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The history of metamaterials begins with artificial dielectrics in microwave engineering as it developed just after World War II. Yet, there are seminal explorations of artificial materials for manipulating electromagnetic waves at the end of the 19th century.
Hence, the history of metamaterials is essentially a history of developing certain types of manufactured materials, which interact at radio frequency, microwave, and later optical frequencies.
As the science of materials has advanced, photonic materials have been developed which use the photon of light as the fundamental carrier of information. This has led to photonic crystals, and at the beginning of the new millennium, the proof of principle for functioning metamaterials with a negative index of refraction in the microwave- (at 10.5 Gigahertz) and optical range. This was followed by the first proof of principle for metamaterial cloaking (shielding an object from view), also in the microwave range, about six years later. However, a cloak that can conceal objects across the entire electromagnetic spectrum is still decades away. Many physics and engineering problems need to be solved.
Nevertheless, negative refractive materials have led to the development of metamaterial antennas and metamaterial microwave lenses for miniature wireless system antennas which are more efficient than their conventional counterparts. Also, metamaterial antennas are now commercially available. Meanwhile, subwavelength focusing with the superlens is also a part of present-day metamaterials research.
== Early wave studies ==
Classical waves transfer energy without transporting matter through the medium (material). For example, waves in a pond do not carry the water molecules from place to place; rather the wave's energy travels through the water, leaving the water molecules in place. Additionally, charged particles, such as electrons and protons create electromagnetic fields when they move, and these fields transport the type of energy known as electromagnetic radiation, or light. A changing magnetic field will induce a changing electric field and vice versa—the two are linked. These changing fields form electromagnetic waves. Electromagnetic waves differ from mechanical waves in that they do not require a medium to propagate. This means that electromagnetic waves can travel not only through air and solid materials, but also through the vacuum of space.
The "history of metamaterials" can have a variety starting points depending on the properties of interest. Related early wave studies started in 1904 and progressed through more than half of the first part of the twentieth century. This early research included the relationship of the phase velocity to group velocity and the relationship of the wave vector and Poynting vector.
In 1904 the possibility of negative phase velocity accompanied by an anti-parallel group velocity were noted by Horace Lamb (book: Hydrodynamics) and Arthur Schuster (Book: Intro to Optics). However both thought practical achievement of these phenomena were not possible. In 1945 Leonid Mandelstam (also "Mandel'shtam") studied the anti-parallel phase and group advance in more detail. He is also noted for examining the electromagnetic characteristics of materials demonstrating negative refraction, as well as the first left-handed material concept. These studies included negative group velocity. He reported that such phenomena occurs in a crystal lattice. This may be considered significant because the metamaterial is a man made crystal lattice (structure). In 1905 H.C. Pocklington also studied certain effects related to negative group velocity.
V.E. Pafomov (1959), and several years later, the research team V.M. Agranovich and V.L. Ginzburg (1966) reported the repercussions of negative permittivity, negative permeability, and negative group velocity in their study of crystals and excitons.
In 1967, V.G. Veselago from Moscow Institute of Physics and Technology considered the theoretical model of medium that is now known as a metamaterial. However, physical experimentation did not occur until 33 years after the paper's publication due to lack of available materials and lack of sufficient computing power. It was not until the 1990s that materials and computing power became available to artificially produce the necessary structures. Veselago also predicted a number of electromagnetic phenomena that would be reversed including the refractive index. In addition, he is credited with coining the term "left handed material" for the present day metamaterial because of the anti-parallel behavior of the wave vector and other electromagnetic fields. Moreover, he noted that the material he was studying was a double negative material, as certain metamaterials are named today, because of the ability to simultaneously produce negative values for two important parameters, e.g. permittivity and permeability. In 1968, his paper was translated and published in English. He was nominated later for a Nobel prize.
Later still, developments in nanofabrication and subwavelength imaging techniques are now taking this work into optical wavelengths.
== Early electromagnetic media ==
In the 19th century Maxwell's equations united all previous observations, experiments, and established propositions pertaining to electricity and magnetism into a consistent theory, which is also fundamental to optics. Maxwell's work demonstrated that electricity, magnetism and even light are all manifestations of the same phenomenon, namely the electromagnetic field.
Likewise, the concept of using certain constructed materials as a method for manipulating electromagnetic waves dates back to the 19th century. Microwave theory had developed significantly during the latter part of the 19th century with the cylindrical parabolic reflector, dielectric lens, microwave absorbers, the cavity radiator, the radiating iris, and the pyramidal electromagnetic horn.
The science involving microwaves also included round, square, and rectangular waveguides precluding Sir Rayleigh's published work on waveguide operation in 1896. Microwave optics, involving the focusing of microwaves, introduced quasi-optical components, and a treatment of microwave optics was published in 1897 (by Righi).

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=== Jagadish Chandra Bose ===
Jagadish Chandra Bose was a scientist involved in original microwave research during the 1890s. As officiating professor of physics at Presidency College he involved himself with laboratory experiments and studies involving refraction, diffraction and polarization, as well as transmitters, receivers and various microwave components.
He connected receivers to a sensitive galvanometer, and developed crystals to be used as a receiver. The crystals operated in the shortwave radio range. Crystals were also developed to detect both white and ultraviolet light. These crystals were patented in 1904 for their capability to detect electromagnetic radiation. Furthermore, it appears that his work also anticipated the existence of p-type and n-type semiconductors by 60 years.
For the general public in 1895, Bose was able to remotely ring a bell and explode gunpowder with the use of electromagnetic waves. In 1896, it was reported that Bose had transmitted electromagnetic signals over almost a mile. In 1897, Bose reported on his microwave research (experiments) at the Royal Institution in London. There he demonstrated his apparatus at wavelengths that ranged from 2.5 centimeters to 5 millimeters.
== Early chiral media ==
In 1898, Jagadish Chandra Bose conducted the first microwave experiment on twisted structures. These twisted structures match the geometries that are known as artificial chiral media in today's terminology. By this time, he had also researched double refraction (birefringence) in crystals. Other research included polarization of electric field "waves" that crystals produce. He discovered this type of polarization in other materials including a class of dielectrics.
In addition, chirality as optical activity in a given material is a phenomenon that has been studied since the 19th century. By 1811, a study of quartz crystals revealed that such crystalline solids rotate the polarization of polarized light denoting optical activity. By 1815, materials other than crystals, such as oil of turpentine were known to exhibit chirality. However, the basic cause was not known. Louis Pasteur solved the problem (chirality of the molecules) originating a new discipline known as stereochemistry. At the macroscopic scale, Lindman applied microwaves to the problem with wire spirals (wire helices) in 1920 and 1922.
Karl F. Lindman, from 1914 and into the 1920s, studied artificial chiral media formed by a collection of randomly oriented small spirals. He was written about by present-day metamaterials scientists: Ismo V. Lindell, Ari H. Sihvola, and Juhani Kurkijarvi.
== 20th century artificial dielectrics ==

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Much of the historic research related to metamaterials is weighted from the view of antenna beam shaping within microwave engineering just after World War II. Furthermore, metamaterials appear to be historically linked to the body of research pertaining to artificial dielectrics throughout the late 1940s, the 1950s and the 1960s. The most common use for artificial dielectrics throughout prior decades has been in the microwave regime for antenna beam shaping. The artificial dielectrics had been proposed as a low cost and lightweight "tool". Research on artificial dielectrics, other than metamaterials, is still ongoing for pertinent parts of the electromagnetic spectrum.
Pioneering works in microwave engineering on artificial dielectrics in microwave were produced by Winston E. Kock, Seymour Cohn, John Brown, and Walter Rotman. Periodic artificial structures were proposed by Kock, Rotman, and Sergei Schelkunoff. There is also an extensive reference list that is focused on the properties of artificial dielectrics in the 1991 book, Field Theory of Guided Waves by Robert E. Collin.
Schelkunoff achieved notice for contributions to antenna theory and electromagnetic wave propagation.
"Magnetic particles made of capacitively loaded loops were also suggested by Sergei Schelkunoff in 1952 (who was a senior colleague of Winston Kock at
Bell Labs at the time). However, Schelkunoff suggested these particles as a means of synthesizing high permeability (and not negative) values
but he recognized that such high permeability artificial dielectrics would be quite dispersive."
W.E. Kock proposed metallic and wire lenses for antennas. Some of these are the metallic delay lens, parallel-wire lens, and the wire mesh lens. In addition, he conducted analytical studies regarding the response of customized metallic particles to a quasistatic electromagnetic radiation. As with the current large group of researchers conveying the behavior of metamaterials, Kock noted behaviors and structure in artificial materials that are similar to metamaterials.
He employed particles, which would be of varying geometric shape; spheres, discs, ellipsoids and prolate or oblate spheroids, and would be either isolated or set in a repeating pattern as part of an array configuration. Furthermore, he was able to determine that such particles behave as a dielectric medium. He also noticed that the permittivity "ε" and permeability "μ" of these particles can be purposely tuned, but not independently.
With metamaterials, however, local values for both ε and μ are designed as part of the fabrication process, or analytically designed in theoretical studies. Because of this process, individual metamaterial inclusions can be independently tuned.
With artificial dielectrics Kock was able to see that any value for permittivity and permeability, arbitrarily large or small, can be achieved, and that this included the possibility of negative values for these parameters. The optical properties of the medium depended solely on the particles' geometrical shape and spacing, rather than on their own intrinsic behavior. His work also anticipated the split-ring resonator, a fabricated periodic structure that is a common workhorse for metamaterials.
Kock, however, did not investigate the simultaneous occurrence of negative values of ε and μ, which has become one of the first achievements defining modern metamaterials. This was because research in artificial materials was oriented toward other goals, such as creating plasma media at RF or microwave frequencies related to the overarching needs of NASA and the space program at that time.
Walter Rotman and R.F. Turner advanced microwave beam shaping systems with a lens that has three perfect focal points; two symmetrically located off-axis and one on-axis. They published the design equations for the improved straight-front-face lens, the evaluation of its phase control capabilities, scanning capabilities, and the demonstrated fabrication techniques applicable to this type of design.
Rotman invented other periodic structures that include many types of surface wave antennas: the trough waveguide, the channel waveguide, and the sandwich wire antenna.
== Photonic structures ==
"At frequencies of a few hundred gigahertz and lower, electrons are the principle particles which serve as the workhorse of devices. On the other hand,
at infrared through optical to ultraviolet wavelengths, the photon is the fundamental particle of choice."
The word 'photonics' appeared in the late 1960s to describe a research field whose goal was to use light to perform functions that traditionally fell within the typical domain of electronics, such as telecommunications, information processing, among other processes. The term photonics more specifically connotes:
The particle properties of light,
The potential of creating signal processing device technologies using photons,
The practical application of optics, and
An analogy to electronics.
Hence, as photonic materials are used, the photons, rather than electrons, become the fundamental carriers of information. Furthermore, the photon appears to be a more efficient carrier of information, and materials that can process photonic signals are both in use and in further development. Additionally, developing photonic materials will lead to further miniaturization of components.
In 1987 Eli Yablonovitch proposed controlling spontaneous emissions and constructing physical zones in periodic dielectrics that forbid certain wavelengths of electromagnetic radiation. These capabilities would be built into three-dimensional periodic dielectric structures (artificial dielectric). He noted that controlling spontaneous emission is desirable for semiconductor processes.
== Exceptional phenomena ==

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=== Invention of the metamaterial ===
Historically, and conventionally, the function or behavior of materials can be altered through their chemistry. This has long been known. For example, adding lead changes the color or hardness of glass. However, at the end of the 20th century this description was expanded by John Pendry, a physicist from Imperial College in London. In the 1990s he was consulting for a British company, Marconi Materials Technology, as a condensed matter physics expert. The company manufactured a stealth technology made of a radiation-absorbing carbon that was for naval vessels. However, the company did not understand the physics of the material. The company asked Pendry if he could understand how the material worked.
Pendry discovered that the radiation absorption property did not come from the molecular or chemical structure of the material, i.e. the carbon per se. This property came from the long and thin, physical shape of the carbon fibers. He realized rather than conventionally altering a material through its chemistry, as lead does with glass, the behavior of a material can be altered by changing a material's internal structure on a very fine scale. The very fine scale was less than the wavelength of the electromagnetic radiation that is applied. The theory applies across the electromagnetic spectrum that is in use by today's technologies. The radiations of interest are from radio waves, and microwaves, through infrared to the visible wavelengths. Scientists view this material as "beyond" conventional materials. Hence, the Greek word "meta" was attached, and these are called metamaterials.
After successfully deducing and realizing the carbon fiber structure, Pendry further proposed that he try to change the magnetic properties of a non-magnetic material, also by altering its physical structure. The material would not be intrinsically magnetic, nor inherently susceptible to being magnetized. Copper wire is such a non-magnetic material. He envisioned fabricating a non-magnetic composite material, which could mimic the movements of electrons orbiting atoms. However, the structures are fabricated on a scale that is magnitudes larger than the atom, yet smaller than the radiated wavelength.
He envisioned and hypothesized miniature loops of copper wire set in a fiberglass substrate could mimic the action of electrons but on a larger scale. Furthermore, this composite material could act like a slab of iron. In addition, he deduced that a current run through the loops of wire results in a magnetic response.
This metamaterial idea resulted in variations. Cutting the loops results in a magnetic resonator, which acts like a switch. The switch, in turn, would allow Pendry to determine or alter the magnetic properties of the material simply by choice. At the time, Pendry didn't realize the significance of the two materials he had engineered. By combining the electrical properties of Marconi's radar-absorbing material with his new man-made magnetic material he had unwittingly placed in his hands a new way to manipulate electromagnetic radiation. In 1999, Pendry published his new conception of artificially produced magnetic materials in a notable physics journal. This was read by scientists all over the world, and it "stoked their imagination".
=== Negative refractive index ===
In 1967, Victor Veselago produced an often cited, seminal work on a theoretical material that could produce extraordinary effects that are difficult or impossible to produce in nature. At that time he proposed that a reversal of Snell's law, an extraordinary lens, and other exceptional phenomena can occur within the laws of physics. This theory lay dormant for a few decades. There were no materials available in nature, or otherwise, that could physically realize Veselago's analysis. Not until thirty-three years later did the properties of this material, a metamaterial, became a subdiscipline of physics and engineering.
However, there were certain observations, demonstrations, and implementations that closely preceded this work. Permittivity of metals, with values that could be stretched from the positive to the negative domain, had been studied extensively. In other words, negative permittivity was a known phenomenon by the time the first metamaterial was produced. Contemporaries of Kock were involved in this type of research. The concentrated effort was led by the US government for researching interactions between the ionosphere and the re-entry of NASA space vehicles.
In the 1990s, Pendry et al. developed sequentially repeating thin wire structures, analogous to crystal structures. These extended the range of material permittivity. However, a more revolutionary structure developed by Pendry et al. was a structure that could control magnetic interactions (permeability) of the radiated light, albeit only at microwave frequencies. This sequentially repeating, split ring structure, extended material magnetic parameters into the negative. This lattice or periodic, "magnetic" structure was constructed from non-magnetic components.
Hence, in electromagnetic domain, a negative value for permittivity and permeability occurring simultaneously was a requirement to produce the first metamaterials. These were beginning steps for proof of principle regarding Veselago's original 1967 proposal.
In 2000, a team of UCSD researchers produced and demonstrated metamaterials, which exhibited unusual physical properties that were never before produced in nature. These materials obey the laws of physics, but behave differently from normal materials. In essence these negative index metamaterials were noted for having the ability to reverse many of the physical properties that govern the behavior of ordinary optical materials. One of those unusual properties is the capability to reverse, for the first time, the Snell's law of refraction. Until this May 2000 demonstration by the UCSD team, the material was unavailable. Advances during the 1990s in fabrication and computation capabilities allowed these first metamaterials to be constructed. Thus, testing the "new" metamaterial began for the effects described by Victor Veselago 30 years earlier, but only at first in the microwave frequency domain. Reversal of group velocity was explicitly announced in the related published paper.
First demonstration of a negative index of refraction in the optical range was done by Vladimir M. Shalaev et al.

