2014). Assynt: the Geologists' Mecca. Edinburgh Geological Society. ISBN 9780904440140.
+Geikie, Archibald (1875). Life of Sir Roderick I. Murchison, bart.; K.C.B., F.R.S.; sometime director-general of the Geological survey of the United Kingdom. Based on his journals and letters; with notices of his scientific contemporaries and a sketch of the rise and growth of palaeozoic geology in Britain. Vol. II. London: John Murray.
+Geikie, Archibald (November 1884). "The Crystalline Rocks of the Scottish Highlands". Nature. 31 (785): 29–31. Bibcode:1884Natur..31...29G. doi:10.1038/031029d0. S2CID 4134079. It would require more space than can be given in these pages to do justice to the views of those geologists, from Nicol downwards, by whom Murchison's sections have been criticised, and to show how far the conclusions to which the Geological Survey has been led, have been anticipated.
+Geikie, Archibald (January 1893). "The Geology of the North-west Highlands". Nature. 47 (1213): 292–293. Bibcode:1893Natur..47..292G. doi:10.1038/047292c0. ISSN 1476-4687. S2CID 3971276.
+Geikie, Archibald (1903). The Text Book Of Geology Volume I. London: Macmillan.
+Gillen, Con (2003). "The Highlands Controversy". Geology and landscapes of Scotland. Harpenden: Terra Publishing. ISBN 1-903544-09-2.
+de Lapparent, A. (January 1893). "Scientific Worthies". Nature. 47 (1210): 217–220. Bibcode:1893Natur..47..217D. doi:10.1038/047217a0. S2CID 186242888.
+Hamilton, Beryl M. (1991). "'A Geological Blunder', 1893: A Scientific Storm in a Journalistic Teacup". Notes and Records of the Royal Society of London. 45 (1): 63–77. doi:10.1098/rsnr.1991.0003. ISSN 0035-9149. JSTOR 531521. S2CID 143857779.
+Johnstone, G. S.; Mykura, W. (1989). British Regional Geology: the Northern Highlands (4th ed.). Her Majesty's Stationery Office. ISBN 0-11-884460-1.
+Lapworth, Charles (1885a). "On the Close of the Highland Controversy". Geological Magazine. 2 (3): 97–106. Bibcode:1885GeoM....2...97L. doi:10.1017/S0016756800005458. S2CID 131045660.
+Lapworth, Charles (1885b). "The Highland Controversy in British Geology : its Causes, Course, and Consequences". Report of the Fifty-fifth Meeting of the British Association for the Advancement if Science: Held at Aberdeen in September 1885: 1025–1027.
+Law, R. D.; Butler, R. W. H.; Holdsworth, R. E.; Krabbendam, M.; Strachan, R. A. (2010). "Continental tectonics and mountain building. The legacy of Peach and Horne: an introduction". Geological Society, London, Special Publications. 335 (1): 1–5. Bibcode:2010GSLSP.335....1L. doi:10.1144/SP335.1. S2CID 128967800.
+Murchison, Roderick; Geikie, Archibald (1861). "On the Altered Rocks of the Western Islands of Scotland, and the North-western and Central Highlands". The Quarterly Journal of the Geological Society of London. 17 (1–2): 171–240. doi:10.1144/GSL.JGS.1861.017.01-02.21. S2CID 140142272. (alternative source at Internet Archive)
+Murchison, Roderick Impey; Geikie, Archibald; Johnston, Alexander Keith (1865). New Geological Map of Scotland. Edinburgh: W. & A.K. Johnston: Blackwood & Sons.
+Nicol, James (1861). "On the Structure of the North-western Highlands, and the Relation of the Gneiss, Red Sandstone, and Quartzite of Sutherland and Ross-shire". The Quarterly Journal of the Geological Society of London. 17 (1–2): 85–113. doi:10.1144/GSL.JGS.1861.017.01-02.11. S2CID 140663553. (alternative source at Internet Archive)
+Oldroyd, David R. (1990). The Highlands Controversy : Constructing Geological Knowledge through Fieldwork in Nineteenth-Century Britain. Chicago and London: the University of Chicago press. ISBN 0-226-62635-0. Oldroyd made some updates to his account at Oldroyd (1996)
+Oldroyd, David (1996). "Sir Archibald Geikie (1835–1924) and the "Highlands Controversy": New archival sources for the History of British Geology in the Nineteenth Century". Earth Sciences History. 15 (2): 141–150. doi:10.17704/eshi.15.2.k64075116m370702. ISSN 0736-623X. JSTOR 24138467.
+Oldroyd, D.R.; Hamilton, B.M. (2002). "2. Themes in the early history of Scottish geology". In Trewin, N.H. (ed.). The Geology of Scotland. Geological Society of London. pp. 22–44. ISBN 978-1-86239-126-0.
+Page, David; Lapworth, Charles (1883). Advanced Text-book of Physical Geography. William Blackwood & Sons. p. 39.
+Peach, B. N.; Horne, John (13 November 1884). "Report on the Geology of the North-West of Sutherland" (PDF). Nature. 31 (785): 31–35. Bibcode:1884Natur..31...31P. doi:10.1038/031031a0. S2CID 4142467.
+Peach, B. N.; Horne, J.; Gunn, W.; Clough, C. T.; Hinxman, L.; Cadell, H. M. (1 January 1888). "Report on the Recent Work of the Geological Survey in the North-west Highlands of Scotland, based on the Field–notes and Maps: (Read April 25, 1888.)". Quarterly Journal of the Geological Society. 44 (1–4): 378–441. doi:10.1144/GSL.JGS.1888.044.01-04.34. S2CID 129572998.
+Peach, B. N.; Horne, J. (1 January 1892). "The Olenellus Zone in the North-west Highlands of Scotland". Quarterly Journal of the Geological Society. 48 (1–4): 227–242. doi:10.1144/gsl.jgs.1892.048.01-04.17. S2CID 140197589.
+Peach, Benjamin; Horne, John; Gunn, William; Clough, Charles; Hinxman, Lionel; Teall, Jethro (1907). Geikie, Archibald (ed.). The Geological Structure of the North-west Highlands of Scotland. H.M. Stationery Office. (alternative source at Internet Archive).
+Peach, B.N.; Horne, J.; Clough, C.T.; Hinxman, L.W.; Cadell, H.M.; Dinham, C.H. (1923). "BGS Assynt Special Sheet". www.largeimages.bgs.ac.uk. British Geological Survey, copyright NERC.. This map is linked to from Gateway to the Earth. "Record details Assynt district". www.bgs.ac.uk. British Geological Survey. Retrieved 5 November 2017.
+Ross, S (1991). "The Geology of Sutherland". In Omand, Donald (ed.). The Sutherland Book. Golspie: Northern Times. ISBN 1-873610-00-9.
+Strachan, R. A.; Holdsworth, R. E.; Krabbendam, M.; Alsop, G. I. (2010). "The Moine Supergroup of NW Scotland: insights into the analysis of polyorogenic supracrustal sequences". Geological Society, London, Special Publications. 335 (1): 233–254. Bibcode:2010GSLSP.335..233S. doi:10.1144/SP335.11. S2CID 129225043.
+Suess, Eduard (1909). "Part V, The Face of the Earth (continued)". The Face Of The Earth Vol. 4. Translated by Sollas, Hertha B.C.; Sollas, Hertha W.J. p. 529.
+Teall, J. J. H. (1888). British petrography: with special reference to the igneous rocks. London: Dulau.
+White, S. H. (2010). "Mylonites: lessons from Eriboll". Geological Society, London, Special Publications. 335 (1): 505–542. Bibcode:2010GSLSP.335..505W. doi:10.1144/sp335.22. hdl:1874/252920. S2CID 140564848.
+
+=== Further reading ===
+Bentley, Callan (19 April 2017). "Travels in Geology: Geo-diversity and geologic history in the North West Highlands of Scotland". Earth. American Geosciences Institute.
+Butler, Robert W. H. (2010). "The Geological Structure of the North-West Highlands of Scotland – revisited: Peach et al. 100 years on". Geological Society, London, Special Publications. 335 (1): 7–27. Bibcode:2010GSLSP.335....7B. doi:10.1144/SP335.2. S2CID 129335860.
+Murchison, Roderick Impey (1854). Siluria : a history of the oldest rocks containing organic remains (1 ed.). London: John Murray.
+"The Highlands Controversy". North West Highlands Geopark. Retrieved 13 March 2022. and subsequent linked pages

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+title: "History of climate change science"
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+
+The history of the scientific discovery of climate change began in the early 19th century when ice ages and other natural changes in paleoclimate were first suspected and the natural greenhouse effect was first identified. In the late 19th century, scientists first argued that human emissions of greenhouse gases could change Earth's energy balance and climate. The existence of the greenhouse effect, while not named as such, was proposed as early as 1824 by Joseph Fourier. The argument and the evidence were further strengthened by Claude Pouillet in 1827 and 1838. In 1856 Eunice Newton Foote demonstrated that the warming effect of the sun is greater for air with water vapour than for dry air, and the effect is even greater with carbon dioxide. 
+John Tyndall was the first to measure the infrared absorption and emission of various gases and vapors. From 1859 onwards, he showed that the effect was due to a very small proportion of the atmosphere, with the main gases having no effect, and was largely due to water vapor, though small percentages of hydrocarbons and carbon dioxide had a significant effect. The effect was more fully quantified by Svante Arrhenius in 1896, who made the first quantitative prediction of global warming due to a hypothetical doubling of atmospheric carbon dioxide. 
+In the 1960s, the evidence for the warming effect of carbon dioxide gas became increasingly convincing. Scientists also discovered that human activities that generated atmospheric aerosols (e.g., "air pollution") could have cooling effects as well (later referred to as global dimming). Other theories for the causes of global warming were also proposed, involving forces from volcanism to solar variation. During the 1970s, scientific understanding of global warming greatly increased.
+By the 1990s, as the result of improving the accuracy of computer models and observational work confirming the Milankovitch theory of the ice ages, a consensus position formed. It became clear that greenhouse gases were deeply involved in most climate changes and human-caused emissions were bringing discernible global warming. 
+Since the 1990s, scientific research on climate change has included multiple disciplines and has expanded. Research has expanded the understanding of causal relations, links with historic data, and abilities to measure and model climate change. Research during this period has been summarized in the Assessment Reports by the Intergovernmental Panel on Climate Change starting in 1990. Extreme event attribution (EEA), also known as attribution science and developed in the early decades of the 21st century, uses climate models to identify and quantify the role that human-caused climate change plays in the frequency, intensity, duration, and impacts of specific individual extreme weather events.
+
+== Prior to the 20th century ==
+
+=== Regional changes, antiquity through 19th century ===
+
+From ancient times, people suspected that the climate of a region could change over the course of centuries. For example, Theophrastus, a pupil of Ancient Greek philosopher Aristotle in the 4th century BC, told how the draining of marshes had made a particular locality more susceptible to freezing, and speculated that lands became warmer when the clearing of forests exposed them to sunlight. In the 1st century BC, Roman writer and architect Vitruvius wrote about climate in relation to housing architecture and how to choose locations for cities. Renaissance European and later scholars saw that deforestation, irrigation, and grazing had altered the lands around the Mediterranean since ancient times; they thought it plausible that these human interventions had affected the local weather. In his book published in 1088, Northern Song dynasty Chinese scholar and statesman Shen Kuo promoted the theory of gradual climate change over centuries of time once ancient petrified bamboos were found to be preserved underground in the dry climate zone and arid northern region of Yanzhou, now modern day Yan'an, Shaanxi, far from the warmer, wetter climate areas of China where bamboos typically grow.
+The 18th and 19th-century conversion of Eastern North America from forest to croplands brought obvious change within a human lifetime. From the early 19th century, many believed the transformation was altering the region's climate—probably for the better.  When farmers in America, dubbed "sodbusters", took over the Great Plains, they held that "rain follows the plow". Other experts disagreed, and some argued that deforestation caused rapid rainwater run-off and flooding, and could even result in reduced rainfall. European academics, suggesting that the temperate zones inhabited by the "Caucasian race" were naturally superior for the spread of civilization, proffered that the Orientals of the Ancient Near East had heedlessly converted their once lush lands into impoverished deserts.
+Meanwhile, national weather agencies had begun to compile masses of reliable observations of temperature, rainfall, and the like. When these figures were analyzed, they showed many rises and dips, but no steady long-term change. By the end of the 19th century, scientific opinion had turned decisively against any belief in a human influence on climate. And whatever the regional effects, few imagined that humans could affect the climate of the planet as a whole.
+
+=== Paleo-climate change and theories of its causes, 19th century ===

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+title: "History of climate change science"
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+
+From the mid-17th century, naturalists attempted to reconcile mechanical philosophy with theology, initially within a biblical timescale. By the late 18th century, there was increasing acceptance of prehistoric epochs. Geologists found evidence of a succession of geological ages with climate changes. There were various competing theories about these changes; Buffon proposed that the Earth had begun as an incandescent globe and was very gradually cooling. James Hutton, whose ideas of cyclic change over huge periods were later dubbed uniformitarianism, was among those who found signs of past glacial activity in places too warm for glaciers in modern times.
+In 1815 Jean-Pierre Perraudin described for the first time how glaciers might be responsible for the giant boulders seen in alpine valleys. As he hiked in the Val de Bagnes, he noticed giant granite rocks that were scattered around the narrow valley. He knew that it would take an exceptional force to move such large rocks. He also noticed how glaciers left stripes on the land and concluded that it was the ice that had carried the boulders down into the valleys.
+His idea was initially met with disbelief. Jean de Charpentier wrote, "I found his hypothesis so extraordinary and even so extravagant that I considered it as not worth examining or even considering." Despite Charpentier's initial rejection, Perraudin eventually convinced Ignaz Venetz that it might be worth studying. Venetz convinced Charpentier, who in turn convinced the influential scientist Louis Agassiz that the glacial theory had merit.
+Agassiz developed a theory of what he termed "Ice age"—when glaciers covered Europe and much of North America. In 1837 Agassiz was the first to scientifically propose that the Earth had been subject to a past ice age. William Buckland had been a leading proponent in Britain of flood geology, later dubbed catastrophism, which accounted for erratic boulders and other "diluvium" as relics of the Biblical flood. This was strongly opposed by Charles Lyell's version of Hutton's uniformitarianism and was gradually abandoned by Buckland and other catastrophist geologists. A field trip to the Alps with Agassiz in October 1838 convinced Buckland that features in Britain had been caused by glaciation, and both he and Lyell strongly supported the ice age theory which became widely accepted by the 1870s.
+
+Before the concept of ice ages was proposed, Joseph Fourier in 1824 reasoned based on physics that Earth's atmosphere kept the planet warmer than would be the case in a vacuum.  Fourier recognized that the atmosphere transmitted visible light waves efficiently to the earth's surface. The earth then absorbed visible light and emitted infrared radiation in response, but the atmosphere did not transmit infrared efficiently, which therefore increased surface temperatures.  He also suspected that human activities could influence the radiation balance and Earth's climate, although he focused primarily on land-use changes.  In an 1827 paper, Fourier stated,The establishment and progress of human societies, the action of natural forces, can notably change, and in vast regions, the state of the surface, the distribution of water and the great movements of the air. Such effects are able to make to vary, in the course of many centuries, the average degree of heat; because the analytic expressions contain coefficients relating to the state of the surface and which greatly influence the temperature.Fourier's work built on previous discoveries: in 1681 Edme Mariotte noted that glass, though transparent to sunlight, obstructs radiant heat. Around 1774 Horace Bénédict de Saussure showed that non-luminous warm objects emit infrared heat, and used a glass-topped insulated box to trap and measure heat from sunlight.
+The physicist Claude Pouillet proposed in 1838 that water vapor and carbon dioxide might trap infrared and warm the atmosphere, but there was still no experimental evidence of these gases absorbing heat from thermal radiation.

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+
+The role of solar activity in climate change has also been calculated over longer time periods using "proxy" datasets, such as tree rings. Models indicate that solar and volcanic forcings can explain periods of relative warmth and cold between AD 1000 and 1900, but human-induced forcings are needed to reproduce the late-20th century warming.
+Another line of evidence against the sun having caused recent climate change comes from looking at how temperatures at different levels in the Earth's atmosphere have changed.
+The US Environmental Protection Agency (US EPA, 2009) responded to public comments on climate change attribution. A number of commenters had argued that recent climate change could be attributed to changes in solar irradiance. According to the US EPA (2009), this attribution was not supported by the bulk of the scientific literature. Citing the work of the IPCC (2007), the US EPA pointed to the low contribution of solar irradiance to radiative forcing since the start of the Industrial Revolution in 1750. Over this time period (1750 to 2005), the estimated contribution of solar irradiance to radiative forcing was 5% the value of the combined radiative forcing due to increases in the atmospheric concentrations of carbon dioxide, methane and nitrous oxide (see graph opposite).
+The role of the Sun in recent climate change has been looked at by climate scientists. Since 1978, output from the Sun has been measured by satellites significantly more accurately than was previously possible from the surface. These measurements indicate that the Sun's total solar irradiance has not increased since 1978, so the warming during the past 30 years cannot be directly attributed to an increase in total solar energy reaching the Earth (see graph above, left). In the three decades since 1978, the combination of solar and volcanic activity probably had a slight cooling influence on the climate.
+Climate models have been used to examine the role of the Sun in recent climate change. Models are unable to reproduce the rapid warming observed in recent decades when they only take into account variations in total solar irradiance and volcanic activity. Models are, however, able to simulate the observed 20th century changes in temperature when they include all of the most important external forcings, including human influences and natural forcings. As has already been stated, Hegerl et al. (2007) concluded that greenhouse gas forcing had "very likely" caused most of the observed global warming since the mid-20th century. In making this conclusion, Hegerl et al. (2007) allowed for the possibility that climate models had been underestimated the effect of solar forcing.
+Models and observations (see figure above, middle) show that greenhouse gas results in warming of the lower atmosphere at the surface (called the troposphere) but cooling of the upper atmosphere (called the stratosphere). Depletion of the ozone layer by chemical refrigerants has also resulted in a cooling effect in the stratosphere. If the Sun was responsible for observed warming, warming of the troposphere at the surface and warming at the top of the stratosphere would be expected as increase solar activity would replenish ozone and oxides of nitrogen. The stratosphere has a reverse temperature gradient than the troposphere so as the temperature of the troposphere cools with altitude, the stratosphere rises with altitude. Hadley cells are the mechanism by which equatorial generated ozone in the tropics (highest area of UV irradiance in the stratosphere) is moved poleward. Global climate models suggest that climate change may widen the Hadley cells and push the jetstream northward thereby expanding the tropics region and resulting in warmer, dryer conditions in those areas overall.
+
+==== Comparison with other planets ====
+Some have argued that the Sun is responsible for recently observed climate change. Warming on Mars was quoted as evidence that global warming on Earth was being caused by changes in the Sun. This has been discredited by scientists: "Wobbles in the orbit of Mars are the main cause of its climate change in the current era" (see also orbital forcing). Also, there are alternative explanations of why warming had occurred on Triton, Pluto, Jupiter and Mars.
+
+=== Effect of cosmic rays ===
+The view that cosmic rays could provide the mechanism by which changes in solar activity affect climate is not supported by the literature. Solomon et al. (2007) state:[..] the cosmic ray time series does not appear to correspond to global total cloud cover after 1991 or to global low-level cloud cover after 1994. Together with the lack of a proven physical mechanism and the plausibility of other causal factors affecting changes in cloud cover, this makes the association between galactic cosmic ray-induced changes in aerosol and cloud formation controversialStudies in 2007 and 2008 found no relation between warming in recent decades and cosmic rays. Pierce and Adams (2009) used a model to simulate the effect of cosmic rays on cloud properties. They concluded that the hypothesized effect of cosmic rays was too small to explain recent climate change. The authors of that study noted that their findings did not rule out a possible connection between cosmic rays and climate change, and recommended further research.
+Erlykin et al. (2009) found that the evidence showed that connections between solar variation and climate were more likely to be mediated by direct variation of insolation rather than cosmic rays, and concluded: "Hence within our assumptions, the effect of varying solar activity, either by direct solar irradiance or by varying cosmic ray rates, must be less than 0.07 °C since 1956, i.e. less than 14% of the observed global warming." Carslaw (2009) and Pittock (2009) reviewed the recent and historical literature in this field and continue to find that the link between cosmic rays and climate is tenuous, though they encourage continued research.
+Henrik Svensmark has suggested that the magnetic activity of the sun deflects cosmic rays, and that this may influence the generation of cloud condensation nuclei, and thereby have an effect on the climate.
+
+== Past estimates of greenhouse gas emissions and temperature rises ==

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+title: "History of climate change science"
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+category: "reference"
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+---
+
+=== Previous estimates for the year 2020 ===
+In 2011, the United Nations Environment Programme looked at how world emissions might develop out to the year 2020 depending on different policy decisions. They convened 55 scientists and experts from 28 scientific groups across 15 countries. Projections, assuming no new efforts to reduce emissions or based on the "business-as-usual" hypothetical trend, suggested global emissions in 2020 of 56 gigatonnes CO2-equivalent (GtCO2-eq), with a range of 55–59 GtCO2-eq. In adopting a different baseline where the pledges to the Copenhagen Accord were met in their most ambitious form, the projected global emission by 2020 will still reach the 50 gigatonnes CO2. Continuing with the current trend, particularly in the case of low-ambition form, there is an expectation of 3° Celsius temperature increase by the end of the century, which is estimated to bring severe environmental, economic, and social consequences.
+The report also considered the effect on emissions of policies put forward by UNFCCC Parties to address climate change. Assuming more stringent efforts to limit emissions lead to projected global emissions in 2020 of between 49 and 52 GtCO2-eq, with a median estimate of 51 GtCO2-eq. Assuming less stringent efforts to limit emissions lead to projected global emissions in 2020 of between 53 and 57 GtCO2-eq, with a median estimate of 55 GtCO2-eq.
+
+== See also ==
+
+Attribution science
+History of climate change policy and politics
+Historical climatology
+History of geology
+History of geophysics
+
+Senate Hearing of James E. Hansen (1988)
+
+== Notes ==
+
+== References ==
+
+=== Works cited ===
+
+Public-domain sources
+
+== Further reading ==
+Dessler, Andrew E.; Parson, Edward A., eds. (2020). The science and politics of global climate change: A guide to the debate (3rd ed.). Cambridge University Press. doi:10.1017/9781316832158. ISBN 978-1-316-83215-8. excerpt
+
+== External links ==
+Arrhenius, Svante (April 1896) On the Influence of Carbonic Acid in the Air upon the Temperature of the Ground
+Dewan, Pandora (17 October 2022). "When Was Climate Change Discovered and How Long Has It Been an Issue?". Newsweek. Archived from the original on 18 October 2022.
+Fleming, James R. (ed.) (April 2008) Climate Change and Anthropogenic Greenhouse Warming: A Selection of Key Articles, 1824–1995, with Interpretive Essays
+Fourier, Joseph (1827) Memoire sur les temperatures du globe terrestre et des espaces planetaires, in French and English, with annotations by William Connolley
+Pulver, Dinah Voyles (10 June 2023). "Climate change warning signs started in the 1800s. Here's what humanity knew and when". USA Today. Archived from the original on 10 June 2023.
+Rice-Oxley, Mark; Nelsson, Richard (2 October 2022). "The climate crisis? We've been investigating it for more than 100 years". The Guardian. Archived from the original on 5 October 2022. (reproduces original clippings as far back as 1890)
+Climate Change Milestones: Timeline (archive), American Institute of Physics

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+
+The warming effect of sunlight on different gases was examined in 1856 by Eunice Newton Foote, who described her experiments using glass tubes exposed to sunlight. The warming effect of the sun was greater for compressed air than for an evacuated tube and greater for moist air than dry air. "Thirdly, the highest effect of the sun's rays I have found to be in carbonic acid gas." (carbon dioxide) She continued: "An atmosphere of that gas would give to our earth a high temperature; and if, as some suppose, at one period of its history, the air had mixed with it a larger proportion than at present, an increased temperature from its action, as well as from an increased weight, must have necessarily resulted." Her work was presented by Prof. Joseph Henry at the American Association for the Advancement of Science meeting in August 1856 and described as a brief note written by then journalist David Ames Wells; her paper was published later that year in the American Journal of Science and Arts. Few noticed the paper and it was only rediscovered in the 21st century,
+John Tyndall took Fourier's work one step further in 1859 when he built an apparatus to investigate the absorption of infrared radiation in different gases. He found that water vapor, hydrocarbons like methane (CH4), and carbon dioxide (CO2) strongly block the radiation. He understood that without these gases the planet would rapidly freeze.
+Some scientists suggested that ice ages and other great climate changes were due to changes in the amount of gases emitted in volcanism. But that was only one of many possible causes. Another obvious possibility was solar variation. Shifts in ocean currents also might explain many climate changes. For changes over millions of years, the raising and lowering of mountain ranges would change patterns of both winds and ocean currents. Or perhaps the climate of a continent had not changed at all, but it had grown warmer or cooler because of polar wander (the North Pole shifting to where the Equator had been or the like). There were dozens of theories.
+For example, in the mid-19th century, James Croll published calculations of how the gravitational pulls of the Sun, Moon, and planets subtly affect the Earth's motion and orientation. The inclination of the Earth's axis and the shape of its orbit around the Sun oscillate gently in cycles lasting tens of thousands of years. During some periods the Northern Hemisphere would get slightly less sunlight during the winter than it would get during other centuries. Snow would accumulate, reflecting sunlight and leading to a self-sustaining ice age. Most scientists, however, found Croll's ideas—and every other theory of climate change—unconvincing.
+
+=== First calculations of greenhouse effect, 1896 ===
+
+By the late 1890s, Samuel Pierpoint Langley along with Frank W. Very had attempted to determine the surface temperature of the Moon by measuring infrared radiation leaving the Moon and reaching the Earth. The angle of the Moon in the sky when a scientist took a measurement determined how much CO2 and water vapor the Moon's radiation had to pass through to reach the Earth's surface, resulting in weaker measurements when the Moon was low in the sky.  This result was unsurprising given that scientists had known about infrared radiation absorption for decades.
+In 1896 Svante Arrhenius used Langley's observations of increased infrared absorption where Moon rays pass through the atmosphere at a low angle, encountering more carbon dioxide (CO2), to estimate an atmospheric cooling effect from a future decrease of CO2.  He realized that the cooler atmosphere would hold less water vapor (another greenhouse gas) and calculated the additional cooling effect. He also realized the cooling would increase snow and ice cover at high latitudes, making the planet reflect more sunlight and thus further cool down, as James Croll had hypothesized. Overall Arrhenius calculated that cutting CO2 in half would suffice to produce an ice age. He further calculated that a doubling of atmospheric CO2 would give a total warming of 5–6 degrees Celsius.
+Further, Arrhenius' colleague Arvid Högbom, who was quoted in length in Arrhenius' 1896 study On the Influence of Carbonic Acid in the Air upon the Temperature of the Earth had been attempting to quantify natural sources of emissions of CO2 for purposes of understanding the global carbon cycle.  Högbom found that estimated carbon production from industrial sources in the 1890s (mainly coal burning) was comparable with the natural sources.
+Arrhenius saw that this human emission of carbon would eventually lead to a warming energy imbalance. However, because of the relatively low rate of CO2 production in 1896, Arrhenius thought the warming would take thousands of years, and he expected it would be beneficial to humanity. In 1908 he revised this prediction to take hundreds of years due to the ever increasing rate of fuel use and that within his lifetime this would benefit humanity.
+In 1899 Thomas Chrowder Chamberlin developed at length the idea that climate changes could result from changes in the concentration of atmospheric carbon dioxide. Chamberlin wrote in his 1899 book, An Attempt to Frame a Working Hypothesis of the Cause of Glacial Periods on an Atmospheric Basis:

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+By the investigations of Tyndall, Lecher and Pretner, Keller, Roentgen, and Arrhenius, it has been shown that the carbon dioxide and water vapor of the atmosphere have remarkable power of absorbing and temporarily retaining heat rays, while the oxygen, nitrogen, and argon of the atmosphere possess this power in a feeble degree only. It follows that the effect of the carbon dioxide and water vapor is to blanket the earth with a thermally absorbent envelope. .. The general results assignable to a greatly increased or a greatly reduced quantity of atmospheric carbon dioxide and water may be summarized as follows:
+a. An increase, by causing a larger absorption of the sun's radiant energy, raises the average temperature, while a reduction lowers it. The estimate of Dr. Arrhenius, based upon an elaborate mathematical discussion of the observations of Professor Langley, is that an increase of the carbon dioxide to the amount of two or three times the present content would elevate the average temperature 8° or 9 °C. and would bring on a mild climate analogous to that which prevailed in the Middle Tertiary age.  On the other hand, a reduction of the quantity of carbon dioxide in the atmosphere to an amount ranging from 55 to 62 per cent, of the present content, would reduce the average temperature 4 or 5 C, which would bring on a glaciation comparable to that of the Pleistocene period.
+b. A second effect of increase and decrease in the amount of atmospheric carbon dioxide is the equalization, on the one hand, of surface temperatures, or their differentiation on the other. [...]
+The term "greenhouse effect" for this warming was introduced by Nils Gustaf Ekholm in 1901. Crucially, Ekholm recognised the fact that water vapour is an amplifier of climate change not a driver because water is condensable. Therefore, the amount of carbon dioxide in the atmosphere plays a key role in mediating the amount of water vapor in the atmosphere.
+
+== 20th century onwards ==
+
+=== Paleoclimates and sunspots, early 1900s to 1950s ===
+Arrhenius's calculations were disputed and subsumed into a larger debate over whether atmospheric changes had caused the ice ages.  Experimental attempts to measure infrared absorption in the laboratory seemed to show little differences resulted from increasing CO2 levels, and also found significant overlap between absorption by CO2 and absorption by water vapor, all of which suggested that increasing carbon dioxide emissions would have little climatic effect. These early experiments were later found to be insufficiently accurate, given the instrumentation of the time. Many scientists also thought that the oceans would quickly absorb any excess carbon dioxide.
+Other theories of the causes of climate change fared no better. The principal advances were in observational paleoclimatology, as scientists in various fields of geology worked out methods to reveal ancient climates.  In 1929, Wilmot H. Bradley found that annual varves of clay laid down in lake beds showed climate cycles. Andrew Ellicott Douglass saw strong indications of climate change in tree rings. Noting that the rings were thinner in dry years, he reported climate effects from solar variations, particularly in connection with the 17th-century dearth of sunspots (the Maunder Minimum) noticed previously by William Herschel and others. Other scientists, however, found good reason to doubt that tree rings could reveal anything beyond random regional variations. The value of tree rings for climate study was not solidly established until the 1960s.
+Through the 1930s the most persistent advocate of a solar-climate connection was astrophysicist Charles Greeley Abbot. By the early 1920s, he had concluded that the solar "constant" was misnamed: his observations showed large variations, which he connected with sunspots passing across the face of the Sun. He and a few others pursued the topic into the 1960s, convinced that sunspot variations were a main cause of climate change. Other scientists were skeptical. Nevertheless, attempts to connect the solar cycle with climate cycles were popular in the 1920s and 1930s. Respected scientists announced correlations that they insisted were reliable enough to make predictions. Sooner or later, every prediction failed, and the subject fell into disrepute.
+
+Meanwhile, Milutin Milankovitch, building on James Croll's theory, improved the tedious calculations of the varying distances and angles of the Sun's radiation as the Sun and Moon gradually perturbed the Earth's orbit. Some observations of varves (layers seen in the mud covering the bottom of lakes) matched the prediction of a Milankovitch cycle lasting about 21,000 years. However, most geologists dismissed the astronomical theory. For they could not fit Milankovitch's timing to the accepted sequence, which had only four ice ages, all of them much longer than 21,000 years.
+In 1938 Guy Stewart Callendar attempted to revive Arrhenius's greenhouse-effect theory. Callendar presented evidence that both temperature and the CO2 level in the atmosphere had been rising over the past half-century, and he argued that newer spectroscopic measurements showed that the gas was effective in absorbing infrared in the atmosphere. Nevertheless, most scientific opinion continued to dispute or ignore the theory.
+
+=== Increasing concern, 1950s–1960s ===

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+Better spectrography in the 1950s showed that CO2 and water vapor absorption lines did not overlap completely.  Climatologists also realized that little water vapor was present in the upper atmosphere.  Both developments showed that the CO2 greenhouse effect would not be overwhelmed by water vapor.
+In 1955, Hans Suess's carbon-14 isotope analysis showed that CO2 released from fossil fuels was not immediately absorbed by the ocean. In 1956, Gilbert Plass published the results of his landmark research on the relationship between atmospheric CO2 and global average temperature. His results indicated that a doubling of CO2 would warm the planet by 3.6 °C. In 1957, better understanding of ocean chemistry led Roger Revelle to a realization that the ocean surface layer had limited ability to absorb carbon dioxide, also predicting the rise in levels of CO2 and later being proven by Charles David Keeling. By the late 1950s, more scientists were arguing that carbon dioxide emissions could be a problem, with some projecting in 1959 that CO2 would rise 25% by the year 2000, with potentially "radical" effects on climate. 
+In the centennial of the American oil industry in 1959, organized by the American Petroleum Institute and the Columbia Graduate School of Business, Edward Teller said "It has been calculated that a temperature rise corresponding to a 10 per cent increase in carbon dioxide will be sufficient to melt the icecap and submerge New York. ... At present the carbon dioxide in the atmosphere has risen by 2 per cent over normal. By 1970, it will be perhaps 4 per cent, by 1980, 8 per cent, by 1990, 16 per cent if we keep on with our exponential rise in the use of purely conventional fuels." 
+In 1960 Charles David Keeling demonstrated that the level of CO2 in the atmosphere was in fact rising. Concern mounted year by year along with the rise of the "Keeling Curve" of atmospheric CO2.
+Another clue to the nature of climate change came in the mid-1960s from analysis of deep-sea cores by Cesare Emiliani and analysis of ancient corals by Wallace Broecker and collaborators. Rather than four long ice ages, they found a large number of shorter ones in a regular sequence. It appeared that the timing of ice ages was set by the small orbital shifts of the Milankovitch cycles. While the matter remained controversial, some began to suggest that the climate system is sensitive to small changes and can readily be flipped from a stable state into an instable one.
+Scientists meanwhile began using computers to develop more sophisticated versions of Arrhenius's calculations. In 1967, taking advantage of the ability of digital computers to integrate absorption curves numerically, Syukuro Manabe and Richard Wetherald made the first detailed calculation of the greenhouse effect incorporating convection (the "Manabe-Wetherald one-dimensional radiative-convective model"). They found that, in the absence of unknown feedbacks such as changes in clouds, a doubling of carbon dioxide from the current level would result in approximately 2 °C increase in global temperature. For this, and related work, Manabe was awarded a share of the 2021 Nobel Prize in Physics.
+By the 1960s, aerosol pollution ("smog") had become a serious local problem in many cities, and some scientists began to consider whether the cooling effect of particulate pollution could affect global temperatures.  Scientists were unsure whether the cooling effect of particulate pollution or warming effect of greenhouse gas emissions would predominate, but regardless, began to suspect that human emissions could be disruptive to climate in the 21st century if not sooner.  In his 1968 book The Population Bomb, Paul R. Ehrlich wrote, "the greenhouse effect is being enhanced now by the greatly increased level of carbon dioxide ... [this] is being countered by low-level clouds generated by contrails, dust, and other contaminants ... At the moment we cannot predict what the overall climatic results will be of our using the atmosphere as a garbage dump."
+Efforts to establish a global temperature record that began in 1938 culminated in 1963, when J. Murray Mitchell presented one of the first up-to-date temperature reconstructions. His study involved data from over 200 weather stations, collected by the World Weather Records, which was used to calculate latitudinal average temperature. In his presentation, Murray showed that, beginning in 1880, global temperatures increased steadily until 1940. After that, a multi-decade cooling trend emerged. Murray's work contributed to the overall acceptance of a possible global cooling trend.
+In 1965, the landmark report "Restoring the Quality of Our Environment" by U.S. President Lyndon B. Johnson's Science Advisory Committee warned of the harmful effects of fossil fuel emissions:
+
+The part that remains in the atmosphere may have a significant effect on climate; carbon dioxide is nearly transparent to visible light, but it is a strong absorber and back radiator of infrared radiation, particularly in the wave lengths from 12 to 18 microns; consequently, an increase of atmospheric carbon dioxide could act, much like the glass in a greenhouse, to raise the temperature of the lower air.
+The committee used the recently available global temperature reconstructions and carbon dioxide data from Charles David Keeling and colleagues to reach their conclusions. They declared the rise of atmospheric carbon dioxide levels to be the direct result of fossil fuel burning. The committee concluded that human activities were sufficiently large to have significant, global impact—beyond the area the activities take place. "Man is unwittingly conducting a vast geophysical experiment", the committee wrote.
+In 1966, Nobel Prize winner Glenn T. Seaborg, Chairperson of the United States Atomic Energy Commission warned of the climate crisis: "At the rate we are currently adding carbon dioxide to our atmosphere (six billion tons a year), within the next few decades the heat balance of the atmosphere could be altered enough to produce marked changes in the climate—changes which we might have no means of controlling even if by that time we have made great advances in our programs of weather modification."