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=== The super lens ===
The super lens or superlens is a practical structure based on John Pendry's work describing a perfect lens that can go beyond the diffraction limit by focusing all four fourier components. Pendry's paper described a theoretical novel lens that could capture images below the diffraction limit by employing the negative refractive index behavior. The super lens is a practical realization of this theory. It is a working lens that can capture images below the diffraction limit even though limitations occur due to the inefficiencies of conventional materials. This means that although there are losses, enough of an image is returned to show this work was a successful demonstration.
=== Invisibility cloak ===
Ulf Leonhardt was born in East Germany, and presently occupies the theoretical physics chair at the University of St. Andrews in Scotland, and is considered one the leaders in the science of creating an invisibility cloak. Around 1999, Leonhardt began work on how to build a cloaking device with a few other colleagues. Leonhardt stated that at the time invisibility was not considered fashionable. He then wrote a theoretical study entitled "Optical Conformal Mapping". The first sentence sums up the objective: "An invisibility device should guide light around an object as if nothing were there."
In 2005, he sent the paper to three notable scientific journals, Nature, Nature Physics, and Science. Each journal, in turn, rejected the paper. In 2006, Physical Review Letters rejected the paper for publication, as well. However, according to the PRL assessment, one of the anonymous reviewers noted that (he or she ) had been to two meetings in the previous months with John Pendry's group, who were also working on a cloaking device. From the meetings, the reviewer also became aware of a patent that Pendry and his colleagues were supposed to file. Leonhardt was at the time unaware of the Pendry group's work. Because of the Pendry meetings, Leonhardt's work was not really considered new physics by the reviewer and, therefore, did not merit publication in Physical Review Letters.
Later in 2006, Science (the journal) reversed its decision and contacted Leonhardt to publish his paper because it had just received a theoretical study from Pendry's team entitled "Controlling Electromagnetic Fields". Science considered both papers strikingly similar and published them both in the same issue of Science Express on May 25, 2006. The published papers touched off research efforts by a dozen groups to build cloaking devices at locations around the globe, which would test out the mathematics of both papers.
Only months after the submission of notable invisibility cloak theories, a practical device was built and demonstrated by David Schurig and David Smith, engineering researchers of Duke University (October 2006). It was limited to the microwave range so the object was not invisible to the human eye. However, it demonstrated proof of principle.
== Transformation optics ==
The original theoretical papers on cloaking opened a new science discipline called transformation optics.
== See also ==
Mechanical Metamaterials
Metamaterial cloaking – Shielding an object from view using materials made to redirect light
Acoustic metamaterials – Material designed to manipulate sound wavesPages displaying short descriptions of redirect targets
Quantum metamaterials – Type of materialPages displaying short descriptions of redirect targets
Photonic metamaterials – Type of electromagnetic metamaterialPages displaying short descriptions of redirect targets
Nonlinear metamaterials
Seismic metamaterials
Metamaterial absorber
Plasmonic metamaterials – Metamaterial that uses surface plasmons to achieve optical properties not seen in naturePages displaying short descriptions of redirect targets
Terahertz metamaterials
Tunable metamaterials
Split-ring resonator – Structure in some metamaterials
Theories of cloaking
== Notes ==
== References ==
== Further reading and general references ==
Rotman, W.; Turner, R. (1963). "Wide-angle microwave lens for line source applications" (PDF). IEEE Transactions on Antennas and Propagation. 11 (6): 623. Bibcode:1963ITAP...11..623R. doi:10.1109/TAP.1963.1138114. Archived from the original (PDF) on October 8, 2012.
Shamonina, E.; Solymar, L. (February 8, 2007). "Metamaterials: How the subject started" (PDF). Metamaterials. 01 (1): 12–18. Bibcode:2007MetaM...1...12S. doi:10.1016/j.metmat.2007.02.001. Archived from the original (PDF) on July 23, 2010. Retrieved 2010-07-18.
Sihvola, Ari (February 12, 2007). "Metamaterials in electromagnetics" (PDF). Metamaterials. 01 (1): 2–11. Bibcode:2007MetaM...1....2S. doi:10.1016/j.metmat.2007.02.003. Retrieved 2010-07-18.
Ziolkowski, Richard W. (September 2006). "Metamaterial-Based Antennas: Research and Developments" (PDF). IEICE Transactions on Electronics. E89-C (9): 1267–1275. doi:10.1093/ietele/e89-c.9.1267. Retrieved February 6, 2011.
Boltasseva, Alexandra; Vladimir M. Shalaev (March 18, 2008). "Fabrication of optical negative-index metamaterials" (PDF). Metamaterials. 2 (1): 1–17. Bibcode:2008MetaM...2....1B. doi:10.1016/j.metmat.2008.03.004. Retrieved 2010-07-18.
Zahn, Markus (instructor). "An artificial dielectric". Course title: MIT 6.013 Electromagnetics and Applications, Fall 20. from Massachusetts Institute of Technology. Retrieved February 28, 2011.
Wade, Paul. "Metal Plate Lens Antennas" (PDF). Chapter 3. Retrieved February 28, 2011. Description of building a mobile metal plate antenna.
Invited paper: Engheta, N. (2003). "Metamaterials with negative permittivity and permeability: background, salient features, and new trends" (PDF). Microwave Symposium Digest, 2003 IEEE MTT-S International. Vol. 1. Vol. 1. p. 187. doi:10.1109/MWSYM.2003.1210912. ISBN 0-7803-7695-1. Archived from the original (PDF) on August 21, 2011.
Johri, Manoj; Harihar Paudyal (May 2010). "Left Handed Materials: a new Pardigm in Structured Electromagnetics" (PDF). Trieste, Italy.: produced by ICTP, UNESCO, and the IAEA. pp. 1–12. IC/2010/015. Archived from the original (PDF) on 2011-04-01. Retrieved 2011-05-03. – Technical review of metamterials research.
Kaku, Michio (April 2008). "Invisibility …". Natural History Magazine. Retrieved February 28, 2011.
Slyusar V.I. Metamaterials on antenna solutions.// 7th International Conference on Antenna Theory and Techniques ICATT'09, Lviv, Ukraine, October 6–9, 2009. - pp. 19 – 24 [3]
== External links ==
"Microwave cloaking". New York Times. June 12, 2007.

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The history of the metric system began during the Age of Enlightenment with measures of length and weight derived from nature, along with their decimal multiples and fractions. The system became the standard of France and Europe within half a century. Other measures with unity ratios were added, and the system went on to be adopted across the world.
The first practical realisation of the metric system came in 1799, during the French Revolution, after the existing system of measures had become impractical for trade, and was replaced by a decimal system based on the kilogram and the metre. The basic units were taken from the natural world. The unit of length, the metre, was based on the dimensions of the Earth, and the unit of mass, the kilogram, was based on the mass of a volume of water of one litre (a cubic decimetre). Reference copies for both units were manufactured in platinum and remained the standards of measure for the next 90 years. After a period of reversion to the mesures usuelles due to unpopularity of the metric system, the metrication of France and much of Europe was complete by the 1850s.
In the middle of the 19th century, James Clerk Maxwell conceived a coherent system where a small number of units of measure were defined as base units, and all other units of measure, called derived units, were defined in terms of the base units. Maxwell proposed three base units for length, mass and time. Advances in electromagnetism in the 19th century necessitated additional units to be defined, and multiple incompatible systems of such units came into use; none could be reconciled with the existing dimensional system. The impasse was resolved by Giovanni Giorgi, who in 1901 proved that a coherent system that incorporated electromagnetic units required a fourth base unit, of electromagnetism.
The seminal 1875 Treaty of the Metre resulted in the fashioning and distribution of metre and kilogram artefacts, the standards of the future coherent system that became the SI, and the creation of an international body Conférence générale des poids et mesures or CGPM to oversee systems of weights and measures based on them.
In 1960, the CGPM launched the International System of Units (in French the Système international d'unités or SI) with six "base units": the metre, kilogram, second, ampere, degree Kelvin (subsequently renamed the "kelvin") and candela, plus 16 more units derived from the base units. A seventh base unit, the mole, and six other derived units were added later in the 20th century. During this period, the metre was redefined in terms of the speed of light, and the second was redefined based on the microwave frequency of a caesium atomic clock.
Due to the instability of the international prototype of the kilogram, a series of initiatives were undertaken, starting in the late 20th century, to redefine the ampere, kilogram, mole and kelvin in terms of invariant constants of physics, ultimately resulting in the 2019 revision of the SI, which finally eliminated the need for any physical reference artefacts—notably, this enabled the retirement of the standard kilogram.
== Age of Enlightenment ==
Foundational aspects of mathematics, together with an increased understanding of the natural world during the Enlightenment, set the stage for the emergence in the late 18th century of a system of measurement with rationally related units and rules for combining them.
=== Preamble ===
In the early ninth century, when much of what later became Holy Roman Empire was part of France, units of measure had been standardised by the Emperor Charlemagne. He had introduced standard units of measure for length and for mass throughout his empire. As the empire disintegrated into separate nations, including France, these standards diverged.
During the early medieval era, Roman numerals were used in Europe to represent numbers, but the Arabs represented numbers using the Hindu numeral system, a positional notation that used ten symbols. In about 1202, Fibonacci published his book Liber Abaci (Book of Calculation) which introduced the concept of positional notation into Europe. These symbols evolved into the numerals "0", "1", "2", etc. At that time, there was dispute regarding the difference between rational numbers and irrational numbers and there was no consistency in the way in which decimal fractions were represented.
Simon Stevin is credited with introducing the decimal system into general use in Europe. In 1586, he published a small pamphlet called De Thiende ("the tenth") which historians credit as being the basis of modern notation for decimal fractions. Stevin felt that this innovation was so significant that he declared the universal introduction of decimal coinage, measures, and weights to be merely a question of time.
=== Body measures and artifacts ===
Since the time of Charlemagne, the standard of length had been a measure of the body, that from fingertip to fingertip of the outstretched arms of a large man, from a family of body measures called fathoms, originally used among other things, to measure the depth of water. An artifact to represent the standard was cast in the most durable substance available in the Middle Ages, an iron bar . The problems of a non-reproducible artefact became apparent over the ages: it rusted, was stolen, beaten into a mortised wall until it bent, and was, at times, lost. When a new royal standard had to be cast, it was a different standard than the old one, so replicas of old ones and new ones came into existence and use. The artefact existed through the 18th century, and was called a teise or later, a toise (from Latin tense: outstretched (arms)). This would lead to a search in the 18th century for a reproducible standard based on some invariant measure of the natural world.

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=== Clocks and pendulums ===
In 1656, Dutch scientist Christiaan Huygens invented the pendulum clock, with its pendulum marking the seconds. This gave rise to proposals to use its length as a standard unit. But it became apparent that the pendulum lengths of calibrated clocks in different locations varied (due to local variations in the acceleration due to gravity), and this was not a good solution. A more uniform standard was needed.
In 1670, Gabriel Mouton, a French abbot and astronomer, published the book Observationes diametrorum solis et lunae apparentium ("Observations of the apparent diameters of the Sun and Moon") in which he proposed a decimal system of measurement of length for use by scientists in international communication, to be based on the dimensions of the Earth. The milliare would be defined as a minute of arc along a meridian (such as the Paris meridian) and would be divided into 10 centuria, the centuria into 10 decuria and so on, successive units being the virga, virgula, decima, centesima, and the millesima. Mouton used Riccioli's estimate that one degree of arc was 321,185 Bolognese feet. Mouton's experiments showed that a pendulum of length one virgula would beat 3959.2 times in half an hour. Mouton believed that, with this information, scientists in a foreign country would be able to construct a copy of the virgula for their own use. Mouton's ideas attracted interest at the time; Picard in his work Mesure de la Terre (1671) and Huygens in his work Horologium Oscillatorium sive de motu pendulorum ("Of oscillating clocks, or concerning the motion of pendulums", 1673) both proposing that a standard unit of length be tied to the beat frequency of a pendulum.
=== Shape and size of the Earth ===
Since at least the Middle Ages, the Earth had been perceived as eternal, unchanging, and of symmetrical shape (close to a sphere), so it was natural that some fractional measure of its surface should be proposed as a standard of length. But first, scientific information about the shape and size of the Earth had to be obtained. One degree of arc would be 60 minutes of arc, on the equator; one milliare would be one minute of arc, or 1 nautical mile, so 60 nautical miles would be one degree of arc on Earth's surface, taken as a sphere. Thus Earth's circumference in nautical miles would be 21 600 (viz., 60 minutes of arc × 360 degrees in four 90-degree quadrants; a quadrant being the length of the quarter-circle from the North Pole to the equator).
In 1669, Jean Picard, a French astronomer, was the first person to measure the Earth accurately. In a survey spanning one degree of latitude, he erred by only 0.44% (Picard's arc measurement).
In Philosophiæ Naturalis Principia Mathematica (1686), Isaac Newton gave a theoretical explanation for the "bulging equator", which also explained the differences found in the lengths of the "second pendulums", theories that were confirmed by the French Geodesic Mission to Peru undertaken by the French Academy of Sciences in 1735.
=== Late 18th century: conflict and lassitude ===
By the mid-18th century, it had become apparent that it was necessary to standardise of weights and measures between nations who traded and exchanged scientific ideas with each other. Spain, for example, had aligned its units of measure with the royal units of France and Peter the Great aligned the Russian units of measure with those of England. In 1783, the British inventor James Watt, who was having difficulties in communicating with German scientists, called for the creation of a global decimal measurement system, proposing a system which used the density of water to link length and mass, and, in 1788, the French chemist Antoine Lavoisier commissioned a set of nine brass cylinders (a [French] pound and decimal subdivisions thereof) for his experimental work.
In 1790, a proposal floated by the French to Britain and the United States, to establish a uniform measure of length, a metre based on the period of a pendulum with a beat of one second, was defeated in the British Parliament and United States Congress. The underlying issue was failure to agree on the latitude for the definition, since gravitational acceleration, and, therefore, the length of the pendulum, varies (inter alia) with latitude: each party wanted a definition according to a major latitude passing through their own country. The direct consequences of the failure were the French unilateral development and deployment of the metric system and its spread by trade to the continent; the British adoption of the Imperial System of Measures throughout the realm in 1824; and the United States' retention of the British common system of measures in place at the time of the independence of the colonies. This was the position that continued for nearly the next 200 years.
== Implementation in Revolutionary France ==
=== Weights and measures of the Ancien Régime ===
It has been estimated that, on the eve of the Revolution in 1789, the eight hundred or so units of measure in use in France had up to a quarter of a million different definitions because the quantity associated with each unit could differ from town to town, and even from trade to trade. Although certain standards, such as the pied du roi (the King's foot) had a degree of pre-eminence and were used by scientists, many traders chose to use their own measuring devices, giving scope for fraud and hindering commerce and industry. These variations were promoted by local vested interests, but hindered trade and taxation.
=== Units of weight and length ===