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+A 1968 study by the Stanford Research Institute for the American Petroleum Institute noted:
+
+If the earth's temperature increases significantly, a number of events might be expected to occur, including the melting of the Antarctic ice cap, a rise in sea levels, warming of the oceans, and an increase in photosynthesis. ... Revelle makes the point that man is now engaged in a vast geophysical experiment with his environment, the earth. Significant temperature changes are almost certain to occur by the year 2000 and these could bring about climatic changes.
+In 1969, NATO was the first candidate to deal with climate change on an international level. It was planned then to establish a hub of research and initiatives of the organization in the civil area, dealing with environmental topics as acid rain and the greenhouse effect. The suggestion of US President Richard Nixon was not very successful with the administration of German Chancellor Kiesinger. But the topics and the preparation work done on the NATO proposal by German authorities gained international momentum, (see e.g. the Stockholm United Nations Conference on the Human Environment 1970) as the government of Willy Brandt started to apply them on the civil sphere instead.
+Also in 1969, Mikhail Budyko published a theory on the ice–albedo feedback, a foundational element of what is today known as Arctic amplification.  The same year a similar model was published by William D. Sellers. Both studies attracted significant attention, since they hinted at the possibility for a runaway positive feedback within the global climate system.
+A 1969 memo from White House Urban Affairs Director Daniel Patrick Moynihan tried to impress the office of U.S. President Nixon with the projected severity of the greenhouse effect. However, action was not taken, even after a 20 December 1971 initiative from the Office of Science and Technology, "Determine the Climate Change Caused by Man and Nature". 
+In the initiative, Nixon's science advisors recommended an international network for monitoring climate trends and human impact on it.
+
+=== Scientists increasingly predict warming, 1970s ===
+
+In the early 1970s, evidence that aerosols were increasing worldwide and that the global temperature series showed cooling encouraged Reid Bryson and some others to warn of the possibility of severe cooling. The questions and concerns put forth by Bryson and others launched a new wave of research into the factors of such global cooling. Meanwhile, the new evidence that the timing of ice ages was set by predictable orbital cycles suggested that the climate would gradually cool, over thousands of years. Several scientific panels from this time period concluded that more research was needed to determine whether warming or cooling was likely, indicating that the trend in the scientific literature had not yet become a consensus. For the century ahead, however, a survey of the scientific literature from 1965 to 1979 found 7 articles predicting cooling and 44 predicting warming (many other articles on climate made no prediction); the warming articles were cited much more often in subsequent scientific literature. Research into warming and greenhouse gases held the greater emphasis, with nearly six times more studies predicting warming than predicting cooling, suggesting concern among scientists was largely over warming as they turned their attention toward the greenhouse effect.
+John Sawyer published the study Man-made Carbon Dioxide and the "Greenhouse" Effect in 1972. He summarized the knowledge of the science at the time, the anthropogenic attribution of the carbon dioxide greenhouse gas, distribution and exponential rise, findings which still hold today. Additionally he accurately predicted the rate of global warming for the period between 1972 and 2000.
+
+The increase of 25% CO2 expected by the end of the century therefore corresponds to an increase of 0.6 °C in the world temperature – an amount somewhat greater than the climatic variation of recent centuries. – John Sawyer, 1972
+The first satellite records compiled in the early 1970s showed snow and ice cover over the Northern Hemisphere to be increasing, prompting further scrutiny into the possibility of global cooling. J. Murray Mitchell updated his global temperature reconstruction in 1972, which continued to show cooling. However, scientists determined that the cooling observed by Mitchell was not a global phenomenon. Global averages were changing, largely in part due to unusually severe winters experienced by Asia and some parts of North America in 1972 and 1973, but these changes were mostly constrained to the Northern Hemisphere. In the Southern Hemisphere, the opposite trend was observed. The severe winters, however, pushed the issue of global cooling into the public eye.
+The mainstream news media at the time exaggerated the warnings of the minority who expected imminent cooling. For example, in 1975, Newsweek magazine published a story titled "The Cooling World" that warned of "ominous signs that the Earth's weather patterns have begun to change". The article drew on studies documenting the increasing snow and ice in regions of the Northern Hemisphere and concerns and claims by Reid Bryson that global cooling by aerosols would dominate carbon dioxide warming. The article continued by stating that evidence of global cooling was so strong that meteorologists were having "a hard time keeping up with it". On 23 October 2006, Newsweek issued an update stating that it had been "spectacularly wrong about the near-term future". Nevertheless, this article and others like it had long-lasting effects on public perception of climate science.

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+---
+title: "History of climate change science"
+chunk: 7/12
+source: "https://en.wikipedia.org/wiki/History_of_climate_change_science"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:54.297571+00:00"
+instance: "kb-cron"
+---
+
+Such media coverage heralding the coming of a new ice age resulted in beliefs that this was the consensus among scientists, despite this not being reflected by the scientific literature. As it became apparent that scientific opinion was in favor of global warming, the public began to express doubt over how trustworthy the science was. The argument that scientists were wrong about global cooling, so therefore may be wrong about global warming has been called "the Ice Age Fallacy" by Time author Bryan Walsh.
+In the first two "Reports for the Club of Rome" in 1972 and 1974, the anthropogenic climate changes by CO2 increase as well as by waste heat were mentioned. About the latter John Holdren wrote in a study cited in the 1st report, "that global thermal pollution is hardly our most immediate environmental threat. It could prove to be the most inexorable, however, if we are fortunate enough to evade all the rest". Simple global-scale estimates that recently have been actualized and confirmed by more refined model calculations show noticeable contributions from waste heat to global warming after the year 2100, if its growth rates are not strongly reduced (below the averaged 2% p.a. which occurred since 1973).
+Evidence for warming accumulated. By 1975, Manabe and Wetherald had developed a three-dimensional global climate model that gave a roughly accurate representation of the current climate. Doubling CO2 in the model's atmosphere gave a roughly 2 °C rise in global temperature. Several other kinds of computer models gave similar results: it was impossible to make a model that gave something resembling the actual climate and not have the temperature rise when the CO2 concentration was increased.
+In a separate development, an analysis of deep-sea cores published in 1976 by Nicholas Shackleton and colleagues showed that the dominating influence on ice age timing came from a 100,000-year Milankovitch orbital change. This was unexpected, since the change in sunlight in that cycle was slight. The result emphasized that the climate system is driven by feedbacks, and thus is strongly susceptible to small changes in conditions.
+A 1977 memo (see quote box) from President Carter's chief science adviser Frank Press warned of the possibility of catastrophic climate change. However, other issues—such as known harms to health from pollutants, and avoiding energy dependence on other nations—seemed more pressing and immediate. Energy Secretary James Schlesinger advised that "the policy implications of this issue are still too uncertain to warrant Presidential involvement and policy initiatives", and the fossil fuel industry began sowing doubt about climate science.
+The 1979 World Climate Conference (12 to 23 February) of the World Meteorological Organization concluded "it appears plausible that an increased amount of carbon dioxide in the atmosphere can contribute to a gradual warming of the lower atmosphere, especially at higher latitudes. ... It is possible that some effects on a regional and global scale may be detectable before the end of this century and become significant before the middle of the next century."
+In July 1979 the United States National Research Council published a report,
+concluding (in part):
+
+When it is assumed that the CO2 content of the atmosphere is doubled and statistical thermal equilibrium is achieved, the more realistic of the modeling efforts predict a global surface warming of between 2 °C and 3.5 °C, with greater increases at high latitudes.
+... we have tried but have been unable to find any overlooked or underestimated physical effects that could reduce the currently estimated global warmings due to a doubling of atmospheric CO2 to negligible proportions or reverse them altogether.
+One week before President Carter left office, the White House Council on Environmental Quality (CEQ) issued reports including a suggestion to limit global average temperature to 2 °C above preindustrial levels, one goal agreed to in the 2015 Paris climate accord.
+
+=== Consensus begins to form, 1980–1988 ===
+
+By the early 1980s, the slight cooling trend from 1945 to 1975 had stopped.  Aerosol pollution had decreased in many areas due to environmental legislation and changes in fuel use, and it became clear that the cooling effect from aerosols was not going to increase substantially while carbon dioxide levels were progressively increasing.
+
+Hansen and others published the 1981 study Climate impact of increasing atmospheric carbon dioxide, and noted: It is shown that the anthropogenic carbon dioxide warming should emerge from the noise level of natural climate variability by the end of the century, and there is a high probability of warming in the 1980s. Potential effects on climate in the 21st century include the creation of drought-prone regions in North America and central Asia as part of a shifting of climatic zones, erosion of the West Antarctic ice sheet with a consequent worldwide rise in sea level, and opening of the fabled Northwest Passage.
+In 1982, Greenland ice cores drilled by Hans Oeschger, Willi Dansgaard, and collaborators revealed dramatic temperature oscillations in the space of a century in the distant past. The most prominent of the changes in their record corresponded to the violent Younger Dryas climate oscillation seen in shifts in types of pollen in lake beds all over Europe. Evidently drastic climate changes were possible within a human lifetime.
+In 1973 James Lovelock speculated that chlorofluorocarbons (CFCs) could have a global warming effect.  In 1975 V. Ramanathan found that a CFC molecule could be 10,000 times more effective in absorbing infrared radiation than a carbon dioxide molecule, making CFCs potentially important despite their very low concentrations in the atmosphere.  While most early work on CFCs focused on their role in ozone depletion, by 1985 Ramanathan and others showed that CFCs together with methane and other trace gases could have nearly as important a climate effect as increases in CO2. In other words, global warming would arrive twice as fast as had been expected.

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+---
+title: "History of climate change science"
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+---
+
+In 1985 a joint UNEP/WMO/ICSU Conference on the "Assessment of the Role of Carbon Dioxide and Other Greenhouse Gases in Climate Variations and Associated Impacts" concluded that greenhouse gases "are expected" to cause significant warming in the next century and that some warming is inevitable.
+Meanwhile, ice cores drilled by a Franco-Soviet team at the Vostok Station in Antarctica showed that CO2 and temperature had gone up and down together in wide swings through past ice ages. This confirmed the CO2-temperature relationship in a manner entirely independent of computer climate models, strongly reinforcing the emerging scientific consensus. The findings also pointed to powerful biological and geochemical feedbacks.
+In January 1986, the German Physical Society published warning of an impending climate catastrophe
+In June 1988, James E. Hansen made one of the first assessments that human-caused warming had already measurably affected global climate. Shortly after, a "World Conference on the Changing Atmosphere: Implications for Global Security" gathered hundreds of scientists and others in Toronto. They concluded that the changes in the atmosphere due to human pollution "represent a major threat to international security and are already having harmful consequences over many parts of the globe", and declared that by 2005 the world would be well-advised to push its emissions some 20% below the 1988 level.
+The 1980s saw important breakthroughs with regard to global environmental challenges. Ozone depletion was mitigated by the Vienna Convention (1985) and the Montreal Protocol (1987). Acid rain was mainly regulated on national and regional levels.
+
+=== Increased consensus amongst scientists: 1988 to present ===
+
+In 1988 the WMO established the Intergovernmental Panel on Climate Change with the support of the UNEP. The IPCC continues its work through the present day, and issues a series of Assessment Reports and supplemental reports that describe the state of scientific understanding at the time each report is prepared. Scientific developments during this period are summarized about once every five to six years in the IPCC Assessment Reports which were published in 1990 (First Assessment Report), 1995 (Second Assessment Report), 2001 (Third Assessment Report), 2007 (Fourth Assessment Report), 2013/2014 (Fifth Assessment Report). and 2021 Sixth Assessment Report 
+The 2001 report was the first to state positively that the observed global temperature increase was "likely" to be due to human activities. The conclusion was influenced especially by the so-called hockey stick graph showing an abrupt historical temperature rise simultaneous with the rise of greenhouse gas emissions, and by observations of changes in ocean heat content that had a "signature" matching the pattern that computer models calculated for the effect of greenhouse warming. By the time of the 2021 report, scientists had much additional evidence. Above all, measurements of paleotemperatures from several eras in the distant past, and the record of temperature change since the mid 19th century, could be matched against measurements of CO2 levels to provide independent confirmation of supercomputer model calculations.
+These developments depended crucially on Weather satellites, other satellites and huge globe-spanning observation programs. Since the 1990s research into historical and modern climate change expanded rapidly. International coordination was provided by the World Climate Research Programme (established in 1980) and was increasingly oriented around providing input to the IPCC reports. Measurement networks such as the Global Ocean Observing System, Integrated Carbon Observation System, and NASA's Earth Observing System enabled monitoring of the causes and effects of ongoing change.  Research also broadened, linking many fields such as Earth sciences, behavioral sciences, economics, and security.
+
+=== Relative importance of human activity versus natural causes ===
+A historically important question in climate change research has regarded the relative importance of human activity and natural causes during the period of instrumental record. In the 1995 Second Assessment Report (SAR), the IPCC made the widely quoted statement that "The balance of evidence suggests a discernible human influence on global climate". The phrase "balance of evidence" suggested the (English) common-law standard of proof required in civil as opposed to criminal courts: not as high as "beyond reasonable doubt". In 2001 the Third Assessment Report (TAR) refined this, saying "There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities". The 2007 Fourth Assessment Report (AR4) strengthened this finding:
+
+"Anthropogenic warming of the climate system is widespread and can be detected in temperature observations taken at the surface, in the free atmosphere and in the oceans. Evidence of the effect of external influences, both anthropogenic and natural, on the climate system has continued to accumulate since the TAR."
+Other findings of the IPCC Fourth Assessment Report include:
+
+"It is extremely unlikely (<5%) that the global pattern of warming during the past half century can be explained without external forcing (i.e., it is inconsistent with being the result of internal variability), and very unlikely that it is due to known natural external causes alone. The warming occurred in both the ocean and the atmosphere and took place at a time when natural external forcing factors would likely have produced cooling."
+"From new estimates of the combined anthropogenic forcing due to greenhouse gases, aerosols, and land surface changes, it is extremely likely (>95%) that human activities have exerted a substantial net warming influence on climate since 1750."
+"It is virtually certain that anthropogenic aerosols produce a net negative radiative forcing (cooling influence) with a greater magnitude in the Northern Hemisphere than in the Southern Hemisphere."
+Some results from scientific studies on this issue are listed below:

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+---
+title: "History of climate change science"
+chunk: 9/12
+source: "https://en.wikipedia.org/wiki/History_of_climate_change_science"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:54.297571+00:00"
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+---
+
+In 1996, in a paper in Nature titled "A search for human influences on the thermal structure of the atmosphere", Benjamin D. Santer et al. wrote: "The observed spatial patterns of temperature change in the free atmosphere from 1963 to 1987 are similar to those predicted by state-of-the-art climate models incorporating various combinations of changes in carbon dioxide, anthropogenic sulphate aerosol and stratospheric ozone concentrations. The degree of pattern similarity between models and observations increases through this period. It is likely that this trend is partially due to human activities, although many uncertainties remain, particularly relating to estimates of natural variability."
+A 2002 paper in the Journal of Geophysical Research says "Our analysis suggests that the early twentieth century warming can best be explained by a combination of warming due to increases in greenhouse gases and natural forcing, some cooling due to other anthropogenic forcings, and a substantial, but not implausible, contribution from internal variability. In the second half of the century we find that the warming is largely caused by changes in greenhouse gases, with changes in sulphates and, perhaps, volcanic aerosol offsetting approximately one third of the warming."
+A 2005 review of detection and attribution studies by the International Ad hoc Detection and Attribution Group found that "natural drivers such as solar variability and volcanic activity are at most partially responsible for the large-scale temperature changes observed over the past century, and that a large fraction of the warming over the last 50 yr can be attributed to greenhouse gas increases. Thus, the recent research supports and strengthens the IPCC Third Assessment Report conclusion that 'most of the global warming over the past 50 years is likely due to the increase in greenhouse gases.'"
+Barnett and colleagues (2005) say that the observed warming of the oceans "cannot be explained by natural internal climate variability or solar and volcanic forcing, but is well simulated by two anthropogenically forced climate models," concluding that "it is of human origin, a conclusion robust to observational sampling and model differences".
+Two papers in the journal Science in August 2005 resolve the problem, evident at the time of the TAR, of tropospheric temperature trends. The UAH version of the record contained errors, and there is evidence of spurious cooling trends in the radiosonde record, particularly in the tropics. See satellite temperature measurements for details; and the 2006 US CCSP report.
+
+=== Extreme event attribution ===
+
+Extreme event attribution (EEA), also known as attribution science, was developed in the early decades of the 21st century. EEA uses climate models to identify and quantify the role that human-caused climate change plays in the frequency, intensity, duration, and impacts of specific individual extreme weather events. Results of attribution studies allow scientists and journalists to make statements such as, "this weather event was made at least n times more likely by human-caused climate change" or "this heatwave was made m degrees hotter than it would have been in a world without global warming" or "this event was effectively impossible without climate change".
+A common EEA approach uses model simulations to compare events in two worlds—a first world with human-caused greenhouse gas emissions and a second world without such emissions—and attributing differences to human influence. Greater computing power of the 2000s allowed weather to be simulated over and over again, and conceptual breakthroughs in the early to mid 2010s  enabled attribution science to detect the effects of climate change on some events with high confidence. Scientists use methods that have already been peer reviewed, allowing "rapid attribution" studies to be published within a "news cycle" time frame.
+
+=== Terminology ===
+
+== Discredited theories and reconciled apparent discrepancies ==
+
+=== Analogy of the greenhouse effect to the atmosphere ===
+The early work of Joseph Fourier found that a greenhouse heats up mainly due to radiation trapping.  This is analogous to radiation trapping in the atmosphere, leading to the term "greenhouse effect".
+An experiment performed by Prof. R. W. Wood in 1909 led him to reject radiation trapping, claiming that a greenhouse is heated merely due to convection blocking.  This theory became a widespread view in the scientific community.
+Moreover, Wood's theory has been used to reject the analogy, and to doubt the existence of a greenhouse effect in the atmosphere. 
+Experiments have discredited Wood's theory. They have confirmed that radiation trapping is indeed the dominant cause of heating in a greenhouse.  Hence the analogy is valid.
+
+=== Discussions around locations of temperature measurement stations ===

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+---
+title: "History of climate change science"
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+tags: "science, encyclopedia"
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+---
+
+There have been attempts to raise public controversy over the accuracy of the instrumental temperature record on the basis of the urban heat island effect, the quality of the surface station network, and assertions that there have been unwarranted adjustments to the temperature record.
+Weather stations that are used to compute global temperature records are not evenly distributed over the planet, and their distribution has changed over time. There were a small number of weather stations in the 1850s, and the number did not reach the current 3000+ until the 1951 to 1990 period
+The 2001 IPCC Third Assessment Report (TAR) acknowledged that the urban heat island is an important local effect, but cited analyses of historical data indicating that the effect of the urban heat island on the global temperature trend is no more than 0.05 °C (0.09 °F) degrees through 1990. Peterson (2003) found no difference between the warming observed in urban and rural areas.
+Parker (2006) found that there was no difference in warming between calm and windy nights. Since the urban heat island effect is strongest for calm nights and is weak or absent on windy nights, this was taken as evidence that global temperature trends are not significantly contaminated by urban effects. Pielke and Matsui published a paper disagreeing with Parker's conclusions.
+In 2005, Roger A. Pielke and Stephen McIntyre criticized the US instrumental temperature record and adjustments to it, and Pielke and others criticized the poor quality siting of a number of weather stations in the United States. A study in 2010 examined the siting of temperature stations and found that those measurement stations that were poorly showed a slight cool bias rather than the warm bias which deniers had postulated.
+The Berkeley Earth Surface Temperature group carried out an independent assessment of land temperature records, which examined issues raised by deniers, such as the urban heat island effect, poor station quality, and the risk of data selection bias. The preliminary results, made public in October 2011, found that these factors had not biased the results obtained by NOAA, the Hadley Centre together with the Climatic Research Unit (HadCRUT) and NASA's GISS in earlier studies. The group also confirmed that over the past 50 years the land surface warmed by 0.911 °C, and their results closely matched those obtained from these earlier studies.
+
+=== Apparent discrepancy for tropospheric temperature increases in the tropics ===
+General circulation models and basic physical considerations predict that in the tropics the temperature of the troposphere should increase more rapidly than the temperature of the surface. A 2006 report to the U.S. Climate Change Science Program noted that models and observations agreed on this amplification for monthly and interannual time scales but not for decadal time scales in most observed data sets. Improved measurement and analysis techniques have reconciled this discrepancy: corrected buoy and satellite surface temperatures are slightly cooler and corrected satellite and radiosonde measurements of the tropical troposphere are slightly warmer. Satellite temperature measurements show that tropospheric temperatures are increasing with "rates similar to those of the surface temperature", leading the IPCC to conclude in 2007 that this discrepancy is reconciled.
+
+=== Iris hypothesis ===
+
+=== Apparent "Antarctica cooling" discrepancy ===
+
+=== Solar variation ===
+
+Some climate change deniers have argued that solar variation is a significant contributor to the observed global warming, which would reduce the relative importance of human-made causes. However, this is not supported by scientific consensus on climate change. Scientists reject the notion that the warming observed in the global mean surface temperature record since about 1850 is the result of solar variations: "The observed rapid rise in global mean temperatures seen after 1985 cannot be ascribed to solar variability, whichever of the mechanisms is invoked and no matter how much the solar variation is amplified."
+The consensus position is that solar radiation may have increased by 0.12 W/m2 since 1750, compared to 1.6 W/m2 for the net anthropogenic forcing. Already in 2001, the IPCC Third Assessment Report had found that, "The combined change in radiative forcing of the two major natural factors (solar variation and volcanic aerosols) is estimated to be negative for the past two, and possibly the past four, decades."
+Many studies say that the recent level of solar activity was historically high as determined by sunspot activity and other factors. This is known as the "Modern Maximum". Solar activity could affect climate either by variation in the Sun's output or, more speculatively, by an indirect effect on the amount of cloud formation. Solanki and co-workers suggest that solar activity for the last 60 to 70 years may be at its highest level in 8,000 years, however they said  "that solar variability is unlikely to have been the dominant cause of the strong warming during the past three decades", and concluded that "at the most 30% of the strong warming since [1970] can be of solar origin". Although the paradigm of the Modern Maximum is broadly accepted, 
+ its recurrence rate is still an open question., and "solar activity reconstructions tell us that only a minor fraction of the recent global warming can be explained by the variable Sun."
+
+=== Solar activity ===

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+---
+title: "History of crystallography before X-rays"
+chunk: 1/9
+source: "https://en.wikipedia.org/wiki/History_of_crystallography_before_X-rays"
+category: "reference"
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+date_saved: "2026-05-05T16:17:30.404709+00:00"
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+---
+
+The history of crystallography before X-rays describes how crystallography developed as a science up to the discovery of X-rays by Wilhelm Conrad Röntgen in 1895. The scientific approach to the study of crystals began in the 17th century with the work of Kepler on the structure of snowflakes and Nicolas Steno's discovery that the angles between corresponding faces in a crystalline substance are always the same. The work René Just Haüy published in 1801 and 1802 marked the point where crystallography split from mineralogy to become a science of its own. Some sources state that the history of crystallography started with the investigation of X-ray diffraction by Max von Laue in 1912 but that ignores over a century of previous scientific work in the field.
+In the period before X-rays, crystallography can be divided into three broad areas: geometrical crystallography culminating in the discovery of the 230 space groups in 1891–4, physical crystallography, and chemical crystallography.
+Up to 1912, crystallography had been largely based on mineralogy. It was the study of minerals in the 18th and 19th centuries that led to a progressive understanding of the relationships between chemical composition, crystal habit and crystal structure. During the 19th century crystallography was progressively transformed into an empirical and mathematical science by the adoption of symmetry concepts.
+
+== Origins ==
+
+=== 16th century ===
+The scientific study of the properties of crystals began in the 16th century. In the first half of the 16th century Paracelsus proposed a theory of mineral formation as an analogy to fruit-bearing plants. In 1546 Georgius Agricola published a study of mineralogy in which morphology, or geometrical shape, was one of the characteristics used to classify minerals. In 1550 Gerolamo Cardano made an early attempt to explain the shape of crystals as the result of a close packing of spheres. In 1591 Thomas Harriot studied the close packing of cannonballs (spheres). In 1597 Andreas Libavius recognised the geometrical characteristics of crystals and identified salts by their crystal shape.
+
+=== 17th century ===
+In 1611 Johannes Kepler published Strena Seu de Nive Sexangula (A New Year's Gift of Hexagonal Snow) which is considered the first treatise on geometrical and atomistic crystallography. Kepler studied the packing of spheres, in order to explain the hexagonal symmetry of snow crystals. He demonstrated that in a compact packing each sphere has six neighbours in the same plane, three in the plane above, and three in the plane below, for a total of twelve touching spheres. Kepler concluded that 0.74084 is the maximum possible density amongst any arrangement of spheres — this became known as the Kepler conjecture. The conjecture was finally proved by Thomas Hales in 1998.
+In 1665 Robert Hooke attempted to explain crystal morphology based on the stacking of atoms. In his work Micrographia he reported on the regularity of quartz crystals observed with the recently invented microscope, and proposed that they are formed by spherules.
+Nicolas Steno rejected Paracelsus's proposed organic origin for crystals. Steno first observed the law of constancy of interfacial angles in 1669 when studying quartz crystals and noted that, although the crystals of a substance differed in appearance from one to another, the angles between corresponding faces were always the same. Steno's work can be considered as the beginning of crystallography as an independent discipline.
+In 1678 Christiaan Huygens proposed a structural explanation of the double refraction of calcite based on ellipsoidal atoms. Huygens published his results in his Traité de la Lumière.
+A geometrical theory of crystal structure based on polyhedra was proposed by Domenico Guglielmini. Guglielmini's publications of 1688 and 1705 concluded that basic forms (cube, rhombohedron, hexagonal prism, and octahedron) of various salt crystals are characteristic of each substance, are identical in form, indivisible, and have faces with identical inclinations to each other.
+By the second half of the 17th century the ideas of Paracelsus had been displaced by a more scientific approach to chemistry, geology, mineralogy, and the emerging field of crystallography. In his book The Sceptical Chymist of 1661, Robert Boyle criticised the traditional composition of materials, as represented by the teaching of Aristotle and Paracelsus, and initiated the modern understanding of chemical elements using the words "perfectly unmingled bodies". Boyle argued that matter's basic elements consisted of various types of particles, termed "corpuscles", which were capable of arranging themselves into groups (molecules). Boyle was one of the earliest researchers to use the term crystal for crystalline substances apart from quartz.
+
+== Geometrical crystallography ==
+
+=== 18th century ===
+In 1723 Moritz Anton Cappeller published Prodromus Crystallographiae, the first treatise on crystal shapes. The introduction of the term crystallography is attributed to Cappeller.
+In 1773 Torbern Bergman, a leader in the field of chemical analysis, described the crystal forms of calcite and stated that all the forms could be built up from the cleavage rhombohedron. Bergman, building on the previous work of Carl Linnaeus, developed a classification of minerals based on chemical characteristics, with subclasses organised by their external shapes, and defined seven primary crystal forms. In 1774 Abraham Gottlob Werner published his classification of minerals. Werner postulated seven primary forms, and showed that some geometrical forms could be derived from one another by truncation.
+With Jean-Baptiste L. Romé de l'Isle's Essai de cristallographie published in 1772 and Cristallographie published in 1783 the scientific approach to crystal structure began. Romé de l'Isle described over 500 crystal forms and accurately measured the interfacial angles of a great variety of crystals, using the goniometer designed by his student Arnould Carangeot. He noted that the angles are characteristic of a substance, thus generalising the law of constancy of angles postulated by Nicolas Steno. Romé de l'Isle considered that the shape of a crystal is a consequence of the packing of elemental particles, and defined six primitive forms. However, he criticised René Just Haüy and Torbern Bergman for speculating on the internal structure of crystals without sufficient observational data.