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In 1790, a panel of five leading French scientists was appointed by the Académie des sciences to investigate weights and measures. They were Jean-Charles de Borda, Joseph-Louis Lagrange, Pierre-Simon Laplace, Gaspard Monge, and Nicolas de Condorcet.
Over the following year, the panel, after studying various alternatives, made a series of recommendations regarding a new system of weights and measures, including that it should have a decimal radix, that the unit of length should be based on a fractional arc of a quadrant of the Earth's meridian, and that the unit of weight should be that of a cube of water whose dimension was a decimal fraction of the unit of length. The proposals were accepted by the French Assembly on 30 March 1791.
Following acceptance, the Académie des sciences was instructed to implement the proposals. The Académie broke the tasks into five operations, allocating each part to a separate working group:
Measuring the difference in latitude between Dunkirk and Barcelona and triangulating between them
Measuring the baselines used for the survey
Verifying the length of the second pendulum at 45° latitude.
Verifying the weight in a vacuum of a given volume of distilled water.
Publishing conversion tables relating the new units of measure to the existing units of measure.
The panel decided that the new measure of length should be equal to one ten-millionth of the distance from the North Pole to the Equator (Earth quadrant), measured along the Paris meridian.
Using Jean Picard's survey of 1670 and Jacques Cassini's survey of 1718, a provisional value of 443.44 lignes was assigned to the metre which, in turn, defined the other units of measure.
While Méchain and Delambre were completing their survey, the commission had ordered a series of platinum bars to be made based on the provisional metre. When the final result was known, the bar whose length was closest to the meridional definition of the metre would be selected.
After 1792, the name of the original defined unit of mass, "gramme", which was too small to serve as a practical realisation for many purposes, was adopted, the new prefix "kilo" was added to it to form the name "kilogramme". Consequently, the kilogram is the only SI base unit that has an SI prefix as part of its unit name.
A provisional kilogram standard was made and work was commissioned to determine the precise mass of a cubic decimetre (later to be defined as equal to one litre) of water.
The regulation of trade and commerce required a "practical realisation": a single-piece, metallic reference standard that was one thousand times more massive that would be known as the grave. This mass unit defined by Lavoisier and René Just Haüy had been in use since 1793. This new, practical realisation would ultimately become the base unit of mass. On 7 April 1795, the gramme, upon which the kilogram is based, was decreed to be equal to "the absolute weight of a volume of pure water equal to a cube of one hundredth of a metre, and at the temperature of the melting ice". Although the definition of the kilogramme specified water at 0 °C—a highly stable temperature point—it was replaced with the temperature at which water reaches maximum density. This temperature, about 4 °C, was not accurately known, but one of the advantages of the new definition was that the precise Celsius value of the temperature was not actually important. The final conclusion was that one cubic decimetre of water at its maximum density was equal to 99.92072% of the mass of the provisional kilogram.
On 7 April 1795, the metric system was formally defined in French law. It defined six new decimal units:
The mètre, for length—defined as one ten-millionth of the distance between the North Pole and the Equator through Paris
The are (100 m2) for area [of land]
The stère (1 m3) for volume of firewood
The litre (1 dm3) for volumes of liquid
The gramme, for mass—defined as the mass of one cubic centimetre of water
The franc, for currency.
Historical note: only the metre and (kilo)gramme defined here went on to become part of later metric systems. Litres and to a lesser extent hectares (100 ares, or 1 hm2) are still in use, but are not SI units.
Decimal multiples of these units were defined by Greek prefixes: "myria-" (10,000), "kilo-" (1000), "hecto-" (100), and "deka-" (10) and submultiples were defined by the Latin prefixes "deci-" (0.1), "centi-" (0.01), and "milli-" (0.001).
For purposes of commerce, units and prefixed-units of weight (mass) and capacity (volume) were prependable by the binary multipliers "double-" (2) and "demi-" (1⁄2), as in double-litre, demi-litre; or double-hectogramme, demi-hectogramme, etc.
The 1795 draft definitions enabled provisional copies of the kilograms and metres to be constructed.
=== Meridional survey ===
The task of surveying the meridian arc, which was estimated to take two years, fell to Pierre Méchain and Jean-Baptiste Delambre. The task eventually took more than six years (1792–1798) with delays caused not only by unforeseen technical difficulties but also by the convulsed period of the aftermath of the Revolution. Apart from the obvious nationalistic considerations, the Paris meridian was also a sound choice for practical scientific reasons: a portion of the quadrant from Dunkirk to Barcelona (about 1000 km, or one-tenth of the total) could be surveyed with start- and end-points at sea level, and that portion was roughly in the middle of the quadrant, where the effects of the Earth's oblateness were expected to be the largest.
The project was split into two parts—the northern section of 742.7 km from the Belfry, Dunkirk to Rodez Cathedral which was surveyed by Delambre and the southern section of 333.0 km from Rodez to the Montjuïc Fortress, Barcelona which was surveyed by Méchain.

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Delambre used a baseline of about 10 km in length along a straight road, located close to Melun. In an operation taking six weeks, the baseline was accurately measured using four platinum rods, each of length two toises (about 3.9 m). Thereafter he used, where possible, the triangulation points used by Cassini in his 1744 survey of France. Méchain's baseline, of a similar length, and also on a straight section of road was in the Perpignan area. Although Méchain's sector was half the length of Delambre, it included the Pyrenees and hitherto unsurveyed parts of Spain. After the two surveyors met, each computed the other's baseline in order to cross-check their results and they then recomputed the metre as 443.296 lignes, notably shorter than the 1795 provisional value of 443.44 lignes. On 15 November 1798, Delambre and Méchain returned to Paris with their data, having completed the survey. The final value of the mètre was defined in 1799 as the computed value from the survey.
Historical note: It soon became apparent that Méchain and Delambre's result (443.296 lignes) was slightly too short for the meridional definition of the metre. Méchain had made a small error measuring the latitude of Barcelona, so he remeasured it, but kept the second set of measurements secret.
=== The French metric system ===
In June 1799, platinum prototypes were fabricated according to the measured quantities, the mètre des archives defined to be a length of 443.296 lignes, and the kilogramme des archives defined to be a weight of 18827.15 grains of the livre poids de marc, and entered into the French National Archives. In December of that year, the metric system based on them became by law the sole system of weights and measures in France from 1801 until 1812.
Despite the law, the populace continued to use the old measures. In 1812, Napoleon revoked the law and issued one called the mesures usuelles, restoring the names and quantities of the customary measures but redefined as round multiples of the metric units, so it was a kind of hybrid system. In 1837, after the collapse of the Napoleonic Empire, the new Assembly reimposed the metric system defined by the laws of 1795 and 1799, to take effect in 1840. The metrication of France took until about 1858 to be completed. Some of the old unit names, especially the livre, originally a unit of mass derived from the Roman libra (as was the English pound), but now meaning 500 grams, are still in use today.
== Development of non-coherent metric systems ==
At the start of the nineteenth century, the French Academy of Sciences' artefacts for length and mass were the only nascent units of the metric system that were defined in terms of formal standards. Other units based on them, except the litre, proved to be short-lived. Pendulum clocks that could keep time in seconds had been in use for about 150 years, but their geometries were local to both latitude and altitude, so there was no standard of timekeeping. Nor had a unit of time been recognised as an essential base unit for the derivation of things like force and acceleration. Some quantities of electricity, like charge and potential, had been identified, but names and interrelationships of units were not yet established. Both Fahrenheit (ca. 1724) and Celsius (ca. 1742) scales of temperature existed, and varied instruments for measuring units or degrees of them. The base/derived unit model had not yet been elaborated, nor was it known how many physical quantities might be interrelated.
A model of interrelated units was first proposed in 1861 by the British Association for the Advancement of Science (BAAS) based on what came to be called the "mechanical" units (length, mass, and time). Over the following decades, this foundation enabled mechanical, electrical, and thermal units to be correlated.
=== Time ===
In 1832, German mathematician Carl-Friedrich Gauss made the first absolute measurements of the Earth's magnetic field using a decimal system based on the use of the millimetre, milligram, and second as the base unit of time. Gauss's second was based on astronomical observations of the rotation of the Earth, and was the sexagesimal second of the ancients: a partitioning of the solar day into two cycles of 12 periods, and each period divided into 60 intervals, and each interval so divided again, so that a second was 1/86,400th of the day. This effectively established a time dimension as a necessary constituent of any useful system of measures, and the astronomical second as the base unit.
=== Work and energy ===
In a paper published in 1843, James Prescott Joule first demonstrated a means of measuring the energy transferred between different systems when work is done thereby relating Nicolas Clément's calorie, defined in 1824 as "the amount of heat required to raise the temperature of 1 kg of water from 0 to 1 °C at 1 atmosphere of pressure" to mechanical work. Energy became the unifying concept of nineteenth century science, initially by bringing thermodynamics and mechanics together and later adding electrical technology.

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=== The first structured metric system: CGS ===
In 1861, a committee of the British Association for the Advancement of Science (BAAS) including William Thomson (later Lord Kelvin), James Clerk Maxwell, and James Prescott Joule among its members was tasked with investigating the "Standards of Electrical Resistance". In their first report (1862), they laid the ground rules for their work—the metric system was to be used, measures of electrical energy must have the same units as measures of mechanical energy, and two sets of electromagnetic units would have to be derived—an electromagnetic system and an electrostatic system. In the second report (1863), they introduced the concept of a coherent system of units whereby units of length, mass, and time were identified as "fundamental units" (now known as base units). All other units of measure could be derived (hence derived units) from these base units. The metre, gram, and second were chosen as base units.
In 1861, before a meeting of the BAAS, Charles Bright and Latimer Clark proposed the names of ohm, volt, and farad in honour of Georg Ohm, Alessandro Volta, and Michael Faraday respectively for the practical units based on the CGS absolute system. This was supported by Thomson (Lord Kelvin). The concept of naming units of measure after noteworthy scientists was subsequently used for other units.
In 1873, another committee of the BAAS (which also included Maxwell and Thomson) tasked with "the Selection and Nomenclature of Dynamical and Electrical Units" recommended using the cgs system of units. The committee also recommended the names of "dyne" and "erg" for the cgs units of force and energy. The cgs system became the basis for scientific work for the next seventy years.
The reports recognised two centimetre–gram–second based systems for electrical units: the Electromagnetic (or absolute) system of units (EMU) and the Electrostatic system of units (ESU).
=== Electrical units ===
In the 1820s, Georg Ohm formulated Ohm's law, which can be extended to relate power to current, electric potential (voltage), and resistance. During the following decades, the realisation of a coherent system of units that incorporated the measurement of electromagnetic phenomena and Ohm's law was beset with problems—several different systems of units were devised.
In the three CGS systems, the constants
k
e
{\displaystyle k_{\text{e}}}
and
k
m
{\displaystyle k_{\text{m}}}
and consequently
ϵ
0
{\displaystyle \epsilon _{0}}
and
μ
0
{\displaystyle \mu _{0}}
were dimensionless, and thus did not require any units to define them.
The electrical units of measure did not easily fit into the coherent system of mechanical units defined by the BAAS. Using dimensional analysis, the dimensions of voltage
M
1
2
L
1
2
T
−
1
{\displaystyle {\mathsf {M}}^{\frac {1}{2}}{\mathsf {L}}^{\frac {1}{2}}{\mathsf {T}}^{-1}}
in the ESU system were identical to the dimensions of current in the EMU system, while resistance had dimensions of velocity in the EMU system, but the inverse of velocity in the ESU system.
==== Electromagnetic (absolute) system of units (EMU) ====
The Electromagnetic system of units (EMU) was developed from André-Marie Ampère's discovery in the 1820s of a relationship between currents in two conductors and the force between them now known as Ampere's law:
F
m
L
=
2
k
m
I
1
I
2
r
{\displaystyle {\frac {F_{\text{m}}}{L}}=2k_{\text{m}}{\frac {I_{1}I_{2}}{r}}}
where
k
m
=
μ
0
4
π
{\displaystyle k_{\text{m}}={\frac {\mu _{0}}{4\pi }}\ }
(SI units)
In 1833, Gauss pointed out the possibility of equating this force with its mechanical equivalent. This proposal received further support from Wilhelm Weber in 1851. In this system, current is defined by setting the magnetic force constant
k
m
{\displaystyle k_{\mathrm {m} }}
to unity and electric potential is defined in such a way as to ensure the unit of power calculated by the relation
P
=
V
I
{\displaystyle P=VI}
is an erg/second. The electromagnetic units of measure were known as the abampere, abvolt, and so on. These units were later scaled for use in the International System.
==== Electrostatic system of units (ESU) ====
The Electrostatic system of units (ESU) was based on Coulomb's quantification in 1783 of the force acting between two charged bodies. This relationship, now known as Coulomb's law, can be written
F
e
=
k
e
q
1
q
2
r
2
,
{\displaystyle F_{\mathrm {e} }=k_{\text{e}}{\frac {q_{1}q_{2}}{r^{2}}},}
where
k
e
=
1
4
π
ϵ
0
{\displaystyle k_{\text{e}}={\frac {1}{4\pi \epsilon _{0}}}}
(SI units)
In this system, the unit for charge is defined by setting the Coulomb force constant (
k
e
{\displaystyle k_{\text{e}}}
) to unity and the unit for electric potential was defined to ensure the unit of energy calculated by the relation
E
=
Q
V
{\displaystyle E=QV}
is one erg. The electrostatic units of measure were the statampere, statvolt, and so on.
==== Gaussian system of units ====
The Gaussian system of units was based on Heinrich Hertz's realisation, while verifying Maxwell's equations in 1888, that the electromagnetic and electrostatic units were related by:
c
2
=
1
ϵ
0
μ
0
{\displaystyle c^{2}={\frac {1}{\epsilon _{0}\mu _{0}}}}
Using this relationship, he proposed merging the EMU and the ESU systems into one system using the EMU units for magnetic quantities (subsequently named the gauss and maxwell) and ESU units elsewhere. He named this combined set of units "Gaussian units".

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==== Quadrant–eleventhgram–second (QES) or International System of Electrical and Magnetic Units ====
The CGS units of measure used in scientific work were not practical for engineering, leading to the development of a more applicable system of electric units especially for telegraphy. The unit of length was 107 m (the hebdometre, nominally the Earth quadrant), the unit of mass was an unnamed unit equal to 10−11 g and the unit of time was the second. The units of mass and length were scaled incongruously to yield more consistent and usable electric units in terms of mechanical measures. Informally called the "practical" system, it was properly termed the quadrant–eleventhgram–second (QES) system of units according to convention.
The definitions of electrical units incorporated the magnetic constant like the EMU system, and the names of the units were carried over from that system, but scaled according to the defined mechanical units. The system was formalised as the International system late in the 19th century and its units later designated the "international ampere", "international volt", etc.
==== Heaviside–Lorentz system of units ====
The factor
4
π
{\displaystyle 4\pi }
that occurs in Maxwell's equations in the gaussian system (and the other CGS systems) comes from the
4
π
{\displaystyle 4\pi }
steradians surrounding a point, such as a point electric charge. This factor could be eliminated from contexts that do not involve spherical coordinates by incorporating the factor into the definitions of the quantities involved. The system was proposed by Oliver Heaviside in 1883 and is also known as the "rationalised Gaussian system of units". The SI later adopted rationalised units based on Heaviside's rationalisation scheme.
=== Thermodynamics ===
Maxwell and Boltzmann had produced theories describing the interrelationship of temperature, pressure, and volume of a gas on a microscopic scale but otherwise, in 1900, there was no understanding of the microscopic nature of temperature.
By the end of the nineteenth century, the fundamental macroscopic laws of thermodynamics had been formulated and, although techniques existed to measure temperature using empirical techniques, the scientific understanding of the nature of temperature was minimal.
== Convention of the metre ==
With increasing international adoption of the metre, the shortcomings of the mètre des Archives as a standard became ever more apparent. Countries which adopted the metre as a legal measure purchased standard metre bars that were intended to be equal in length to the mètre des Archives, but there was no systematic way of ensuring that the countries were actually working to the same standard. The meridional definition, which had been intended to ensure international reproducibility, quickly proved so impractical that it was all but abandoned in favour of the artefact standards, but the mètre des Archives (and most of its copies) were "end standards": such standards (bars which are exactly one metre in length) are prone to wear with use, and different standard bars could be expected to wear at different rates.
In 1867, it was proposed that a new international standard metre be created, and the length was taken to be that of the mètre des Archives "in the state in which it shall be found". The International Conference on Geodesy in 1867 called for the creation of a new international prototype of the metre and of a system by which national standards could be compared with it. The international prototype would also be a "line standard", that is the metre was defined as the distance between two lines marked on the bar, so avoiding the wear problems of end standards. The French government gave practical support to the creation of an International Metre Commission, which met in Paris in 1870 and again in 1872 with the participation of about thirty countries.
On 20 May 1875, an international treaty known as the Convention du Mètre (Metre Convention) was signed by 17 states. This treaty established the following organisations to conduct international activities relating to a uniform system for measurements:

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Conférence générale des poids et mesures (CGPM or General Conference on Weights and Measures), an intergovernmental conference of official delegates of member nations and the supreme authority for all actions;
Comité international des poids et mesures (CIPM or International Committee for Weights and Measures), consisting of selected scientists and metrologists, which prepares and executes the decisions of the CGPM and is responsible for the supervision of the International Bureau of Weights and Measures;
Bureau international des poids et mesures (BIPM or International Bureau of Weights and Measures), a permanent laboratory and world centre of scientific metrology, the activities of which include the establishment of the basic standards and scales of the principal physical quantities, maintenance of the international prototype standards, and oversight of regular comparisons between the international prototype and the various national standards.
The international prototype of the metre and international prototype of the kilogram were both made from a 90% platinum, 10% iridium alloy which is exceptionally hard and which has good electrical and thermal conductivity properties. The prototype had a special X-shaped (Tresca) cross section to minimise the effects of torsional strain during length comparisons and the prototype kilograms were cylindrical in shape. The London firm Johnson Matthey delivered 30 prototype metres and 40 prototype kilograms. At the first meeting of the CGPM in 1889, bar No. 6 and cylinder No. X were accepted as the international prototypes. The remainder were either kept as BIPM working copies or distributed to member states as national prototypes.
Following the Convention of the Metre, in 1889, the BIPM had custody of two artefacts—one to define length and the other to define mass. Other units of measure which did not rely on specific artefacts were controlled by other bodies.
Although the definition of the kilogram remained unchanged throughout the 20th century, the 3rd CGPM in 1901 clarified that the kilogram was a unit of mass, not of weight. The original batch of 40 prototypes (adopted in 1889) were supplemented from time to time with further prototypes for use by new signatories to the Metre Convention.
In 1921, the Treaty of the Metre was extended to cover electrical units, with the CGPM merging its work with that of the IEC.
== Measurement systems before World War II ==
The 20th century history of measurement is marked by five periods: the 1901 definition of the coherent MKS system; the intervening 50 years of coexistence of the MKS, cgs and common systems of measures; the 1948 Practical system of units prototype of the SI; the introduction of the SI in 1960; and the evolution of the SI in the latter half century.
=== A coherent system ===
The need for an independent electromagnetic dimension to resolve the difficulties related to defining such units in terms of length, mass, and time was identified by Giorgi in 1901. This led to Giorgi presenting a paper in October 1901 to the congress of the Associazione Elettrotecnica Italiana (A.E.I.) in which he showed that a coherent electro-mechanical system of units could be obtained by adding a fourth base unit of an electrical nature (e.g., ampere, volt, or ohm) to the three base units proposed in the 1861 BAAS report. This gave physical dimensions to the constants ke and km and hence also to the electro-mechanical quantities ε0 (permittivity of free space) and μ0 (permeability of free space). His work also recognised the relevance of energy in the establishment of a coherent, rational system of units, with the joule as the unit of energy, and the electrical units in the International System of Units remaining unchanged. However, it took more than thirty years before Giorgi's work was accepted in practice by the IEC.
=== Systems of measurement in the industrial era ===
As industry developed around the world, the cgs system of units as adopted by the British Association for the Advancement of Science in 1873 with its plethora of electrical units continued to be the dominant system of measurement, and remained so for at least the next 60 years. The advantages were several: it had a comprehensive set of derived units which, while not quite coherent, were at least homologous; the MKS system lacked a defined unit of electromagnetism at all; the MKS units were inconveniently large for the sciences; customary systems of measures held sway in the United States, Britain, and the British empire, and even to some extent in France, the birthplace of the metric system, which inhibited adoption of any competing system. Finally, war, nationalism, and other political forces inhibited development of the science favouring a coherent system of units.
At the 8th CGPM in 1933, the need to replace the "international" electrical units with "absolute" units was raised. The IEC proposal that Giorgi's 'system', denoted informally as MKSX, be adopted was accepted, but no decision was made as to which electrical unit should be the fourth base unit. In 1935, J. E. Sears proposed that this should be the ampere, but World War II prevented this being formalised until 1946. The first (and only) follow-up comparison of the national standards with the international prototype of the metre was carried out between 1921 and 1936, and indicated that the definition of the metre was preserved to within 0.2 μm. During this follow-up comparison, the way in which the prototype metre should be measured was more clearly defined—the 1889 definition had defined the metre as being the length of the prototype at the temperature of melting ice, but, in 1927, the 7th CGPM extended this definition to specify that the prototype metre shall be "supported on two cylinders of at least one centimetre diameter, symmetrically placed in the same horizontal plane at a distance of 571 mm from each other". The choice of 571 mm represents the Airy points of the prototype—the points at which the bending or droop of the bar is minimised.

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== Working draft of SI: Practical system of units ==
The 9th CGPM met in 1948, fifteen years after the 8th CGPM. In response to formal requests made by the International Union of Pure and Applied Physics and by the French government to establish a practical system of units of measure, the CGPM requested the CIPM to prepare recommendations for a single practical system of units of measurement, suitable for adoption by all countries adhering to the Metre Convention. The CIPM's draft proposal was an extensive revision and simplification of the metric unit definitions, symbols, and terminology based on the MKS system of units.
Following astronomical observations, the second was set as a fraction of the year 1900. The electromagnetic base unit, as required by Giorgi, was accepted as the ampere. After negotiations with the CIS and IUPAP, two additional units—the degree kelvin and the candela—were also proposed as base units. For the first time, the CGPM made recommendations concerning derived units. At the same time, the CGPM adopted conventions for the writing and printing of unit symbols and numbers and catalogued the symbols for the most important MKS and CGS units of measure.
=== Time ===
Until the advent of the atomic clock, the most reliable timekeeper available to humanity was the Earth's rotation. It was natural, therefore, that the astronomers under the auspices of the International Astronomical Union (IAU) took the lead in maintaining the standards relating to time. During the 20th century, it became apparent that the Earth's rotation was slowing down, resulting in days becoming 1.4 milliseconds longer each century—this was verified by comparing the calculated timings of eclipses of the Sun with those observed in antiquity going back to Chinese records of 763 BC. In 1956, the 10th CGPM instructed the CIPM to prepare a definition of the second; in 1958, the definition was published stating that the second (called an ephemeris second) would be calculated by extrapolation using Earth's rotational speed in 1900.
=== Electrical unit ===
Per Giorgi's proposals of 1901, the CIPM also recommended that the ampere be the base unit from which electromechanical units would be derived. The definitions for the ohm and volt that had previously been in use were discarded, and these units became derived units based on the ampere. In 1946, the CIPM formally adopted a definition of the ampere based on the original EMU definition and redefined the ohm in terms of other base units. The definitions for the absolute electrical system, based on the ampere, were formalised in 1948. The draft proposed units with these names are very close, but not identical, to the international units.
=== Temperature ===
In the Celsius scale from the 18th century, temperature was expressed in degrees Celsius with the definition that ice melted at 0 °C and (at standard atmospheric pressure) water boiled at 100 °C. A series of lookup tables defined temperature in terms of interrelated empirical measurements made using various devices. In 1948, definitions relating to temperature had to be clarified. (The degree, as an angular measure, was adopted for general use in many countries, so, in 1948, the General Conference on Weights and Measures (CGPM) recommended that the degree centigrade, as used for the measurement of temperature, be renamed the degree Celsius.)
At the 9th CGPM, the centigrade temperature scale was renamed the Celsius scale, and the scale itself was fixed by defining the triple point of water as 0.01 °C, though the CGPM left the formal definition of absolute zero until the 10th CGPM when the name "Kelvin" was assigned to the absolute temperature scale, and the triple point of water was defined as being 273.16 °K.
=== Luminosity ===
Before 1937, the International Commission on Illumination (CIE from its French title, the Commission Internationale de l'Eclairage), in conjunction with the CIPM, produced a standard for luminous intensity to replace the various national standards. This standard, the candela (cd), which was defined as "the brightness of the full radiator at the temperature of solidification of platinum is 60 new candles per square centimetre", was ratified by the CGPM in 1948.
=== Derived units ===
The newly accepted definition of the ampere allowed practical and useful coherent definitions of a set of electromagnetic derived units, including farad, henry, watt, tesla, weber, volt, ohm, and coulomb. Two derived units, lux and lumen, were based on the new candela, and one, degree Celsius, equivalent to the degree Kelvin. Five other miscellaneous derived units completed the draft proposal: radian, steradian, hertz, joule, and newton.
== International System of Units (SI) ==
In 1952, the CIPM proposed the use of wavelength of a specific light source as the standard for defining length, and, in 1960, the CGPM accepted this proposal using radiation corresponding to a transition between specified energy levels of the krypton 86 atom as the new standard for the metre. The standard metre artefact was retired.
In 1960, Giorgi's proposals were adopted as the basis of the Système International d'Unités (International System of Units), the SI. This initial definition of the SI included six base units, the metre, kilogram, second, ampere, degree Kelvin, and candela, and sixteen coherent derived units.
== Evolution of the modern SI ==
The evolution of the SI after its publication in 1960 has seen the addition of a seventh base unit, the mole, and six more derived units, the pascal for pressure, the gray, sievert, and becquerel for radiation, the siemens for electrical conductance, and katal for catalytic (enzymatic) activity. Several units have also been redefined in terms of physical constants.

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=== New base and derived units ===
Over the ensuing years, the BIPM developed and maintained cross-correlations relating various measuring devices such as thermocouples, light spectra, and the like to the equivalent temperatures.
The mole was originally known as a gram-atom or a gram-molecule—the amount of a substance measured in grams divided by its atomic weight. Originally chemists and physicists had differing views regarding the definition of the atomic weight—both assigned a value of 16 atomic mass units (amu) to oxygen, but physicists defined oxygen in terms of the 16O isotope whereas chemists assigned 16 amu to 16O, 17O and 18O isotopes mixed in the proportion that they occur in nature. Finally, an agreement between the International Union of Pure and Applied Physics (IUPAP) and the International Union of Pure and Applied Chemistry (IUPAC) brought this duality to an end in 1959/60, both parties agreeing to define the atomic weight of 12C as being exactly 12 amu. This agreement was confirmed by ISO and in 1969 the CIPM recommended its inclusion in SI as a base unit. This was done in 1971 at the 14th CGPM.
=== Start of migration to constant definitions ===
The second major trend in the post-modern SI was the migration of unit definitions in terms of physical constants of nature.
In 1967, at the 13th CGPM, the degree Kelvin (°K) was renamed the "kelvin" (K).
Astronomers from the US Naval Observatory (USNO) and the National Physical Laboratory determined a relationship between the frequency of radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom and the estimated rate of rotation of the earth in 1900. Their atomic definition of the second was adopted in 1968 by the 13th CGPM.
By 1975, when the second had been defined in terms of a physical phenomenon rather than the earth's rotation, the CGPM authorised the CIPM to investigate the use of the speed of light as the basis for the definition of the metre. This proposal was accepted in 1983.
The candela definition proved difficult to implement so, in 1979, the definition was revised and the reference to the radiation source was replaced by defining the candela in terms of the power of a specified frequency of monochromatic yellowish-green visible light, which is close to the frequency where the human eye, when adapted to bright conditions, has greatest sensitivity.
=== Kilogram artefact instability ===
After the metre was redefined in 1960, the kilogram remained the only SI base defined by a physical artefact. During the years that followed, the definitions of the base units and particularly the mise en pratique to realise these definitions have been refined.
The third periodic recalibration in 1988–1989 revealed that the average difference between the IPK and adjusted baseline for the national prototypes was 50 μg—in 1889, the baseline of the national prototypes had been adjusted so that the difference was zero. As the IPK is the definitive kilogram, there is no way of telling whether the IPK had been losing mass or the national prototypes had been gaining mass.
During the course of the century, the various national prototypes of the kilogram were recalibrated against the international prototype of the kilogram (IPK) and, therefore, against each other. The initial 1889 starting-value offsets of the national prototypes relative to the IPK were nulled, with any subsequent mass changes being relative to the IPK.
=== Proposed replacements for the IPK ===
A number of replacements were proposed for the IPK.
From the early 1990s, the International Avogadro Project worked on creating a 1 kg, 94 mm, sphere made of a uniform silicon-28 crystal, with the intention of being able replace the IPK with a physical object which would be precisely reproducible from an exact specification. Due to its precise construction, the Avogadro Project's sphere is likely to be the most precisely spherical object ever created by humans.
Other groups worked on concepts such as creating a reference mass via precise electrodeposition of gold or bismuth atoms, and defining the kilogram in terms of the ampere by relating it to forces generated by electromagnetic repulsion of electric currents.
Eventually, the choices were narrowed down to the use of the Kibble balance and the International Avogadro Project sphere.
Ultimately, a decision was made not to create any physical replacement for the IPK, but instead to define all SI units in terms of assigning precise values to a number of physical constants which had previously been measured in terms of the earlier unit definitions.
== Redefinition in terms of fundamental constants ==

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At its 23rd meeting (2007), the CGPM mandated the CIPM to investigate the use of natural constants as the basis for all units of measure rather than the artefacts that were then in use.
The following year, this was endorsed by the International Union of Pure and Applied Physics (IUPAP). At a meeting of the CCU held in Reading, United Kingdom, in September 2010, a resolution and draft changes to the SI brochure that were to be presented to the next meeting of the CIPM in October 2010 were agreed in principle. The CIPM meeting of October 2010 found that "the conditions set by the General Conference at its 23rd meeting have not yet been fully met. For this reason the CIPM does not propose a revision of the SI at the present time". The CIPM, however, presented a resolution for consideration at the 24th CGPM (17–21 October 2011) to agree to the new definitions in principle, but not to implement them until the details had been finalised.
In the revision, four of the seven SI base units—the kilogram, ampere, kelvin, and mole—were redefined by setting exact numerical values for the Planck constant (h), the elementary electric charge (e), the Boltzmann constant (kB), and the Avogadro constant (NA), respectively. The second, metre, and candela were already defined by physical constants and were subject to correction to their definitions. The new definitions aimed to improve the SI without changing the value of any units, ensuring continuity with existing measurements.
This resolution was accepted by the conference, and, in addition, the CGPM moved the date of the 25th meeting forward from 2015 to 2014. At the 25th meeting on 18 to 20 November 2014, it was found that "despite [progress in the necessary requirements] the data do not yet appear to be sufficiently robust for the CGPM to adopt the revised SI at its 25th meeting", thus postponing the revision to the next meeting in 2018.
Measurements accurate enough to meet the conditions were available in 2017 and the revision was adopted at the 26th CGPM (13–16 November 2018), with the changes finally coming into force in 2019, creating a system of definitions which is intended to be stable for the long term.
== See also ==
History of the metre
History of measurement
Metrication
== Notes ==
== References ==

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The International Conference on Cold Fusion (ICCF) (also referred to as Annual Conference on Cold Fusion in 1990-1991 and mostly as International Conference on Condensed Matter Nuclear Science since 2007) is an annual or biennial conference on the topic of cold fusion. An international conference on cold fusion was held in Santa Fe, New Mexico, USA in 1989. However, the first ICCF conference (ICCF1) took place in 1990 in Salt Lake City, Utah, USA, under the title "First Annual Conference on Cold Fusion". Its location has since rotated between Russia, the USA, Europe, and Asia. It was held in India for the first time in 2011. The conferences have been criticized as events which attract "crackpots" and "pseudo-scientists".
== Reception ==
The First Annual Conference on Cold Fusion was held in March 1990 in Salt Lake City, Utah, United States. Robert L. Park of the American Physical Society derisively referred to it as a "seance of true believers." The conference was attended by more than 200 researchers from the United States, Italy, Japan, India and Taiwan and dozens of reporters from all over the U.S. and abroad.
The Third International Conference on Cold Fusion was held in 1992 in Nagoya, Japan. It was described by The New York Times, "depending on one's point of view" as "either a turning point in which evidence was presented that will convince the skeptics that cold fusion exists or a religious revival where claims of miracles were lapped up by ardent believers." The conference was sponsored by seven Japanese scientific societies, it was attended by 200 Japanese scientists and more than 100 from abroad. Tomohiro Taniguchi, then director of the Electric Power Technology Division at Japan's Ministry of International Trade and Industry, reportedly said that the Ministry of International Trade and Industry was willing to finance research in the field in view of "encouraging evidence, especially after the conference." The conference was also covered by the Associated Press.
A journalist for the Wired magazine attended the 1998 conference in Vancouver—apparently the only mainstream journalist who attended—and reported that he found there "about 200 extremely conventional-looking scientists, almost all of them male and over 50" with some apparently over 70. He then inferred that "[the] younger ones had bailed years ago, fearing career damage from the cold fusion stigma." He reported seeing "highly technical presentations" and "was amazed by the quantity of the work, its quality, and the credentials of the people pursuing it", whereas "[a] few obvious pseudoscientists, promoting their ideas in an adjoining room used for poster sessions, were politely ignored."
By 1999, attendance by researchers at the ICCF meetings drew comment from the field of science studies. Although scientific debate over cold fusion had effectively ended in 1990, attendance at the ICCF meetings for the next 8 years had been relatively stable at between 100 and 300. Sociologist Bart Simon of Concordia University described the state of the field as "undead", and considered that the conference evidenced that "as far as normal science is concerned, [cold fusion] is of interest to crackpots, pseudo-scientists, frauds and a few sociologists of science".
David Goodstein has written that although an ICCF event had "all the trappings of a normal scientific meeting", it was in fact "no normal scientific conference" since "cold fusion was a pariah field, cast out by the scientific establishment". It was an environment, he added, "...in which crackpots flourished, and this made matters worse for those who were at least willing to entertain the notion that there might have been some serious science going on."
== Conferences ==
The conference is organized by The International Society for Condensed Matter Nuclear Science. Conference attendees include "a mix of professional scientists, along with retired, semi-retired and amateur scientists, engineers and technicians, and a number of entrepreneurs, inventors, and interested lay people." Conferences have been held in Europe, USA, Canada, China, India, Russia, Korea, Japan.
ICCF-1 - 1989, Santa Fe, New Mexico, USA
ICCF-23 - June 2021, Fujian, China
ICCF-24 - July 2022, Mountain View, California
ICCF-25 - August 2023, Szczecin, Poland
ICCF-26 - 26-30 May 2025, Morioka, Japan
See the Japanese version of this page for a comprehensive list of past conferences.
== References ==
== Further reading ==
Huizenga, John R. (1993), Cold Fusion: The Scientific Fiasco of the Century (2 ed.), Oxford and New York: Oxford University Press, ISBN 0-19-855817-1 – The first three conferences are commented in detail on pp. 237–247, 274–285, specially 240, 275–277.
== External links ==
The International Society for Condensed Matter Nuclear Science home page

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The International Scientific Committee on Price History was created in 1929 by William Beveridge and Edwin Francis Gay after receiving a five-year grant from the Rockefeller Foundation. The national representatives were William Beveridge for Great Britain, Moritz John Elsas for Germany, Edwin Francis Gay for the United States, Earl J. Hamilton for Spain, Henri Hauser for France and Alfred Francis Pribram for Austria; later, Franciszek Bujak for Poland and Nicolaas Wilhelmus Posthumus for the Netherlands also joined; Arthur H. Cole was in charge of finances for the whole project.
== Books by the committee ==
Hamilton (Earl J.), American Treasure and the Price Revolution in Spain (1501–1650), 1934.
Hamilton (Earl J.), Money, Prices and Wages in Valencia, Aragon and Navarre (1351–1500), 1936.
Hauser (Henri), Recherches et documents sur l’histoire des prix en France de 1500 à 1800, 1936.
Elsas (Moritz John), Umriß einer Geschichte der Preise und Löhne in Deutschland vom ausgehenden Mittelalter bis zum Beginn des 19. Jarhunderts, 3 vol., 1936–1949.
Přibram (Alfred Francis), Materialien zur Geschichte der Preise und Löhne in Österreich, 1938.
Cole (Arthur Harrison), Wholesale Commodity Prices in the United States 1700–1861, 1938.
Beveridge (William H.), Prices and Wages in England from the 12th to the 19th Century, 1939.
Posthumus (Nicolaas), Nederlandsche Prijsgeschiedenis, 1943–1964.
Hamilton (Earl J.), War and Prices in Spain (1651–1800), 1947.
== References ==
Olivier Dumoulin, "Aux origines de l'histoire des prix", Annales. Économies, sociétés, civilisations, 45/2, 1990, p. 507-522[1].
Julien Demade, Produire un fait scientifique. Beveridge et le Comité international d'histoire des prix, Paris, Publications de la Sorbonne, 2018.

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Isis was an encyclopedic journal that focused on articles on natural science, medicine, technology, economics as well as art and history. It also published important articles on science policy and the organization of science. Edited by Lorenz Oken and published by Friedrich Arnold Brockhaus, Isis was the first interdisciplinary journal in the German-speaking world.
The 41 volumes of the journal named after the Egyptian goddess Isis were nominally published from 1817 to 1848. However, the first issue appeared on August 1, 1816, while the printing of the last issue was delayed until February 1850. Until 1832, Isis bore the title Encyclopädische Zeitung. After the focus of the articles published in it had changed, Oken changed the title to Encyclopädische Zeitschrift, vorzüglich für Naturgeschichte, vergleichende Anatomie und Physiologie in 1833. Initially printed in Jena, the journal was banned in the Grand Duchy of Saxe-Weimar-Eisenach and from the summer of 1819 was produced in nearby Rudolstadt in the court printing works of the Principality of Schwarzburg-Rudolstadt. The magazine's original print run of 1,500 copies fell rapidly in the first few years of its existence and amounted to around 200 copies in the last few years.
Originally conceived as a non-political journal, Oken was forced to vehemently defend the freedom of the press in the first years of Isis' existence. This resulted in numerous lawsuits against Oken, some of which overlapped in time, which led to temporary bans on Isis in the Grand Duchy of Saxe-Weimar-Eisenach. In the run-up to the Carlsbad Decrees, this led to Oken's dismissal as a professor at the University of Jena at the end of June 1819 under pressure from the states of the Holy Alliance.
From 2006 to 2013, a project funded by the German Research Foundation at the Friedrich Schiller University Jena studied the significance of Isis for scientific communication and the popularization of the natural sciences in the first half of the 19th century.
== Origin ==
In a letter dated April 11, 1814, Lorenz Oken contacted the publisher Friedrich Arnold Brockhaus for the first time and offered him his publication Neue Bewaffnung, neues Frankreich, neues Theutschland for printing. Brockhaus did not print it, but Oken subsequently contributed to Brockhaus' Conversations-Lexikon and, from June 1815 at the latest, was a contributor to the Deutsche Blätter, which Brockhaus had been publishing since October 1813 following the Battle of Leipzig and which became the most important journal in central Germany in 1813/1814. Presumably at the end of June/beginning of July 1815, Oken took over the editorship of the Tagesgeschichte, a supplement to the Deutsche Blätter, which was dedicated to daily politics and for which he wrote and edited numbers 1 to 16. With the end of the Wars of Liberation, the focus of the Deutsche Blätter shifted from war reporting to general daily politics, which was associated with a considerable decline in circulation from an initial 4000 to 1100 copies. On February 22, 1816, Brockhaus announced that he would discontinue the Deutsche Blätter. Oken regretted this decision and repeatedly urged Brockhaus to continue the Deutsche Blätter in another form. He presented Brockhaus with his encyclopedic concept of a new journal, which would not focus on current politics, but on the natural sciences, critique, history and political science. Brockhaus was only to bear the printing and postage costs. The first publishing contract for the Encyclopädische Blätter was signed with Brockhaus on March 31, 1816. Oken presented his concept to readers in the last issue of Deutsche Blätter.
== Conception ==
The design concept for Isis was delayed until July 1816, as Oken was still working on the zoological section of his textbook on natural history. Oken reached an agreement with Brockhaus that a copper plate should appear in each booklet, and he worked towards a low sales price. They were at odds over the arrangement of the information in the title head and the text and image design. Oken had a woodcut made for the title head, in the middle of which the goddess Isis is depicted on an ancient Egyptian throne. On the left, she is flanked by her husband Osiris, who carries a vulture's head and a staff. To her right is Anubis with a jackal's head, palm branch and snake sceptre. Oken commissioned the rector of the Academy of Fine Arts Leipzig, Veit Schnorr von Carolsfeld (1764–1841), to create the frontispiece and later copper plates. There were differences of opinion as to whether foreign-language contributions should be translated into German. Oken spoke out against it due to the difficulty of translating certain technical terms. Brockhaus was in favour of a translation for reasons of popularization.
The title Isis first appeared in correspondence between Oken and Brockhaus at the end of July, shortly before the first issue went to press. The two agreed on Encyclopädische Zeitung as the additional title, in line with the originally intended title of the journal. Oken sent the draft of the first edition, produced by the printer Johann Georg Schreiber in Jena, to Brockhaus' publishing house in Altenburg on July 13, 1816, with the remark that it was to be published in a new edition. Oken introduced this first issue of Isis, which appeared on August 1, 1816, with an excerpt from the Basic Law on the State Constitution of the Grand Duchy of Saxe-Weimar-Eisenach. In it, he presented the programmatic orientation of his new journal. Isis was to cover natural sciences, medicine, mathematics, technology, economics, art and history. Law and theology were expressly excluded. Oken wrote "That is why history is the mirror of this journal, nature its floor, art its pillar wall. We leave the sky open." Anyone could send articles to Isis for publication. Oken did not pay a fee for published articles.
== Oken's fight for freedom of expression and the press ==
=== Legal dispute with Eichstädt ===

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Even before Isis was published, the classical philologist Abraham Eichstädt from Jena learned of the planned new journal. Eichstädt, who published the Jenaische allgemeine Literatur-Zeitung, had held an exclusive right to publish reviews in Saxe-Weimar-Eisenach since 1803. As he feared for the financial security of his paper, Eichstädt turned to the President of the State Ministry in Weimar, Christian Gottlob Voigt, and obtained a renewal of this privilege on July 17, 1816. Oken saw this as a violation of the freedom of the press guaranteed in the Weimar Constitution of May 15, 1816 and sneered in the second issue of Isis: "Whether we really have freedom of the press, or whether it is to be mocked as a grimace through literary privileges and arbitrary interpretation and extension of the same, will be taught by the progress of Isis." Eichstädt filed a lawsuit against Oken and Isis on August 1, 1816. In a judgment dated August 23, Oken was ordered to refrain from publishing reviews and political articles. In the event of non-compliance, he was threatened with a fine of 50 thalers and a ban on Isis. Oken, who became aware of the verdict eight days later, protested against it to the Weimar government on September 2 and attached the first five issues of Isis to his letter in support of his position. In the course of September 1816, the verdict against Oken and Isis was finally withdrawn. Looking ahead, Johann Wolfgang von Goethe commented on the events in his diary on July 30, 1816, with the remark: "Isis as Hydra."
=== Goethe's recommendation for a ban ===
In order not to exacerbate the disputes with Eichstädt, Oken had filled the first four issues exclusively with scientific topics and suggested to Brockhaus that he initially refrain from including controversial political articles, as political newspapers in the Duchy of Saxe-Weimar-Eisenach were still subject to censorship. However, Brockhaus did not agree to this and delayed the delivery of the first four issues. As the dispute with Eichstädt progressed, Oken finally felt compelled to include political topics in Isis. In the sixth issue of Isis, he placed a prize issue in which he questioned the legitimacy of literary privileges. In the ninth issue and the two following issues, Oken criticized the Basic Law on the Landständische Verfassung des Großherzogthums Sachsen-Weimar-Eisenach, which came into force on 5 May 1816. In the third issue of Isis, Oken also printed a letter dated December 5, 1811, from the Rostock professors Samuel Gottlieb Vogel, Wilhelm Josephi, Georg Heinrich Masius (1771–1823) and Karl Ernst Theodor Brandenburg (1772–1827), in which they rejected Oken's appointment to the vacant chair of natural history at the University of Rostock due to his pompous natural philosophy. Oken illustrated the print with a vignette depicting donkey heads.
On September 10, 1816, Christian Gottlob von Voigt drew up an indictment in response to these Isis editions. Oken was accused of insulting the highest royal dignity of the sovereign, insulting official dignity, attacking some German governments and their rulers, as well as insulting foreign official authorities and the Rostock professors. A week later, Grand Duke Karl August sent the indictment to the State Directorate for examination. The expert opinions written by Anton Ziegesar (1783–1843), the head of the administrative and police authority Karl Wilhelm von Fritsch, and the head of the school and church system Ernst Christian August von Gersdorff were collected together with the first eleven issues of Isis in a file entitled Acta Geheimer Staats-Canzley Den Unfug der Preßfrechheit besonders der Isis betr. 1816.
Grand Duke Carl August sent this file to Goethe at the end of September and asked him for his judgment. As can be seen from his diary notes, Goethe needed several days to consider the matter of Isis. In his reply of 5 October, Goethe recommended to the Grand Duke not to prosecute Oken personally, but to take action against the printer of Isis and thus enforce a ban on printing the journal. Carl August did not follow Goethe's advice, but instead discontinued the prosecution.
=== The Wartburgfest and the confiscated number 195 of Isis ===

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Before the end of 1816, Isis was banned in Austria. Meanwhile, Oken continued to campaign for freedom of the press and, for example, published a report on the meeting of the Dutch estates under the title "Against the Restriction of Freedom of the Press". In June 1817, the Prussian Minister of Police, Wilhelm Ludwig Georg Fürst zu Wittgenstein, complained to Carl August about a derogatory criticism of a Prussian decree of 1811 that had appeared in the Oppositions-Blatt and a small note in Isis, in which Oken complained about Prussia's presumption in wanting to interfere even in insignificant matters such as those of the Vienna Agricultural Society. Six days later, a serious warning was issued to the editor of the opposition journal Friedrich Justin Bertuch and Oken, stating "that in the event of further disregard of the sovereign's or authorities' orders, the suppression of this journal will be pursued".
During the Wartburg Festival, which Oken and other professors from Jena attended, an auto-da-fé took place on the evening of October 18, 1817, during which parts of a Prussian Uhlan uniform, a Hessian soldier's braid and an Austrian corporal's baton, as well as several books by authors considered reactionary, including Karl Albert von Kamptz, Theodor Schmalz, Karl Ludwig von Haller and August von Kotzebue, were burned. Fourteen days later, Oken published a report on the meeting at Wartburg Castle, which also contained a list of the burned books and objects, along with mocking signs.
Kamptz, the head of the Ministry of Police in Berlin, whose Codex der Gensd'armerie was one of the burned books, railed in a letter dated November 9, 1817 to Grand Duke Carl August about the "bunch of feral professors and seduced students" and went on to write: "If true freedom of thought and freedom of the press really flourishes in Your Royal Highness's states, then censorship practiced by fire and pitchforks, by enthusiasts and minors, and terrorist proceedings against freedom of thought and freedom of the press in other states are certainly not compatible with this." The following day, a report by Weimar State Minister Karl Wilhelm von Fritsch exonerated Oken and the other professors, stating that they had not taken part in the burning. Nevertheless, on November 27, 1817, number 195 was confiscated and a temporary ban on the printing of Isis was issued, which was lifted on December 15. From December 2 onwards, a commission consisting of members of the Weimar state government investigated the Isis incidents. Oken was interrogated several times in Weimar. The commission submitted its report to the state government on December 20. The government was willing to return the confiscated copies of Isis if the disputed passages were removed. Oken did not agree to this deal. On January 24, 1818, Oken was sentenced to six weeks in prison for "offenses against the highest dignity of the sovereign, offenses against the official dignity of the upper state authorities and the academic senate in Jena, denigration of German rulers and governments and insulting foreign official authorities". Together with his statement published by the Bremer Zeitung at the end of March 1818, Oken had the sentence printed in full in Isis. Oken appealed against the sentence to the Jena High Court of Appeal and was acquitted on April 29, 1818.
=== The August von Kotzebue incident ===
Through an indiscretion, the history professor Heinrich Luden from Jena came into possession of one of the numerous bulletins written by the Russian consul general Kotzebue and intended for Tsar Alexander I in mid-December 1817. He wrote a biting commentary on it for the journal Nemesis, although Kotzebue was able to prevent its publication and dissemination by court order on January 15, 1818. Oken nevertheless published Luden's article in the first issue of Isis in 1818. After the issue was published, the remaining copies were confiscated. Isis was banned again on January 31, 1818, and was not published again until the end of April. Both Luden and Oken were sentenced to three months imprisonment and a fine of 60 thalers by the Königlich Sächsischen Schöppengericht in Leipzig. Oken chose the fine and again published the files relating to the trial in Isis. On March 23, 1819, Kotzebue was murdered in Mannheim by the Jena fraternity member and theology student Karl Ludwig Sand.