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+title: "History of crystallography before X-rays"
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+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:30.404709+00:00"
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+---
+
+In 1781 René Just Haüy (often termed the "Father of crystallography") discovered that crystals always cleave along crystallographic planes. Based on this observation, and the fact that the interfacial angles in each crystal species always have the same value, Haüy concluded that crystals must be periodic and composed of regularly arranged layers of tiny polyhedra (molécules intégrantes). This theory explained why all crystal planes are related by small rational numbers (the law of rational indices). In 1784 René-Just Haüy published his law of decrements: a crystal is composed of molecules arranged periodically in three dimensions without leaving any gaps. Haüy's molecular crystal structure theory assumed that molécules intégrantes were specific in shape and composition for every compound. Haüy developed his mathematical theory of crystal structure over many years. His theory turned out to be remarkably accurate, and gave crystallography a legitimate place among the sciences.
+Haüy's crystal structure theory was criticised as over-simplistic by William Hyde Wollaston in 1813 and by Henry James Brooke in 1819. Haüy also tended to ignore experimental results that contradicted his structural theory, such as those achieved with the more accurate reflection goniometer invented by Wollaston in 1809. In 1819 Eilhard Mitscherlich discovered the law of isomorphism, which states that compounds which contain the same number of atoms, and have similar structures, tend to exhibit similar crystal forms. The discovery of the phenomena of isomorphism and polymorphism dealt a clear blow to Haüy's crystal structure theory.
+
+=== Atomism versus Dynamism ===
+
+Christian Samuel Weiss became familiar with Haüy's theory by translating his Traité de mineralogie (1801). In 1804 Weiss added an appendix to volume 1 of the translation in which he first outlined his dynamical theory of crystals. In contrast to Haüy, Weiss took a purely geometric approach to external crystal morphology, completely disregarding any attempt at modelling the internal structure of crystals. Weiss has been termed "the founder of geometric crystallography".
+Weiss rejected Haüy's static "atomistic" theory of crystals instead using a "dynamic" approach that was typical of the German natural philosophers of the early 19th century. Weiss understood the external forms of crystals as a consequence of internal attractions and repulsions which could be observed as one or more axes of rotation. Weiss used crystallographic axes as the basis of his systematic classification of crystals.
+Weiss and his followers Moritz Ludwig Frankenheim and Johann F. C. Hessel studied the symmetry of crystals. Up until 1800 the concept of symmetry had a variety of meanings, however during the 19th century crystallography was progressively transformed into an empirical and mathematical science by the adoption of symmetry concepts. By the second half of the 19th century the study of crystals was focused more on their geometry and mathematical analysis than their physical properties.
+French scientists did not adopt the dynamic crystallographic theory, but they did attempt to learn from it. Gabriel Delafosse continued Haüy's work in France. He was the first to use the terms lattice (réseau) and unit cell (maille). He stated that the orientation of the axes in a substance is constant, which implies symmetry of translation (a defining feature of a lattice), and that the external symmetry of a crystal reflects its inner symmetry, namely the symmetry of the constituent atoms and their arrangement. In other words, the law of symmetry applies to both the inside and the outside of a crystal. Delafosse's approach explained the behaviour of hemihedral crystals, which were not adequately accounted for by Haüy.
+
+=== Crystal systems ===
+Christian Samuel Weiss introduced the concept of crystal systems in 1815. Weiss defined seven crystal systems: five based on three orthogonal axes (cubic, tetragonal, orthorhombic, monoclinic and triclinic), and two (trigonal and hexagonal) based on three axes in a plane at 60° to each other and a fourth axis orthogonal to the plane. The number and type of the crystal systems of Weiss correspond to the modern systems apart from the triclinic and monoclinic cases which have non-orthogonal axes.
+Friedrich Mohs established a classification system for minerals based solely on their external shape. Mohs distinguished four crystal systems rather than the seven identified by Weiss. In 1824 Carl Friedrich Naumann confirmed Mohs' observation that the triclinic and monoclinic systems required inclined rather than orthogonal axes.
+
+=== Crystal classes ===
+In 1826 Moritz Ludwig Frankenheim published the first derivation of the 32 crystal classes, but his work was forgotten for many decades. In 1830, Johann Hessel proved that, as a consequence of the law of rational indices, morphological forms can combine to give exactly 32 kinds of crystal symmetry in Euclidean space, since only two-, three-, four-, and six-fold rotation axes can occur (the crystallographic restriction). However, Hessel's work remained practically unknown for over 60 years and, in 1867, Axel Gadolin independently rediscovered his results. Gadolin, who was unaware of the work of his predecessors, found the crystal classes using stereographic projection to represent the symmetry elements of the 32 groups. Gadolin's work had a clarity that attracted widespread attention, and caused Hessel's earlier work to be neglected.
+
+=== Miller indices ===
+The first to introduce indices to denote crystal planes was Christian Samuel Weiss. In 1823 Franz Ernst Neumann suggested that the inverse of the Weiss indices were simpler and easier to use. In 1825 William Whewell, independently from Neumann, proposed essentially the same indices.
+William Hallowes Miller, a student of Whewell introduced the Miller indices in his book A Treatise on Crystallography (1839). The Miller indices are essentially the same as those of Neumann and Whewell. Miller's indices were accepted by his contemporaries because of their algebraic convenience, and it is his notation that is currently used in crystallography.

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+---
+title: "History of crystallography before X-rays"
+chunk: 3/9
+source: "https://en.wikipedia.org/wiki/History_of_crystallography_before_X-rays"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:30.404709+00:00"
+instance: "kb-cron"
+---
+
+=== Bravais lattices ===
+In 1835 Moritz Ludwig Frankenheim introduced the notion of lattice, independently of Ludwig August Seeber, and derived 15 lattice types; these correspond to the 14 Bravais lattices, but Frankenheim double-counted one of the monoclinic lattices.
+In 1848 Auguste Bravais derived the 14 Bravais lattices. The work was published in 1850, and translated into English in 1949. Bravais's work can be considered as drawing on a combination of the approaches of Haüy and Weiss. Bravais constructed his mathematical lattices as finite sets of points in space, thus avoiding the need for the packing of spheres or polyhedra to represent physical atoms or molecules. He defined axes, planes and centres of inversion as symmetry elements, and identified all of their possible combinations. Bravais assumed that every atom or molecule in the lattice had the same orientation; in 1879 Leonhard Sohncke removed this restriction to derive his "Sohncke groups".
+
+=== Space groups ===
+The identification of the 230 space groups has been extensively documented and is now regarded as a major achievement of 19th century science. The space groups became important in the 20th century after the discovery of X-ray diffraction and the founding of the field of X-ray crystallography.
+Ludwig August Seeber first put forward the concept of the space lattice in 1824. In 1879 Leonhard Sohncke combined the 14 Bravais lattices with the rotation axes and the screw axes to arrive at his 65 spatial arrangements of points in which chiral crystal structures form. Sohncke enumerated the space groups containing only the translations and rotations.
+Rotoinversions and glide reflections were introduced by Evgraf Fedorov and Arthur Moritz Schoenflies to derive the 230 space groups. Fedorov and Schoenflies used different methods, but collaborated to reach the final list of space groups in 1891. William Barlow also derived the 230 space groups in 1894 using a method based on patterns of oriented motifs. Schoenflies work was more influential than Fedorov's because he published his work in German rather than Russian, and Schoenflies' notation was more convenient and became widely adopted.
+
+The discovery of the space groups was not universally recognised as an important scientific breakthrough at the time, but after the invention of X-ray crystallography their physical significance was fully appreciated.
+
+=== Crystal structure prediction ===
+Until the use of X-rays there was no way to determine the actual crystal structure of even the simplest substances such as salt (NaCl). For example, in the 1880s, William Barlow proposed several crystal structures based on close-packing of spheres some of which were validated later by X-ray crystallography; however the available data were too scarce in the 1880s to accept his models as conclusive.
+
+== Physical crystallography ==
+
+Physical crystallography is concerned with the physical properties of crystals, such as their optical, electrical, magnetic, thermal, and mechanical properties. Unlike geometrical crystallography, the history of physical crystallography has no central story, but is a collection of developments in different areas.
+
+=== Symmetry ===
+During the 19th century physical crystallography was progressively transformed into an empirical and mathematical science by the adoption of symmetry concepts. In 1885 Woldemar Voigt formalized Neumann's principle as "if a crystal is invariant with respect to certain symmetry operations, any of its physical properties must also be invariant with respect to the same symmetry operations". Neumann's principle is sometimes referred to as the Neumann–Minnigerode–Curie principle based on later work by Bernhard Minnigerode and Pierre Curie. Curie's principle "the symmetries of the causes are to be found in the effects" is a generalisation of Neumann's principle. At the end of the 19th century Voigt introduced tensor calculus to model the physical properties of anisotropic crystals.
+
+=== Interaction with electromagnetic radiation ===
+
+==== Double refraction ====
+In 1810 Étienne-Louis Malus determined that natural light, when reflected through a certain angle, behaves like one of the rays exiting a double-refracting crystal. Malus called this phenomenon polarization. In 1819 David Brewster found that all crystals could be classified as isotropic, uniaxial or biaxial. Augustin-Jean Fresnel published a paper on double refraction in 1827 in which he described light as a wave with field components in transverse polarization. Crystal optics was an active research area during the 19th century.
+
+==== Rotary polarization ====
+In 1811 François Arago, who favoured the corpuscular theory of light, discovered the rotation of the plane of polarization of light travelling through quartz. In 1812 Jean-Baptiste Biot, who favoured the wave theory of light discovered that while some crystals rotate the light to the right others rotate it to the left, and determined that the rotation is proportional to the thickness of substance traversed and to the wavelength of the light.
+In 1821 John Herschel pointed out the relation between the direction of rotation and the development of faces on quartz crystals. Suspecting that rotatory polarization is an effect of a lack of symmetry, Herschel established that quartz crystals often present faces placed in such a way that those belonging to certain crystals are mirror images of the corresponding faces of other crystals. He explained the connection between this arrangement and the respective rotation of light to the right and to the left. In 1822 Augustin-Jean Fresnel explained the rotation by postulating oppositely circularly polarized beams travelling with different velocities along the optic axis. In 1846 Michael Faraday discovered that the plane of polarization may also be rotated when light passes through an isotropic medium in a magnetic field.
+In 1848 Louis Pasteur gave the general relation between crystal morphology and rotatory polarization. Pasteur discovered the phenomenon of molecular asymmetry, that is that molecules could be chiral and exist as a pair of enantiomers. Pasteur's method was to physically separate the crystals of a racemic mixture of sodium ammonium tartrate into right- and left-handed crystals, and then dissolve them to make two separate solutions which rotated polarized light in opposite directions.

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+---
+title: "History of crystallography before X-rays"
+chunk: 4/9
+source: "https://en.wikipedia.org/wiki/History_of_crystallography_before_X-rays"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:30.404709+00:00"
+instance: "kb-cron"
+---
+
+==== Conical refraction ====
+Conical refraction is an optical phenomenon in which a ray of light, passing through a biaxial crystal along certain directions, is refracted into a hollow cone of light. There are two possible conical refractions, one internal and one external. In 1821–1822 Augustin-Jean Fresnel developed a theory of double refraction in both uniaxial and biaxial crystals. Fresnel derived the equation for the wavevector surface in 1823, and André-Marie Ampère rederived it in 1828.
+William Rowan Hamilton discovered the wavevector surface has four conoidal points and four tangent conics. This implies that, under certain conditions, a ray of light could be refracted into a cone of light within the crystal. He termed this phenomenon "conical refraction" and predicted two distinct types: internal and external. Hamilton announced his discovery on 22 October 1832. He then asked Humphrey Lloyd to prove his theory experimentally. Lloyd first observed conical refraction on 14 December 1832 with a specimen of aragonite, and published his results in early 1833.
+Hamilton and Lloyd's discovery was a significant victory for the wave theory of light and solidified Fresnel's theory of double refraction. The discovery of conical refraction is an example of a mathematical prediction being subsequently verified by experiment.
+
+==== Absorption and pleochroism ====
+In 1809 Louis Cordier discovered the phenomenon of pleochroism while investigating a new mineral that he named dichröıte (cordierite), whereby its crystals showed different colours when viewed along different axes. From 1817 to 1819 David Brewster made a systematic study of light absorption and pleochroism in various minerals and showed that, in uniaxial crystals, the absorption is smallest in the direction of, and greatest at right angles to, the optical axis. In 1838 Jacques Babinet discovered that the greatest absorption in a crystal generally coincided with the direction of greatest refractive index. In 1906 Friedrich Pockels published his Lehrbuch der Kristalloptik which gave an overview of the subject.
+
+==== Luminescence ====
+Luminescence is the non-thermal emission of visible light by a substance; an example is the emission of visible light by minerals in response to irradiation by ultraviolet light. The term luminescence was first used by Eilhard Wiedemann in 1888; he stated that luminescence was separate from thermal radiation, and he distinguished six different forms of luminescence according to their excitation.
+Fluorescence is luminescence which occurs during the irradiation of a substance by electromagnetic radiation; fluorescent materials stop emitting light nearly immediately after the irradiation is halted, except in the case of certain materials exhibiting delayed fluorescence (e.g., TADF, TTA). The term fluorescence was coined by George Stokes in 1852, and was derived from the behaviour of fluorite when exposed to ultraviolet light.
+Phosphorescence is long-lived luminescence; phosphorescent materials continue to emit light for some time after the radiation stops. In 1857 Edmond Becquerel invented the phosphoroscope, and in a detailed study of phosphorescence and fluorescence, showed that the duration of phosphorescence varies by substance, and that phosphorescence in solids is due to the presence of finely dispersed foreign substances.
+Some additional kinds of luminescence from crystals can arise from energy sources other than electromagnetic radiation.
+
+=== Effect of electricity and magnetism ===
+
+==== Electrical conduction ====
+The first observations on the variation of electrical conductivity with direction in a crystal (anisotropy) were made by Henri Hureau de Sénarmont in 1850 on 36 different substances. The results showed a correlation between the axes of symmetry and the directions of maximum or minimum conductivity.
+
+==== Magnetic properties ====
+Until the 19th century crystals were regarded either as magnetic or non-magnetic. Magnetic crystals are now called ferromagnetic to distinguish them from the several other kinds which have since been discovered. Siméon Denis Poisson (1826) put forward a theory of magnetism as applied to crystals and predicted the behaviour of crystals in a magnetic field which was verified by Julius Plücker in 1847. Plücker studied various natural crystals, such as quartz and related the reaction of the crystal to a magnetic field to its symmetry. All these crystals were repelled from a strong field, unlike ferromagnetic crystals; they were termed diamagnetic. In 1850 a number of investigations were carried out by Plücker and August Beer using torsion balances to measure the small forces involved in most observations. Not only were some crystals repelled from a strong field but others were slightly attracted. These were called paramagnetic. Between 1850 and 1856 John Tyndall studied diamagnetism in crystals.
+By the end of the 19th century the three types of crystal—ferromagnetic, diamagnetic and paramagnetic—were well established and theoretical studies had related diamagnetic and paramagnetic crystals to their crystal symmetry.
+
+==== Dielectric properties ====
+A dielectric is an electrical insulator that can be polarized by an applied electric field. In 1851 the first experiments on the behaviour of crystals in an electric field were carried out by Hermann Knoblauch in a manner similar to that used for the study of magnetic properties. The conductivity of the crystals, both over the surface and through the body of the crystal, made these experiments unreliable. In 1876 Elihu Root avoided some of these difficulties by employing a rapidly alternating field between parallel plates. A brief history on the theories of dielectrics in the 19th century has been written.
+
+=== Effect of temperature change ===

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+---
+title: "History of crystallography before X-rays"
+chunk: 5/9
+source: "https://en.wikipedia.org/wiki/History_of_crystallography_before_X-rays"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:30.404709+00:00"
+instance: "kb-cron"
+---
+
+==== Thermal expansion ====
+In 1824 Eilhard Mitscherlich observed that the angle between the cleavage faces of calcite changed with the temperature of the crystal. Mitscherlich concluded that, on heating, calcite contracts (has a negative coefficient of thermal expansion) in a direction perpendicular to the trigonal axis while expanding (positive coefficient) along that axis. This implies that there is a cone of directions along which there is no thermal expansion. In 1864 Hippolyte Fizeau used an optical interference method to make measurements on many crystals. The measurements of the change of interfacial angle and the expansion of cut plates and bars were applied to crystals of all symmetries.
+Crystals with less than cubic symmetry are anisotropic and will generally have different expansion coefficients in different directions. If the crystal symmetry is monoclinic or triclinic, even the angles between the axes are subject to thermal changes. In these cases the coefficient of thermal expansion is a symmetric tensor of second rank.
+
+==== Thermal conduction ====
+The first experiments on thermal conduction in crystals were carried out by Jean-Marie Duhamel in 1832. Henri Hureau de Sénarmont conducted experiments to determine if heat would move through crystals with directional dependence. He found that, for non-cubic crystals, the isothermal envelope surrounding a point source of heat in a crystal plate had an elliptical shape whose exact form depended on the orientation of the crystal. Sénarmont's results qualitatively established that thermal conductivity is directionally dependent (thermal anisotropy), with characteristic directions related to crystallographic axes. In 1848 Duhamel provided an analysis of Sénermont's findings.
+George Gabriel Stokes and William Thomson provided mathematical theories to explain Sénarmont's observations. Stokes acknowledged the connection between the phenomena and the symmetry of the crystal, and showed that the number of constants of heat conductivity reduces from nine to six in the case of two planes of symmetry. The matrix of thermal conductivity components resulting from Stoke's derivation constituted a tensor.
+
+==== Thermoelectricity ====
+Thomas Johann Seebeck discovered the thermoelectric effect in 1821, although it has been claimed that Alessandro Volta should be given the priority. In 1850 Jöns Svanberg used bismuth and antimony crystals to demonstrate a directional variation of the thermoelectric effect. In 1854 William Thomson put forward a mechanical theory of thermoelectric currents in crystalline solids. In 1889 Theodor Liebisch analysed the dependence of the thermoelectric force on the crystallographic direction in anisotropic crystals.
+
+==== Pyroelectricity ====
+Pyroelectricity is the generation of a temporary voltage in a crystal when subjected to a temperature change. The appearance of electrostatic charges upon a change of temperature has been observed since ancient times. Haüy made detailed investigations of pyroelectricity; he detected pyroelectricity in calamine and showed that electricity in tourmaline was strongest at the poles of the crystal and became imperceptible at the middle. Haüy later showed that hemihedral crystals are electrified by temperature change while holohedral (symmetric) crystals are not.
+Research into pyroelectricity became more quantitative in the 19th century. In 1824 David Brewster gave the effect the name it has today. In 1840 Gabriel Delafosse theorised that only molecules which are not symmetrical can be polarized electrically. Both William Thomson in 1878 and Woldemar Voigt in 1897 helped develop a theory for the processes behind pyroelectricity. A detailed history of pyroelectricity has been written by Sidney Lang; shorter histories have also been published.
+
+=== Effect of mechanical force ===
+
+==== Elasticity ====
+Some minerals, for example mica, are highly elastic, springing back to their original shape after being bent. Others, for example talc, may be readily bent but do not return to their original form when released. In 1828 Cauchy showed that 36 independent constants were required to describe elasticity in crystals. William Thomson (1857) showed that the thermodynamic requirements of a reversible process require only 21 constants.
+In the period 1874–1888 Woldemar Voigt was the leading researcher on the elasticity of crystals. Voigt showed that the number of elasticity constants reduces as more symmetry is introduced into the crystal. For a triclinic crystal, which is the most general case, 21 elasticity constants are required. For a monoclinic crystal there are 13 elasticity constants, for a rhombic crystal 9, for a hexagonal crystal 7, for a tetragonal crystal 6, and finally for a cubic crystal there are only 3.
+
+==== Photoelasticity ====
+Photoelasticity describes changes in the optical properties of a material under mechanical deformation. David Brewster detected the effect in crystals and showed that uniaxial crystals could be made biaxial. In 1822 Augustin-Jean Fresnel experimentally confirmed that the photoelastic effect was a stress-induced birefringence.
+Franz Ernst Neumann investigated double refraction in stressed transparent bodies. In 1841 Neumann published his elastic equations, which describe, in differential form, the changes which polarized light experiences when travelling through a stressed body. The Neumann equations are the basis of all subsequent photoelasticity research.
+The photoelastic effect was analysed by Friedrich Pockels, who also discovered the Pockels electro-optic effect (the production of birefringence of light on the application of an electric field). In 1889–1890 Pockels produced a phenomenological theory for both of these effects for all crystal classes.
+
+==== Piezoelectricity ====
+In 1880 Pierre and Jacques Curie discovered piezoelectricity (an electric charge that accumulates in response to applied mechanical stress) in quartz, tourmaline, and other crystals. The Curies, however, did not predict the converse piezoelectric effect (the internal generation of a mechanical strain resulting from an applied electric field). The converse effect was deduced by Gabriel Lippmann in 1881. The Curies immediately confirmed the existence of the effect, and went on to obtain quantitative proof of the complete reversibility of electro-elasto-mechanical deformations in piezoelectric crystals.
+In 1890 Woldemar Voigt published a phenomenological theory of the piezoelectric effect based on the symmetry of crystals without centrosymmetry.
+
+== Chemical crystallography ==

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+---
+title: "History of crystallography before X-rays"
+chunk: 6/9
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+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:30.404709+00:00"
+instance: "kb-cron"
+---
+
+Up until 1800 neither crystallography nor chemistry were established sciences in the modern sense; as the 19th century progressed both sciences developed in parallel. In the 18th century chemistry was in a transitional period as it moved from the mystical and philosophical approach of the alchemists, to the experimental and logical approach of the scientific chemists such as Antoine Lavoisier, Humphry Davy and John Dalton.
+
+=== Early 19th century ===
+From the late 18th century it became apparent that a crystal of a substance was composed of units, whether thought of as atoms, ions, molecules, or polyhedra, in a regular spatial arrangement, termed its crystal structure.
+The most notable early theory for crystal structures was that of René Just Haüy. In 1801 Haüy, published his Traité de Minéralogie In this work Haüy described how the law of rational indices establishes relationships between the orientations of the crystal faces, and explains that crystalline solids are formed by replicas of what would now be considered a unit cell. Haüy's theory called for fixed mineral species, fixed crystal morphology, and constant chemical composition. This was a mineralogical equivalent to the law of definite proportions in chemistry. In 1822 Haüy published Traité de Cristallographie an updated version of his work of 1801. Haüy postulated, "to each specific substance with a well defined chemical composition, capable of existence in a crystalline form, there corresponds a shape that is specific and characteristic of that substance."
+In 1808 John Dalton published his atomic theory of matter in A New System of Chemical Philosophy,. In Dalton's theory, there were four key assertions: "matter is made up of roughly spherical atoms, which were indivisible and indestructible; all atoms of a given element are identical in mass and properties; compounds are formed by a combination of two or more different kinds of atoms; and chemical reactions involve the rearrangement of atoms". Thomas Kuhn proposed Dalton's atomic theory as an example of a paradigm in which Dalton asserted that atoms can only combine in simple, whole-number ratios (law of multiple proportions). Under this new paradigm, any reaction which did not occur in fixed proportion could not be a chemical process.
+There was a contradiction between the crystallographic and chemical paradigms. Haüy's theory asserted that crystals were composed of polyhedral units stacked up in three dimensions without gaps; Dalton's theory, by contrast, implied that crystals were constructed by a periodic arrangement of spherical atoms in space. Haüy's theory was generally accepted by his fellow mineralogists in the period 1801–1815 but then came under attack from the German dynamist school led by Christian Samuel Weiss.  Weiss and his followers studied the external symmetry of crystals rather than their internal structure. In 1819, Weiss demonstrated the generality of the phenomenon of hemihedry, thus challenging Haüy's holohedral approach.
+In 1813 William Hyde Wollaston adopted Dalton's ideas and proposed using sphere packing to model crystal structures.  In 1822 John Herschel proposed a causal relationship between the handedness of quartz crystals and the direction of their optical rotation. In a paper published in 1830 Brewster attempted to relate the phenomenon of double refraction to the arrangement of the molecules in crystals. If a crystal has three axes at right angles to each other then, if they are equivalent, the crystal is isotropic, if two are equivalent and the third different, the crystal is uniaxial, and if all three are different, the crystal is biaxial.
+
+=== Isomorphism ===
+Originally, René Just Haüy considered that each chemical compound had a characteristic crystalline form. However, based on his 1808 work with aragonite and his earlier studies of calcite Haüy had to concede that substances with the same chemical composition but different molecular arrangements could have different crystalline forms.
+In 1819 Eilhard Mitscherlich discovered the law of isomorphism which states that compounds which contain the same number of atoms, and have similar structures, tend to exhibit similar crystal forms. Mitscherlich carried out the first systematic research on the dependence of crystal forms on their chemical nature. The discovery of isomorphism was the first major step in chemical crystallography and Emil Wohlwill regarded Mitscherlich's work on isomorphism as a milestone in the history of the atomic-molecular theory. The discovery of the phenomena of isomorphism and polymorphism dealt a clear blow to Haüy's crystal structure theory.
+Mitscherlich's findings were a central consideration of the atomic weight determinations in 1819 by Jöns Jacob Berzelius, a leading proponent of Dalton's atomic theory. Berzelius classified minerals by their chemical composition rather than by their crystal morphology, as was the established practice. Mitscherlich's research, together with the work of Alexis Thérèse Petit and Pierre-Louis Dulong that heat capacities of solids vary with temperature and inversely with atomic weight, led Berzelius to declare them as a positive confirmation of the atomic theory.
+A contemporary historical review of the development of isomorphism in the 19th century was written by Andreas Artsruni.

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+title: "History of crystallography before X-rays"
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+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:30.404709+00:00"
+instance: "kb-cron"
+---
+
+=== Polymorphism ===
+In crystallography, polymorphism is the phenomenon where a compound can crystallize into more than one crystal structure; in the case of elements the term allotropy is sometimes used.
+Eilhard Mitscherlich discovered polymorphism in his studies of sodium phosphate and sulphur in 1821–3. In the 1830s the development of the microscope enhanced observations of polymorphism and aided Moritz Ludwig Frankenheim's studies. Frankenheim was able to demonstrate methods to induce crystal phase changes. Soon after, the more sophisticated polarized light microscope came into use, and it provided better visualization of crystalline phases allowing crystallographers to distinguish between different polymorphs. The hot stage was invented and fitted to a polarized light microscope by Otto Lehmann in about 1877. This invention helped crystallographers determine melting points and observe polymorphic transitions.
+In 1870 Paul Groth defined morphotropy as the state of two crystals whose similar physical structure is due to similar chemical composition. Groth examined the change in symmetry of a crystal as a result of the replacement of a hydrogen atom by another univalent atom or radical. In 1897 Wilhelm Ostwald introduced Ostwald's rule, to describe the formation of polymorphs. The rule states that usually the less stable polymorph crystallizes first. Ostwald's rule is not a universal law but a common tendency observed in nature.
+
+=== Molecular chirality ===
+In 1811 François Arago constructed a polariscope and used it to discover that quartz crystals would rotate the plane of polarization of polarized light. Shortly after Jean-Baptiste Biot found a similar optical rotation effect for solutions and concluded that the effect was an inherent property of certain molecules. In 1830 Jöns Jacob Berzelius discovered that tartaric and racemic acids have the same chemical composition, and concluded that a difference in the arrangement of the atoms in the molecules creates compounds with different properties; in the same paper Berzelius suggested the term "isomerism" for the phenomenon.
+In 1831 Mitscherlich studied the tartrates in order to determine the differences between the isomers tartaric acid and racemic acid. By 1832 Biot had discovered that tartaric acid from grape juice was dextrorotatory and that racemic acid was optically inactive. In 1844 Mitscherlich found that the solution of sodium ammonium tartrate was optically active, but that of sodium ammonium paratartrate was optically inactive. The work of Biot and Mitscherlich was the starting point for research by Louis Pasteur. Pasteur discovered the phenomenon of molecular asymmetry, that is that molecules could be chiral and exist as a pair of enantiomers. Pasteur's research was in part informed by considerations of molecular symmetry.
+William Thomson (Lord Kelvin) introduced the word "chiral" in 1904 to describe handed figures. Objects that do not exhibit optical isomerism are said to be "achiral", that is their image in a plane mirror can be made congruent with itself. The term chirality has almost completely displaced the term "dissymmetry" which was used by Pasteur.
+
+=== Liquid crystals ===
+In 1888 Friedrich Reinitzer examined the properties of various derivatives of cholesterol. Previously, other researchers had observed distinct colour effects when cooling cholesterol derivatives just above the freezing point, but had not associated it with a new phenomenon. Reinitzer found that cholesteryl benzoate does not melt in the same way as most substances, but has two melting points. Reinitzer consulted Otto Lehmann and they exchanged letters and samples. Lehmann examined the intermediate cloudy fluid, and reported seeing crystallites. Reinitzer published his results on 3 May 1888.
+Reinitzer discovered three important features of liquid crystals: the existence of two melting points, the reflection of circularly polarized light, and the ability to rotate the direction of polarized light. The research was continued by Lehmann who started a systematic study, first of cholesteryl benzoate, and then of related compounds which exhibited the double-melting phenomenon. He was able to make observations in polarized light, and his microscope was equipped with a hot stage (sample holder equipped with a heater) enabling high temperature observations. The intermediate cloudy phase clearly sustained flow, but other features convinced Lehmann that he was dealing with a solid. By the end of August 1889 he had published his results. Liquid crystals are now known to have one- or two-dimensional periodicity, with rod or layer symmetry respectively.
+
+=== Late 19th century ===
+From the 1830s Haüy's molecular crystal structure theory started to be combined with the atomic theory of the chemists to produce a view of a crystal as the regular arrangement of atoms or molecules in space. In 1849 Auguste Bravais related the symmetry of the crystal, considered as one of 14 space lattices, to that of its constituting molecules and formalized the reticular interpretation of hemihedry given by Gabriel Delafosse. In 1852 Delafosse attempted to relate the structure of the molecule to the external shape of the crystal.
+Developments in chemistry in the 1850s and 1860s were largely independent of the mathematical and geometrical direction of crystallography in the period 1850–1895 which had little concern with the practicalities of atomic and molecular arrangement.
+In 1874 Jacobus Henricus van 't Hoff and Joseph Le Bel independently proposed the tetrahedral arrangement of the atoms bound to carbon in organic molecules. Van't Hoff's theory validated and explained Pasteur's results with tartrate crystals, and was fundamental to the further development of stereochemistry.
+Until the use of X-rays there was no way to determine the actual crystal structure of even the simplest substances such as salt (NaCl). In the period between the discovery of X-rays (1895) and X-ray diffraction (1912) William Barlow and William Jackson Pope developed the principles of packing, and showed how to deduce the structures of some simple compounds. William Johnson Sollas emphasised the importance of different atomic sizes in constructing simple crystals, and correctly concluded that the sodium and chlorine atoms in salt would be of different sizes.
+In his preface to Andreas Fock's An introduction to chemical crystallography Pope summarised the state of chemical crystallography in 1895 as follows:

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+---
+title: "History of crystallography before X-rays"
+chunk: 8/9
+source: "https://en.wikipedia.org/wiki/History_of_crystallography_before_X-rays"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:30.404709+00:00"
+instance: "kb-cron"
+---
+
+"Our knowledge of the physical and geometrical properties of crystals is now very complete, but their relations to chemical constitution and composition are as yet but little known."
+After 1912 crystallography would develop dramatically with the widespread adoption of X-ray diffraction to determine crystal structures.
+
+== Instrumentation ==
+
+=== Goniometry ===
+
+Before the development of X-ray diffraction, the study of crystals was based on physical measurements of their geometry using a goniometer. This involved measuring the angles of crystal faces relative to each other and to crystallographic axes in order to establish the symmetry of the crystal.
+Quantitative crystallography began with Arnould Carangeot’s invention of the contact goniometer in 1780, a handheld instrument with which the angles between the faces of a large crystal could be measured to an accuracy of, at best, a quarter of a degree (15′). Carangeot was a student of Jean-Baptiste L. Romé de l'Isle at the time of his invention of the basic crystallographic measuring instrument. Romé de l'Isle described over 500 crystal forms and accurately measured the interfacial angles of a great variety of crystals, using Carangeot's goniometer. Romé de l'Isle noted that the angles are characteristic of a substance, thus generalizing the law of constancy of interfacial angles postulated by Nicolas Steno in 1669.
+
+William Hyde Wollaston invented the reflection goniometer in 1809. This instrument could be used with small crystals with an accuracy of one twelfth of a degree (5′) and was stated by John Herschel to have had a significant influence on the scientific development of mineralogy. The more precise angular measurements produced by the reflection goniometer challenged the crystal structure theory of René Just Haüy.
+In 1817 Étienne-Louis Malus improved measuring conditions by introduced the first goniometer to incorporate a telescope. in 1839 Jacques Babinet's horizontal circle goniometer was the first to incorporate a collimator.
+The invention of the two-circle reflection goniometer allowed a crystal to be rotated around two perpendicular axes. The advantage of this type of goniometer is that a crystal face could be brought into reflection without having to remount the crystal. Although there is some evidence that William Hallowes Miller invented a form of two-circle reflection goniometer in 1874, the credit is usually shared between Evgraf Fedorov who first described the invention in 1889, and Victor Goldschmidt and Siegfried Czapski who constructed two different models in 1893. In 1900 three-circle goniometers were designed but their high cost and complexity meant that they were not widely adopted.
+
+=== Polarimetry ===
+
+In the 17th century optical microscopes were used by, amongst others, Robert Hooke, Antonie van Leeuwenhoek and Henry Baker to examine crystal morphology.
+The instruments necessary for the study of the optical properties of crystals developed in parallel with the theoretical work. In 1809 Étienne-Louis Malus discovered that light becomes polarized when reflected by glass. Jean-Baptiste Biot was an early investigator of polarized light and produced a polarimeter (or polariscope) with a polarizer and an analyser but no lenses. In 1829 William Nicol described his polarizing prism. Giovanni Battista Amici devised a polarizing microscope around 1830 and in 1844 was probably the first to use lenses in conjunction with a polarizer and an analyser.
+Compensators for the measurement of double refraction were introduced by David Brewster in 1830. The Amici-Bertrand lens was introduced by Émile Bertrand in 1878 based on Amici's original design of 1844. The universal stage for the polarizing microscope was introduced by Evgraf Fedorov in 1891.
+
+=== Reflection from opaque materials ===
+
+The study of the optical properties of opaque substances has been closely linked with the development of suitable microscopes. The first instrument adapted to reflected light was the Lieberkühn reflector attributed to Johann Nathanael Lieberkühn. The use of polished and etched surfaces for this type of study was introduced by Jöns Jacob Berzelius in 1813. In 1858 Henry Clifton Sorby established the technique of cutting minerals and crystals into thin sections for examination under the polarizing microscope.
+
+=== Crystal models ===
+
+Drawings of crystal morphology were a feature of early writings on mineralogy. The descriptive period of mineralogy came to a conclusion with Paul Heinrich von Groth's systematic classification of minerals based on their chemical composition and crystal structure which were published in his monumental 5-volume Chemische Kristallographie of 1906–1919, which contained crystalline morphology and physical property data on nearly 10,000 substances.
+Crystal drawings were useful in understanding morphology but, as teaching aids, they were inferior to three-dimensional crystal models. A crystal model allowed the easier identification of symmetry elements such as rotation axes and reflection planes.
+Early collections of crystal models were made by Jean-Baptiste L. Romé de l'Isle to support the sale of his 1783 work Crystallographie, and by René Just Haüy to support the sale of his 1801 work Traité de Minéralogie. Models were made in a variety of materials including pear wood, terracotta, paper, plaster, cardboard, plate glass, and box wood. From 1850 Adam August Krantz offered a wide variety of collections of crystal models for sale.
+
+== Academic community ==
+
+Before the 20th century crystallography was not a well-established academic discipline. There were no academic positions specifically in crystallography. Workers in the field normally carried out their crystallographic research as an ancillary to other employment(s), or had independent means.  The leading workers in the field were employed as follows:
+
+Professors
+Mathematics or science: Airy, Arago, E. Becquerel, Bergman, Berzelius, Biot, Bravais, Curie, Drude, Fedorov, Frankenheim, Guglielmini, Hamilton, Kepler, Lehmann, Liebig, Linnaeus, Mitscherlich, Ostwald, Pasteur, Plücker, Pockels, Reinitzer, Schoenflies, Seeber, Sohncke, Stokes, Thomson, Tyndall, Voigt Wöhler
+Mineralogy: Delafosse, Groth, Haüy, Hessel, Liebisch, Mallard, Miller, Mohs, Naumann, Neumann, Sénarmont Weiss, Whewell
+Other fields: Libavius (history)
+Physicians: Bartholinus, Cappeller, Hessel, Steno, Wollaston
+Clerics: Haüy, Steno
+Officials:
+Military officers: Bravais, Gadolin, Malus
+Municipal officials: Hooke, van Leeuwenhoek
+Other employment:  Brewster (editor), Carangeot (business manager), Fresnel (engineer), Romé de l'Isle (cataloguer), Sohncke (meteorological service)
+Independently wealthy: Barlow, Herschel, Huygens
+In the nineteenth century there were informal schools of crystallography researchers in France, Germany and England.

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+---
+title: "History of crystallography before X-rays"
+chunk: 9/9
+source: "https://en.wikipedia.org/wiki/History_of_crystallography_before_X-rays"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:30.404709+00:00"
+instance: "kb-cron"
+---
+
+Until the founding of Zeitschrift für Krystallographie und Mineralogie by Paul Groth in 1877 there was no lead journal for the publication of crystallographic papers. The majority of crystallographic research was published in the journals of national scientific societies, or in mineralogical journals. The inauguration of Groth's  journal marked the emergence of crystallography as a mature science independent of geology.
+
+== Bibliography ==
+
+The following books have significant coverage of the history of crystallography before X-rays:
+
+1825: Carl Michael Marx, Geschichte der Crystallkunde, in German Crystallography up to the early 19th century.
+1837: William Whewell, History of the Inductive Sciences: From the Earliest to the Present Times Wide-ranging history of the sciences including a section on the history of mineralogy.
+1918: Hélène Metzger, La Gènese de la Science de Cristaux, in French History of crystallography from the 17th to the early 18th century, with a particular focus on French scientists.
+1926: Paul Heinrich von Groth, Entwicklungsgeschichte der Mineralogischen Wissenschaften, in German Mineralogical and crystallographical history to the end of the 19th century.
+1962: Paul Peter Ewald, Fifty Years of X-ray diffraction Covers the historical background to the discovery of X-ray diffraction.
+1966: John G. Burke, Origins of the science of crystals The development of crystallography from the mid-18th to the early 19th century with detailed consideration of the work of René Just Haüy; the book received generally positive reviews.
+1976: Seymour H. Mauskopf, Crystals and compounds: molecular structure and composition in nineteenth-century French science. A well-reviewed monograph on the intersection of crystallography and molecular theory in the 19th century.
+1978: Ilarion I. Shafranovskii, The History of Crystallography, in Russian, 2 vols. A detailed history of crystallography to 1912 with a particular focus on Russian scientists.
+1986: Eginhard Fabian, Die Entdeckung der Kristalle: der historische Weg der Kristallforschung zur Wissenschaft, in German.
+1988: Johann Jakob Burckhardt, Die Symmetrie der Kristalle: Von René-Just Haüy zur kristallographischen Schule in Zürich, in German. A study of the development of symmetry in crystallography.
+1989: Erhard Scholz, Symmetrie, Gruppe, Dualität, in German. The first part traces the development of symmetry in crystallography in the 19th century. The book received mixed reviews.
+1990: José Lima-de-Faria, Historical atlas of crystallographyl A collection of timelines, historical essays, portraits and book title pages.
+2007: Curtis P. Schuh, Mineralogy & Crystallography: On the History of these Sciences through 1919 and Mineralogy and Crystallography: An Annotated Biobibliography, 2 vols. A large, unpublished compendium of historical and bibliographic information on crystallography and mineralogy.
+2013: André Authier, Early days of x-ray crystallography. A detailed, up-to-date, and generally well-reviewed history of crystallography.
+
+== See also ==
+Chemical crystallography before X-rays
+Geometrical crystallography before X-rays
+Physical crystallography before X-rays
+Timeline of crystallography
+
+== Citations ==
+
+== Works cited ==

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+---
+title: "History of geomagnetism"
+chunk: 1/4
+source: "https://en.wikipedia.org/wiki/History_of_geomagnetism"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:55.648373+00:00"
+instance: "kb-cron"
+---
+
+The history of geomagnetism is concerned with the history of the study of Earth's magnetic field. It encompasses the history of navigation using compasses, studies of the prehistoric magnetic field (archeomagnetism and paleomagnetism), and applications to plate tectonics.
+Magnetism has been known since prehistory, but knowledge of the Earth's field developed slowly. The horizontal direction of the Earth's field was first measured in the fourth century BC but the vertical direction was not measured until 1544 AD and the intensity was first measured in 1791. At first, compasses were thought to point towards locations in the heavens, then towards magnetic mountains. A modern experimental approach to understanding the Earth's field began with de Magnete, a book published by William Gilbert in 1600. His experiments with a magnetic model of the Earth convinced him that the Earth itself is a large magnet.
+
+== Early ideas on magnetism ==
+Knowledge of the existence of magnetism probably dates back to the prehistoric development of iron smelting. Iron can be obtained on the Earth's surface from meteorites; the mineral lodestone is rich in the magnetic mineral magnetite and can be magnetized by a lightning strike.  In his Natural History, Pliny the Elder recounts a legend about a Magnes the shepherd on the island of Crete whose iron-studded boots kept sticking to the path.  The earliest ideas on the nature of magnetism are attributed to Thales (c. 624 BC – c. 546 BC).
+In classical antiquity, little was known about the nature of magnetism. No sources mention the two poles of a magnet or its tendency to point northward. There were two main theories about the origins of magnetism. One, proposed by Empedocles of Acragas and taken up by Plato and Plutarch, invoked an invisible effluvium seeping through the pores of materials; Democritus of Abdera replaced this effluvium by atoms, but the mechanism was essentially the same. The other theory evoked the metaphysical principle of sympathy between similar objects. This was mediated by a purposeful life force that strove toward perfection. This theory can be found in the writings of Pliny the Elder and Aristotle, who claimed that Thales attributed a soul to the magnet. In China, a similar life force, or qi, was believed to animate magnets, so the Chinese used early compasses for feng shui.
+Some classical ideas lingered until well after the first scientific experiments on magnetism. One belief, dating back to Pliny, was that fumes from eating garlic and onions could destroy the magnetism in a compass, rendering it useless. Even after William Gilbert disproved this in 1600, there were reports of helmsmen on British ships being flogged for eating garlic. However, this belief was far from universal. In 1558 Giambattista della Porta reported "When I enquired of mariners whether it were so that they were forbid to eat onyones and garlick for that reason, they said they were old wives’ fables and things ridiculous, and that sea-men would sooner lose their lives then abstain from eating onyons and garlick."
+
+== Measurement of the field ==
+
+At a given location, a full representation of the Earth's magnetic field requires a vector with three coordinates (see figure). These can be Cartesian (north, east, and down) or spherical (declination, inclination, and intensity). In the latter system, the declination (the deviation from true north, a horizontal angle) must be measured first to establish the direction of magnetic North; then the dip (a vertical angle) can be measured relative to magnetic North. In China, the horizontal direction was measured as early as the fourth century BC, and the existence of declination first recognized in 1088. In Europe, this was not widely accepted until the middle of the fifteenth century AD. Inclination (also known as magnetic dip) was first measured in 1544 AD. The intensity was not measured until 1791, after advances in the understanding of electromagnetism.
+
+=== Declination ===
+
+The magnetic compass existed in China back as far as the fourth century BC. It was used as much for feng shui as for navigation on land. It was not until good steel needles could be forged that compasses were used for navigation at sea; before that, they could not retain their magnetism for long. The existence of magnetic declination, the difference between magnetic north and true north, was first recognized by Shen Kuo in 1088.
+The first mention of a compass in Europe was in 1190 AD by Alexander Neckam. He described it as a common navigational aid for sailors, so the compass must have been introduced to Europe some time earlier. Whether the knowledge came from China to Europe, or was invented separately, is not clear. If the knowledge was transmitted, the most likely intermediary was Arab merchants, but Arabic literature does not mention the compass until after Neckam. There is also a difference in convention: Chinese compasses point south while European compasses point north.
+In 1269, Pierre de Maricourt (commonly referred to as Petrus Peregrinus) wrote a letter to a friend in which he described two kinds of compass, one in which an oval lodestone floated in a bowl of water, and the first dry compass with the needle mounted on a pivot. He also was the first to write about experiments with magnetism and describe the laws of attraction. An example is the experiment where a magnet is broken into two pieces and the two pieces can attract and repel each other (in modern terms, they both have north and south poles). This letter, generally referred to as Epistola de Magnete, was a landmark in the history of science.
+Petrus Peregrinus assumed that compasses point towards true north. While his contemporary Roger Bacon is reputed to observe that compasses deviated from true north, the idea of magnetic declination was only gradually accepted. At first it was thought that the declination must be the result of systematic error. However, by the middle of the fifteenth century, sundials in Germany were oriented using corrections for declination.

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+---
+title: "History of geomagnetism"
+chunk: 2/4
+source: "https://en.wikipedia.org/wiki/History_of_geomagnetism"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:55.648373+00:00"
+instance: "kb-cron"
+---
+
+=== Inclination ===
+A compass must be balanced to counter the tendency of the needle to dip in the direction of the Earth's field. Otherwise, it will not spin freely. Often, compasses that are balanced for one latitude do not work as well at a different latitude. This problem was first reported by Georg Hartmann, a vicar in Nuremberg, in 1544. The English mariner Robert Norman was the first to recognize that this occurs because the Earth's field itself is tilted from the vertical. In his book The Newe Attractive, Norman called inclination "a newe discouered secret and subtil propertie concernyng the Declinyng of the Needle." He created a compass in which the needle was floated in a goblet of water, attached to a cork to make it neutrally buoyant. The needle could orient itself in any direction, so it dipped to align itself with the Earth's field. Norman also created a dip circle, a compass needle pivoted about a horizontal axis, to measure the effect.
+
+== Early ideas about the source ==
+
+In early attempts to understand the Earth's magnetic field, measuring it was only part of the challenge. Understanding the measurements was also difficult because the mathematical and physical concepts had not yet been developed – in particular, the concept of a vector field that associates a vector with each point in space. The Earth's field is generally represented by field lines that run from pole to pole; the field at any point is parallel to a field line but does not have to point at either pole.  As late as the eighteenth century, however, a natural philosopher would believe that a magnet had to be pointing directly at something. Thus, the Earth's magnetic field had to be explained by localized sources, and as more was learned about the Earth's field, these sources became increasingly complex.
+At first, in both China and Europe, the source was assumed to be in the heavens – either the celestial poles or the Pole star. These theories required that magnets point at (or very close to) true north, so they ran into difficulty when the existence of declination was accepted. Then natural philosophers began to propose earthly sources such as a rock or mountain.
+Legends about magnetic mountains go back to the classical era. Ptolemy recounted a legend about magnetic islands (now thought to be near Borneo) that exerted such a strong attraction on ships with nails that the ships were held in place and could not move. Even more dramatic was the Arab legend (recounted in One Thousand and One Nights) that a magnetic mountain could pull all the nails out of a ship, causing the ship to fall apart and founder. The story passed to Europe and became part of several epic tales.
+Europeans started to place magnetic mountains on their maps in the sixteenth century. A notable example is Gerardus Mercator, whose famous maps included a magnetic mountain or two near the North Pole. At first, he just placed a mountain in an arbitrary location; but later he attempted to measure its location based on declinations from different locations in Europe. When subsequent measurements resulted in two contradictory estimates for the mountain, he simply placed two mountains on the map.
+
+== Beginnings of modern science ==
+
+=== William Gilbert ===
+Magnus magnes ipse est globus terrestris. (The Earth itself is a great magnet.)
+1600 was a notable year for William Gilbert. He became president of the Royal College of Physicians of London, was appointed personal physician for Queen Elizabeth I, and wrote De Magnete, one of the books that mark the beginning of modern science. De Magnete is most famous for introducing (or at least popularizing) an experimental approach to science and deducing that the Earth is a great magnet.
+Gilbert's book is divided into six chapters. The first is an introduction in which he discusses the importance of experiment and various facts about the Earth, including the insignificance of surface topography compared to the radius of the Earth. He also announces his deduction that the Earth is a great magnet. In book 2, Gilbert deals with "coition", or the laws of attraction. Gilbert distinguishes between magnetism and static electricity (the latter being induced by rubbing amber) and reports many experiments with both (some dating back to Peregrinus). One involves breaking a magnet in two and showing that both parts have a north and south pole. He also dismisses the idea of perpetual motion. The third book has a general description of magnetic directions along with details on how to magnetize a needle. He also introduces his terella, or "little Earth". This is a magnetized sphere that he uses to model the magnetic properties of the Earth. In chapters 4 and 5 he goes into more detail about the two components of the direction, declination and inclination.

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+---
+title: "History of geomagnetism"
+chunk: 3/4
+source: "https://en.wikipedia.org/wiki/History_of_geomagnetism"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:55.648373+00:00"
+instance: "kb-cron"
+---
+
+In the late 1590s Henry Briggs, a professor of geometry at Gresham College in London, had published a table of magnetic inclination with latitude for the earth. It agreed well with the inclinations that Gilbert measured around the circumference of his terrella. Gilbert deduced that the Earth's magnetic field is equivalent to that of a uniformly magnetized sphere, magnetized parallel to the axis of rotation (in modern terms, a geocentric axial dipole). However, he was aware that declinations were not consistent with this model. Based on the declinations that were known at the time, he proposed that the continents, because of their raised topography, formed centers of attraction that made compass needles deviate. He even demonstrated this effect by gouging out some topography on his terella and measuring the effect on declinations. A Jesuit monk, Niccolò Cabeo, later took a leaf from Gilbert's book and showed that, if the topography was on the correct scale for the Earth, the differences between the highs and lows would only be about one tenth of a millimeter. Therefore, the continents could not noticeably affect the declination.
+The sixth book of de Magnete was devoted to cosmology. He dismissed the prevailing Ptolemaic model of the universe, in which the planets and stars are organized in a series of concentric shells rotating about the Earth, on the grounds that the speeds involved would be absurdly large ("there cannot be diurnal motion of infinity"). Instead, the Earth was rotating about its own axis. In place of the concentric shells, he proposed that the heavenly bodies interacted with each other and Earth through magnetic forces. Magnetism maintained the Earth's position and made it rotate, while the magnetic attraction of the Moon drove the tides. Some obscure reasoning led to the peculiar conclusion that a terella, if freely suspended, would orient itself in the same direction as the Earth and rotate daily.  Both Kepler and Galileo would adopt Gilbert's idea of magnetic attraction between heavenly bodies, but Newton's law of universal gravitation would render it obsolete.
+
+=== Guillaume le Nautonier ===
+
+In about 1603, the Frenchman Guillaume le Nautonier (William the Navigator), Sieur de Castelfranc, published a rival theory of the Earth's field in his book Mecometrie de l'eymant (Measurement of longitude with a magnet). Le Nautonier was a mathematician, astronomer and Royal Geographer in the court of Henry IV. He disagreed with Gilbert's assumption that the Earth had to be magnetized parallel to the rotational axis, and instead produced a model in which the magnetic moment was tilted by 22.5° – in effect, the first tilted dipole model. The last 196 pages of his book were taken up with tables of latitudes and longitudes with declination and inclination for use by mariners. If his model had been accurate, it could have been used to determine both latitude and longitude using a combination of magnetic declination and astronomical observations.
+Le Nautonier tried to sell his model to Henry IV, and his son to the English leader Oliver Cromwell, both without success. It was widely criticized, with Didier Dounot concluding that the work was based on "unfounded assumptions, errors in calculation and data manipulation". However, the geophysicist Jean-Paul Poirier examined the works of both le Nautonier and Dounot, and found that the error was in Dounot's reasoning.
+
+=== Temporal variation ===
+
+One of Gilbert's conclusions was that the Earth's field could not vary in time. This was soon to be proved false by a series of measurements in London. In 1580, William Borough measured the declination and found it to be 111⁄4° NE. In 1622, Edmund Gunter found it to be 5° 56' NE. He noted the difference from Borough's result but concluded that Borough must have made a measurement error. In 1633, Henry Gellibrand measured the declination in the same location and found it to be 4° 05' NE. Because of the care with which Gunther had made his measurements, Gellibrand was confident that the changes were real. In 1635 he published A Discourse Mathematical on the Variation of the Magneticall Needle stating that the declination had changed by more than 7° in 54 years. The reality of geomagnetic secular variation was rapidly accepted in England, where Gellibrand had a high reputation, but in other countries it was met with skepticism until it was confirmed by further measurements.
+The observations of Gellibrand inspired extensive efforts to determine the nature of variation - global or local, predictable or erratic. It also inspired new models for the origin of the field. Henry Bond Senior gained notoriety by successfully predicting in 1639 that the declination would be zero in London in 1657. His model, which involved a precessing dipole, was strongly criticized by a royal commission, but it continued to be published in navigational instruction manuals for decades. Dynamic models involving multiple poles were also proposed by Peter Perkins (1680) and Edmond Halley (1683, 1692), among others. In Halley's model, the Earth consisted of concentric spheres. Two magnetic poles were on a fixed outer sphere and two more were on an inner sphere that rotated westwards, giving rise to a "westward drift". Halley was so proud of this theory that a portrait of him at the age of eighty included a diagram of it (above right).
+
+== Magnetic navigation ==
+
+Early mariners used portolan charts for navigation. These charts showed coastline with windrose lines connecting ports. A mariner could navigate by aligning the chart with a compass and following the compass heading. Early charts had distorted coastlines because the cartographers did not know about declination, but the charts still worked because mariners were sailing in straight lines.
+An accurate determination of longitude was necessary to determine the proper "magnetic declination", that is, the difference between indicated magnetic north and true north, which can differ by up to 10 degrees in the important trade latitudes of the Atlantic and Indian Oceans.

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+---
+title: "History of geomagnetism"
+chunk: 4/4
+source: "https://en.wikipedia.org/wiki/History_of_geomagnetism"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:55.648373+00:00"
+instance: "kb-cron"
+---
+
+=== Expeditions to the magnetic poles ===
+The magnetic North Pole differs from the geographic North Pole (Earth's rotation axis), magnetic north which is the direction of north given by a compass, and the theoretical Geomagnetic pole. 
+The search for the magnetic north pole began in 1818 with a British expedition exploring the Northwest Passage. 
+In 1831 James Clark Ross from the ship Victory first located the Earth's magnetic North Pole on the west coast of the Boothia Peninsula (Arctic Archipelago). In 1842 the Antarctic Ross expedition inferred the position of the South Magnetic Pole, which was not formally located until the twentieth century.
+Since then, the North magnetic pole has migrated on a north-northwest direction, towards Siberia, and since 2017 has been located a few hundred kilometres into the Arctic Ocean. Owing to liquid motion of the Earth's core, the actual magnetic poles are constantly moving (secular variation). The poles also daily swing in an oval of around 80 km (50 miles) in diameter due to solar wind deflecting the magnetic field. The position of the North Magnetic Pole is reassessed every five years by the British Geological Survey (BGS) and the US National Oceanic and Atmospheric Administration (NOAA), which are responsible for the World Magnetic Model (WMM).
+
+=== Magnetic observation campaigns ===
+
+A magnetic survey (1698-1700) by the British yielded the 1702 magnetic chart of the world by Edmond Halley.
+Early magnetic observatories were established in Munich(1819) and Berlin (1827). Observed variations in magnetic direction, strength and dip led to determinations by Alexander von Humboldt, Carl Friedrich Gauss and Edward Sabine that the Earth's magnetic field should be systematically surveyed and monitored globally to perhaps reveal important geophysical aspects of the planet. This led to the establishment of more magnetic observatories and campaigns in Germany (Humboldtian Magnetic Association/Humboldtsche Magnetische Verein (1829–1834), Göttingen Magnetic Union/Göttingen Magnetischer Verein  (1836-41)), Britain (Magnetic Survey of the British Islands (1833), British Empire, East India Company), and Russia (1841-1862). With a total of 53 stations across the globe, terrestrial magnetism became one of the most data producing geosciences of the era.
+This was followed by global geomagnetism campaigns during the First International Polar Year (1882–1883), Second International Polar Year (1932–1933), International Geophysical Year (1957–1958), International Year of the Quiet Sun (1964–1965), International Year of the Active Sun (1969–1971), International Magnetospheric Study (1976–1979), and Fourth International Polar Year (2007–2008).
+
+== See also ==
+History of geophysics
+Timeline of electromagnetic theory
+Rhumbline network
+
+== Notes and references ==
+
+== Further reading ==

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

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+title: "History of numerical weather prediction"
+chunk: 1/5
+source: "https://en.wikipedia.org/wiki/History_of_numerical_weather_prediction"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:19.879931+00:00"
+instance: "kb-cron"
+---
+
+The history of numerical weather prediction considers how current weather conditions as input into mathematical models of the atmosphere and oceans to predict the weather and future sea state (the process of numerical weather prediction) has changed over the years. Though first attempted manually in the 1920s, it was not until the advent of the computer and computer simulation that computation time was reduced to less than the forecast period itself.  ENIAC was used to create the first forecasts via computer in 1950, and over the years more powerful computers have been used to increase the size of initial datasets and use more complicated versions of the equations of motion. The development of global forecasting models led to the first climate models. The development of limited area (regional) models facilitated advances in forecasting the tracks of tropical cyclone as well as air quality in the 1970s and 1980s.
+Because the output of forecast models based on atmospheric dynamics requires corrections near ground level, model output statistics (MOS) were developed in the 1970s and 1980s for individual forecast points (locations). The MOS apply statistical techniques to post-process the output of dynamical models with the most recent surface observations and the forecast point's climatology. This technique can correct for model resolution as well as model biases. Even with the increasing power of supercomputers, the forecast skill of numerical weather models only extends to about two weeks into the future, since the density and quality of observations—together with the chaotic nature of the partial differential equations used to calculate the forecast—introduce errors which double every five days. The use of model ensemble forecasts since the 1990s helps to define the forecast uncertainty and extend weather forecasting farther into the future than otherwise possible.
+
+== Background ==
+Until the end of the 19th century, weather prediction was entirely subjective and based on empirical rules, with only limited understanding of the physical mechanisms behind weather processes. In 1901 Cleveland Abbe, founder of the United States Weather Bureau, proposed that the atmosphere is governed by the same principles of thermodynamics and hydrodynamics that were studied in the previous century. In 1904, Vilhelm Bjerknes derived a two-step procedure for model-based weather forecasting. First, a diagnostic step is used to process data to generate initial conditions, which are then advanced in time by a prognostic step that solves the initial value problem. He also identified seven variables that defined the state of the atmosphere at a given point: pressure, temperature, density, humidity, and the three components of the flow velocity vector. Bjerknes pointed out that equations based on mass continuity, conservation of momentum, the first and second laws of thermodynamics, and the ideal gas law could be used to estimate the state of the atmosphere in the future through numerical methods. With the exception of the second law of thermodynamics, these equations form the basis of the primitive equations used in present-day weather models.
+In 1922, Lewis Fry Richardson published the first attempt at forecasting the weather numerically. Using a hydrostatic variation of Bjerknes's primitive equations, Richardson produced by hand a 6-hour forecast for the state of the atmosphere over two points in central Europe, taking at least six weeks to do so. His forecast calculated that the change in surface pressure would be 145 millibars (4.3 inHg), an unrealistic value incorrect by two orders of magnitude. The large error was caused by an imbalance in the pressure and wind velocity fields used as the initial conditions in his analysis.
+The first successful numerical prediction was performed using the ENIAC digital computer in 1950 by a team led by American meteorologist Jule Charney. The team include Philip Thompson, Larry Gates, and Norwegian meteorologist Ragnar Fjørtoft, applied mathematician John von Neumann, and computer programmer Klara Dan von Neumann, M. H. Frankel, Jerome Namias, John C. Freeman Jr., Francis Reichelderfer, George Platzman, and Joseph Smagorinsky. They used a simplified form of atmospheric dynamics based on solving the barotropic vorticity equation over a single layer of the atmosphere, by computing the geopotential height of the atmosphere's 500 millibars (15 inHg) pressure surface.  This simplification greatly reduced demands on computer time and memory, so the computations could be performed on the relatively primitive computers of the day.  When news of the first weather forecast by ENIAC was received by Richardson in 1950, he remarked that the results were an "enormous scientific advance." The first calculations for a 24‑hour forecast took ENIAC nearly 24 hours to produce, but Charney's group noted that most of that time was spent in "manual operations", and expressed hope that forecasts of the weather before it occurs would soon be realized.
+
+In the United Kingdom the Meteorological Office first numerical weather prediction was completed by F. H. Bushby and Mavis Hinds in 1952 under the guidance of John Sawyer. These experimental forecasts were generated using a 12 × 8 grid with a grid spacing of 260 km, a one-hour time-step, and required four hours of computing time for a 24-hour forecast on the EDSAC computer at the University of Cambridge and the LEO computer developed by J. Lyons and Co. Following these initial experiments, work moved to the Ferranti Mark 1 computer at the Manchester University Department of Electrical Engineering and in 1959 a Ferranti Mercury computer, known as 'Meteor', was installed at the Met Office.

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+title: "History of numerical weather prediction"
+chunk: 2/5
+source: "https://en.wikipedia.org/wiki/History_of_numerical_weather_prediction"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:19.879931+00:00"
+instance: "kb-cron"
+---
+
+== Early years ==
+In September 1954, Carl-Gustav Rossby assembled an international group of meteorologists in Stockholm and produced the first operational forecast (i.e. routine predictions for practical use) based on the barotropic equation. Operational numerical weather prediction in the United States began in 1955 under the Joint Numerical Weather Prediction Unit (JNWPU), a joint project by the U.S. Air Force, Navy, and Weather Bureau.  The JNWPU model was originally a three-layer barotropic model, also developed by Charney.  It only modeled the atmosphere in the Northern Hemisphere.  In 1956, the JNWPU switched to a two-layer thermotropic model developed by Thompson and Gates. The main assumption made by the thermotropic model is that while the magnitude of the thermal wind may change, its direction does not change with respect to height, and thus the baroclinicity in the atmosphere can be simulated using the 500-and-1,000 mb (15-and-30 inHg) geopotential height surfaces and the average thermal wind between them.   However, due to the low skill showed by the thermotropic model, the JNWPU reverted to the single-layer barotropic model in 1958.  The Japanese Meteorological Agency became the third organization to initiate operational numerical weather prediction in 1959.  The first real-time forecasts made by Australia's Bureau of Meteorology in 1969 for portions of the Southern Hemisphere were also based on the single-layer barotropic model.
+Later models used more complete equations for atmospheric dynamics and thermodynamics. In 1959, Karl-Heinz Hinkelmann produced the first reasonable primitive equation forecast, 37 years after Richardson's failed attempt. Hinkelmann did so by removing small oscillations from the numerical model during initialization. In 1966, West Germany and the United States began producing operational forecasts based on primitive-equation models, followed by the United Kingdom in 1972 and Australia in 1977. Later additions to primitive equation models allowed additional insight into different weather phenomena. In the United States, solar radiation effects were added to the primitive equation model in 1967; moisture effects and latent heat were added in 1968; and feedback effects from rain on convection were incorporated in 1971. Three years later, the first global forecast model was introduced.  Sea ice began to be initialized in forecast models in 1971.  Efforts to involve sea surface temperature in model initialization began in 1972 due to its role in modulating weather in higher latitudes of the Pacific.
+
+== Global forecast models ==
+
+A global forecast model is a weather forecasting model which initializes and forecasts the weather throughout the Earth's troposphere. It is a computer program that produces meteorological information for future times at given locations and altitudes.   Within any modern model is a set of equations, known as the primitive equations, used to predict the future state of the atmosphere.  These equations—along with the ideal gas law—are used to evolve the density, pressure, and potential temperature scalar fields and the flow velocity vector field of the atmosphere through time. Additional transport equations for pollutants and other aerosols are included in some primitive-equation high-resolution models as well. The equations used are nonlinear partial differential equations which are impossible to solve exactly through analytical methods, with the exception of a few idealized cases. Therefore, numerical methods obtain approximate solutions. Different models use different solution methods: some global models and almost all regional models use finite difference methods for all three spatial dimensions, while other global models and a few regional models use spectral methods for the horizontal dimensions and finite-difference methods in the vertical.
+The National Meteorological Center's Global Spectral Model was introduced during August 1980.  The European Centre for Medium-Range Weather Forecasts model debuted on May 1, 1985.  The United Kingdom Met Office has been running their global model since the late 1980s, adding a 3D-Var data assimilation scheme in mid-1999.  The Canadian Meteorological Centre has been running a global model since 1991. The United States ran the Nested Grid Model (NGM) from 1987 to 2000, with some features lasting as late as 2009. Between 2000 and 2002, the Environmental Modeling Center ran the Aviation (AVN) model for shorter range forecasts and the Medium Range Forecast (MRF) model at longer time ranges. During this time, the AVN model was extended to the end of the forecast period, eliminating the need of the MRF and thereby replacing it. In late 2002, the AVN model was renamed the Global Forecast System (GFS).  The German Weather Service has been running their global hydrostatic model, the GME, using a hexagonal icosahedral grid since 2002. The GFS is slated to eventually be supplanted by the Flow-following, finite-volume Icosahedral Model (FIM), which like the GME is gridded on a truncated icosahedron, in the mid-2010s.
+
+== Global climate models ==
+In 1956, Norman A. Phillips developed a mathematical model which could realistically depict monthly and seasonal patterns in the troposphere, which became the first successful climate model. Following Phillips's work, several groups began working to create general circulation models. The first general circulation climate model that combined both oceanic and atmospheric processes was developed in the late 1960s at the NOAA Geophysical Fluid Dynamics Laboratory.  By the early 1980s, the United States' National Center for Atmospheric Research had developed the Community Atmosphere Model; this model has been continuously refined into the 2000s.  In 1986, efforts began to initialize and model soil and vegetation types, which led to more realistic forecasts. For example, the Center for Ocean-Land Atmosphere Studies (COLA) model showed a warm temperature bias of 2–4 °C (36–39 °F) and a low precipitation bias due to incorrect parameterization of crop and vegetation type across the central United States.  Coupled ocean-atmosphere climate models such as the Hadley Centre for Climate Prediction and Research's HadCM3 model are currently being used as inputs for climate change studies.  The importance of gravity waves was neglected within these models until the mid-1980s. Now, gravity waves are required within global climate models in order to properly simulate regional and global scale circulations, though their broad spectrum makes their incorporation complicated.  The Climate System Model (CSM) was developed at the National Center for Atmospheric Research in January 1994.