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=== Oken's dismissal ===
The attacks against Oken's Isis from the states of the Holy Alliance continued relentlessly. On January 29, 1819, Karl August von Hardenberg submitted a complaint to Grand Duke Karl August because of a derisive remark about the Prussian King Friedrich Wilhelm III, which was printed in the twelfth issue of 1818, but this time without consequences for Oken and Isis.
At the Aachen Congress in the fall of 1818, the Russian Tsar Alexander I distributed an anonymously written memorandum by Alexander Scarlatovich Sturdsa (1791–1854) entitled Memoire sur l'état actuel de l'Allemagne, in which Sturdsa commented on the dangerous activities at German universities. Oken's replies again caused a sensation. Under pressure from the Russian envoy to the Saxon court, Vasily Vasilyevich Chanykov (1759–1829), the Weimar state treasurer Carl August Constantin Schnauss (1782–1832) was forced to file charges against Oken on April 20, 1819. On May 11, Grand Duke Carl August of Weimar and Duke August of Gotha instructed the Senate of the University of Jena to give Oken the choice of either discontinuing Isis or resigning his professorship. The Senate tried to give in, but had to present Oken with this choice eleven days later. After three days of deliberation, Oken responded evasively: "I have no answer to the request made to me. Perhaps they have come to a different conclusion that an answer is unnecessary." In its reply to the dukes, the Senate once again referred to Oken's outstanding reputation as a teacher and researcher, but to no avail. On June 1, 1819, Duke Carl Friedrich ordered Oken's dismissal and the withholding of his salary from June 15 onwards in the name and on behalf of his father. A similar order from the Duchy of Saxe-Gotha-Altenburg followed six days later. On June 26, 1818, the printing of Isis was provisionally banned.
To avoid the ban, Oken moved the printing of Isis to nearby Rudolstadt in the Principality of Schwarzburg-Rudolstadt. There, Carl Popo Fröbel (1786–1824), stepbrother of the educator Friedrich Fröbel and owner of the court printing works since 1815, took over the printing of Isis from August 1819. After Fröbel's death in 1824, the print shop was initially taken over by Fröbel's widow and finally continued by his son Günther Fröbel from 1832, who produced the last issues of Isis in 1850. A small part of Isis was produced in Eisenberg until 1824/25.
After the Carlsbad Decrees of September 1819, it became increasingly difficult to deal with political issues. Their share of articles in Isis fell sharply. After Brockhaus' death, Oken announced in the first issue of 1824 that Isis would no longer print political articles.
== Content ==
In addition to Oken, many natural scientists and humanities scholars, writers and artists contributed to the content of Isis. Among the authors who published articles in the first volume of Isis were Alexander von Humboldt, Christoph Wilhelm Hufeland, Madame de Staël, August Wilhelm Schlegel, Georges Cuvier and Johannes Peter Müller. There were reviews of Goethe's Aus meinem Leben. Dichtung und Wahrheit, Luigi Valentino Brugnatelli's (1761–1818) Kreistafel der chemischen Aequivalente, Christian Gottfried Daniel Nees von Esenbeck's System der Pilze und Schwämme, Leopoldo Cicognara's (1767–1834) Von den vier venetianischen Kunstpferden, Charles Robert Cockerell's Ueber die ursprüngliche Anwendung der Niobe und ihrer Kinder and Ludwig Wachler's Deutschlands Zukunft in der Gegenwart. Isis reported on the state of affairs at German universities, published their course catalogs and also regularly set prizes.
From the outset, Isis devoted considerable space to summaries and abstracts of publications published in foreign scientific and academic journals. Initially, the relevant journals came from the United Kingdom, France, Italy and Switzerland. These were later supplemented by journals from Scandinavia, Belgium, the Netherlands, Russia and the United States. Oken's approach to editing the articles varied greatly. Sometimes Oken's texts consisted of an abridged translation of the corresponding article, usually they summarized its main content in one paragraph. As a rule, the majority of the articles were only listed with their title - usually translated into German.
In 1821, Oken published the first call for an assembly of German naturalists in Isis, which led to the founding of the Society of German Natural Scientists and Physicians in September 1822. Detailed reports on the society's annual meetings were published regularly until the end.
From 1833, Isis bore the new title Encyclopädische Zeitschrift, vorzüglich für Naturgeschichte, vergleichende Anatomie und Physiologie. This change reflected the changing focus of the articles over time. The already small number of articles dealing with mathematics and physics decreased further.
In the last volume of 1848, Christian Ludwig Brehm published original articles in Isis with Ueber das allmählige Fortrücken der Vögel, Carl Friedrich Wilhelm Siedhofs (1803 - ca. 1867) with Naturgeschichtliches aus den Vereinigten Staaten von Nordamerica, Johann Jakob Kaup with Uebersicht der Eulen (Strigidae) and Christian Gottfried Giebel with Das subhercynische Becken um Quedlinburg in geognostisch-paläontologischer Beziehung. Some of the publications discussed in this volume were Sebastian Egger's (1803–1866) Ueber die Pflichten gegen die Thiere, Franz von Kobell's Mineralogie, Christian Gottfried Giebel's Fauna der Vorwelt, Mauro Rusconi's (1776–1849) Riflessioni sopra il sistema linfatico dei rettili, Johann Malfatti's Neue Heilversuche, Karl Bernhard Stark's Kunst und Schule and Joseph Hippolyt Pultes (1805–1869) Organon der Weltgeschichte.
In the last edition, Oken ended Isis with the words: "This is the end of Isis."

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== Circulation ==
In the initial period from August 1816 to February 1817, the circulation of Isis, which cost eight thalers a year, was 1500 copies. On March 4, 1817, Brockhaus reduced the print run to 1100 copies due to a lack of sales and reduced it by a further 100 copies a week later. When the actual sales figures were known in June 1817, there was a further drastic reduction of 650 copies. In 1825/1826, only 400 copies were printed. This was followed by a slight increase to up to 500 copies for the next few years until 1830. After that, the circulation fell continuously and was around 200 copies in the last ten years of Isis' existence. This relatively low circulation was nothing unusual. For example, the circulation of the Jahrbücher für wissenschaftliche Kritik, one of the most important journals for scientific reviews, was around 500 copies in the years from 1827 to 1846 and that of the Medizinische Annalen, edited by Johann Friedrich Pierer, was 500 to 700 copies.
== Research ==
In 2001, the German historian of science Dietrich von Engelhardt characterized Isis as "a first-rate scientific and cultural-historical document from that transitional epoch from idealism and romanticism to positivism and realism", the analysis of which was still pending. Since 2006, the Institute for the History of Medicine, Natural Science and Technology at the Friedrich Schiller University of Jena, headed by Olaf Breidbach, has been investigating the significance of Isis for scientific communication and the popularization of the natural sciences in the first half of the 19th century, as well as its economic structure, in a project funded by the German Research Foundation. In a three-year project that began in July 2006, Claudia Taszus initially focused on the company documents found in the Fröbel court printing works. This was followed in 2009 by a project aimed at cataloguing the correspondence between Oken and the Brockhaus publishing house. The activities funded by the German Research Foundation also include the project carried out by the Thuringian University and State Library and the Ereignis Weimar-Jena. Kultur um 1800 at the University of Jena, the digitization, indexing and online presentation of Isis.
== References ==
== Articles in Isis ==
== Bibliography ==
Brockhaus, Heinrich Eduard, ed. (1876). Oken's "Isis". Friedrich Arnold Brockhaus. Sein Leben und Wirken nach Briefen und anderen Aufzeichnungen. Leipzig: Brockhaus. pp. 165–201.
Degen, Heinz (1955). "Lorenz Oken und seine Isis um die Gründungszeit der Gesellschaft Deutscher Naturforscher und Ärzte". Naturwissenschaftliche Rundschau. 8: 45–150, 180–189.
von Engelhardt, Dietrich (2003). "Lorenz Oken und das Wartburgfest 1817 mit einem Abdruck des konfiszierten Heftes 195 der Isis". NTM Zeitschrift für Geschichte der Wissenschaften, Technik und Medizin. 11 (1): 1–12. doi:10.1007/BF02908582.
Kertesz, G. A. (1986). "Notes on Isis von Oken, 1817–1848". Isis. 77 (3): 497–503. doi:10.1086/354208. JSTOR 231611.
Schweizer, Claudia, ed. (2004). Lorenz Okens "Isis". Johann Wolfgang von Goethe und Kaspar Maria von Sternberg. Naturforscher und Gleichgesinnte. LIT Verlag Münster. pp. 179–198. ISBN 3-8258-7579-2.
Taszus, Claudia (2009). Breidbach, Olaf; Poggi, Stefano (eds.). Okens Isis. Pressefreiheit, Restriktionen und Zensur in Mitteldeutschland in der ersten Hälfte des 19. Jahrhunderts. Jahrbuch für Europäische Wissenschaftskultur. Vol. 4. Stuttgart: Steiner. pp. 205–241.
Taszus, Claudia (2009). Lorenz Okens Isis (1816–1848). Zur konzeptionellen, organisatorischen und technischen Realisierung der Zeitschrift. Blätter der Gesellschaft für Buchkultur und Geschichte. Rudolstadt: Jahrgang. pp. 85–154.
== External links ==
Volumes 1-5 (1817–1819), volumes 6-41 (1820–1848) of Isis in the Biodiversity Heritage Library

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The Islamic Scientific Manuscripts Initiative (ISMI) (Arabic: مبادرة المخطوطات العلمية الإسلامية) is an online database that supports research on mathematics history in the Islamic world to 1350 CE. The initiative aims to provide accessible information on all Islamic manuscripts in the exact sciences, including astronomy, mathematics, theories, mathematical geography, music, mechanics, and related subjects.
It is an initiative of the Max Planck Institute for the History of Science (MPIWG), which is dedicated to advancing scientific knowledge and research.
== References ==

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Languages of science are vehicular languages used by one or several scientific communities for international communication. According to the science historian Michael Gordin, scientific languages are "either specific forms of a given language that are used in conducting science, or they are the set of distinct languages in which science is done." These two meanings are different, since the first describes a distinct prose in a given language (i.e., scientific writing), while the second describes which languages are used in mainstream science.
Until the 19th century, classical languages—such as Latin, Classical Arabic, Sanskrit, Classical Malay and Classical Chinese—were commonly used across Afro-Eurasia for international scientific communication. A combination of structural factors, the emergence of nation-states in Europe, the Industrial Revolution, and the expansion of colonization entailed the global use of three European national languages: French, German, and English. Yet new languages of science, such as Russian and Italian, had started to emerge by the end of the 19th century—to the point that international scientific organizations began promoting the use of constructed languages such as Esperanto as a non-national global standard.
After the First World War, English gradually outpaced French and German; it became the leading language of science, but not the only international standard. Research in the Soviet Union (USSR) rapidly expanded in the years after the Second World War, and access to Russian journals became a major policy issue in the United States, prompting the early development of machine translation. In the last decades of the 20th century, an increasing number of scientific publications were written primarily in English, in part due to the preeminence of English-speaking scientific infrastructure, indexes, and metrics such as the Science Citation Index. Local languages remain largely relevant for science in major countries and world regions such as China, Latin America, and Indonesia. Disciplines and fields of study with a significant degree of public engagement—such as social sciences, environmental studies, and medicine—have also maintained the relevance of local languages.
The development of open science has revived the debate over linguistic diversity in science, as social and local impact has become an important objective of open science infrastructure and platforms. In 2019, 120 international research organizations cosigned the Helsinki Initiative on Multilingualism in Scholarly Communication; they also called for supporting multilingualism and the development of an "infrastructure of scholarly communication in national languages". In 2021, UNESCO's Recommendation for Open Science included "linguistic diversity" as one of the core features of open science, since this diversity aims to "make multilingual scientific knowledge openly available, accessible and reusable for everyone." In 2022, the Council of the European Union officially supported "initiatives to promote multilingualism" in science, such as the Helsinki Initiative.
== History ==
=== From classical languages to vernaculars ===
Until the 19th century, classical languages played an instrumental role in the diffusion of languages in Europe, Asia, and North Africa.
In Europe, starting in the 12th century, Latin was the primary language of religion, law, and administration until the Early Modern period. It became a language of science "through its encounter with Arabic"; during the Renaissance of the 12th century, a large corpus of Arabic scholarly texts was translated into Latin, so that it would be available in the emerging network of European universities and centers of knowledge. In this process, the Latin language changed and acquired the specific features of scholastic Latin through numerous lexical and even syntactic borrowings from Greek and Arabic. The use of scientific Latin persisted long after the replacement of Latin by vernacular languages in most European administrations: "Latin's status as a language of science rested on the contrast it made with the use of the vernacular in other contexts" and created "a European community of learning" entirely distinct from the local communities where the scholars lived. Latin was never the sole language of science and education. Beyond local publications, vernaculars quite early attained the status of international scientific languages, which could be expected to be understood and translated across Europe. In the mid-16th century, a significant amount of printed output in France was in Italian.
In India and South Asia, Sanskrit was a leading vehicular language for science. Sanskrit was remodeled even more radically than Latin for scientific communication, as it shifted "toward ever more complex noun forms to encompass the kinds of abstractions demanded by scientific and mathematical thinking." Classical Chinese held a similarly prestigious position in East Asia, being largely adopted by scientific and Buddhist communities beyond the Chinese Empire, notably in Japan and Korea.
Classical languages declined throughout Eurasia during the second millennium. Sanskrit was increasingly marginalized after the 13th century. Until the end of the 17th century in Europe, Latin resisted displacement by vernacular languages: although medical books in the 16th century began to use French as well, this trend was reversed after 1597, and most medical literature in France remained accessible only in Latin until the 1680s. In 1670, as many books were printed in Latin as in German in the German states; in 1787, such books accounted for no more than 10% of the total. At this point, Latin's decline became irreversible: since ever fewer European scholars were conversant with the language, publications using it dwindled, and there was reduced incentive to maintain linguistic training in Latin.
The emergence of scientific journals was both a symptom and a cause of the declining use of a classical language. The first two modern scientific journals were published simultaneously in 1665: the Journal des Sçavans in France and the Philosophical Transactions of the Royal Society in England. Both journals used the local vernacular, which "made perfect historical sense", as both the Kingdom of France and the Kingdom of England were engaged in an active policy of linguistic promotion of their language standard.