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+title: "History of numerical weather prediction"
+chunk: 3/5
+source: "https://en.wikipedia.org/wiki/History_of_numerical_weather_prediction"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:19.879931+00:00"
+instance: "kb-cron"
+---
+
+== AI-Enhanced Modeling Framework ==
+In comparison to traditional physics-based methods, machine learning (ML), or more broadly, artificial intelligence (AI) approaches, have demonstrated potential in enhancing weather forecasts (refer to the review by Shen et al.). As detailed in Table 4 of Shen et al., these AI-driven models were trained with ERA5 reanalysis data and CMIP6 datasets and evaluated using a variety of metrics such as root mean square errors (RMSE), anomaly correlation coefficients (ACC), Continuous Ranked Probability Score (CRPS), Temporal Anomaly Correlation Coefficient (TCC), Ranked Probability Skill Score (RPSS), Brier Skill Score (BSS), and bivariate correlation (COR).
+By utilizing deep convolutional neural networks (CNNs), Weyn et al. achieved lead times of 14 days. Notably, recent advancements in AI, especially transformer models (e.g., Vaswani et al.) and their derivatives, such as the “vision transformer” (Dosovitskiy et al. 2020 ), have created substantial opportunities to lower the cost of weather forecasting and revisit the predictability limits. Among the AI-powered models mentioned, all provided forecasts that were comparable to or slightly better than those from PDE-physics-based systems for short-term forecasts (3–14 days).
+Three studies have attempted to conduct simulations at subseasonal or larger scales. Of these, the ClimX system was presented in a conference paper. The enhanced Fu-Xi system, along with its base version, was documented in both a preprint and a journal article. In the third study, Bach et al. (2024)  utilized a hybrid dynamical and data-driven approach to show potential improvements in subseasonal monsoon prediction. Their findings indicate a correlation above 0.5 over a 46-day period in two predictions.
+
+== Limited-area models ==
+The horizontal domain of a model is either global, covering the entire Earth, or regional, covering only part of the Earth. Regional models (also known as limited-area models, or LAMs) allow for the use of finer (or smaller) grid spacing than global models. The available computational resources are focused on a specific area instead of being spread over the globe. This allows regional models to resolve explicitly smaller-scale meteorological phenomena that cannot be represented on the coarser grid of a global model. Regional models use a global model for initial conditions of the edge of their domain in order to allow systems from outside the regional model domain to move into its area. Uncertainty and errors within regional models are introduced by the global model used for the boundary conditions of the edge of the regional model, as well as errors attributable to the regional model itself.
+In the United States, the first operational regional model, the limited-area fine-mesh (LFM) model, was introduced in 1971.  Its development was halted, or frozen, in 1986. The NGM debuted in 1987 and was also used to create model output statistics for the United States.  Its development was frozen in 1991. The ETA model was implemented for the United States in 1993 and in turn was upgraded to the NAM in 2006. The U.S. also offers the Rapid Refresh (which replaced the RUC in 2012) for short-range and high-resolution applications; both the Rapid Refresh and NAM are built on the same framework, the WRF. Météo-France has been running their Action de Recherche Petite Échelle Grande Échelle (ALADIN) mesoscale model for France, based upon the ECMWF global model, since 1995.  In July 1996, the Bureau of Meteorology implemented the Limited Area Prediction System (LAPS). The Canadian Regional Finite-Elements model (RFE) went into operational use on April 22, 1986.   It was followed by the Canadian Global Environmental Multiscale Model (GEM) mesoscale model on February 24, 1997.
+The German Weather Service developed the High Resolution Regional Model (HRM) in 1999, which is widely run within the operational and research meteorological communities and run with hydrostatic assumptions.  The Antarctic Mesoscale Prediction System (AMPS) was developed for the southernmost continent in 2000 by the United States Antarctic Program. The German non-hydrostatic Lokal-Modell for Europe (LME) has been run since 2002, and an increase in areal domain became operational on September 28, 2005.  The Japan Meteorological Agency has run a high-resolution, non-hydrostatic mesoscale model since September 2004.
+
+== Air quality models ==

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+title: "History of numerical weather prediction"
+chunk: 4/5
+source: "https://en.wikipedia.org/wiki/History_of_numerical_weather_prediction"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:19.879931+00:00"
+instance: "kb-cron"
+---
+
+The technical literature on air pollution dispersion is quite extensive and dates back to the 1930s and earlier. One of the early air pollutant plume dispersion equations was derived by Bosanquet and Pearson. Their equation did not assume Gaussian distribution nor did it include the effect of ground reflection of the pollutant plume. Sir Graham Sutton derived an air pollutant plume dispersion equation in 1947 which did include the assumption of Gaussian distribution for the vertical and crosswind dispersion of the plume and also included the effect of ground reflection of the plume.  Under the stimulus provided by the advent of stringent environmental control regulations, there was an immense growth in the use of air pollutant plume dispersion calculations between the late 1960s and today. A great many computer programs for calculating the dispersion of air pollutant emissions were developed during that period of time and they were called "air dispersion models". The basis for most of those models was the Complete Equation For Gaussian Dispersion Modeling Of Continuous, Buoyant Air Pollution Plumes  The Gaussian air pollutant dispersion equation requires the input of H which is the pollutant plume's centerline height above ground level—and H is the sum of Hs (the actual physical height of the pollutant plume's emission source point) plus ΔH (the plume rise due to the plume's buoyancy).
+To determine ΔH, many if not most of the air dispersion models developed between the late 1960s and the early 2000s used what are known as "the Briggs equations." G. A. Briggs first published his plume rise observations and comparisons in 1965. In 1968, at a symposium sponsored by Conservation of Clean Air and Water in Europe, he compared many of the plume rise models then available in the literature. In that same year, Briggs also wrote the section of the publication edited by Slade dealing with the comparative analyses of plume rise models. That was followed in 1969 by his classical critical review of the entire plume rise literature, in which he proposed a set of plume rise equations which have become widely known as "the Briggs equations". Subsequently, Briggs modified his 1969 plume rise equations in 1971 and in 1972.
+The Urban Airshed Model, a regional forecast model for the effects of air pollution and acid rain, was developed by a private company in the US in 1970. Development of this model was taken over by the Environmental Protection Agency and improved in the mid to late 1970s using results from a regional air pollution study. While developed in California, this model was later used in other areas of North America, Europe and Asia during the 1980s.  The Community Multiscale Air Quality model (CMAQ) is an open source air quality model run within the United States in conjunction with the NAM mesoscale model since 2004.  The first operational air quality model in Canada, Canadian Hemispheric and Regional Ozone and NOx System (CHRONOS), began to be run in 2001. It was replaced with the Global Environmental Multiscale model – Modelling Air quality and Chemistry (GEM-MACH) model in November 2009.
+
+== Tropical cyclone models ==
+
+During 1972, the first model to forecast storm surge along the continental shelf was developed, known as the Special Program to List the Amplitude of Surges from Hurricanes (SPLASH).  In 1978, the first hurricane-tracking model based on atmospheric dynamics – the movable fine-mesh (MFM) model – began operating.  Within the field of tropical cyclone track forecasting, despite the ever-improving dynamical model guidance which occurred with increased computational power, it was not until the decade of the 1980s when numerical weather prediction showed skill, and until the 1990s when it consistently outperformed statistical or simple dynamical models.  In the early 1980s, the assimilation of satellite-derived winds from water vapor, infrared, and visible satellite imagery was found to improve tropical cyclones track forecasting.  The Geophysical Fluid Dynamics Laboratory (GFDL) hurricane model was used for research purposes between 1973 and the mid-1980s. Once it was determined that it could show skill in hurricane prediction, a multi-year transition transformed the research model into an operational model which could be used by the National Weather Service in 1995.
+The Hurricane Weather Research and Forecasting (HWRF) model is a specialized version of the Weather Research and Forecasting (WRF) model and is used to forecast the track and intensity of tropical cyclones. The model was developed by the National Oceanic and Atmospheric Administration (NOAA), the U.S. Naval Research Laboratory, the University of Rhode Island, and Florida State University. It became operational in 2007.  Despite improvements in track forecasting, predictions of the intensity of a tropical cyclone based on numerical weather prediction continue to be a challenge, since statiscal methods continue to show higher skill over dynamical guidance.

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+title: "History of numerical weather prediction"
+chunk: 5/5
+source: "https://en.wikipedia.org/wiki/History_of_numerical_weather_prediction"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:19.879931+00:00"
+instance: "kb-cron"
+---
+
+== Ocean models ==
+The first ocean wave models were developed in the 1960s and 1970s. These models had the tendency to overestimate the role of wind in wave development and underplayed wave interactions. A lack of knowledge concerning how waves interacted among each other, assumptions regarding a maximum wave height, and deficiencies in computer power limited the performance of the models. After experiments were performed in 1968, 1969, and 1973, wind input from the Earth's atmosphere was weighted more accurately in the predictions. A second generation of models was developed in the 1980s, but they could not realistically model swell nor depict wind-driven waves (also known as wind waves) caused by rapidly changing wind fields, such as those within tropical cyclones. This caused the development of a third generation of wave models from 1988 onward.
+Within this third generation of models, the spectral wave transport equation is used to describe the change in wave spectrum over changing topography. It simulates wave generation, wave movement (propagation within a fluid), wave shoaling, refraction, energy transfer between waves, and wave dissipation.  Since surface winds are the primary forcing mechanism in the spectral wave transport equation, ocean wave models use information produced by numerical weather prediction models as inputs to determine how much energy is transferred from the atmosphere into the layer at the surface of the ocean. Along with dissipation of energy through whitecaps and resonance between waves, surface winds from numerical weather models allow for more accurate predictions of the state of the sea surface.
+
+== Model output statistics ==
+
+Because forecast models based upon the equations for atmospheric dynamics do not perfectly determine weather conditions near the ground, statistical corrections were developed to attempt to resolve this problem. Statistical models were created based upon the three-dimensional fields produced by numerical weather models, surface observations, and the climatological conditions for specific locations. These statistical models are collectively referred to as model output statistics (MOS), and were developed by the National Weather Service for their suite of weather forecasting models by 1976.  The United States Air Force developed its own set of MOS based upon their dynamical weather model by 1983.
+
+== Ensembles ==
+
+As proposed by Edward Lorenz in 1963, it is impossible for long-range forecasts—those made more than two weeks in advance—to predict the state of the atmosphere with any degree of skill, owing to the chaotic nature of the fluid dynamics equations involved. Extremely small errors in temperature, winds, or other initial inputs given to numerical models will amplify and double every five days.  Furthermore, existing observation networks have limited spatial and temporal resolution (for example, over large bodies of water such as the Pacific Ocean), which introduces uncertainty into the true initial state of the atmosphere. While a set of equations, known as the Liouville equations, exists to determine the initial uncertainty in the model initialization, the equations are too complex to run in real-time, even with the use of supercomputers.  These uncertainties limit forecast model accuracy to about six days into the future.
+Edward Epstein recognized in 1969 that the atmosphere could not be completely described with a single forecast run due to inherent uncertainty, and proposed a stochastic dynamic model that produced means and variances for the state of the atmosphere.  While these Monte Carlo simulations showed skill, in 1974 Cecil Leith revealed that they produced adequate forecasts only when the ensemble probability distribution was a representative sample of the probability distribution in the atmosphere.  It was not until 1992 that ensemble forecasts began being prepared by the European Centre for Medium-Range Weather Forecasts, the Canadian Meteorological Centre, and the National Centers for Environmental Prediction. The ECMWF model, the Ensemble Prediction System, uses singular vectors to simulate the initial probability density, while the NCEP ensemble, the Global Ensemble Forecasting System, uses a technique known as vector breeding.
+
+== See also ==
+André Robert
+Atmospheric model
+Frederick Gale Shuman
+Timeline of scientific computing
+
+== References ==

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+title: "History of programming languages"
+chunk: 1/4
+source: "https://en.wikipedia.org/wiki/History_of_programming_languages"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:21.154089+00:00"
+instance: "kb-cron"
+---
+
+The history of programming languages spans from documentation of early mechanical computers to modern tools for software development. Early programming languages were highly specialized, relying on mathematical notation and similarly obscure syntax. Throughout the 20th century, research in compiler theory led to the creation of high-level programming languages, which use a more accessible syntax to communicate instructions.
+The first high-level programming language was Plankalkül, created by Konrad Zuse between 1942 and 1945. The first high-level language to have an associated compiler was created by Corrado Böhm in 1951, for his PhD thesis. The first commercially available language was FORTRAN (FORmula TRANslation), developed in 1956 (first manual appeared in 1956, but first developed in 1954) by a team led by John Backus at IBM.
+
+== Early history ==
+During 1842–1849, Ada Lovelace translated the memoir of Italian mathematician Luigi Menabrea about Charles Babbage's newest proposed machine: the Analytical Engine; she supplemented the memoir with notes that specified in detail a method for calculating Bernoulli numbers with the engine, recognized by most historians as the world's first published computer program.
+Jacquard Looms and Charles Babbage's Difference Engine both were designed to utilize punched cards, which would describe the sequence of operations that their programmable machines should perform.
+The first computer codes were specialized for their applications: e.g., Alonzo Church was able to express the lambda calculus in a formulaic way, and the Turing machine was an abstraction of the operation of a tape-marking machine.
+
+== First programming languages ==
+In the 1940s, the first recognizably modern electrically powered computers were created. The limited speed and memory capacity forced programmers to write hand-tuned assembly language programs. It was eventually realized that programming in assembly language required a great deal of intellectual effort.
+An early proposal for a high-level programming language was Plankalkül, developed by Konrad Zuse for his Z1 computer between 1942 and 1945, but not implemented at the time.
+The first functioning programming languages designed to communicate instructions to a computer were written in the early 1950s. John Mauchly's Short Code, proposed in 1949, was one of the first high-level languages ever developed for an electronic computer. Unlike machine code, Short Code statements represented mathematical expressions in an understandable form. However, the program had to be interpreted into machine code every time it ran, making the process much slower than running the equivalent machine code.
+In the early 1950s, Alick Glennie developed Autocode, possibly the first compiled programming language, at the University of Manchester. In 1954, a second iteration of the language, known as the "Mark 1 Autocode", was developed for the Mark 1 by R. A. Brooker. Brooker, with the University of Manchester, also developed an autocode for the Ferranti Mercury in the 1950s. The version for the EDSAC 2 was devised by Douglas Hartree of the University of Cambridge Mathematical Laboratory in 1961. Known as EDSAC 2 Autocode, it was a straight development from Mercury Autocode, adapted for local circumstances, and was noted for its object code optimization and source-language diagnostics, which were advanced for the time. A contemporary but separate thread of development, Atlas Autocode was developed for the University of Manchester Atlas 1 machine.
+In 1954, FORTRAN was invented at IBM by a team led by John Backus; it was the first widely used high-level general-purpose language to have a functional implementation, in contrast to only a design on paper. When FORTRAN was first introduced, it was viewed with skepticism due to bugs, delays in development, and the comparative efficiency of "hand-coded" programs written in assembly. However, in a hardware market that was rapidly evolving, the language eventually became known for its efficiency. It is still a popular language for high-performance computing and is used for programs that benchmark and rank the world's TOP500 fastest supercomputers.
+Another early programming language was devised by Grace Hopper in the US, named FLOW-MATIC. It was developed for the UNIVAC I at Remington Rand during the period from 1955 until 1959. Hopper found that business data processing customers were uncomfortable with mathematical notation, and in early 1955, she and her team wrote a specification for an English language programming language and implemented a prototype. The FLOW-MATIC compiler became publicly available in early 1958 and was substantially complete in 1959. Flow-Matic was a major influence in the design of COBOL, since only it and its direct descendant AIMACO were in use at the time.
+Other languages still in use today include LISP (1958), invented by John McCarthy, and COBOL (1960), created by the Short Range Committee. Another milestone in the late 1950s was the publication, by a committee of American and European computer scientists, of "a new language for algorithms"; the ALGOL 60 Report (the "ALGOrithmic Language"). This report consolidated many ideas circulating at the time and featured three key language innovations:
+
+nested block structure: code sequences and associated declarations could be grouped into blocks without having to be turned into separate, explicitly named procedures;
+lexical scoping: a block could have its own private variables, procedures, and functions, invisible to code outside that block, that is, information hiding.
+Another innovation, related to this, was in how the language was described:
+
+a mathematically exact notation, Backus–Naur form (BNF), was used to describe the language's syntax. Nearly all subsequent programming languages have used a variant of BNF to describe the context-free portion of their syntax.
+ALGOL 60 was particularly influential in the design of later languages, some of which soon became more popular. The Burroughs Large Systems were designed to be programmed in an extended subset of ALGOL.
+ALGOL's key ideas were continued, producing ALGOL 68:

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+title: "History of programming languages"
+chunk: 2/4
+source: "https://en.wikipedia.org/wiki/History_of_programming_languages"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:21.154089+00:00"
+instance: "kb-cron"
+---
+
+syntax and semantics became even more orthogonal, with anonymous routines, a recursive typing system with higher-order functions, etc.;
+not only the context-free part, but the full language syntax and semantics were defined formally, in terms of Van Wijngaarden grammar, a formalism designed specifically for this purpose.
+ALGOL 68's many little-used language features (for example, concurrent and parallel blocks) and its complex system of syntactic shortcuts and automatic type coercions made it unpopular with implementers and gained it a reputation for being difficult. Niklaus Wirth actually walked out of the design committee to create the simpler Pascal language.
+
+Some notable languages that were developed in this period include:
+
+== Establishing fundamental paradigms ==
+
+The period from the late 1960s to the late 1970s brought a major flowering of programming languages. Most of the major language paradigms now in use were invented in this period:
+
+Speakeasy, developed in 1964 at Argonne National Laboratory (ANL) by Stanley Cohen, is an object-oriented programming system (OOPS), much like the later MATLAB, IDL and Mathematica numerical package. Speakeasy has a clear Fortran foundation syntax. It first addressed efficient physics computing internally at ANL, was modified for research use (as "Modeleasy") for the Federal Reserve Board in the early 1970s and then was made available commercially; Speakeasy and Modeleasy are still in use.
+Simula, invented in the late 1960s by Nygaard and Dahl as a superset of ALGOL 60, was the first language designed to support object-oriented programming.
+FORTH, the earliest concatenative programming language was designed by Charles Moore in 1969 as a personal development system while at the National Radio Astronomy Observatory (NRAO).
+C, an early systems programming language, was developed by Dennis Ritchie and Ken Thompson at Bell Labs between 1969 and 1973.
+Smalltalk (mid-1970s) provided a complete ground-up design of an object-oriented language.
+Prolog, designed in 1972 by Alain Colmerauer, Phillipe Roussel, and Robert Kowalski, was the first logic programming language.
+ML built a polymorphic type system (invented by Robin Milner in 1973) on Lisp, pioneering statically typed functional programming languages.
+Each of these languages spawned an entire family of descendants, and most modern languages count at least one of them in their ancestry.
+The 1960s and 1970s also saw considerable debate over the merits of "structured programming", which essentially meant programming without the use of goto. A significant fraction of programmers believed that, even in languages that provide goto, it is bad programming style to use it except in rare circumstances. This debate was closely related to language design: some languages had no goto, which forced the use of structured programming.
+To provide even faster compile times, some languages were structured for "one-pass compilers" which expect subordinate routines to be defined first, as with Pascal, where the main routine, or driver function, is the final section of the program listing.
+Some notable languages that were developed in this period include:
+
+== 1980s: consolidation, modules, performance ==
+
+The 1980s were years of relative consolidation in imperative languages. Rather than inventing new paradigms, all of these movements elaborated upon the ideas invented in the prior decade. C++ combined object-oriented and systems programming. The United States government standardized Ada, a systems programming language intended for use by defense contractors. In Japan and elsewhere, vast sums were spent investigating so-called fifth-generation programming languages that incorporated logic programming constructs. The functional languages community moved to standardize ML and Lisp. Research in Miranda, a functional language with lazy evaluation, began to take hold in this decade.
+One important new trend in language design was an increased focus on programming for large-scale systems through the use of modules, or large-scale organizational units of code. Modula, Ada, and ML all developed notable module systems in the 1980s. Module systems were often wedded to generic programming constructs: generics being, in essence, parametrized modules (see also Polymorphism (computer science)).
+Although major new paradigms for imperative programming languages did not appear, many researchers expanded on the ideas of prior languages and adapted them to new contexts. For example, the languages of the Argus and Emerald systems adapted object-oriented programming to distributed computing systems.
+The 1980s also brought advances in programming language implementation. The reduced instruction set computer (RISC) movement in computer architecture postulated that hardware should be designed for compilers rather than for human assembly programmers. Aided by central processing unit (CPU) speed improvements that enabled increasingly aggressive compiling methods, the RISC movement sparked greater interest in compiler technology for high-level languages.
+Language technology continued along these lines well into the 1990s. 
+Some notable languages that were developed in this period include:
+
+== 1990s: the Internet age ==

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+---
+title: "History of programming languages"
+chunk: 3/4
+source: "https://en.wikipedia.org/wiki/History_of_programming_languages"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:21.154089+00:00"
+instance: "kb-cron"
+---
+
+The rapid growth of the Internet in the mid-1990s was the next major historic event in programming languages. By opening up a radically new platform for computer systems, the Internet created an opportunity for new languages to be adopted. The JavaScript language rose rapidly to popularity because of its early integration with the Netscape Navigator web browser. Various other scripting languages achieved widespread use in developing customized applications for web servers such as PHP. The 1990s saw no fundamental novelty in imperative programming languages, but much recombining and maturing of old ideas. This era began the spread of functional programming languages. A big driving philosophy was programmer productivity. Many rapid application development (RAD) languages emerged, which usually came with an integrated development environment (IDE), garbage collection, and were descendants of older languages. All such languages were object-oriented. These included Object Pascal, Objective Caml (renamed OCaml), Visual Basic, and Java. Java received much attention.
+More radical and innovative than the RAD languages were the new scripting languages. These did not directly descend from other languages and featured new syntaxes and more liberal incorporation of features. Many consider these scripting languages to be more productive than even the RAD languages, but often because of choices that make small programs simpler but large programs more difficult to write and maintain. Nevertheless, scripting languages came to be the most prominent ones used relative to the Web.
+Some programming languages included other languages in their distribution to save the development time. For example, both of Python and Ruby included Tcl to support graphical user interface (GUI) programming through libraries like Tkinter.
+Some notable languages that were developed in this period include:
+
+== 2000s: programming paradigms ==
+
+Programming language evolution continues, and more programming paradigms are used in production.
+Some of the trends have included:
+
+Increasing support for functional programming in mainstream languages used commercially, including purely functional programming for making code easier to reason about and to parallelize (at both micro- and macro- levels)
+Constructs to support concurrent and distributed programming.
+Mechanisms for adding security and reliability verification to the language: extended static checking, dependent typing, information flow control, static thread safety.
+Alternative mechanisms for composability and modularity: mixins, traits, typeclasses, delegates, aspects.
+Component-oriented software development.
+More interest in visual programming languages like Scratch and LabVIEW
+Metaprogramming, reflective programming (reflection), or access to the abstract syntax tree
+Aspect-oriented programming (AOP) allowing developers to insert code in another module or class at "join points"
+Domain-specific languages and code generation
+XML for graphical interface (XUL, Extensible Application Markup Language (XAML))
+Big Tech companies introduced multiple new programming languages that are designed to serve their needs. for example:
+
+Microsoft introduced C# and F#
+Google introduced Go
+Some notable languages developed during this period include:
+
+== 2010s: the Mobile age ==
+
+Programming language evolution continues with the rise of new programming domains.
+
+Increased interest in distribution and mobility.
+Integration with databases, including XML and relational databases.
+Open source as a developmental philosophy for languages, including the GNU Compiler Collection (GCC) and languages such as PHP, Python, Ruby, and Scala.
+Massively parallel languages for graphics processing units (GPUs) and supercomputer arrays, including OpenCL
+Early research into quantum computing and quantum programming languages
+Multiple new programming languages tried to provide a modern replacement for the C programming language.
+Many new programming languages are influenced by the popular dynamic languages and promised adding type safety without decreasing the productivity.
+Many new programming languages uses LLVM in their implementation.
+Many Big Tech companies continued introducing new programming languages that are designed to serve their needs and provides first-class support for their platforms. for example:
+
+Microsoft introduced TypeScript, Q# and Bosque
+Google introduced Dart
+Apple introduced Swift.
+Meta introduced Hack.
+Some notable languages developed during this period include:
+
+Other new programming languages include Elm, Ballerina, Red, Crystal, V (Vlang), Reason.
+
+== 2020s: Current trends ==
+
+The development of new programming languages continues. Some new languages try to provide the advantages of a known language like C++ (versatile and fast) while adding safety or reducing complexity. Other new languages try to bring ease of use as provided by Python while adding performance as a priority.
+Some notable new programming languages include:
+
+2021 – Power Fx
+2022 – Carbon
+2023 – Mojo
+
+== Key figures ==
+
+Some key people who helped develop programming languages:

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+---
+title: "History of programming languages"
+chunk: 4/4
+source: "https://en.wikipedia.org/wiki/History_of_programming_languages"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:21.154089+00:00"
+instance: "kb-cron"
+---
+
+Ada Lovelace, published first computer program
+Alan Cooper, developer of Visual Basic.
+Alan Kay, pioneering work on object-oriented programming, and originator of Smalltalk.
+Anders Hejlsberg, developer of Turbo Pascal, Delphi, C#, and TypeScript.
+Arthur Whitney, developer of A+, k, and q.
+Bertrand Meyer, inventor of Eiffel.
+Bjarne Stroustrup, developer of C++.
+Brad Cox, co-creator of Objective-C.
+Brendan Eich, developer of JavaScript.
+Brian Kernighan, co-author of the first book on the C programming language with Dennis Ritchie, coauthor of the AWK and AMPL programming languages.
+Chuck Moore, inventor of Forth, the first concatenative programming language, and a prominent name in stack machine microprocessor design.
+Chris Lattner, creator of Swift, Mojo and Clang/LLVM.
+Cleve Moler, creator of MATLAB.
+Dennis Ritchie, inventor of C. Unix Operating System, Plan 9 Operating System.
+Douglas McIlroy, influenced and designed such languages as SNOBOL, TRAC, PL/I, ALTRAN, TMG and C++.
+Grace Hopper, first to use the term compiler and developer of FLOW-MATIC, influenced development of COBOL. Popularized machine-independent programming languages and the term "debugging".
+Guido van Rossum, creator of Python.
+James Gosling, lead developer of Java and its precursor, Oak.
+Jean Ichbiah, chief designer of Ada, Ada 83.
+Jean-Yves Girard, co-inventor of the polymorphic lambda calculus (System F).
+Jeff Bezanson, main designer, and one of the core developers of Julia.
+Jeffrey Snover, inventor of PowerShell.
+Joe Armstrong, creator of Erlang.
+John Backus, inventor of Fortran, cooperated in designing ALGOL 58 and ALGOL 60.
+John C. Reynolds, co-inventor of the polymorphic lambda calculus (System F).
+John McCarthy, inventor of LISP, design committee of ALGOL 60.
+John von Neumann, originator of the operating system concept.
+Graydon Hoare, inventor of Rust.
+Ken Thompson, inventor of B and Go.
+Kenneth E. Iverson, developer of APL, co-developer of J with Roger Hui.
+Konrad Zuse, designed the first high-level programming language, Plankalkül (which influenced ALGOL 58).
+Kristen Nygaard, pioneered object-oriented programming, co-invented Simula.
+Larry Wall, creator of the Perl programming language (see Perl and Raku).
+Martin Odersky, creator of Scala, and previously a contributor to the design of Java.
+Martin Richards developed the BCPL programming language, forerunner of the B and C languages.
+Nathaniel Rochester, inventor of first assembler (IBM 701).
+Niklaus Wirth, inventor of Pascal, Modula and Oberon.
+Ole-Johan Dahl, pioneered object-oriented programming, co-invented Simula.
+Rasmus Lerdorf, creator of PHP.
+Rich Hickey, creator of Clojure.
+Robert Gentleman, co-creator of R.
+Robert Griesemer, co-creator of Go.
+Robin Milner, inventor of ML, and sharing credit for Hindley–Milner polymorphic type inference.
+Rob Pike, co-creator of Go, Inferno (operating system) and Plan 9 (operating system) Operating System co-author.
+Ross Ihaka, co-creator of R.
+Stanley Cohen, inventor of Speakeasy, which was created with an OOPS, object-oriented programming system, the first instance, in 1964.
+Stephen Wolfram, creator of Mathematica.
+Walter Bright, creator of D.
+Yukihiro Matsumoto, creator of Ruby.
+
+== See also ==
+
+== References ==
+
+== Further reading ==
+Rosen, Saul, (editor), Programming Systems and Languages, McGraw-Hill, 1967.
+Sammet, Jean E., Programming Languages: History and Fundamentals, Prentice-Hall, 1969.
+Sammet, Jean E. (July 1972). "Programming Languages: History and Future". Communications of the ACM. 15 (7): 601–610. doi:10.1145/361454.361485. S2CID 2003242.
+Richard L. Wexelblat (ed.): History of Programming Languages, Academic Press 1981.
+Thomas J. Bergin and Richard G. Gibson (eds.): History of Programming Languages, Addison Wesley, 1996.
+Sebesta, Robert W. Concepts of programming languages. Pearson Education India, 2004.
+
+== External links ==
+History and evolution of programming languages
+Graph of programming language history
+Online Historical Encyclopaedia of Programming Languages

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+---
+title: "Physical crystallography before X-rays"
+chunk: 1/5
+source: "https://en.wikipedia.org/wiki/Physical_crystallography_before_X-rays"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:31.939542+00:00"
+instance: "kb-cron"
+---
+
+Physical crystallography before X-rays describes how physical crystallography developed as a science up to the discovery of X-rays by Wilhelm Conrad Röntgen in 1895. In the period before X-rays, crystallography can be divided into three broad areas: geometrical crystallography culminating in the discovery of the 230 space groups in 1891–1894, chemical crystallography and physical crystallography.
+Physical crystallography is concerned with the physical properties of crystals, such as their optical, electrical, magnetic, thermal, and mechanical properties. 
+
+The interaction between crystals and electromagnetic radiation is covered in the following sections: double refraction, rotary polarization, conical refraction, absorption and pleochroism, luminescence, reflection from opaque materials, and infrared optics.
+The effect of electricity and magnetism on crystals is covered in: electrical conduction, magnetic properties, and dielectric properties.
+The effect of temperature change on crystals is covered in: thermal expansion, thermal conduction, thermoelectricity, and pyroelectricity.
+The effect of mechanical force on crystals is covered in: elasticity, photoelasticity, and piezoelectricity.
+The study of crystals in the time before X-rays was focused more on their geometry and mathematical analysis than their physical properties. Unlike geometrical crystallography, the history of physical crystallography has no central story, but is a collection of developments in different areas.
+
+== Symmetry ==
+During the 19th century crystallography was progressively transformed into an empirical and mathematical science by the adoption of symmetry concepts. In 1832 Franz Ernst Neumann used symmetry considerations when studying double refraction. Woldemar Voigt, who was a student of Neumann, in 1885 formalized Neumann's principle as "if a crystal is invariant with respect to certain symmetry operations, any of its physical properties must also be invariant with respect to the same symmetry operations". Neumann's principle is sometimes referred to as the Neumann–Minnigerode–Curie principle based on later work by Bernhard Minnigerode (another student of Neumann) and Pierre Curie. Curie's principle "the symmetries of the causes are to be found in the effects" is a generalization of Neumann's principle. At the end of the 19th century Voigt introduced tensor calculus to model the physical properties of anisotropic crystals.
+
+== Interaction with electromagnetic radiation ==
+
+=== Double refraction ===
+
+Double refraction occurs when a ray of light incident upon a birefringent material, is split by polarization into two rays taking slightly different paths. The double refraction and rhomboidal cleavage of crystals of calcite, or Iceland spar, were first recorded in 1669 by Rasmus Bartholin In 1690 Christiaan Huygens analyzed double refraction in his book Traité de la lumière. Huygens reasoned that the cleavage rhombohedron resulted from the stacking of spherical particles and that the peculiarities of the transmission of light can be traced to the particular asymmetry of the crystal.
+In 1810 Étienne-Louis Malus determined that natural light, too, when reflected through a certain angle, behaves like one of the rays exiting a double-refracting crystal. Malus called this phenomenon polarization. In 1812 Jean-Baptiste Biot defined optically positive and negative crystals for the first time. In 1819 David Brewster found that all crystals could be classified as isotropic, uniaxial or biaxial. Augustin-Jean Fresnel was a significant researcher in the whole field of crystal optics, and published a detailed paper on double refraction in 1827 in which he described the phenomenon in terms of polarization, understanding light as a wave with field components in transverse polarization. Crystal optics was an active research area during the 19th century and comprehensive accounts of the field were published by Lazarus Fletcher (1891), Theodor Liebisch (1891) and Friedrich Pockels (1906).
+
+=== Rotary polarization ===

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+---
+title: "Physical crystallography before X-rays"
+chunk: 2/5
+source: "https://en.wikipedia.org/wiki/Physical_crystallography_before_X-rays"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:31.939542+00:00"
+instance: "kb-cron"
+---
+
+In 1811 François Arago, who favoured the corpuscular theory of light, discovered the rotation of the plane of polarization of light travelling through quartz. In 1812 Jean-Baptiste Biot, who favoured the wave theory of light, enunciated the laws of rotary polarization and their application to the analysis of various substances. Biot discovered that while some crystals rotate the light to the right others rotate it to the left, and determined that the rotation is proportional to the thickness of substance traversed and to the wavelength of the light.
+In 1821 John Herschel pointed out the relation between the direction of rotation and the development of faces on quartz crystals. Suspecting that rotatory polarization is an effect of a lack of symmetry, Herschel established that quartz crystals often present faces placed in such a way that those belonging to certain crystals are mirror images of the corresponding faces of other crystals. He explained the connection between this arrangement and the respective rotation of light to the right and to the left. In 1822 Augustin-Jean Fresnel explained the rotation by postulating oppositely circularly polarized beams travelling with different velocities along the optic axis. In 1831 George Biddell Airy gave an explanation of the formation of the spirals which bear his name. In 1846 Michael Faraday discovered that the plane of polarization may also be rotated when light passes through an isotropic medium when it is in a magnetic field. The corresponding Kerr effect can be observed on reflecting plane-polarized light from a polished ferromagnetic mirror when in a magnetized state.
+In 1848 Louis Pasteur gave the general relation between crystal morphology and rotatory polarization. Pasteur solved the mystery of polarized light acting differently with chemically identical crystals and solutions. Pasteur discovered the phenomenon of molecular asymmetry, that is that molecules could be chiral and exist as a pair of enantiomers. Pasteur's method was to physically separate the crystals of a racemic mixture of sodium ammonium tartrate into right- and left-handed crystals, and then dissolve them to make two separate solutions which rotated polarized light in opposite directions.
+In 1855 Christian August Hermann Marbach discovered that crystals of sodium chlorate, sodium bromate, sodium ammonium sulfate and sodium amyl acetate have the property of rotating the polarization plane. In 1857 Alfred Des Cloizeaux advanced a general theory of rotatory polarization whilst studying cinnabar and strychnine sulphate. In 1864 Josef Stefan introduced the banded spectrum in the study of rotatory polarization. Theories of magnetic optics in ferromagnetic crystals were published in 1892 by D. A. Goldhammer, and in 1893 by Paul Drude.
+
+=== Conical refraction ===
+
+Conical refraction is an optical phenomenon in which a ray of light, passing through a biaxial crystal along certain directions, is refracted into a hollow cone of light. There are two possible conical refractions, one internal and one external.
+In 1821–1822 Augustin-Jean Fresnel developed a theory of double refraction in both uniaxial and biaxial crystals. Fresnel derived the equation for the wavevector surface in 1823, and André-Marie Ampère rederived it in 1828. Many others investigated the wavevector surface of the biaxial crystal, but they all missed its physical implications.
+William Rowan Hamilton, in his work on Hamiltonian optics, discovered the wavevector surface has four conoidal points and four tangent conics. This implies that, under certain conditions, a ray of light could be refracted into a cone of light within the crystal. He termed this phenomenon "conical refraction" and predicted two distinct types: internal and external, corresponding respectively to the conoidal points and tangent conics. Hamilton announced his discovery on 22 October 1832. He then asked Humphrey Lloyd to prove his theory experimentally. Lloyd first observed conical refraction on 14 December 1832 with a specimen of aragonite, and published his results in early 1833. In 1833 James MacCullagh claimed that Hamilton's work was a special case of a theorem he had published in 1830. Hamilton also exchanged letters with George Biddell Airy who was skeptical that conical refraction could be observed experimentally but became convinced after Lloyd's report.
+Hamilton and Lloyd's discovery was a significant victory for the wave theory of light and solidified Fresnel's theory of double refraction. The discovery of conical refraction is an example of a mathematical prediction being subsequently verified by experiment.
+Later theoretical work on conical refraction was published in 1860 by Robert Bellamy Clifton and in 1874 by Jules Antoine Lissajous, and experimental work in 1888 by Theodor Liebisch and in 1889 by Albrecht Schrauf.
+
+=== Absorption and pleochroism ===
+
+In 1809 Louis Cordier discovered the phenomenon of pleochroism while investigating a new mineral that he named dichröıte (cordierite), whereby its crystals showed different colors when viewed along different axes. From 1817 to 1819 David Brewster made a systematic study of light absorption and pleochroism in various minerals and showed that, in uniaxial crystals, the absorption is smallest in the direction of, and greatest at right angles to, the optical axis. In 1820 John Herschel studied the absorption of light in biaxial crystals and explained the interference rings first observed by David Brewster. In 1838 Jacques Babinet discovered that the greatest absorption in a crystal generally coincided with the direction of greatest refractive index. In 1845 Wilhelm Haidinger published a general account of pleochroism in crystals. In 1854 Henri Hureau de Sénarmont showed that transparent crystals stained by a dye during crystal growth became pleochroic.
+In 1877 Paul Glan performed photometric observations on absorption. In 1880 Hugo Laspeyres pointed out the existence of absorption axes (directions of least, intermediate, and greatest absorption). He investigated certain biaxial crystals and found that the absorption axes, although subject to the symmetry of the crystal, did not necessarily coincide with the principal directions of the indicatrix. In 1888 Henri Becquerel made qualitative and quantitative observations. Woldemar Voigt (1885) and Paul Drude (1890) presented theories of the absorption of light in crystals. In 1906 Friedrich Pockels published his Lehrbuch der Kristalloptik which gave an overview of the subject.
+
+=== Luminescence ===

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+---
+title: "Physical crystallography before X-rays"
+chunk: 3/5
+source: "https://en.wikipedia.org/wiki/Physical_crystallography_before_X-rays"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:31.939542+00:00"
+instance: "kb-cron"
+---
+
+Luminescence is the non-thermal emission of visible light by a substance; an example is the emission of visible light by minerals in response to irradiation by ultraviolet light. The term luminescence was first used by Eilhard Wiedemann in 1888; he stated that luminescence was separate from thermal radiation, and he distinguished six different forms of luminescence according to their excitation.
+Fluorescence is luminescence which occurs during the irradiation of a substance by electromagnetic radiation; fluorescent materials stop emitting light nearly immediately after the irradiation is halted, except in the case of certain materials exhibiting delayed fluorescence (e.g., TADF, TTA). The term fluorescence was coined by George Stokes in 1852, and was derived from the behavior of fluorite when exposed to ultraviolet light.
+Phosphorescence is long-lived luminescence; phosphorescent materials continue to emit light for some time after the radiation stops. In 1857 Edmond Becquerel invented the phosphoroscope, and in a detailed study of phosphorescence and fluorescence, showed that the duration of phosphorescence varies by substance, and that phosphorescence in solids is due to the presence of finely dispersed foreign substances. Becquerel suggested that fluorescence is simply phosphorescence of a very short duration. The most prominent phosphorescent material for 130 years was ZnS doped with Cu+, or later Co2+, ions. The material was discovered in 1866 by Théodore Sidot who succeeded in growing tiny ZnS crystals by a sublimation method.
+Some additional kinds of luminescence from crystals can arise from energy sources other than electromagnetic radiation. 
+
+Crystalloluminescence is the emission of light during crystal growth from solution, specifically during nucleation. The first observation was that of potassium sulfate which was reported by a number of researchers in the eighteenth century; other substances reported in the early literature which exhibit crystalloluminescence include strontium nitrate, cobalt sulfate, potassium hydrogen sulfate, sodium sulfate, and arsenious acid.  In 1918 Harry Weiser summarised the research on crystalloluminescence up to that date. Neither the spectral distribution nor the excitation mechanisms of crystalloluminescence are understood.
+Triboluminescence is the generation of light when certain materials, for example quartz, are rubbed; fractoluminescence is the emission of light from the fracture of a crystal. The first recorded observation is attributed to Francis Bacon when he recorded in his 1620 Novum Organum that sugar sparkles when broken or scraped in the dark. The scientist Robert Boyle also reported on some of his work on triboluminescence in 1664.
+In 1677 Henry Oldenburg described the luminescence of fluorite, CaF2, on heating; this is termed thermoluminescence.
+In 1830 Thomas Pearsall observed that colourless fluorite could be coloured by discharging sparks from a Leyden jar held against it. In 1881 luminescence excited by cathode rays was described by William Crookes, and in 1885 Edmond Becquerel found that when crystals were bombarded by cathode rays they became coloured and also emitted light; this has been termed cathodoluminescence. In 1894 Eugen Goldstein showed that ultraviolet light has the same effect as cathode rays.
+
+=== Reflection from opaque materials ===
+
+The study of the optical properties of opaque substances has been closely linked with the development of suitable microscopes. The first instrument adapted to reflected light was the Lieberkühn reflector attributed to Johann Nathanael Lieberkühn. The use of polished and etched surfaces for this type of study was introduced by Jöns Jacob Berzelius in 1813. A theory of the light reflected from metals was put forward by Augustin-Louis Cauchy in 1848. In 1858 Henry Clifton Sorby established the technique of cutting minerals and crystals into thin sections for examination under the polarizing microscope. In 1864 Sorby studied the microscopical structure of minerals from meteorites. In 1888 Paul Drude published work on reflection from antimony sulfide.
+
+=== Infrared optics ===
+Heinrich Rubens measured the dependence of the refractive index of quartz on wavelength, and found absorption in particular infrared wavelength ranges. By 1896 Rubens saw these bands as a potential filter that would allow him to separate out an almost monochromatic beam from the broad range of infrared radiation that his sources produced. In 1897 Rubens and his student Ernest Fox Nichols studied the reststrahlen (residual rays) obtained when infrared rays of appropriate wavelength are reflected from the surfaces of crystals.
+
+== Effect of electricity and magnetism ==
+
+=== Electrical conduction ===
+The first observations on the variation of electrical conductivity with direction in a crystal (anisotropy) were made by Henri Hureau de Sénarmont in 1850 on 36 different substances. The results showed a correlation between the axes of symmetry and the directions of maximum or minimum conductivity. In 1855 Carlo Matteucci performed experiments on bismuth. In 1888, Helge Bäckström performed electrical conduction measurements on hematite, another crystal of rhombohedral symmetry.
+Electrical conductivity in a crystal is now defined as a second rank symmetric tensor relating two vectors: 
+  
+    
+      
+        
+          
+            J
+          
+          
+            i
+          
+        
+        =
+        
+          
+            σ
+          
+          
+            i
+            j
+          
+        
+        
+          
+            E
+          
+          
+            j
+          
+        
+        ,
+      
+    
+    {\displaystyle \mathbf {J} _{i}={\boldsymbol {\sigma }}_{ij}\mathbf {E} _{j},}
+  
+ where 
+  
+    
+      
+        
+          
+            J
+          
+          
+            i
+          
+        
+      
+    
+    {\displaystyle \mathbf {J} _{i}}
+  
+ is the current density, 
+  
+    
+      
+        
+          
+            σ
+          
+          
+            i
+            j
+          
+        
+      
+    
+    {\displaystyle {\boldsymbol {\sigma }}_{ij}}
+  
+ is the electrical conductivity tensor, and 
+  
+    
+      
+        
+          
+            E
+          
+          
+            j
+          
+        
+      
+    
+    {\displaystyle \mathbf {E} _{j}}
+  
+ is the electric field intensity.
+
+=== Magnetic properties ===

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+---
+title: "Physical crystallography before X-rays"
+chunk: 4/5
+source: "https://en.wikipedia.org/wiki/Physical_crystallography_before_X-rays"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:31.939542+00:00"
+instance: "kb-cron"
+---
+
+Until the 19th century crystals were regarded either as magnetic or nonmagnetic. Magnetic crystals are now called ferromagnetic to distinguish them from the several other kinds which have since been discovered. Siméon Denis Poisson (1826) put forward a theory of magnetism as applied to crystals and predicted the behaviour of crystals in a magnetic field which was verified by Julius Plücker in 1847. Plücker studied various natural crystals, such as quartz and related the reaction of the crystal to a magnetic field to its symmetry. All these crystals were repelled from a strong field, unlike ferromagnetic crystals. They were therefore called diamagnetic. In 1850 a number of investigations were carried out by Plücker and August Beer using torsion balances to measure the small forces involved in most observations. Not only were some crystals repelled from a strong field but others were slightly attracted. These were called paramagnetic. Between 1850 and 1856 John Tyndall studied diamagnetism in crystals.
+By the end of the 19th century the three types of crystal—ferromagnetic, diamagnetic and paramagnetic—were well established and successful theories had related diamagnetic and paramagnetic crystals to their crystal symmetry. Ferromagnetic properties were dealt with by Pierre Weiss (1896) who explained the hysteresis by assuming that the atoms have permanent magnetic poles which are normally in random positions, but arrange themselves in parallel under the influence of a magnetic field. On removing the field the mutual effect of the parallel dipoles tends to maintain the magnetized state. He further postulated that there were domains within which all the atomic dipoles were similarly orientated and that the N-S axis could be differently orientated in neighbouring domains.
+
+=== Dielectric properties ===
+A dielectric is an electrical insulator that can be polarised by an applied electric field. In 1851 the first experiments on the behaviour of crystals in an electric field were carried out by Hermann Knoblauch in a manner similar to that used for the study of magnetic properties. The conductivity of the crystals, both over the surface and through the body of the crystal, made these experiments unreliable. In 1876 Elihu Root avoided some of these difficulties by employing a rapidly alternating field between parallel plates. In 1893 Friedrich Pockels gave an account of the abnormally large piezoelectric constants of Rochelle salt. A brief history on the theories of dielectrics in the 19th century has been written.
+
+== Effect of temperature change ==
+
+=== Thermal expansion ===
+
+In 1824 Eilhard Mitscherlich observed that the angle between the cleavage faces of calcite changed with the temperature of the crystal. Mitscherlich concluded that, on heating, calcite contracts (has a negative coefficient of thermal expansion) in a direction perpendicular to the trigonal axis while expanding (positive coefficient) along that axis. This implies that there is a cone of directions along which there is no thermal expansion. In 1864 Hippolyte Fizeau used an optical interference method to make measurements on many crystals. The measurements of the change of interfacial angle and the expansion of cut plates and bars were applied to crystals of all symmetries.
+Crystals with less than cubic symmetry are anisotropic and will generally have different expansion coefficients in different directions. If the crystal symmetry is monoclinic or triclinic, even the angles between the axes are subject to thermal changes. In these cases the coefficient of thermal expansion is a tensor. If the temperature T of a crystal is raised by an amount ΔT, a deformation takes place that is described by the strain tensor uij = αijΔT. The quantities αij are the coefficients of thermal expansion. Since uij is a symmetrical polar tensor of second rank and T is a scalar, αij is a symmetric tensor of second rank. The contemporary usage of the term tensor was introduced by Woldemar Voigt in 1898.
+
+=== Thermal conduction ===
+
+Joseph Fourier was an early researcher in thermal conduction, publishing Théorie analytique de la chaleur in 1822. The first experiments on thermal conduction in crystals were carried out by Jean-Marie Duhamel in 1832.
+Henri Hureau de Sénarmont conducted experiments to determine if heat would move through crystals with directional dependence. He found that, for non-cubic crystals, the isothermal envelope surrounding a point source of heat in a crystal plate had an elliptical shape whose exact form depended on the orientation of the crystal. Sénarmont's results qualitatively established that thermal conductivity is directionally dependent (thermal anisotropy), with characteristic directions related to crystallographic axes. In 1848 Duhamel provided an analysis of Sénermont's findings.
+George Gabriel Stokes and William Thomson provided mathematical theories to explain Sénarmont's observations. Stokes acknowledged the connection between the phenomena and the symmetry of the crystal, and showed that the number of constants of heat conductivity reduces from nine to six in the case of two planes of symmetry. The matrix of thermal conductivity components resulting from Stoke's derivation constituted a tensor. Experiments by Franz Stenger in 1884 examined the theories put forward by Stokes and Thomson and disproved some of their theoretical speculations.
+
+=== Thermoelectricity ===
+
+Thomas Johann Seebeck discovered the thermoelectric effect in 1821, although it has been claimed that Alessandro Volta should be given the priority. In 1844 Wilhelm Gottlieb Hankel investigated thermoelectricity in cobalt and iron sulfide crystals. Hankel showed that when certain external faces were developed the crystals were thermoelectrically positive relative to copper, whereas with other facial forms they were negative. In 1850 Jöns Svanberg used bismuth and antimony crystals to demonstrate a directional variation of the thermoelectric effect. In 1854 William Thomson put forward a mechanical theory of thermoelectric currents in crystalline solids. In 1889 Theodor Liebisch analyzed the dependence of the thermoelectric force on the crystallographic direction in anisotropic crystals.
+
+=== Pyroelectricity ===

data/en.wikipedia.org/wiki/Physical_crystallography_before_X-rays-4.md

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+---
+title: "Physical crystallography before X-rays"
+chunk: 5/5
+source: "https://en.wikipedia.org/wiki/Physical_crystallography_before_X-rays"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:31.939542+00:00"
+instance: "kb-cron"
+---
+
+Pyroelectricity is the generation of a temporary voltage in a crystal when subjected to a temperature change. The appearance of electrostatic charges upon a change of temperature has been observed since ancient times, in particular with tourmaline and was described, among others, by Steno, Linnaeus, Aepinus  and René Just Haüy. Aepinus published an account of his observations in 1756. Haüy made detailed investigations of pyroelectricity; he detected pyroelectricity in calamine and showed that electricity in tourmaline was strongest at the poles of the crystal and became imperceptible at the middle. Haüy published a book on electricity and magnetism in 1787. Haüy later showed that hemihedral crystals are electrified by temperature change while holohedral (symmetric) crystals are not.
+Research into pyroelectricity became more quantitative in the 19th century. In 1824 David Brewster gave the effect the name it has today. In 1840 Gabriel Delafosse, Haüy's student, theorized that only molecules which are not symmetrical can be polarized electrically. Both William Thomson in 1878 and Woldemar Voigt in 1897 helped develop a theory for the processes behind pyroelectricity.
+A detailed history of pyroelectricity has been written by Sidney Lang; shorter histories have also been published.
+
+== Effect of mechanical force ==
+
+=== Elasticity ===
+
+Some minerals, for example mica, are highly elastic, springing back to their original shape after being bent. Others, for example talc, may be readily bent but do not return to their original form when released. The initial theory of the elasticity of solid bodies were developed in the 1820s. Augustin-Louis Cauchy and Siméon Denis Poisson published theories of the mutual action of a regular arrangement of particles for a non-cubic body in 1823 and 1829 respectively. In 1827 Claude-Louis Navier published a theory for an isotropic body. Also during the 1820s Friedrich Mohs introduced his eponymous scale of hardness. In 1834 Franz Ernst Neumann published a paper on the elasticity of homohedral crystals.
+In 1828 Cauchy generalised the problem and showed that 36 independent constants were required to describe elasticity in crystals. George Green (1837) introduced the limitation that the force between any two elements of a crystal, however small, must lie along the line joining their centres. This reduced the number of constants from 36 to 21. William Thomson (1857) showed that Green's assumption was unnecessary and that the thermodynamic requirements of a reversible process require only 21 constants, without any special assumptions.  In 1874 Woldemar Voigt measured the elasticity of rock salt and G. Baumgarten measured the elasticity of calcite. In 1887 Wilhelm Röntgen and J. Schneider measured the cubic compressibility of sodium and potassium chlorides. In 1877 Lambros Koromilas measured the elasticity of gypsum and mica by twisting mineral bars.; in 1881 H. Klang carried out similar experiments with fluorites.
+In the period 1874–1888 Voigt was the leading researcher on the elasticity of crystals. Voigt showed that the number of elasticity constants reduces as more symmetry is introduced into the crystal. For a triclinic crystal, which is the most general case, 21 elasticity constants are required. For a monoclinic crystal there are 13 elasticity constants, for a rhombic crystal 9, for a hexagonal crystal 7, for a tetragonal crystal 6, and finally for a cubic crystal there are only 3. A summary of developments in the field was published by W. A. Wooster.
+
+=== Photoelasticity ===
+Photoelasticity describes changes in the optical properties of a material under mechanical deformation. The photoelastic phenomenon in transparent, non-crystalline materials (gels and glasses) was first discovered by David Brewster in 1815. Brewster then detected the effect in crystals and showed that uniaxial crystals could be made biaxial. In 1822 Augustin-Jean Fresnel experimentally confirmed that the photoelastic effect was a stress-induced birefringence.
+Franz Ernst Neumann investigated double refraction in stressed transparent bodies. In 1841 Neumann published his elastic equations, which describe, in differential form, the changes which polarized light experiences when travelling through a stressed body. The Neumann equations are the basis of all subsequent photoelasticity research.
+The photoelastic effect was analyzed by Friedrich Pockels, who also discovered the Pockels electro-optic effect (the production of birefringence of light on the application of an electric field). In 1889–1890 Pockels produced a phenomenological theory for both of these effects for all crystal classes.
+
+=== Piezoelectricity ===
+
+In 1880 Pierre and Jacques Curie discovered piezoelectricity (an electric charge that accumulates in response to applied mechanical stress) in certain crystals, including quartz, tourmaline, cane sugar and sodium chlorate. The Curies, however, did not predict the converse piezoelectric effect (the internal generation of a mechanical strain resulting from an applied electric field). The converse effect was deduced by Gabriel Lippmann in 1881. The Curies immediately confirmed the existence of the effect, and went on to obtain quantitative proof of the complete reversibility of electro-elasto-mechanical deformations in piezoelectric crystals.
+In 1890 Woldemar Voigt published a phenomenological theory of the piezoelectric effect based on the symmetry of crystals without centrosymmetry.
+
+== Research community ==
+
+Before the 20th century crystallography was not a well-established academic discipline. There were no academic positions specifically in crystallography. Workers in the field normally carried out their crystallographic research as an ancillary to other employment(s), or had independent means.  The leading workers in the field of physical crystallography were employed as follows:
+
+Professors
+Mathematics or science: Airy, Arago, E. Becquerel, Biot, Curie, Drude, Hamilton, Linnaeus, Mitscherlich, Pasteur, Pockels, Plücker, Stokes, Tyndall, Thomson, Voigt
+Mineralogy: Groth, Haüy, Liebisch, Mohs, Neumann, Sénarmont
+Other employment: Bartholinus (physician), Brewster (editor), Fresnel (engineer), Hooke (municipal official), Malus (military officer)
+Independently wealthy: Herschel,  Huygens
+In the nineteenth century there were informal schools of physical crystallography researchers in France (Arago, E. Becquerel, Biot, Fresnel, Haüy, Sénarmont), Germany (Drude, Groth, Liebisch, Mitscherlich, Mohs, Neumann, Pockels, Voigt) and the British Isles (Airy, Brewster, Hamilton, Stokes, Thomson).
+Until the founding of Zeitschrift für Krystallographie und Mineralogie by Paul Groth in 1877 there was no lead journal for the publication of crystallographic papers. The majority of crystallographic research was published in the journals of national scientific societies, or in mineralogical journals. The inauguration of Groth's journal marked the emergence of crystallography as a mature science independent of geology.
+
+== See also ==
+History of crystallography before X-rays
+Chemical crystallography before X-rays
+Geometrical crystallography before X-rays
+Timeline of crystallography
+
+== Citations ==
+
+== Works cited ==

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

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+---
+title: "Timeline of crystallography"
+chunk: 1/6
+source: "https://en.wikipedia.org/wiki/Timeline_of_crystallography"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:33.515741+00:00"
+instance: "kb-cron"
+---
+
+This is a timeline of crystallography.
+
+== 17th century ==
+1669 - In his book De solido intra solidum naturaliter contento Nicolas Steno asserted that, although the number and size of crystal faces may vary from one crystal to another, the angles between corresponding faces are always the same. This was the original statement of the first law of crystallography (Steno's law).
+
+== 18th century ==
+1723 - Moritz Anton Cappeller introduced the term crystallography in his book Prodromus Crystallographiae De Crystallis Improprie Sic Dictis Commentarium.
+1766 - Pierre-Joseph Macquer, in his Dictionnaire de Chymie, promoted mechanisms of crystallization based on the idea that crystals are composed of polyhedral molecules (primitive integrantes).
+1772 - Jean-Baptiste L. Romé de l'Isle developed geometrical ideas on crystal structure in his Essai de Cristallographie. He also described the twinning phenomenon in crystals.
+1781 - Abbé René Just Haüy (often termed the "Father of Modern Crystallography") discovered that crystals always cleave along crystallographic planes. Based on this observation, and the fact that the inter-facial angles in each crystal species always have the same value, Haüy concluded that crystals must be periodic and composed of regularly arranged rows of tiny polyhedra (molécules intégrantes). This theory explained why all crystal planes are related by small rational numbers (the law of rational indices).
+1783 - Jean-Baptiste L. Romé de l'Isle in the second edition of his Cristallographie used the contact goniometer to discover the law of constancy of interfacial angles: angles are constant and characteristic for crystals of the same chemical substance.
+1784 - René Just Haüy published his law of decrements: a crystal is composed of molecules arranged periodically in three dimensions.
+1795 - René Just Haüy lectured on his law of symmetry: "the manner in which Nature creates crystals is always obeying ... the law of the greatest possible symmetry, in the sense that oppositely situated but corresponding parts are always equal in number, arrangement, and form of their faces".
+
+== 19th century ==
+1801 - René Just Haüy published his multi-volume Traité de Minéralogie in Paris. A second edition under the title Traité de Cristallographie was published in 1822.
+1801 - Déodat de Dolomieu published his Sur la philosophie minéralogique et sur l'espèce minéralogique in Paris.
+1815 - René Just Haüy published his law of symmetry.
+1815 - Christian Samuel Weiss, founder of the dynamist school of crystallography, developed a geometric treatment of crystals in which crystallographic axes are the basis for classification of crystals rather than Haüy's polyhedral molecules.
+1819 - Eilhard Mitscherlich discovered crystallographic isomorphism.
+1822 - Friedrich Mohs attempted to bring the molecular approach of Haüy and the geometric approach of Weiss into agreement.
+1823 - Franz Ernst Neumann invented a system of crystal face notation, by using the reciprocals of the intercepts with crystal axes, which becomes the standard for the next 60 years.
+1824 - Ludwig August Seeber conceived of the concept of using an array of discrete (molecular) points to represent a crystal.
+1826 - Moritz Ludwig Frankenheim derived the 32 crystal classes by using the crystallographic restriction, consistent with Haüy's laws, that only 2, 3, 4 and 6-fold rotational axes are permitted.
+1830 - Johann F. C. Hessel published an independent geometrical derivation of the 32 point groups (crystal classes).
+1832 - Friedrich Wöhler and Justus von Liebig discovered polymorphism in molecular crystals, using the example of benzamide.
+1839 - William Hallowes Miller invented zonal relations by projecting the faces of a crystal upon the surface of a circumscribed sphere. Miller indices are defined which form a notation system in crystallography for planes in crystal (Bravais) lattices.
+1840 - Gabriel Delafosse, independently of Seeber, represented crystal structure as an array of discrete points generated by defined translations.
+1842 - Moritz Frankenheim derived 15 different theoretical networks of points in space not dependent on molecular shape.
+1848 - Louis Pasteur discovered that sodium ammonium tartrate can crystallize in left- and right-handed forms and showed that the two forms can rotate polarized light in opposite directions. This was the first demonstration of molecular chirality, and also the first explanation of isomerism.
+1850 - Auguste Bravais derived the 14 space lattices.
+1869 - Axel Gadolin, independently of Hessel, derived the 32 crystal classes using stereographic projection.
+1877 - Paul Heinrich von Groth founded the journal Zeitschrift für Krystallographie und Mineralogie, and served as its editor for 44 years.
+1877 - Ernest-François Mallard, building on the work of Auguste Bravais, published a memoir on optically "anomalous" crystals (that is, those crystals the morphology of which seems to be of greater symmetry than their optics), in which the importance of crystal twinning and "pseudosymmetry" were used as explanatory concepts.
+1879 - Leonhard Sohncke listed the 65 crystallographic point systems using rotations and reflections in addition to translations.
+1888 - Friedrich Reinitzer discovered the existence of liquid crystals during investigations of cholesteryl benzoate.
+1889 - Otto Lehmann, after receiving a letter from Friedrich Reinitzer, used polarizing light to explain the phenomenon of liquid crystals.
+1891 - Derivation of the 230 space groups (by adding mirror-image symmetry to Sohncke's work) by a collaborative effort of Evgraf Fedorov and Arthur Schoenflies.
+1894 - William Barlow, using a method based on patterns of oriented motifs, independently derived the 230 space groups.
+1894 - Pierre Curie described the now called Curie's principle for the symmetry properties of crystals.
+1895 - Wilhelm Conrad Röntgen on 8 November 1895 produced and detected electromagnetic radiation in a wavelength range now known as X-rays or Röntgen rays, an achievement that earned him the first Nobel Prize in Physics in 1901. X-rays became the major mode of crystallographic research in the 20th century.
+1899 - Hermanus Haga and Cornelis Wind observed X-ray diffuse broadening through a slit and deduced that the wavelength of X-rays is on the order of an angstrom.

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

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+---
+
+== 20th century ==
+1905 - Charles Glover Barkla discovered the X-ray polarization effect. 1908 - Bernhard Walter and Robert Wichard Pohl observed X-ray diffraction from a slit. 1912 - Max von Laue discovered diffraction patterns from crystals in an x-ray beam. 1912 - Bragg diffraction, expressed through Bragg's law, is first presented by Lawrence Bragg on 11 November 1912 to the Cambridge Philosophical Society. 1912 - Heinrich Baumhauer discovered and described polytypism in crystals of carborundum, or silicon carbide. 1913 - Lawrence Bragg published the first observation of x-ray diffraction by crystals. Similar observations were also published by Torahiko Terada in the same year. 1913 - Georges Friedel stated Friedel's law, a property of Fourier transforms of real functions. Friedel's law is used in X-ray diffraction, crystallography and scattering from real potential within the Born approximation. 1914 - Max von Laue won the Nobel Prize in Physics "for his discovery of the diffraction of X-rays by crystals."
+1915 - William and Lawrence Bragg published the book X rays and crystal structure and shared the Nobel Prize in Physics "for their services in the analysis of crystal structure by means of X-rays."
+1916 - Peter Debye and Paul Scherrer discovered powder (polycrystalline) diffraction. 1916 - Paul Peter Ewald predicted the Pendellösung effect, which is a foundational aspect of the dynamical diffraction theory of X rays. 1917 - Albert W. Hull independently discovered powder diffraction in researching the crystal structure of metals. 1920 - Reginald Oliver Herzog and Willi Jancke published the first systematic analysis of X-ray diffraction patterns of cellulose extracted from a variety of sources. 1921 - Paul Peter Ewald introduced a spherical construction for explaining the occurrence of diffraction spots, which is now called Ewald's sphere. 1922 - Charles Galton Darwin formulated the theory of X-ray diffraction from imperfect crystals and introduced the concept of mosaicity in crystallography. 1922 - Ralph Wyckoff published a book containing tables with the positional coordinates permitted by the symmetry elements. These positions are now known as Wyckoff positions. This book was the forerunner of the International tables for crystallography, which first appeared in 1935. 1923 - Roscoe Dickinson and Albert Raymond, and independently, H.J. Gonell and Hermann Mark, first showed that an organic molecule, specifically hexamethylenetetramine, could be characterized by x-ray crystallography. 1923 - William H. Bragg and Reginald E. Gibbs elucidated the structure of quartz. 1923 - Paul Peter Ewald published his book Kristalle und Röntgenstrahlen (Crystals and X-rays). 1924 - Louis de Broglie in his PhD thesis Recherches sur la théorie des quanta introduced his theory of electron waves. This was the start of electron and neutron diffraction and crystallography. 1924 - J.D. Bernal established the structure of graphite. 1926 - Victor Goldschmidt distinguished between atomic and ionic radii and postulated some rules for atom substitution in crystal structures. 1927 - Frits Zernike and Jan Albert Prins proposed the pair distribution function for analyzing molecular structures in solution-phase diffraction. 1927 - Two groups demonstrated electron diffraction, the first the Davisson–Germer experiment, the other by George Paget Thomson and Alexander Reid. Alexander Reid, who was Thomson's graduate student, performed the first experiments, but he died soon after in a motorcycle accident. 1928 - Felix Machatschki, working with Goldschmidt, showed that silicon can be replaced by aluminium in feldspar structures. 1928 - Kathleen Lonsdale used x-rays to determine that the structure of benzene is a flat hexagonal ring. 1928 - Paul Niggli introduced reduced cells for simplifying structures using a technique now known as Niggli reduction. 1928 - Hans Bethe published the first non-relativistic explanation of electron diffraction based upon Schrödinger's equation, which remains central to all further analysis. 1928 - Carl Hermann introduced and Charles Mauguin modified the international standard notation for crystallographic groups called Hermann–Mauguin notation. 1929 - Linus Pauling formulated a set of rules (later called Pauling's rules) to describe the structure of complex ionic crystals. 1929 - William Howard Barnes published the crystal structure of ice. 1930 - Lawrence Bragg assembled the first classification of silicates, describing their structure in terms of grouping of SiO4 tetrahedra. 1930 - Gas electron diffraction was developed by Herman Mark and Raymond Wierl,
+1931 - Paul Ewald and Carl Hermann published the first volume of the Strukturbericht (Structure Report), which established the systematic classification of crystal structure prototypes, also known as the Strukturbericht designation. 1931 - Fritz Laves enumerated the Laves tilings for the first time. 1932 - W. H. Zachariasen published an article entitled The atomic arrangement in glass, which perhaps had more influence than any other published work on the science of glass. 1932 - Friedrich Rinne introduced the concept of paracrystallinity for liquid crystals and amorphous materials. 1932 - Vadim E. Lashkaryov and Ilya D. Usyskin determined of the positions of hydrogen atoms in ammonium chloride crystals using electron diffraction. 1934 - Arthur Patterson introduced the Patterson function which uses diffraction intensities to determine the interatomic distances within a crystal, setting limits to the possible phase values for the reflected x-rays. 1934 - Martin Julian Buerger developed the equi-inclination Weissenberg X-ray camera. Buerger invented the precession camera in 1942. 1934 - C. Arnold Beevers and Henry Lipson invented the Beevers–Lipson strip as a calculation aid for Fourier methods for the determination of the crystal structure of CuSO4.5H2O. 1934 - Fritz Laves investigated the structures of intermetallic compounds of formula AB2. These structures were subsequently named Laves phases. 1935 - First publication of the International tables for the determination of crystal structures edited by Carl Hermann. The successor volumes are currently published by IUCr as the International tables for crystallography. 1935 - William Astbury established the structure of keratin using x-ray crystallography; this work provided the foundation for Linus Pauling's 1951 discovery of the α-helix. 1936 - Peter Debye won the Nobel Prize in Chemistry "for his contributions to our knowledge of molecular structure through his investigations on dipole moments and on the diffraction of X-rays and electrons in gases."
+1936 - Hans Boersch showed that electron microscope could be used as micro-diffraction cameras with an aperture—the birth of selected area electron diffraction. 1937 - Clinton Joseph Davisson and George Paget Thomson shared the Nobel Prize in physics "for their experimental discovery of the diffraction of electrons by crystals."
+1939 - Linus Pauling published the book The Nature of the Chemical Bond and the Structure of Molecules and Crystals. 1939 - André Guinier discovered small-angle X-ray scattering. 1939 - Walther Kossel and Gottfried Möllenstedt published the first work on convergent beam electron diffraction (CBED), It was extended by Peter Goodman and Gunter Lehmpfuhl, then mainly by the groups of John Steeds and Michiyoshi Tanaka who showed how to use CBED patterns to determine point groups and space groups. 1941 - The International Centre for Diffraction Data was founded. 1945 - George W. Brindley and Keith Robinson solved the crystal structure of kaolinite. 1945 - The crystal structure of the perovskite BaTiO3 was first published by Helen Megaw based on barium titanate X-ray diffraction data. 1945 - A.F. Wells published the classic reference book, Structural inorganic chemistry, which subsequently went through five editions. 1946 - Foundation of the International Union of Crystallography.