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=== European and auxiliary languages (1800–1920) ===
The gradual disuse of Latin opened an uneasy transition period, as more and more works were accessible only in local languages. Many national European languages held the potential to become a language of science within a specific research field: some scholars "took measures to learn Swedish so they could follow the work of [the Swedish chemist] Bergman and his compatriots."
Language preferences and use across scientific communities were gradually consolidated into a triumvirate or triad of dominant languages of science: French, English, and German. While each language could be expected to be understood for international scientific communication, each also followed "different functional distributions evident in various scientific fields". French had been almost acknowledged as the international standard for European science in the late 18th century, and it remained "essential" throughout the 19th century. German became a major scientific language during the 19th century, since it "covered portions of the physical sciences, particularly physics and chemistry, in addition to mathematics and medicine." English was used largely by researchers and engineers because of the seminal contribution of English technology to the Industrial Revolution.
In the years preceding the First World War, the linguistic diversity of scientific publications increased significantly. The emergence of modern nationalities and early decolonization movements created new incentives to publish scientific knowledge in one's national language. Russian was one of the most successful developments as a new language of science. During the 1860s and 1870s, Russian researchers in chemistry and other physical sciences ceased publishing in German in favor of local periodicals (in Russian), following major work in adapting and creating names for scientific concepts or elements (such as chemical compounds). A controversy over the meaning of Dmitri Mendeleev's periodic table contributed to acknowledging original publications in Russian in global scientific debate: the original version was deemed more authoritative than its first "imperfect" translation in German.
Linguistic diversity became framed as a structural problem that ultimately limited the spread of scientific knowledge. In 1924, the linguist Roland Grubb Kent underlined that scientific communication could soon be significantly disrupted by the use of as many as "twenty" languages of science:
Today with the recrudescence of certain minor linguistic units and the increased nationalistic spirit of certain larger ones, we face a time when scientific publications of value may appear in perhaps twenty languages [and] be facing an era in which important publications will appear in Finnish, Lithuanian, Hungarian, Serbian, Irish, Turkish, Hebrew, Arabic, Hindustani, Japanese, Chinese.
The definition of an auxiliary language for science became a major issue discussed in emerging international scientific institutions. On January 17, 1901, the newly established International Association of Academies created the Delegation for the Adoption of an International Auxiliary Language "with support from 310 member organizations". This delegation was tasked with finding an auxiliary language that could be used for "scientific and philosophical exchanges", and it could not be any "national language". In the context of increased nationalistic tensions, any of the dominant languages of science would have appeared as a partisan choice. The delegation consequently had a limited set of options: these included the unlikely revival of a classical language such as Latin, or a new constructed language such as Volapük, Idiom Neutral, or Esperanto.
Throughout the first part of the 20th century, Esperanto was seriously considered as a potential international language of science. As late as 1954, UNESCO passed a recommendation to promote the use of Esperanto for scientific communication. In contrast with Idiom Neutral—or the simplified version of Latin, Interlingua—Esperanto was not conceived primarily as a scientific language. Yet, by the early 1900s, Esperanto was by far the most successful constructed language, with a large international community and numerous dedicated publications. Starting in 1904, the Internacia Science Revuo aimed to adapt Esperanto to the specific needs of scientific communication. The development of a specialized technical vocabulary was a challenging task, since Esperanto's extensive derivation system made it complicated to directly import words commonly used in German, French, or English scientific publications. In 1907, the Delegation for the Adoption of an International Auxiliary Language seemed close to retaining Esperanto as its preferred language. Nevertheless, significant criticism was still addressed at a few remaining complexities of the language, as well as its lack of scientific purpose and technical vocabulary. Unexpectedly, the delegation supported a new variant of Esperanto, Ido, which was submitted late in the process by an unknown contributor. While this decision was framed as a compromise between the Esperantist and the anti-Esperantist factions, it ultimately disappointed all proponents of an international medium for scientific communication, and it durably harmed the adoption of constructed languages in academic circles.

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9 (1): 168–174. doi:10.1002/nop2.1115. ISSN 2054-1058. PMC 8685880. PMID 34725950. Zhang, Lin; Sivertsen, Gunnar (2020-05-12). "The New Research Assessment Reform in China and Its Implementation". Scholarly Assessment Reports. 2 (1): 3. doi:10.29024/sar.15. hdl:11250/2733873. ISSN 2689-5870. Retrieved 2023-09-10.

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=== Conferences ===
Shearer, Kathleen; Chan, Leslie; Kuchma, Iryna; Mounier, Pierre (2020-04-15). Fostering Bibliodiversity in Scholarly Communications: A Call for Action. Retrieved 2020-06-17.
Beigel, Fernanda (2022). Research evaluation in the southern road to open science (PDF). OSEC 2022. Paris.
=== Other articles ===
Garfield, Eugene (1967). "English – An international language for science?" (PDF). Current Contents.
Huttner-Koros, Adam (2015-08-21). "Why Science's Universal Language Is a Problem for Research". The Atlantic. Retrieved 2020-09-24.
van Weijen, Daphne (November 2012). "The Language of (Future) Scientific Communication". Research Trends. No. 31. Archived from the original on 2020-09-20. Retrieved 2020-09-24.
Gordin, Michael D. "How did science come to speak only English? – Michael D Gordin | Aeon Essays". Aeon. Retrieved 2020-09-24.
Taşkın, Zehra; Dogan, Guleda; Kulczycki, Emanuel; Zuccala, Alesia Ann (2020-06-18). "Science needs to inform the public. That can't be done solely in English". LSE COVID-19. Retrieved 2022-01-21.
Pölönen, Janne; Kulczycki, Emanuel; Mustajoki, Henriikka; Røeggen, Vidar (2021-12-07). "Multilingualism is integral to accessibility and should be part of European research assessment reform". Impact of Social Sciences. Retrieved 2022-01-20.
=== Declaration ===
Bundy, McGeorge. "Memorandum # 332, U.S. Government Policy on English Language Teaching Abroad, 6/11/1965" (June 11, 1965). National Security Files, Series: National Security Action Memorandums, Box: 6. LBJ Presidential Library. – via DiscoverLBJ.
Helsinki Initiative (2019). "Helsinki Initiative on Multilingualism in Scholarly Communication". Helsinki: Federation of Finnish Learned Societies, Committee for Public Information, Finnish Association for Scholarly Publishing, Universities Norway & European Network for Research Evaluation in the Social Sciences and the Humanities. doi:10.6084/m9.figshare.7887059. Retrieved 2020-09-24.
== External links ==
A Call to Diversify the Lingua Franca of Academic STEM Communities
AmeliCA Ciencia Abierta
GOAP: UNESCO's Global Open Access Portal, providing "status of open access to scientific information around the world."
Helsinki Initiative on Multilingualism in Scholarly Communication

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=== English, competitors, and machine translation (1920–1965) ===
The two world wars had a lasting impact on scientific languages. A combination of political, economic, and social factors durably weakened the triumvirate of the three main languages of science in the 19th century; this combination paved the way for the predominance of English in the latter part of the 20th century. There is ongoing debate about whether the world wars accelerated a structural tendency toward English predominance or merely created the conditions for it. Ulrich Ammon wrote that "even without the World Wars the English language community would have gained economic and, consequently, scientific superiority and, thus, preference of its language for international scientific communication." By contrast, Michael Gordin emphasizes that the privileged status of English was far from settled until the 1960s.
The First World War had an immediate impact on the global use of German in academic settings. For nearly a decade after this war, international scientific events boycotted German researchers. The German scientific communities had been compromised by nationalistic propaganda in favor of German science during the war, in addition to the exploitation of scientific research for war crimes. German was no longer acknowledged as a global scientific language. While the boycott did not last, its effects were long-term. In 1919, the International Research Council was created to replace the International Association of Academies, and it used only French and English as working languages. In 1932, fully 98.5% of international scientific conferences admitted contributions in French, 83.5% in English, and only 60% in German. At the same time, the focus of German periodicals and conferences had become increasingly local, and it included research from non-Germanic countries ever less frequently. German never recovered its privileged status as a leading language of science in the United States; due to the lack of alternatives beyond French, American education became "increasingly monoglot" and isolationist. Unaffected by the international boycott, the use of French reached "a plateau between the 1920s and 1940s"; while it did not decline, it did not profit from the marginalization of German, but instead it decreased relative to the expansion of English.
The rise of totalitarianism in the 1930s reinforced the status of English as the leading scientific language. In absolute terms, German publications retained some relevance, but German scientific research was structurally weakened by anti-Semitic and political purges, rejection of international collaborations, and emigration. The German language was not boycotted again in international scientific conferences after the Second World War, since its use had quickly become marginal, even in Germany itself; even after the period of the occupied zone, English (in the West) and Russian (in the East) became major vehicular languages for higher education.
In the two decades after the Second World War, English had become the leading language of science. However, a large share of global research continued to be published in other languages, and language diversity even seemed to increase until the 1960s. Russian publications in numerous fields, especially chemistry and astronomy, had grown rapidly after the war: "in 1948, more than 33% of all technical data published in a foreign language now appeared in Russian." As late as 1962, Christopher Wharton Hanson raised doubts about the future of English as the leading language in science, with Russian and Japanese rising as major languages of science, and the new decolonized states seemingly poised to favor local languages:

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It seems wise to assume that in the long run the number of significant contributions to scientific knowledge by different countries will be roughly proportional to their populations, and that except where populations are very small contributions will normally be published in native languages.
The expansion of Russian scientific publishing became a source of recurring tension in the United States during the decade of the Cold War. Very few American researchers were able to read Russian, which contrasted with a remaining widespread familiarity with the two oldest languages of science, French and German. "In a 1958 survey, 49% of American scientific and technical personnel claimed they could read at least one foreign language, yet only 1.2% could handle Russian." Science administrators and funders had recurring concerns about their ability to efficiently track the progress of academic research in the USSR. This ongoing anxiety became an overt crisis after the successful launch of the Sputnik 1 satellite in 1958, as the decentralized American research system seemed for a time outpaced by the efficiency of Soviet planning.
Although the Sputnik crisis was relatively brief, it had far-reaching consequences for linguistic practices in science—in particular, the development of machine translation. Research in this area emerged precociously: automated translation appeared as a natural extension of the purpose of the first computers, which was code-breaking. Leading figures in computing, such as Norbert Wiener, were initially reluctant. Nevertheless, several well-connected science administrators in the US, such as Warren Weaver and Léon Dostert, established a series of major conferences and experiments in the nascent field, out of a concern that "translation was vital to national security". On January 7, 1954, Dostert coordinated the Georgetown–IBM experiment, which aimed to demonstrate that the technique was sufficiently mature, despite the significant shortcomings of computing infrastructure at the time. Some sentences from Russian scientific articles were automatically translated, using a dictionary of 250 words and six basic syntax rules. It was not disclosed at the time that these sentences had been purposely selected for their suitability for automated translation. At most, Dostert argued that "scientific Russian" was easier to translate, since it was more formulaic and less grammatically diverse than everyday Russian.
Machine translation became a major priority in US federal research funding in 1956 because of an emerging arms race with Soviet researchers. While the Georgetown–IBM experiment did not have a large impact in the United States initially, it was immediately noticed in the USSR. The first articles in the field appeared in 1955; only a year later, a major conference was held that attracted 340 representatives. In 1956, Léon Dostert secured significant funding with the support of the CIA, and he had enough resources to overcome the technical limitations of existing computing infrastructure. In 1957, automated translation from Russian to English could run on a vastly expanded dictionary of 24,000 words, and it could rely on hundreds of predefined syntax rules. At this scale, automated translation remained costly, since it relied on numerous computer operators using thousands of punch cards. Nevertheless, the quality of the output did not improve significantly: in 1964, the automated translation of the few sentences submitted during the Georgetown–IBM experiment yielded a much less readable output, since it was no longer possible to tweak the rules for a predefined corpus.
=== English as a global standard (1965 onward) ===

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During the 1960s and 1970s, English was no longer a majority language of science, but a scientific lingua franca instead. The transformation had more wide-ranging consequences than the replacement of two or three main languages of science by a single language: it marked "the transition from a triumvirate that valued, at least in a limited way, the expression of identity within science, to an overwhelming emphasis on communication and thus a single vehicular language." Ulrich Ammon characterizes English as an "asymmetrical lingua franca", since it is "the native tongue and the national language of the most influential segment of the global scientific community, but a foreign language for the rest of the world." This paradigm is usually associated with the globalization of American and English-speaking culture in the latter part of the 20th century.
No specific event accounts for the full shift, though numerous transformations highlight an accelerated conversion to English science in the later part of the 1960s. On June 11, 1965, US President Lyndon B. Johnson stated that the English language had become a lingua franca that opened "doors to scientific and technical knowledge" and whose promotion should be a "major policy" of the United States. In 1969, the most prestigious collection of abstracts in chemistry in the early 20th century—the German Chemisches Zentralblatt—was discontinued. This polyglot compilation in 36 languages could no longer compete with the English-focused Chemical Abstract, since more than 65% of publications in the field were in English. By 1982, a report of the French Academy of Sciences admitted that "English is by now the international standard language of science and it could very nearly become its unique language", and it is already the main "means of communication" in European countries with a long-standing tradition of publication in local languages such as Germany and Italy. In the European Union, the Bologna Declaration of 1999 "obliged universities throughout Europe and beyond to align their systems with that of the United Kingdom", and it created strong incentives to publish academic results in English. From 1999 to 2014, the number of English-speaking courses in European universities increased tenfold.
Machine translation, which had been booming since 1954 thanks to Soviet-American competition, was immediately affected by the new paradigm. In 1964, the US National Science Foundation underlined that "there is no emergency in the field of translation" and that translators were easily up to the task of making foreign research accessible. Funding stopped simultaneously in the United States and the Soviet Union, and machine translation did not recover from this research "winter" until the 1980s; by that time, translating scientific publications was no longer the main motivation. Research in this area was still pursued in a few countries where bilingualism was an important political and cultural issue; in Canada, for example, the METEO system was successfully established to "translate weather forecasts from English into French".
English content gradually became prevalent in originally non-English journals—first as an additional language, and then as the default language. Before 1998, seven leading European journals had published in their local languages: Acta Physica Hungarica, Anales de Física, Il Nuovo Cimento, Journal de Physique, Portugaliae Physica, and Zeitschrift für Physik. In 1998, these journals merged and became the European Physical Journal, an international journal accepting only English submissions. The same process occurred repeatedly in less prestigious publications:
The pattern has become so routine as to be almost cliché: first, a periodical publishes only in a particular ethnic language (French, German, Italian); then, it permits publication in that language and also a foreign tongue, always including English but sometimes also others; finally, the journal excludes all other languages but English and becomes purely Anglophone.
Early scientific infrastructure was a leading factor in the conversion to a single vernacular language. Critical developments in applied scientific computing and information retrieval systems occurred in the United States after the 1960s. The Sputnik crisis was the main incentive, since it "turned the librarians' problem of bibliographic control into a national information crisis"; in addition, it favored ambitious research plans such as the following:
SCITEL—an ultimately failed proposal to create a centrally planned system of electronic publication in the early 1960s
MEDLINE—for medicine journals
NASA/RECON—for astronomy and engineering
By contrast with the decline of machine translation, scientific infrastructure and databases emerged as a profitable business in the 1970s. Even before the emergence of a global network such as the World Wide Web, "it was estimated in 1986 that fully 85% of the information available in worldwide networks was already in English."
The predominant use of English went beyond the architecture of networks and infrastructures, and it affected the content as well. The Science Citation Index—created by Eugene Garfield in the aftermath of SCITEL—had a significant and lasting influence on the structure of global scientific publication in the last decades of the 20th century, providing its most important metrics. The journal impact factor, "ultimately came to provide the metric tool needed to structure a competitive market among journals." The Science Citation Index had better coverage of English-speaking journals, which gave them a stronger journal impact factor and created incentives to publish in English: "Publishing in English placed the lowest barriers toward making one's work 'detectable' to researchers." Because it was convenient to deal with a monolingual corpus, Eugene Garfield called for acknowledging English as the only international language for science:
Since Current Contents has an international audience, one might say that the ideal publication would be multi-lingual, listing all titles in five languages -- one or more of which is read by most of our subscribers, including German, French, Russian and Japanese, as well as English. This is, of course, impractical since it would quadruple the size of Current Contents (…) the only reasonable solution is to publish as many contents pages in English as is economically and technically feasible. To do this we need the cooperation of publishers and authors.
== Current trends ==