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+1946 - James Batcheller Sumner shared the Nobel Prize in Chemistry "for his discovery that enzymes can be crystallized". 1947 - Lewis Stephen Ramsdell systematically classified the polytypes of silicon carbide, and introduced the Ramsdell notation. 1948 - The first congress and general assembly of the International Union of Crystallography was held at Harvard University. 1948 - Acta Crystallographica was founded by the International Union of Crystallography (IUCr) with P.P. Ewald as its first editor. 1948 - Ernest O. Wollan and Clifford Shull published the first series of neutron diffraction experiments for crystallography performed at the Oak Ridge National Laboratory. 1948 - George Pake used solid state NMR spectroscopy to determine hydrogen atom distances in a single crystal of gypsum. 1949 - Clifford Shull opened a new field of magnetic crystallography based on neutron diffraction. 1950 - Jerome Karle and Herbert A. Hauptman introduced formulae for phase determination known as direct methods. 1951 - Johannes Martin Bijvoet and his colleagues, using anomalous scattering, confirmed Emil Fischer's arbitrary assignment of absolute configuration, in relation to the direction of optical rotation of polarized light, was correct in practice. 1951 - Linus Pauling determined the structure of the α-helix and the β-sheet in polypeptide chains. 1951 - Alexei Vasilievich Shubnikov published Symmetry and antisymmetry of finite figures which opened up the field of antisymmetry in magnetic structures. 1952 - David Sayre suggested that the phase problem could be more easily solved by having at least one more intensity measurement beyond those of the Bragg peaks in each dimension. This concept is understood today as oversampling. 1952 - Geoffrey Wilkinson and Ernst Otto Fischer determined the structure of ferrocene, the first metallic sandwich compound, for which they won the 1973 Nobel prize in Chemistry. The structure was soon refined by Jack Dunitz, Leslie Orgel, and Alexander Rich. 1953 - Arne Magnéli introduced the term homologous series to describe polytypes of transition metal oxides that exhibit crystallographic shear structures. 1953 - Determination of the structure of DNA by three British teams, for which James Watson, Francis Crick and Maurice Wilkins won the 1962 Nobel Prize in Physiology or Medicine in 1962 (Franklin's death in 1958 made her ineligible for the award). 1954 - Ukichiro Nakaya's book Snow Crystals: Natural and Artificial, dedicated to the modern study of snow crystals, is published. 1954 - Linus Pauling won the Nobel Prize in Chemistry "for his research into the nature of the chemical bond and its application to the elucidation of the structure of complex substances"."
+1956 - Durward W. J. Cruickshank developed the theoretical framework for anisotropic displacement parameters, also known as the thermal ellipsoid. 1956 - James Menter published the first electron microscope images showing the lattice structure of a material. 1958 - William Burton Pearson published A Handbook of Lattice Spacings and Structures of Metals and Alloys, where he introduced the Pearson symbols for crystal structure types. 1959 - Norio Kato and Andrew Richard Lang observed Pendellösung fringes in X-ray diffraction from silicon and quartz. The observation of similar fringes in neutron diffraction was made by Clifford Shull in 1968. 1960 - John Kendrew determined the structure of myoglobin for which he shared the 1962 Nobel Prize in Chemistry. 1960 - After many years of research, Max Perutz determined the structure of haemoglobin for which he shared the 1962 Nobel Prize in Chemistry. 1960 - Lester Germer and his coworkers at Bell Labs using a flat phosphor screen for the first modern low-energy electron diffraction camera combined with ultra-high vacuum, the start of quantitative surface crystallography. 1962 - Alan Mackay demonstrated that there exists close packing of spheres to yield icosahedral structures. 1962 - Michael Rossmann and David Blow laid the foundation for the molecular replacement approach which provides phase information without requiring additional experimental effort. 1962 - Max Perutz and John Kendrew shared the Nobel Prize for Chemistry "for their studies of the structures of globular proteins", namely haemoglobin and myoglobin respectively
+1962 - James Watson, Francis Crick and Maurice Wilkins won the Nobel Prize in Physiology or Medicine "for their discoveries concerning the molecular structure of nucleic acids and its significance for information transfer in living material," specifically for their determination of the structure of DNA. 1963 - Isabella Karle developed the symbolic addition procedure in direct methods for inverting X-ray diffraction data. 1963 - Jürg Waser introduced restrained least square method, also known as regularized least squares, for crystallographic structure fitting. 1964 - Dorothy Hodgkin won the Nobel Prize for Chemistry "for her determinations by X-ray techniques of the structures of important biochemical substances." The substances included penicillin and vitamin B12. 1965 - David Chilton Phillips, Louise Johnson and their co-workers published the structure of Lysozyme, the first enzyme to have its structure determined. 1965 - Olga Kennard established the Cambridge Structural Database. 1967 - Hugo Rietveld invented the Rietveld refinement method for computation of crystal structures. 1968 - Erwin Félix Lewy-Bertaut introduced magnetic space groups to account for the spin ordering of magnetic structures observed in neutron crystallography. 1968 - Aaron Klug and David DeRosier used electron microscopy to visualise the structure of the tail of bacteriophage T4, a common virus, thus signalling a breakthrough in macromolecular structure determination. 1968 - Dorothy Hodgkin, after 35 years of work, finally deciphered the structure of insulin. 1969 - Benno P. Schoenborn conducted the first structural study of macromolecules (myoglobin) by neutron diffraction  at the Brookhaven National Laboratory. 1970 - Albert Crewe demonstrated imaging of single atoms in a scanning transmission electron microscopy. 1971 - Establishment of the Protein Data Bank (PDB). At PDB, Edgar Meyer develops the first general software tools for handling and visualizing protein structural data. 1971 - Gerd Rosenbaum, Kenneth Holmes, and Jean Witz first discussed the potential of synchrotron X-ray diffraction for biological applications. 1972 - The first quantitative matching of atomic scale images and dynamical simulations was published by J. G. Allpress, E. A. Hewat, A. F. Moodie and J. V. Sanders. 1972 - Michael Glazer established the classification of octahedral tilting patterns in perovskite crystal structures, later also known as the Glazer tilts. 1973 - Alex Rich's group published the first report of a polynucleotide crystal structure - that of the yeast transfer RNA (tRNA) for phenylalanine. 1973 - Geoffrey Wilkinson and Ernst Fischer shared the Nobel Prize in Chemistry "for their pioneering work, performed independently, on the chemistry of the organometallic, so called sandwich compounds", specifically the structure of ferrocene. 1976 - Douglas L. Dorset and Herbert A. Hauptman used direct methods to solve crystal structures from electron diffraction data. 1976 - Boris Delaunay, building on his work in the 1930s, proved that the regularity of a system of points, an (r, R) system or Delone set, can be established by postulating the points' congruence within a sphere of a defined finite radius. 1976 - William Lipscomb won the Nobel Prize in Chemistry "for his studies on the structure of boranes illuminating problems of chemical bonding."
+1978 - Stephen C. Harrison provided the first high-resolution structure of a virus: tomato bushy stunt virus which is icosahedral in form. 1978 - Günter Bergerhoff and I. David Brown initiated the Inorganic Crystal Structure Database.

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+---
+
+1979 - The first award of the Gregori Aminoff Prize for a contribution in the field of crystallography is made by the Royal Swedish Academy of Sciences to Paul Peter Ewald. 1979 - A team involving Alfred Y. Cho and others at Bell Labs made the first reconstruction of atomic structures at the materials interface between gallium arsenide and aluminium using X-ray diffraction. 1980 - Jerome Karle and Wayne Hendrickson developed multi-wavelength anomalous dispersion (MAD) a technique to facilitate the determination of the three-dimensional structure of biological macromolecules via a solution of the phase problem. 1982 - Aaron Klug won the Nobel Prize in Chemistry "for his development of crystallographic electron microscopy and his structural elucidation of biologically important nucleic acid-protein complexes."
+1983 - John R. Helliwell promoted the use of synchrotron radiation in the crystallography of molecular biology. 1983 - Effectively simultaneously Ian Robinson used surface X-ray Diffraction (SXRD) to solve the structure of the gold 2x1 (110) surface, Laurence D. Marks used electron microscopy and Gerd Binnig and Heinrich Rohrer used scanning tunneling microscope. 1984 - A team led by Dan Shechtman also involving Ilan Blech, Denis Gratias, and John W. Cahn discovered quasicrystals in a metallic alloy. These structures have no unit cell and no periodic translational order but have long-range bond orientational order, which generates a defined diffraction pattern. 1984 - Aaron Klug and his colleagues provided an advance in determining the structure of protein–nucleic acid complexes when they solved the structure of the 206-kDa nucleosome core particle. 1985 - Jerome Karle shared the Nobel Prize in Chemistry with Herbert A. Hauptman "for their outstanding achievements in the development of direct methods for the determination of crystal structures". Karle developed the theoretical basis for multiple-wavelength anomalous diffraction (MAD). 1985 - Hartmut Michel and his colleagues reported the first high-resolution X-ray crystal structure of an integral membrane protein when they published the structure of a photosynthetic reaction centre. 1985 - Kunio Takanayagi led a team which solved the structure of the 7x7 reconstruction of the silicon (111) surface using Patterson function methods with ultra-high vacuum electron diffraction. This surface structure had defeated many prior attempts. 1986 - Ernst Ruska shared the Nobel Prize in Physics "for his fundamental work in electron optics, and for the design of the first electron microscope". 1987 - John M. Cowley and Alexander F. Moodie shared the first IUCr Ewald Prize "for their outstanding achievements in electron diffraction and microscopy. They carried out pioneering work on the dynamical scattering of electrons and the direct imaging of crystal structures and structure defects by high-resolution electron microscopy. The physical optics approach used by Cowley and Moodie takes into account many hundreds of scattered beams, and represents a far-reaching extension of the dynamical theory for X-rays, first developed by P.P. Ewald". 1987 - Don Craig Wiley and Jack L. Strominger solved the structure of the soluble portion of a class I MHC molecule known as HLA-A2. This structure revealed the presence of a pocket which  holds the antigenic peptide, which is recognized by the receptors of T cells only when firmly bound to the MHC product and presented at the surface of an infected cell. This structure strongly influenced the concept of T cell recognition in future work. 1988 - Johann Deisenhofer, Robert Huber and Hartmut Michel shared the Nobel Prize in Chemistry "for the determination of the three-dimensional structure of a photosynthetic reaction centre."
+1989 - Gautam R. Desiraju defined crystal engineering as "the understanding of intermolecular interactions in the context of crystal packing and the utilization of such understanding in the design of new solids with desired physical and chemical properties."
+1991 - Georg E. Schulz and colleagues reported the structure of a bacterial porin, a membrane protein with a cylindrical shape (a ‘β-barrel'). 1991 - The crystallographic information file (CIF) format was introduced by Sydney R. Hall, Frank H. Allen, and I. David Brown based on the self-defining text archive and retrieval (STAR) file format developed by Sydney R. Hall. 1991 - Sumio Iijima used electron diffraction to determine the structure of carbon nanotubes. 1992 - The International Union of Crystallography changed the IUCr's definition of a crystal to "any solid having an essentially discrete diffraction pattern" thus formally recognizing quasicrystals. 1992 - First release of the CNS software package by Axel T. Brunger. CNS is an extension of X-PLOR released in 1987, and is used for solving structures based on X-ray diffraction or solution NMR data. 1994 - Jan Pieter Abrahams et al. reported the structure of an F1-ATPase which uses the proton-motive force across the inner mitochondrial membrane to facilitate the synthesis of adenosine triphosphate (ATP). 1994 - Roger Vincent and Paul Midgley invented the precession electron diffraction method for electron crystallography in a transmission electron microscope. 1994 - Bertram Brockhouse and Clifford Shull shared the Nobel Prize in Physics "for pioneering contributions to the development of neutron scattering techniques for studies of condensed matter". Specifically, Brockhouse "for the development of neutron spectroscopy" and Shull "for the development of the neutron diffraction technique."
+1994 - Philip Coppens led a team of researchers to uncover the transient structure of sodium nitroprusside, a first example in X-ray excited-state crystallography. 1995 - Douglas L. Dorset published Structural Electron Crystallography, a major text on electron crystallography. 1997 - The Bilbao Crystallographic Server was launched at the University of the Basque Country, led by Mois Ilia Aroyo, Juan Manuel Perez-Mato. 1997 - The X-ray crystal structure of bacteriorhodopsin was the first time the lipidic cubic phase (LCP) was used to facilitate the crystallization of a membrane protein; LCP has since been used to obtain the structures of many unique membrane proteins, including G protein-coupled receptors (GPCRs). 1997 - Paul D. Boyer and John E. Walker shared one half of the Nobel Prize in Chemistry "for their elucidation of the enzymatic mechanism underlying the synthesis of adenosine triphosphate (ATP)" Walker determined the crystal structure of ATP synthase, and this structure confirmed a mechanism earlier proposed by Boyer, mainly on the basis of isotopic studies. 1997 - Nobuo Niimura led a team that first used a neutron image plate for structure determination of lysozyme at the Institut Laue–Langevin. 1998 - The structure of tubulin and the location of the taxol-binding site is first determined by Eva Nogales and her team using electron crystallography. 1998 - A group led by Jon Gjønnes combined three-dimensional electron diffraction with precession electron diffraction and direct methods to solve an intermetallic, combining this with dynamical refinements. 1999 - Jianwei Miao, Janos Kirz, David Sayre and co-workers performed the first experiment to extend crystallography to allow structural determination of non-crystalline specimens which has become known as coherent diffraction imaging (CDI), lensless imaging, or computational microscopy. 1999 - A team led by Michael O'Keefe and Omar Yaghi synthesized and determined the structure of MOF-5, the first metal-organic framework (MOF) compound. In the ensuing years, the duo and mathematician Olaf Delgado-Friedrichs further developed the periodic net theory proposed by Alexander F. Wells to characterize MOFs.

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

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+---
+title: "Timeline of crystallography"
+chunk: 5/6
+source: "https://en.wikipedia.org/wiki/Timeline_of_crystallography"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:33.515741+00:00"
+instance: "kb-cron"
+---
+
+== 21st century ==
+2000 - Janos Hajdu, Richard Neutze, and colleagues calculated that they could use Sayre's ideas from the 1950s, to implement a ‘diffraction before destruction' concept, using an X-ray free-electron laser (XFEL).
+2001 - Harry F. Noller's group published the 5.5-Å structure of the complete Thermus thermophilus 70S ribosome. This structure revealed that the major functional regions of the ribosome were based on RNA, establishing the primordial role of RNA in translation.
+2001 - Roger Kornberg's group published the 2.8-Å structure of Saccharomyces cerevisiae RNA polymerase. The structure allowed both transcription initiation and elongation mechanisms to be deduced. Simultaneously, this group reported the structure of free RNA polymerase II, which contributed towards the eventual visualisation of the interaction between DNA, RNA, and the ribosome.
+2003 - Raimond Ravelli et al. demonstrated X-ray radiation damage-induced phasing method for structure determination.
+2005 - The first X-ray free-electron laser in the soft X-ray regime, FLASH, became an operational user facility at DESY for X-ray diffraction experiments.
+2007 - Ute Kolb and co-workers developed automated diffraction tomography for electron crystallography by combining diffraction and tomography within a transmission electron microscope.
+2007 - Two X-ray crystal structures of a GPCR, the human β2 adrenergic receptor, were published. Because many drugs elicit their biological effect(s) by binding to a GPCR, the structures of these and other GPCRs may be used to develop efficacious drugs with few side effects.
+2009 - The first hard X-ray free-electron laser, the Linac Coherent Light Source, became operational at the SLAC National Accelerator Laboratory.
+2009 - Luca Bindi, Paul Steinhardt, Nan Yao, and Peter Lu identified the first naturally occurring quasicrystal using X-ray and electron crystallography.
+2009 - Venkatraman Ramakrishnan, Thomas A. Steitz and Ada E. Yonath shared the Nobel Prize in Chemistry "for studies of the structure and function of the ribosome."
+2009 - Judith Howard and her collaborators created the Olex2 crystallographic software package.
+2011 - Gustaaf Van Tendeloo led a team including Sandra Van Aert, Kees Joost Batenburg et. al. determined the 3D atomic positions of a silver nanoparticle using electron tomography.
+2011 - Dan Shechtman received the Nobel Prize in chemistry "for the discovery of quasicrystals."
+2011 - Henry N. Chapman, Petra Fromme, John C. H. Spence and 85 co-workers used femtosecond pulses from a Free-electron laser (XFEL) to examine the structure of nanocrystals of Photosystem I. By using very brief x-ray pulses, most radiation damage is mitigated using the technique called serial femtosecond crystallography.
+2012 - Jianwei Miao and his co-workers applied the coherent diffraction imaging (CDI) method in Atomic Electron Tomography (AET).
+2013 - Tamir Gonen and his co-workers demonstrated microcrystal electron diffraction (microED) for lysozyme microcrystals at the Janelia Farm Research Campus.
+2014 - Carmelo Giacovazzo published Phasing in Crystallography: A Modern Perspective, a comprehensive opus on phasing methods in X-ray and electron crystallography.
+2014 - The International Union of Crystallography and UNESCO named 2014 the International Year of Crystallography to commemorate the century of discovery since the invention of X-ray diffraction.
+2017 - Lukas Palatinus and co-workers used dynamical structure refinement to resolve hydrogen atom positions in nanocrystals using electron diffraction.
+2017 - Jacques Dubochet, Joachim Frank and Richard Henderson shared the Nobel Prize in chemistry "for developing cryo-electron microscopy for the high-resolution structure determination of biomolecules in solution."
+2019 - The Cambridge Structural Database reached the milestone of one million structures.
+2020 - Two independent groups led respectively by Holger Stark and Sjors Scheres demonstrated that single-particle cryoelectron microscopy has reached atomic resolution.
+2021 - Kenneth G. Libbrecht published the book Snow Crystals: A Case Study in Spontaneous Structure Formation, summarizing his decade-spanning work on the subject for engineering conditions for designer ice crystals.
+2022 - Leonid Dubrovinsky, Igor A. Abrikosov, and Natalia Dubrovinskaia led a team that demonstrates high-pressure crystallography in the terapascal regime.
+2024 - A team led by Anders Madsen developed a deep learning model, PhAI, to solve crystallographic phase problem for small molecules.
+
+== See also ==
+History of crystallography before X-rays
+Chemical
+Geometrical
+Physical
+
+== References ==
+
+== Further reading ==
+
+=== Crystallography before 20th century ===
+Whitlock, H. P. (1934). "A century of progress in crystallography" (PDF). The American Mineralogist. 19: 93–100.
+Burke, John G. (1966), Origins of the science of crystals, University of California Press. LCCN 66--13584
+Lima-de-Faria, José (ed.) (1990), Historical atlas of crystallography, Springer Netherlands
+Kubbinga, Henk (2012). "Crystallography from Haüy to Laue: Controversies on the molecular and atomistic nature of solids". Zeitschrift für Kristallographie. 227 (1): 1–26. Bibcode:2012ZK....227....1K. doi:10.1524/zkri.2012.1459.
+Molčanov, Krešimir; Stilinović, Vladimir (2014-01-13). "Chemical Crystallography before X-ray Diffraction". Angewandte Chemie International Edition. 53 (3): 638–652. Bibcode:2014ACIE...53..638M. doi:10.1002/anie.201301319. ISSN 1433-7851. PMID 24065378.
+"Bernard MAITTE René-Just Haüy (1743-1822) et la naissance de la cristallographie*". annales.org. Retrieved 2024-05-15.
+
+=== Crystallography in the 20th century and beyond ===
+"100 Years of X-ray Crystallography". Chemical & Engineering News. Retrieved 2024-05-14.
+Milestones in crystallography, Nature, August 2014
+Schwarzenbach, Dieter (2012-01-01). "The success story of crystallography". Acta Crystallographica Section A. 68 (1): 57–67. Bibcode:2012AcCrA..68...57S. doi:10.1107/S0108767311030303. ISSN 0108-7673. PMID 22186283.
+"Timelines of Crystallography". iycr2014.org. Retrieved 2024-08-19.
+McMahon, Malcolm I. (2011), Rissanen, Kari (ed.), "High-Pressure Crystallography", Advanced X-Ray Crystallography, Topics in Current Chemistry, vol. 315, Berlin, Heidelberg: Springer Berlin Heidelberg, pp. 69–109, doi:10.1007/128_2011_132, ISBN 978-3-642-27406-0, PMID 21567312, retrieved 2024-05-22{{citation}}:  CS1 maint: work parameter with ISBN (link)
+Baur, Werner H. (2014-04-03). "One hundred years of inorganic crystal chemistry – a personal view". Crystallography Reviews. 20 (2): 64–116. Bibcode:2014CryRv..20...64B. doi:10.1080/0889311X.2013.879648. ISSN 0889-311X.
+Pinheiro, Carlos Basílio; Abakumov, Artem M. (2015-01-01). "Superspace crystallography: a key to the chemistry and properties". IUCrJ. 2 (1): 137–154. Bibcode:2015IUCrJ...2..137P. doi:10.1107/S2052252514023550. ISSN 2052-2525. PMC 4285887. PMID 25610634.
+Kopský, Vojtěch (2015-02-02). "Crystallography and Magnetic Phenomena". Symmetry. 7 (1): 125–145. Bibcode:2015Symm....7..125K. doi:10.3390/sym7010125. ISSN 2073-8994.
+Gratias, Denis; Quiquandon, Marianne (2019-05-23). "Discovery of quasicrystals: The early days". Comptes Rendus. Physique. 20 (7–8): 803–816. Bibcode:2019CRPhy..20..803G. doi:10.1016/j.crhy.2019.05.009. ISSN 1878-1535.

data/en.wikipedia.org/wiki/Timeline_of_crystallography-5.md

@@ -0,0 +1,52 @@
+---
+title: "Timeline of crystallography"
+chunk: 6/6
+source: "https://en.wikipedia.org/wiki/Timeline_of_crystallography"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:33.515741+00:00"
+instance: "kb-cron"
+---
+
+=== History of X-ray crystallography ===
+Ewald, P. P. (ed.) (1962), 50 Years of x-ray diffraction, IUCR, Oosthoek
+Arndt, U. W. (2001-09-22). "Instrumentation in X-ray crystallography: Past, present and future". Notes and Records of the Royal Society of London. 55 (3): 457–472. doi:10.1098/rsnr.2001.0157. ISSN 0035-9149.
+Watkin, David J. (2010). "Chemical crystallography–science, technology or a black art". Crystallography Reviews. 16 (3): 197–230. Bibcode:2010CryRv..16..197W. doi:10.1080/08893110903483246. ISSN 0889-311X.
+Authier, André (2013), Early days of x-ray crystallography, Oxford Univ. Press. ISBN 9780198754053
+Etter, Martin; Dinnebier, Robert E. (2014). "A Century of Powder Diffraction: a Brief History". Zeitschrift für anorganische und allgemeine Chemie. 640 (15): 3015–3028. Bibcode:2014ZAACh.640.3015E. doi:10.1002/zaac.201400526. ISSN 0044-2313.
+Mingos, D. Michael P.; Raithby, Paul R., eds. (2020). 21st Century Challenges in Chemical Crystallography I: History and Technical Developments. Structure and Bonding. Vol. 185. Cham: Springer International Publishing. doi:10.1007/978-3-030-64743-8. ISBN 978-3-030-64742-1.
+
+=== History of electron crystallography ===
+Thomson, George (1968). "The early history of electron diffraction". Contemporary Physics. 9 (1): 1–15. Bibcode:1968ConPh...9....1T. doi:10.1080/00107516808204390. ISSN 0010-7514.
+Tong, S.Y (1994). "Electron-diffraction for surface studies — the first 30 years". Surface Science. 299–300: 358–374. Bibcode:1994SurSc.299..358T. doi:10.1016/0039-6028(94)90667-X.
+Dorset, D. L. (1996-10-01). "Electron crystallography". Acta Crystallographica Section B. 52 (5): 753–769. Bibcode:1996AcCrB..52..753D. doi:10.1107/S0108768196005599. ISSN 0108-7681. PMID 8900031.
+Saha, Ambarneil; Nia, Shervin S.; Rodríguez, José A. (2022-09-14). "Electron Diffraction of 3D Molecular Crystals". Chemical Reviews. 122 (17): 13883–13914. doi:10.1021/acs.chemrev.1c00879. ISSN 0009-2665. PMC 9479085. PMID 35970513.
+
+=== History of neutron crystallography ===
+Schoenborn, B. P.; Nunes, A. C. (1972). "Neutron Scattering". Annual Review of Biophysics and Bioengineering. 1 (1): 529–552. doi:10.1146/annurev.bb.01.060172.002525. ISSN 0084-6589. PMID 4567759.
+Bacon, G. E., ed. (1986). Fifty years of neutron diffraction: the advent of neutron scattering. Bristol: A. Hilger, published with the assistance of the International Union of Crystallography. ISBN 978-0-85274-587-8.
+Harrison, R. J. (2006-01-01). "Neutron Diffraction of Magnetic Materials". Reviews in Mineralogy and Geochemistry. 63 (1): 113–143. Bibcode:2006RvMG...63..113H. doi:10.2138/rmg.2006.63.6. ISSN 1529-6466.
+Blakeley, M.P. (2009). "Neutron macromolecular crystallography". Crystallography Reviews. 15 (3): 157–218. Bibcode:2009CryRv..15..157B. doi:10.1080/08893110902965003. ISSN 0889-311X.
+Mason, T. E.; Gawne, T. J.; Nagler, S. E.; Nestor, M. B.; Carpenter, J. M. (2013-01-01). "The early development of neutron diffraction: science in the wings of the Manhattan Project". Acta Crystallographica Section A. 69 (1): 37–44. doi:10.1107/S0108767312036021. ISSN 0108-7673. PMC 3526866. PMID 23250059.
+
+=== History of NMR crystallography ===
+Andrew, E.R.; Szczesniak, E. (1995). "A historical account of NMR in the solid state". Progress in Nuclear Magnetic Resonance Spectroscopy. 28 (1): 11–36. Bibcode:1995PNMRS..28...11A. doi:10.1016/0079-6565(95)01018-1.
+Harris, Robin K. (2008-12-15), "Crystallography and NMR: An Overview", in Harris, Robin K. (ed.), Encyclopedia of Magnetic Resonance, Chichester, UK: John Wiley & Sons, Ltd, doi:10.1002/9780470034590.emrstm1007, ISBN 978-0-470-03459-0, retrieved 2024-05-17
+
+=== History of structure determination ===
+Beevers, Ca; Lipson, H (1985). "A Brief History of Fourier Methods in Crystal-structure Determination". Australian Journal of Physics. 38 (3): 263. Bibcode:1985AuJPh..38..263B. doi:10.1071/PH850263. ISSN 0004-9506.
+Hauptman, Herbert (1997-10-01). "Phasing methods for protein crystallography". Current Opinion in Structural Biology. 7 (5): 672–680. doi:10.1016/S0959-440X(97)80077-2. ISSN 0959-440X. PMID 9345626.
+Hendrickson, Wayne A. (2013). "Evolution of diffraction methods for solving crystal structures". Acta Crystallographica Section A. 69 (1): 51–59. Bibcode:2013AcCrA..69...51H. doi:10.1107/S0108767312050453. ISSN 0108-7673. PMID 23250061.
+Agirre, Jon; Dodson, Eleanor (2018). "Forty years of collaborative computational crystallography". Protein Science. 27 (1): 202–206. doi:10.1002/pro.3298. ISSN 0961-8368. PMC 5734308. PMID 28901632.
+Hendrickson, Wayne A. (2023-09-01). "Facing the phase problem". IUCrJ. 10 (5): 521–543. Bibcode:2023IUCrJ..10..521H. doi:10.1107/S2052252523006449. ISSN 2052-2525. PMC 10478523. PMID 37668214.
+
+=== History of macromolecular crystallography ===
+Berman, Helen M. (2008-01-01). "The Protein Data Bank: a historical perspective". Acta Crystallographica Section A. 64 (1): 88–95. doi:10.1107/S0108767307035623. ISSN 0108-7673. PMID 18156675.
+Jaskolski, Mariusz; Dauter, Zbigniew; Wlodawer, Alexander (2014). "A brief history of macromolecular crystallography, illustrated by a family tree and its Nobel fruits". The FEBS Journal. 281 (18): 3985–4009. doi:10.1111/febs.12796. ISSN 1742-464X. PMC 6309182. PMID 24698025.
+Haas, David J. (2020-03-01). "The early history of cryo-cooling for macromolecular crystallography". IUCrJ. 7 (2): 148–157. Bibcode:2020IUCrJ...7..148H. doi:10.1107/S2052252519016993. ISSN 2052-2525. PMC 7055388. PMID 32148843.
+Khusainov, Georgii; Standfuss, Joerg; Weinert, Tobias (2024-03-01). "The time revolution in macromolecular crystallography". Structural Dynamics. 11 (2): 020901. doi:10.1063/4.0000247. ISSN 2329-7778. PMC 11015943. PMID 38616866.
+
+=== History of crystallographic organizations and journals ===
+Kamminga, H. (1989-09-01). "The International Union of Crystallography: its formation and early development". Acta Crystallographica Section A. 45 (9): 581–601. Bibcode:1989AcCrA..45..581K. doi:10.1107/S0108767389003910. ISSN 0108-7673.
+Cruickshank, D. W. J. (1998-11-01). "Aspects of the History of the International Union of Crystallography". Acta Crystallographica Section A. 54 (6): 687–696. Bibcode:1998AcCrA..54..687C. doi:10.1107/S0108767398011477.
+Authier, André (2009-05-01). "60 years of IUCr journals". Acta Crystallographica Section A. 65 (3): 167–182. Bibcode:2009AcCrA..65..167A. doi:10.1107/S0108767309007235. ISSN 0108-7673. PMID 19349661.

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

@@ -0,0 +1,70 @@
+---
+title: "Timeline of programming languages"
+chunk: 1/1
+source: "https://en.wikipedia.org/wiki/Timeline_of_programming_languages"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:22.511792+00:00"
+instance: "kb-cron"
+---
+
+This is a record of notable programming languages, by decade.
+
+
+== 1790s ==
+
+
+== 1800s ==
+
+
+== 1830s ==
+
+
+== 1840s ==
+
+
+== 1870s ==
+
+
+== 1940s ==
+
+
+== 1950s ==
+
+
+== 1960s ==
+
+
+== 1970s ==
+
+
+== 1980s ==
+
+
+== 1990s ==
+
+
+== 2000s ==
+
+
+== 2010s ==
+
+
+== 2020s ==
+
+
+== See also ==
+History of computing hardware
+History of programming languages
+Programming language
+Timeline of computing
+Timeline of programming language theory
+
+
+== References ==
+
+
+== External links ==
+Online Historical Encyclopaedia of Programming Languages
+Diagram & history of programming languages
+Eric Levenez's timeline diagram of computer languages history

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

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+---
+title: "Women in computing"
+chunk: 1/10
+source: "https://en.wikipedia.org/wiki/Women_in_computing"
+category: "reference"
+tags: "science, encyclopedia"
+date_saved: "2026-05-05T16:17:23.795787+00:00"
+instance: "kb-cron"
+---
+
+Women in computing were among the first programmers in the early 20th century, and contributed substantially to the industry. As technology and practices altered, the role of women as programmers has changed, and the recorded history of the field has downplayed their achievements. Since the 18th century, women have developed scientific computations, including Nicole-Reine Lepaute's prediction of Halley's Comet, and Maria Mitchell's computation of the motion of Venus.
+The first algorithm intended to be executed by a computer was designed by Ada Lovelace who was a pioneer in the field. Grace Hopper was the first person to design a compiler for a programming language. Throughout the 19th and early 20th century, and up to World War II, programming was predominantly done by women; significant examples include the Harvard Computers, codebreaking at Bletchley Park and engineering at NASA. After the 1960s, the computing work that had been dominated by women evolved into modern software, and the importance of women decreased.
+The gender disparity and the lack of women in computing from the late 20th century onward has been examined, but no firm explanations have been established. Nevertheless, many women continued to make significant and important contributions to the IT industry, and attempts were made to readdress the gender disparity in the industry. In the 21st century, women held leadership roles in multiple tech companies, such as Meg Cushing Whitman, president and chief executive officer of Hewlett Packard Enterprise, and Marissa Mayer, president and CEO of Yahoo! and key spokesperson at Google.
+In November 2023, national media reported an ICT training programme for female founders in Abuja organised through the National Information Technology Development Agency (NITDA).
+
+== History ==
+
+=== 1800s ===
+
+One of the first computers for the American Nautical Almanac was Maria Mitchell. Her work on the assignment was to compute the motion of the planet Venus. The Almanac never became a reality, but Mitchell became the first astronomy professor at Vassar.
+Ada Lovelace was the first person to publish an algorithm intended to be executed by the first modern computer, the Analytical Engine created by Charles Babbage. As a result, she is often regarded as the first computer programmer. Lovelace was introduced to Babbage's difference engine when she was 17. In 1840, she wrote to Babbage and asked if she could become involved with his first machine. By this time, Babbage had moved on to his idea for the Analytical Engine. A paper describing the Analytical Engine, Notions sur la machine analytique, published by L.F. Menabrea, came to the attention of Lovelace, who not only translated it into English, but corrected mistakes made by Menabrea. Babbage suggested that she expand the translation of the paper with her own ideas, which, signed only with her initials, AAL, "synthesized the vast scope of Babbage's vision." Lovelace imagined the kind of impact of the Analytical Engine might have on society. She drew up explanations of how the engine could handle inputs, outputs, processing and data storage. She also created several proofs to show how the engine would handle calculations of Bernoulli Numbers on its own. The proofs are considered the first examples of a computer program. Lovelace downplayed her role in her work during her life, for example, in signing her contributions with AAL so as not be "accused of bragging."
+After the Civil War in the United States, more women were hired as human computers. Many were war widows looking for ways to support themselves. Others were hired when the government opened positions to women because of a shortage of men to fill the roles.
+
+Anna Winlock asked to become a computer for the Harvard Observatory in 1875 and was hired to work for 25 cents an hour. By 1880, Edward Charles Pickering had hired several women to work for him at Harvard because he knew that women could do the job as well as men and he could ask them to volunteer or work for less pay. The women, described as "Pickering's harem" and also as the Harvard Computers, performed clerical work that the male employees and scholars considered to be tedious at a fraction of the cost of hiring a man. The women working for Pickering cataloged around ten thousand stars, discovered the Horsehead Nebula and developed the system to describe stars. One of the "computers," Annie Jump Cannon, could classify stars at a rate of three stars per minute. The work for Pickering became so popular that women volunteered to work for free even when the computers were being paid. Even though they performed an important role, the Harvard Computers were paid less than factory workers.
+By the 1890s, women computers were college graduates looking for jobs where they could use their training in a useful way. Florence Tebb Weldon, was part of this group and provided computations relating to biology and evidence for evolution, working with her husband, W.F. Raphael Weldon. Florence Weldon's calculations demonstrated that statistics could be used to support Darwin's theory of evolution. Another human computer involved in biology was Alice Lee, who worked with Karl Pearson. Pearson hired two sisters to work as part-time computers at his Biometrics Lab, Beatrice and Frances Cave-Brown-Cave.
+
+=== 1910s ===
+During World War I, Karl Pearson and his Biometrics Lab helped produce ballistics calculations for the British Ministry of Munitions. Beatrice Cave-Browne-Cave helped calculate trajectories for bomb shells. In 1916, Cave-Brown-Cave left Pearson's employ and started working full-time for the Ministry. In the United States, women computers were hired to calculate ballistics in 1918, working in a building on the Washington Mall. One of the women, Elizabeth Webb Wilson, worked as the chief computer. After the war, women who worked as ballistics computers for the U.S. government had trouble finding jobs in computing and Wilson eventually taught high school math.
+
+=== 1920s ===

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+title: "Women in computing"
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+category: "reference"
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+date_saved: "2026-05-05T16:17:23.795787+00:00"
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+
+In the early 1920s, Iowa State College, professor George Snedecor worked to improve the school's science and engineering departments, experimenting with new punch-card machines and calculators. Snedecor also worked with human calculators most of them women, including Mary Clem. Clem coined the term "zero check" to help identify errors in calculations. The computing lab, run by Clem, became one of the most powerful computing facilities of the time.
+Women computers also worked at the American Telephone and Telegraph company. These human computers worked with electrical engineers to help figure out how to boost signals with vacuum tube amplifiers. One of the computers, Clara Froelich, was eventually moved along with the other computers to their own division where they worked with a mathematician, Thornton Fry, to create new computational methods. Froelich studied IBM tabulating equipment and desk calculating machines to see if she could adapt the machine method to calculations.
+Edith Clarke was the first woman to earn a degree in electrical engineering and who worked as the first professionally employed electrical engineer in the United States. She was hired by General Electric as a full engineer in 1923. Clarke also filed a patent in 1921 for a graphical calculator to be used in solving problems in power lines. It was granted in 1925.
+
+=== 1930s ===
+The National Advisory Committee for Aeronautics (NACA) which became NASA hired a group of five women in 1935 to work as a computer pool. The women worked on the data coming from wind tunnel and flight tests.
+The Works Progress Administration hired women as human calculators in order to support engineers during World War II. This was largely seen as menial labor, and much of the work was focused on calculations and less on problem solving.
+Barbara “Barby” Canright was recruited for California’s Jet Propulsion Laboratory in 1939 as a human calculator, largely working with engineers in order to determine thrust-to-weight ratios and other various important aeronautics calculations.
+
+=== 1940s ===
+
+"Tedious" computing and calculating was seen as "women's work" through the 1940s resulting in the term "kilogirl", invented by a member of the Applied Mathematics Panel in the early 1940s. A kilogirl of energy was "equivalent to roughly a thousand hours of computing labor." While women's contributions to the United States war effort during World War II was championed in the media, their roles and the work they did was minimized. This included minimizing the complexity, skill and knowledge needed to work on computers or work as human computers. During WWII, women did most of the ballistics computing, seen by male engineers as being below their level of expertise. Black women computers worked as hard (or more often, even harder) as their white counterparts, but in segregated situations. By 1943, almost all people employed as computers were women; one report said "programming requires lots of patience, persistence and a capacity for detail and those are traits that many girls have".
+NACA expanded its pool of women human computers in the 1940s. NACA recognized in 1942 that "the engineers admit themselves that the girl computers do the work more rapidly and accurately than they could." In 1943 two groups, segregated by race, worked on the east and west side of Langley Air Force Base. The black women were the West Area Computers. Unlike their white counterparts, the black women were asked by NACA to re-do college courses they had already passed and many never received promotions.
+Women were also working on ballistic missile calculations. In 1948, women such as Barbara Paulson were working on the WAC Corporal, determining trajectories the missiles would take after launch.
+Women worked with cryptography and, after some initial resistance, many operated and worked on the Bombe machines. Joyce Aylard operated the Bombe machine testing different methods to break the Enigma code. Joan Clarke was a cryptographer who worked with her friend, Alan Turing, on the Enigma machine at Bletchley Park. When she was promoted to a higher salary grade, there were no positions in the civil service for a "senior female cryptanalyst," and she was listed as a linguist instead. While Clarke developed a method of increasing the speed of double-encrypted messages, unlike many of the men, her decryption technique was not named after her. Other cryptographers at Bletchley included Margaret Rock, Mavis Lever (later Batey), Ruth Briggs and Kerry Howard. In 1941, Batey's work enabled the Allies to break the Italians' naval code before the Battle of Cape Matapan. In the United States, several faster Bombe machines were created. Women, like Louise Pearsall, were recruited from the WAVES to work on code breaking and operate the American Bombe machines.
+Hedy Lamarr and co-inventor, George Antheil, worked on a frequency hopping method to help the Navy control torpedoes remotely. The Navy passed on their idea, but Lamarr and Antheil received a patent for the work on August 11, 1942. This technique would later be used again, first in the 1950s at Sylvania Electronic Systems Division and is used in everyday technology such as Bluetooth and Wi-Fi.

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+title: "Women in computing"
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+
+The programmers of the ENIAC computer in 1944, were six female mathematicians; Marlyn Meltzer, Betty Holberton, Kathleen Antonelli, Ruth Teitelbaum, Jean Bartik, and Frances Spence, who were human computers at the Moore School's computation lab. Adele Goldstine was their teacher and trainer and they were known as the "ENIAC girls." The women who worked on ENIAC were warned that they would not be promoted into professional ratings which were only for men. Designing the hardware was "men's work" and programming the software was "women's work." Sometimes women were given blueprints and wiring diagrams to figure out how the machine worked and how to program it. They learned how the ENIAC worked by repairing it, sometimes crawling through the computer, and by fixing "bugs" in the machinery. Even though the programmers were supposed to be doing the "soft" work of programming, in reality, they did that and fully understood and worked with the hardware of the ENIAC. When the ENIAC was revealed in 1946, Goldstine and the other women prepared the machine and the demonstration programs it ran for the public. None of their work in preparing the demonstrations was mentioned in the official accounts of the public events. After the demonstration, the university hosted an expensive celebratory dinner to which none of the ENIAC six were invited.
+In Canada, Beatrice Worsley started working at the National Research Council of Canada in 1947 where she was an aerodynamics research officer. A year later, she started working in the new Computational Centre at the University of Toronto. She built a differential analyzer in 1948 and also worked with IBM machines in order to do calculations for Atomic Energy of Canada Limited. She went to study the EDSAC at the University of Cambridge in 1949. She wrote the program that was run the first time EDSAC performed its first calculations on May 6, 1949.
+Grace Hopper was the first person to create a compiler for a programming language and one of the first programmers of the Harvard Mark I computer, an electro-mechanical computer based on Analytical Engine. Hopper's work with computers started in 1943, when she started working at the Bureau of Ordnance's Computation Project at Harvard where she programmed the Harvard Mark I. Hopper not only programmed the computer, but created a 500-page comprehensive manual for it. Even though Hopper created the manual, which was widely cited and published, she was not specifically credited in it. Hopper is often credited with the coining of the term "bug" and "debugging" when a moth caused the Mark II to malfunction. While a moth was found and the process of removing it called "debugging," the terms were already part of the language of programmers.
+
+=== 1950s ===
+
+Grace Hopper continued to contribute to computer science through the 1950s. She brought the idea of using compilers from her time at Harvard to UNIVAC which she joined in 1949. Other women who were hired to program UNIVAC included Adele Mildred Koss, Frances E. Holberton, Jean Bartik, Frances Morello and Lillian Jay. To program the UNIVAC, Hopper and her team used the FLOW-MATIC programming language, which she developed. Holberton wrote a code, C-10, that allowed for keyboard inputs into a general-purpose computer. Holberton also developed the Sort-Merge Generator in 1951 which was used on the UNIVAC I. The Sort-Merge Generator marked the first time a computer "used a program to write a program." Holberton suggested that computer housing should be beige or oatmeal in color which became a long-lasting trend. Koss worked with Hopper on various algorithms and a program that was a precursor to a report generator.
+Klara Dan von Neumann was one of the main programmers of the MANIAC, a more advanced version of ENIAC. Her work helped the field of meteorology and weather prediction.
+Mary Tsingou developed and ran code on MANIAC to model the evolution of interacting waves on a string, a problem suggested by Enrico Fermi, John Pasta, and Stanislaw Ulam. They discovered a paradox whereby a system expected to thermalise instead showed quasi-periodic behaviour. The problem became known as the Fermi-Pasta-Ulam-Tsingou problem, and spawned the use of computers for numerical experiments in nonlinear science.
+The NACA, and subsequently NASA, recruited women computers following World War II. By the 1950s, a team was performing mathematical calculations at the Lewis Research Center in Cleveland, Ohio, including Annie Easley, Katherine Johnson and Kathryn Peddrew. At the National Bureau of Standards, Margaret R. Fox was hired to work as part of the technical staff of the Electronic Computer Laboratory in 1951. In 1956, Gladys West was hired by the U.S. Naval Weapons Laboratory as a human computer. West was involved in calculations that let to the development of GPS.
+At Convair Aircraft Corporation, Joyce Currie Little was one of the original programmers for analyzing data received from the wind tunnels. She used punch cards on an IBM 650 which was located in a different building from the wind tunnel. To save time in the physical delivery of the punch cards, she and her colleague, Maggie DeCaro, put on roller skates to get to and from the building faster.
+In Israel, Thelma Estrin worked on the design and development of WEIZAC, one of the world's first large-scale programmable electronic computers. In the Soviet Union a team of women helped design and build the first digital computer in 1951. In the UK, Kathleen Booth worked with her husband, Andrew Booth on several computers at Birkbeck College. Kathleen Booth was the programmer and Andrew built the machines. Kathleen developed Assembly Language at this time.
+Mary Coombs (of England) was employed in 1952 as the first female programmer to work on the LEO computers, and as such she is recognized as the first female commercial programmer.
+Ukrainian Kateryna Yushchenko created Address (programming language) for the cоmputer "Kyiv" in 1955 and invented indirect addressing of the highest rank, called pointers.
+
+=== 1960s ===

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+
+Milly Koss who had worked at UNIVAC with Hopper, started work at Control Data Corporation (CDC) in 1965. There she developed algorithms for graphics, including graphic storage and retrieval.
+Mary K. Hawes of Burroughs Corporation set up a meeting in 1959 to discuss the creation a computer language that would be shared between businesses. Six people, including Hopper, attended to discuss the philosophy of creating a common business language (CBL). Hopper became involved in developing COBOL (Common Business Oriented Language) where she innovated new symbolic ways to write computer code. Hopper developed programming language that was easier to read and "self-documenting." After COBOL was submitted to the CODASYL Executive Committee, Betty Holberton did further editing on the language before it was submitted to the Government Printing Office in 1960. IBM were slow to adopt COBOL, which hindered its progress but it was accepted as a standard in 1962, after Hopper had demonstrated the compiler working both on UNIVAC and RCA computers. The development of COBOL led to the generation of compilers and generators, most of which were created or refined by women such as Koss, Nora Moser, Deborah Davidson, Sue Knapp, Gertrude Tierney and Jean E. Sammet.
+Sammet, who worked at IBM starting in 1961 was responsible for developing the programming language, FORMAC. She published a book, Programming Languages: History and Fundamentals (1969), which was considered the "standard work on programming languages," according to Denise Gürer It was "one of the most used books in the field," according to The Times in 1972.
+
+Between 1961 and 1963, Margaret Hamilton began to study software reliability while she was working at the US SAGE air defense system. In 1965, she was responsible for programming the software for the onboard flight software on the Apollo mission computers. After Hamilton had completed the program, the code was sent to Raytheon where "expert seamstresses" called the "Little Old Ladies" actually hardwired the code by threading copper wire through magnetic rings. Each system could store more than 12,000 words that were represented by the copper wires.
+In 1964, the British Prime Minister Harold Wilson announced a "White-Hot" revolution in technology, that would give greater prominence to IT work. As women still held most computing and programming positions at this time, it was hoped that it would give them more positive career prospects. In 1965, Sister Mary Kenneth Keller became the first American woman to earn a doctorate in computer science. Keller helped develop BASIC while working as a graduate student at Dartmouth, where the university "broke the 'men only' rule" so she could use its computer science center.
+In 1966, Frances "Fran" Elizabeth Allen who was developing programming language compilers at IBM Research, published a paper entitled "Program Optimization,". It laid the conceptual basis for systematic analysis and transformation of computer programs. This paper introduced the use of graph-theoretic structures to encode program content in order to automatically and efficiently derive relationships and identify opportunities for optimization.
+Christine Darden began working for NASA's computing pool in 1967 having graduated from the Hampton Institute. Women were involved in the development of Whirlwind, including Judy Clapp. She created the prototype for an air defense system for Whirlwind which used radar input to track planes in the air and could direct aircraft courses.
+In 1969, Elizabeth "Jake" Feinler, who was working for Stanford, made the first Resource Handbook for ARPANET. This led to the creation of the ARPANET directory, which was built by Feinler with a staff of mostly women. Without the directory, "it was nearly impossible to navigate the ARPANET."
+
+By the end of the decade, the general demographics of programmers had shifted away from being predominantly women, as they had before the 1940s. Though women accounted for around 30 to 50 percent of computer programmers during the 1960s, few were promoted to leadership roles and women were paid significantly less than their male counterparts. Cosmopolitan ran an article in the April 1967 issue about women in programming called "The Computer Girls." Even while magazines such as Cosmopolitan saw a bright future for women in computers and computer programming in the 1960s, the reality was that women were still being marginalized. 
+
+=== 1970s ===

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+
+In the early 1970s, Pam Hardt-English led a group to create a computer network they named Resource One and which was part of a group called Project One. Her idea to connect Bay Area bookstores, libraries and Project One was an early prototype of the Internet. To work on the project, Hardt-English obtained an expensive SDS-940 computer as a donation from TransAmerica Leasing Corporation in April 1972. They created an electronic library and housed it in a record store called Leopold's in Berkeley. This became the Community Memory database and was maintained by hacker Jude Milhon. After 1975, the SDS-940 computer was repurposed by Sherry Reson, Mya Shone, Chris Macie and Mary Janowitz to create a social services database and a Social Services Referral Directory. Hard copies of the directory, printed out as a subscription service, were kept at city buildings and libraries. The database was maintained and in use until 2009.
+In the early 1970s, Elizabeth "Jake" Feinler, who worked on the Resource Directory for ARPANET, and her team created the first WHOIS directory. Feinler set up a server at the Network Information Center (NIC) at Stanford which would work as a directory that could retrieve relevant information about a person or entity. She and her team worked on the creation of domains, with Feinler suggesting that domains be divided by categories based on where the computers were kept. For example, military computers would have the domain of .mil, computers at educational institutions would have .edu. Feinler worked for NIC until 1989.
+Jean E. Sammet served as the first woman president of the Association for Computing Machinery (ACM), holding the position between 1974 and 1976.
+Adele Goldberg was one of seven programmers that developed Smalltalk in the 1970s, and wrote the majority of the language's documentation. It was one of the first object-oriented programming languages the base of the current graphic user interface, that has its roots in the 1968 The Mother of All Demos by Douglas Engelbart. Smalltalk was used by Apple to launch Apple Lisa in 1983, the first personal computer with a GUI, and a year later its Macintosh. Windows 1.0, based on the same principles, was launched a few months later in 1985.
+In the late 1970s, women such as Paulson and Sue Finley wrote programs for the Voyager mission. Voyager continues to carry their codes inside its own memory banks as it leaves the Solar System. In 1979, Ruzena Bajcsy founded the General Robotics, Automation, Sensing and Perception (GRASP) Lab at the University of Pennsylvania.
+In the mid-70s, Joan Margaret Winters began working at IBM as part of a "human factors project," called SHARE. In 1978, Winters was the deputy manager of the project and went on to lead the project between 1983 and 1987. The SHARE group worked on researching how software should be designed to consider human factors.
+Erna Schneider Hoover developed a computerized switching system for telephone calls that would replace switchboards. Her software patent for the system, issued in 1971, was one of the first software patents ever issued.
+
+=== 1980s ===

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+
+Gwen Bell developed the Computer Museum in 1980. The museum, which collected computer artifacts became a non-profit organization in 1982 and in 1984, Bell moved it to downtown Boston. Adele Goldberg served as president of ACM between 1984 and 1986.
+In 1981, Deborah Washington Brown became the first African American woman to earn a Ph.D. in computer science from Harvard University (at the time the degree was part of the applied mathematics program). Her thesis was titled "The solution of difference equations describing array manipulation in program loops". Shortly after, in 1982, Marsha R. Williams became the second African American woman to earn a Ph.D. in computer science.
+Sometimes known as the "Betsy Ross of the personal computer," according to the New York Times, Susan Kare worked with Steve Jobs to design the original icons for the Macintosh. Kare designed the moving watch, paintbrush and trash can elements that made using a Mac user-friendly. Kare worked for Apple until the mid-1980s, going on to work on icons for Windows 3.0. Other types of computer graphics were being developed by Nadia Magnenat Thalmann in Canada. Thalmann started working on computer animation to develop "realistic virtual actors" first at the University of Montréal  in 1980 and later in 1988 at the École Polytechnique Fédérale de Lausanne.
+Computer and video games became popular in the 1980s, but many were primarily action-oriented and not designed from a woman's point of view. Stereotypical characters such as the damsel in distress featured prominently and consequently were not inviting towards women. Dona Bailey designed Centipede, where the player shoots insects, as a reaction to such games, later saying "It didn't seem bad to shoot a bug". Carol Shaw, considered to be the first modern female games designer, released a 3D version of tic-tac-toe for the Atari 2600 in 1980. Roberta Williams and her husband Ken, founded Sierra Online and pioneered the graphic adventure game format in Mystery House and the King's Quest series. The games had a friendly graphical user interface and introduced humor and puzzles. Cited as an important game designer, her influence spread from Sierra to other companies such as LucasArts and beyond. Brenda Laurel ported games from arcade versions to the Atari 8-bit computers in the late 1970s and early 1980s. She then went to work for Activision and later wrote the manual for Maniac Mansion.
+1984 was the year of Women into Science and Engineering (WISE Campaign). A 1984 report by Ebury Publishing reported that in a typical family, only 5% of mothers and 19% of daughters were using a computer at home, compared to 25% of fathers and 51% of sons. To counteract this, the company launched a series of software titles designed towards women and publicized in Good Housekeeping. Anita Borg, who had been noticing that women were under-represented in computer science, founded an email support group, Systers, in 1987.
+As Ethernet became the standard for networking computers locally, Radia Perlman, who worked at Digital Equipment Corporation (DEC), was asked to "fix" limitations that Ethernet imposed on large network traffic. In 1985, Perlman came up with a way to route information packets from one computer to another in an "infinitely scalable" way that allowed large networks like the Internet to function. Her solution took less than a few days to design and write up. The name of the algorithm she created is the Spanning Tree Protocol. In 1986, Lixia Zhang was the only woman and graduate student to participate in the early Internet Engineering Task Force (IETF) meetings. Zhang was involved in early Internet development.
+In Europe, project was developed in the mid-1980s to create an academic network in Europe using the Open System Interconnection (OSI) standards. Borka Jerman Blažič, a Yugoslavian computer scientist was invited to work on the project. She was involved in establishing a Yugoslav Research and Academic Network (YUNAC) in 1989 and registered the domain of .yu for the country.
+In the field of human–computer interaction (HCI), French computer scientist, Joëlle Coutaz developed the presentation-abstraction-control (PAC) model in 1987. She founded the User Interface group at the Laboratorire de Génie Informatique of IMAG where they worked on different problems relating to user interface and other software tools.
+In 1988, Stacy Horn, who had been introduced to bulletin board systems (BBS) through The WELL, decided to create her own online community in New York, which she called the East Coast Hang Out (ECHO). Horn invested her own money and pitched the idea for ECHO to others after bankers refused to hear her business plan. Horn built her BBS using UNIX, which she and her friends taught to one another. Eventually ECHO moved an office in Tribeca in the early 1990s and started getting press attention. ECHO's users could post about topics that interested them, and chat with one another, and were provided email accounts. Around half of ECHO's users were women. ECHO was still online as of 2018.
+
+=== 1990s ===

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+
+By the 1990s, computing was dominated by men. The proportion of female computer science graduates peaked in 1984 around 37 per cent, and then steadily declined. Although the end of the 20th century saw an increase in women scientists and engineers, this did not hold true for computing, which stagnated. Despite this, they were very involved in working on hypertext and hypermedia projects in the late 1980s and early 1990s. A team of women at Brown University, including Nicole Yankelovich and Karen Catlin, developed Intermedia and invented the anchor link. Apple partially funded their project and incorporated their concepts into Apple operating systems. Sun Microsystems Sun Link Service was developed by Amy Pearl. Janet Walker developed the first system to use bookmarks when she created the Symbolics Document Examiner. In 1989, Wendy Hall created a hypertext project called Microcosm, which was based on digitized multimedia material found in the Mountbatten archive. Cathy Marshall worked on the NoteCards system at Xerox PARC. NoteCards went on to influence Apple's HyperCard. As the Internet became the World Wide Web, developers like Hall adapted their programs to include Web viewers. Her Microcosm was especially adaptable to new technologies, including animation and 3-D models. In 1994, Hall helped organize the first conference for the Web.
+Sarah Allen, the co-founder of After Effects, co-founded a commercial software company called CoSA in 1990. In 1995, she started working on the Shockwave team for Macromedia where she was the lead developer of the Shockwave Mulituser Server, the Flash Media Server and Flash video.
+Following the increased popularity of the Internet in the 1990s, online spaces were set up to cater for women, including the online community Women's WIRE and the technical and support forum LinuxChix. Women's WIRE, launched by Nancy Rhine and Ellen Pack in October 1993, was the first Internet company to specifically target this demographic. A conference for women in computer-related jobs, the Grace Hopper Celebration of Women in Computing, was first launched in 1994 by Anita Borg.
+Game designer Brenda Laurel started working at Interval Research in 1992, and began to think about the differences in the way girls and boys experienced playing video games. After interviewing around 1,000 children and 500 adults, she determined that games weren't designed with girls' interests in mind. The girls she spoke with wanted more games with open worlds and characters they could interact with. Her research led to Interval Research giving Laurel's research team their own company in 1996, Purple Moon. Also in 1996, Mattel's game, Barbie Fashion Designer, became the first best-selling game for girls. Purple Moon's first two games based on a character called Rockett, made it to the 100 best-selling games in the years they were released. In 1999, Mattel bought out Purple Moon.
+Jaime Levy created one of the first e-Zines in the early 1990s, starting with CyberRag, which included articles, games and animations loaded onto diskettes that anyone with a Mac could access. Later, she renamed the zine to Electronic Hollywood. Billy Idol commissioned Levy to create a disk for his album, Cyberpunk. She was hired to be the creative director of the online magazine, Word, in 1995.
+Cyberfeminists, VNS Matrix, made up of Josephine Starrs, Juliane Pierce, Francesca da Rimini and Virginia Barratt, created art in the early 1990s linking computer technology and women's bodies. In 1997, there was a gathering of cyberfeminists in Kassel, called the First Cyberfeminist International.
+In China, Hu Qiheng, was the leader of the team who installed the first TCP/IP connection for China, connecting to the Internet on April 20, 1994. In 1995, Rosemary Candlin went to write software for CERN in Geneva. In the early 1990s, Nancy Hafkin was an important figure in working with the Association for Progressive Communications (APC) in enabling email connections in 10 African countries. Starting in 1999, Anne-Marie Eklund Löwinder began to work with Domain Name System Security Extensions (DNSSEC) in Sweden. She later made sure that the domain, .se, was the world's first top level domain name to be signed with DNSSEC.
+In the late 1990s, research by Jane Margolis led Carnegie Mellon to try to correct the male-female imbalance in computer science.
+From the late 1980s until the mid-1990s, Misha Mahowald developed several key foundations of the field of Neuromorphic engineering, while working at the California Institute of Technology and later at the ETH Zurich. More than 20 years after her untimely death, the Misha Mahowald Prize was named after her to recognize excellence in the field which she helped to create.
+
+=== 2000s ===
+
+In the 21st century, several attempts have been made to reduce the gender disparity in IT and get more women involved in computing again. A 2001 survey found that while both sexes use computers and the internet in equal measure, women were still five times less likely to choose it as a career or study the subject beyond standard secondary education. Journalist Emily Chang said a key problem has been personality tests in job interviews and the belief that good programmers are introverts, which tends to self-select the stereotype of an asocial white male nerd.
+In 2004, the National Center for Women & Information Technology was established by Lucy Sanders to address the gender gap. Carnegie Mellon University has made a concerted attempt to increase gender diversity in the computer science field, by selecting students based on a wide criteria including leadership ability, a sense of "giving back to the community" and high attainment in maths and science, instead of traditional computer programming expertise. As well as increase the intake of women into CMU, the programme produced better quality students because of the increased diversity making a stronger team.

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+
+=== 2010s ===
+Despite the pioneering work of some designers, video games are still considered biased towards men. A 2013 survey by the International Game Developers Association revealed only 22% of game designers are women, although this is substantially higher than figures in previous decades. Working to bring inclusion to the world of open source project development, Coraline Ada Ehmke drafted the Contributor Covenant in 2014. By 2018, over 40,000 software projects have started using the Contributor Covenant, including TensorFlow, Vue and Linux. In 2014, Danielle George, professor at the School of Electrical and Electronic Engineering, University of Manchester spoke at the Royal Institution Christmas Lectures on the subject of "how to hack your home", describing simple experiments involving computer hardware and demonstrating a giant game of Tetris by remote controlling lights in an office building.
+In 2017, Michelle Simmons founded the first quantum computing company in Australia. The team, which has made "great strides" in 2018, plans to develop a 10-qubit prototype silicon quantum integrated circuit by 2022. In the same year, Doina Precup became the head of DeepMind Montreal, working on artificial intelligence. Xaviera Kowo is a programmer from Cameroon, who won the Margaret award, for programming a robot which processes waste in 2022.
+
+=== 2020s ===
+In 2023 the EU-Startups, the leading online publication with a focus on startups in Europe, published the list of top 100 of the most influential women in the startup and venture capital space in Europe. The theme of the list reflects the era of innovation and technological change, and encourages a new generation of female for entrepreneurship and innovation.
+
+== Gender gap in computing ==

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+
+While computing began as a field heavily dominated by women, this changed in western countries shortly after World War II. In the US, recognizing software development was a significant expense, companies wanted to hire an "ideal programmer". Psychologists William Cannon and Dallis Perry were hired to develop an aptitude test for programmers, and from an industry that was more than 50% women they selected 1400 people, 1200 of whom were male. This paper was highly influential and claimed to have "trained the industry" in hiring programmers, with a heavy focus on introverts and men. In Britain, following the war, women programmers were selected for redundancy and forced retirement, leading to the country losing its position as computer science leader by 1974.
+Popular theories are favored about the lack of women in computer science, which discount historical and social circumstances. In 1992, John Gray's Men Are from Mars, Women Are from Venus theorized that men and women tend to differ in ways of thinking, leading to them approaching technology and computing in different ways. A significant issue is that women find themselves working in an environment that is largely unpleasant, so they decline to continue in those careers. A further issue is that if a class of computer scientists contains few women, those few can be singled out, leading to isolation and feelings of non-belonging, which can culminate in leaving the area.
+The gender disparity in IT is not global. The ratio of female to male computer scientists is significantly higher in India compared to the West, and in 2015, over half of internet entrepreneurs in China were women. In Europe, Bulgaria and Romania have the highest rates of women going into computer programming. In government universities in Saudi Arabia in 2014, Arab women made up 59% of students enrolled in computer science. It has been suggested there is a greater gap in countries where people of both sexes are treated more equally, contradicting any theories that society in general is to blame for any disparity. However, the ratio of African American female computer scientists in the US is significantly lower than the global average. In IT-based organisations, the ratio of men to women can vary between roles; for example, while most software developers at InfoWatch are male, half of usability designers and 80% of project managers are female.
+In 1991, Massachusetts Institute of Technology undergraduate Ellen Spertus wrote an essay "Why Are There So Few Women in Computer Science?", examining inherent sexism in IT, which was responsible for a lack of women in computing. She subsequently taught computer science at Mills College, Oakland in order to increase interest in IT for women. A key problem is a lack of female role models in the IT industry, alongside computer programmers in fiction and the media generally being male.
+The University of Southampton's Wendy Hall has said the attractiveness of computers to women decreased significantly in the 1980s when they "were sold as toys for boys", and believes the cultural stigma has remained ever since, and may even be getting worse. Kathleen Lehman, project manager of the BRAID Initiative at UCLA has said a problem is that typically women aim for perfection and feel disillusioned when code does not compile, whereas men may simply treat it as a learning experience. A report in the Daily Telegraph suggested that women generally prefer people-facing jobs, which many computing and IT positions do not have, while men prefer jobs geared towards objects and tasks. One issue is that the history of computing has focused on the hardware, which was a male dominated field, despite software being written predominantly by women in the early to mid 20th century.
+In 2013, a National Public Radio report said 20% of computer programmers in the US are female. There is no general consensus for any key reason there are less women in computing. In 2017, an engineer was fired from Google after claiming there was a biological reason for a lack of female computer scientists. Recent comparative research has traced the Western survival of intellectual stereotypes of female inferiority in scientific fields to the legacies of colonial hierarchies of intelligence. At the height of scientific racism, in the 19th century, white women began to be perceived to be on par with black men and apes in terms of mathematical and scientific ability, a framework that colonized national cultures rejected entirely.
+Dame Stephanie Shirley using the name Steve Shirley addressed some of the problems facing women in computing in the UK by setting up the software company Freelance Programmers (later F.I, then Xansa now Steria Sopra) offering the chance for women to work from home and part-time work.
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+== Awards ==
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+The Association for Computing Machinery Turing Award, sometimes referred to as the "Nobel Prize" of computing, was named in honor of Alan Turing. This award has been won by three women between 1966 and 2015.
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+2006 – Frances "Fran" Elizabeth Allen
+2008 – Barbara Liskov
+2012 – Shafi Goldwasser
+The British Computer Society Information Retrieval Specialist Group (BCS IRSG) in conjunction with the British Computer Society created an award in 2008 to commemorate the achievements of Karen Spärck Jones, a Professor Emerita of Computers and Information at the University of Cambridge and one of the most remarkable women in computer science. The KSJ award has been won by four women between 2009 and 2017:
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+2009 – Mirella Lapata
+2012 – Diane Kelly
+2016 – Jaime Teevan