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=== English standardization ===
Nearly all the scientific publications indexed on the leading commercial academic search engines are in English. As of 2022, this observation covers 95.86% of the 28,142,849 references indexed on the Web of Science platform, in addition to 84.35% of the 20,600,733 references indexed in the Scopus system.
The minimal coverage of non-English languages creates a feedback loop—non-English publications can be considered less valuable because they are not indexed in international rankings and fare poorly in evaluation metrics. As many as 75,000 articles, book titles, and book reviews from Germany were excluded from Biological Abstracts between 1970 and 1996. In 2009, at least 6555 journals were published in Spanish and Portuguese on a global scale, and "only a small fraction are included in the Scopus and Web of Science indices."
Criteria for inclusion in commercial databases not only favor English journals but also incentivize non-English journals to discontinue their local journals. They "demand that articles be in English, have abstracts in English, or at least have their references in English". In 2012, the Web of Science was explicitly committed to the anglicization (and Romanization) of published knowledge:
English is the universal language of science. For this reason, Thomson Reuters focuses on journals that publish full text in English, or at very least, bibliographic information in English. There are many journals covered in Web of Science that publish articles with bibliographic information in English and full text in another language. However, going forward, it is clear that the journals most important to the international research community will publish full text in English. This is especially true in the natural sciences. There are notable exceptions to this rule in the Arts & Humanities and in Social Sciences topics.
This commitment to English science has a significant performative effect. The influence that commercial databases "now wield on the international stage is considerable and works very much in favor of English", since they provide a wide range of indicators of research quality. They contributed to "large-scale inequality, notably between Northern and Southern countries". While leading scientific publishers had initially "failed to grasp the significance of electronic publishing," they successfully pivoted to a "data analytics business" by the 2010s. Actors such as Elsevier and Springer are increasingly able to control "all aspects of the research lifecycle, from submission to publication and beyond". Due to this vertical integration, commercial metrics are no longer restricted to journal article metadata, but they can include a wide range of individual and social data extracted from scientific communities.
National databases of scientific publications show that the use of English continued to expand during the 2000s and 2010s at the expense of local languages. According to a comparison of seven national databases in Europe from 2011 to 2014, in "all countries, there was a growth in the proportion of English publications". In France, data from the Open Science Barometer shows that the share of publications in French has shrunk from 23% in 2013 to 12-16% by 2019–2020.
According to Ulrich Ammon, the predominance of English has created a hierarchy and a "central-peripheral dimension" within the global scientific publication landscape, which negatively affects the reception of research published in a non-English language. The unique use of English has discriminatory effects on scholars who are not sufficiently conversant in the language; in a survey organized in Germany in 1991, 30% of researchers in all disciplines gave up on publishing when English was the only option. In this context, the emergence of new scientific powers is no longer linked with the appearance of a new language of science, which was the case until the 1960s. China has quickly become a major player in international research, placing second after the United States in numerous rankings and disciplines. Nevertheless, most of this research is English-speaking and abides by the linguistic norms established by commercial indexes.
The dominant position of English has also been strengthened by the "lexical deficit" accumulated during past decades by alternative languages of sciences; after the 1960s, "new terms were being coined in English at a much faster rate than they were being created in French."

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=== Persistence of linguistic diversity ===
Several languages have retained a secondary status as an international language of science, due to the extent of the local scientific production or to their continued use as a vehicular language in specific contexts. These languages generally include "Chinese, French, German, Italian, Japanese, Russian, and Spanish." Local languages have remained prevalent in major scientific countries: "most scientific publications are still published in Chinese in China".
Empirical studies of the languages used in scientific publications have long been constrained by structural bias in the most readily accessible sources—commercial databases such as the Web of Science. Atypical access to a large corpus not covered by global indexes showed that multilingualism remains non-negligible, although little studied; as of 2022, there are "few examples of analyses at scale" for multilingualism in science. However, a 2026 study found that the proportion of English publications in Dimensions went down from 93.86% in 1990 to 85.52% in 2023, with Indonesian, Spanish and Portuguese expanding at a faster rate than English.
In seven European countries with limited international reach for each local language, one third of researchers in social sciences and the humanities publish in two or more languages; "research is international, but multilingual publishing keeps locally relevant research alive with the added potential for creating impact." Because of the discrepancy between actual practices and their visibility, multilingualism has been described as a "hidden norm of academic publication".
Overall, the social sciences and the humanities (SSH) have preserved more diverse linguistic practices; "while natural scientists of any linguistic background have largely shifted to English as their language of publication, social scientists and scholars of the humanities have not done so to the same extent." In these disciplines, the need for global communication is balanced by the significance for local culture; "the SSH are typically collaborating with, influencing and improving culture and society. To achieve this, their scholarly publishing is partly in the native languages." Nevertheless, the distinctiveness of the social sciences and the humanities in this regard was progressively reduced after 2000; by the 2010s, a large proportion of German and French articles on art and the humanities (as indexed in the Web of Science) were in English. While German has been outpaced by English even in Germanic-speaking countries since the Second World War, German continues to be marginally used as a vernacular scientific language in specific disciplines or research fields (the so-called Nischenfächer or "niche-disciplines"). Linguistic diversity is not specific to the social sciences, but this persistence may be obscured by the high prestige attached to international commercial databases; in the Earth sciences, "the proportion of English-language documents in the regional or national databases (KCI, RSCI, SciELO) was approximately 26%, whereas virtually all the documents (approximately 98%) in Scopus and WoS were in English."
Beyond the general distinction between the social sciences and the natural sciences, there are finer-grained distributions of language practices. In 2018, a bibliometric analysis was performed on the publications in the social sciences and the humanities of eight European countries; this analysis highlighted that "patterns in the language and type of SSH publications are related not only to the norms, culture, and expectations of each SSH discipline but also to each country's specific cultural and historic heritage." The use of English was more prevalent in Northern Europe than in Eastern Europe, and publication in the local languages remains especially significant in Poland due to a large "'local' market of academic output". Local research policies may have a significant impact: preference for international commercial database (such as Scopus or the Web of Science) may account for a steeper decline in publications in the local language in the Czech Republic, relative to Poland. Additional factors include the distribution of economic models within the journals; non-commercial publications have much stronger "language diversity" than do commercial publications.
Since the 2000s, the expansion of digital collections has contributed to a relative increase in linguistic diversity in academic indexes and search engines. The Web of Science enhanced its regional coverage during 2005-2010, which caused the index to "increase the number of non-English papers such as Spanish papers". In Portuguese research communities, there has been a sharp increase in Portuguese-language papers in commercial indexes during 2007-2018, which is indicative of remaining "spaces of resilience and contestation of some hegemonic practices" and of a potential new paradigm in scientific publishing "steered towards plurilingual diversity". Multilingualism as a practice and competency has also increased; as of 2022, 65% of early-career researchers in Poland had published in two or more languages, whereas only 54% of the older generations had done so.
In 2022, Bianca Kramer and Cameron Neylon led a large-scale analysis of the metadata available for 122 million objects indexed with a digital object identifier (DOI) by the Crossref organization. Overall, non-English publications made up "less than 20%", although this percentage could be underestimated for two reasons: a lower adoption rate for DOIs, or the use of local DOIs (for example, through the Chinese National Knowledge Infrastructure). Nevertheless, multilingualism seems to have improved during the last 20 years, with a significant increase in publications in Portuguese, Spanish, and Indonesian.

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=== Machine translation ===
Scientific publication has been the first major use case for machine translation, with early experiments dating back to 1954. Development in this area slowed after 1965, because of the increasing predominance of English, limitations in computing infrastructure, and the shortcomings of the leading approach—rule-based machine translation. By design, rule-based methods favored translation between a few major languages (English, Russian, French, German, ...), since a "transfer module" needed to be developed for "each pair of languages"; this situation led to a combinatorial explosion when more languages were considered. After the 1980s, the field of machine translation was revived as it underwent a "full-scale paradigm shift": explicit rules were replaced by statistical and machine learning methods applied to a large aligned corpus. By that time, most of the demand no longer came from scientific publishing, but instead from commercial documents such as technical and engineering manuals. A second paradigm shift occurred in the 2010s, with the development of deep learning methods, which can be partially trained on a non-aligned corpus (i.e., "zero-shot translation"). Requiring few supervision inputs, deep learning models make it possible to incorporate a wider diversity of languages, but also a wider diversity of linguistic contexts within one language. The results are significantly more accurate than with rule-based machine translation: after 2018, automated translation of PubMed biomedical abstracts was deemed superior to human translation for a few languages (such as Portuguese). Scientific publications are an appropriate use case for neural-network translation models, since they work best "in restricted fields for which it has a lot of training data."
In 2021, there were "few in-depth studies on the efficiency of Machine Translation in social science and the humanities" since "most research in translation studies are focused on technical, commercial or law texts". Uses of machine translation are especially difficult to estimate, since freely available tools such as Google Translate have become ubiquitous. "There is an emerging yet rapidly increasing need for machine translation literacy among members of the scientific research and scholarly communication communities. Yet in spite of this, there are very few resources to help these community members acquire and teach this type of literacy."
In an academic setting, machine translation includes a variety of uses. Production of written translations remains constrained by a lack of accuracy and consequently efficiency, since the post-editing of an imperfect machine translation should ideally take less time than a human translation. Automated translation of foreign-language text is more widespread in the context of a literature survey or "information assimilation", since the quality requirements are generally lower and a global understanding of a text is sufficient. The impact of machine translation on linguistic diversity in science depends on these uses:
If machine translation for assimilation purposes makes it possible, in principle, for researchers to publish in their own language and still reach a wide audience, then machine translation for dissemination purposes could be seen to favor the opposite and to support the use of a common language for research publication.
The increased use of machine translation has created concerns about "uniform multilingualism". Research in the field has largely focused on English and a few major European languages; "While we live in a multilingual world, this is paradoxically not taken into account by machine translation". English has often been used as a pivot language, serving as a hidden intermediary state in translation between two non-English languages. From a training corpus, probabilistic methods tend to favor the most expected possible translation and to rule out more unusual alternatives. "A common argument against the statistical methods in translation is that when the algorithm suggests the most probable translation, it eliminates alternative options and makes the language of the text so produced conform to well-documented modes of expression." While deep learning models can deal with a wider diversity of language construct, they can still be limited by collection bias in the original corpus; "the translation of a word can be affected by the prevailing theories or paradigms in the corpus harvested to train the AI".
In its 2022 research assessment of open science, the Council of the European Union welcomed the "promising developments that have recently emerged in the area of automatic translation"; the council supported a more widespread use of "semi-automatic translation of scholarly publications within Europe" because of its "major potential in terms of market creation".
== Open science and multilingualism ==

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=== Open science infrastructure ===
The development of open science infrastructure or "community-controlled infrastructure" has become a major policy issue in the open science movement. In the 2010s, the expansion of commercial scientific infrastructure led to major acknowledgment of the fragility of open scholarly publishing and open archives. The concept of open science infrastructure emerged in 2015 with the publication of the Principles for Open Scholarly Infrastructures. In November 2021, a UNESCO recommendation acknowledged open science infrastructure as one of the four pillars of open science, along with open science knowledge, open engagement of societal actors, and open dialogue with other knowledge systems. UNESCO called for sustained investment and funding: "open science infrastructures are often the result of community-building efforts, which are crucial for their long-term sustainability and therefore should be not-for-profit and guarantee permanent and unrestricted access to all public to the largest extent possible." Examples of open science infrastructure include indexes, publishing platforms, shared databases, and computer grids.
Open infrastructures have supported linguistic diversity in science. The leading free software for scientific publishing, Open Journal Systems, is available in 50 languages; it is widespread among non-commercial open-access journals. A landscape study was conducted by the SPARC alliance in 2021; it shows that European open science infrastructures "provide access to a range of language content of local and international significance." In 2019, leading open science infrastructures endorsed the Helsinki Initiative on Multilingualism in Scholarly Communication, and they thus committed to "protect national infrastructures for publishing locally relevant research." Signatories include the Directory of Open Access Journals (DOAJ), Digital Research Infrastructure for the Arts and Humanities (DARIAH), Latindex, OpenEdition, Open Scholarly Communication in the European Research Area for Social Sciences and Humanities (OPERAS), and SPARC Europe.
In contrast with commercial indexes, the DOAJ does not prescribe the use of English. As a consequence, only half of the journals indexed are published primarily in English; this is a sharp contrast with the overwhelming prevalence of English in commercial indexes such as the Web of Science (more than 95% in English). Six languages are represented by more than 500 journals: Spanish (2776 journals), Portuguese (1917 journals), Indonesian (1329 journals), French (993 journals), Russian (733 journals), and Italian (529 journals). Most of this language diversity is due to non-commercial journals (or diamond open access); 25.7% of these publications accept contributions in Spanish, compared with only 2.4% of journals based on an article processing charge (APC). In 2020-2022, "for English articles in DOAJ journals, 21% are in non-APC journals, but for articles in languages other than English, this percentage is a massive 86%."
Non-English open infrastructures have experienced significant growth; as of 2022, "national repositories and databases are growing everywhere (see the databases such as Latindex in Latin America, or the new repositories in Asia, China, Russia, India)". This development opens up new research opportunities for the study of multilingualism in a scientific context. It will become increasingly feasible to study the "differences between locally published research in non-English speaking contexts and English-speaking international authors".
=== Multilingualism and social impact ===
Publication on open-access platforms has created new incentives for publishing in a local language. In commercial indexes, non-English publications were penalized by the lack of international reception, and they had a significantly lower impact factor. Without a paywall, a local language publication can find its specific audience among a large non-academic public who may be less proficient in English.
During the 2010s, quantitative studies began to highlight the positive impact of local languages on the reuse of open-access resources in nations such as Finland, Québec, Croatia, and Mexico. A study of the Finnish platform Journal.fi shows that the audience for Finnish-language articles is significantly more diverse: "in case of the national language publications students (42%) are clearly the largest group, and besides researchers (25%), also private citizens (12%) and other experts (11%)". By contrast, English-language publications attract mostly professional researchers. Because of ease of access, open science platforms in a local language can also achieve more global reach. The French-Canadian journal consortium Érudit has a primarily international audience, with less than one third of readers coming from Canada.
A strong network of open science infrastructures has been developed in South America (e.g., Scielo and Redalyc) and the Iberian region; this has contributed to the resurgence of Spanish and Portuguese in international scientific communication. Regional growth may also be associated with the boom in open-access publishing. Both Portuguese and Spanish play important roles in open-access publishing (as do Brazil and Spain themselves).
Although multilingualism has been either neglected or even discriminated against in commercial databases, it has been valued as central to the social impact of open science platforms and infrastructure. In 2015, Juan Pablo Alperin introduced a systematic measure of social impact that highlighted the relevance of scientific content for local communities: "By looking at a broad range of indicators of impact and reach, far beyond the typical measures of one article citing another, I argue, it is possible to gain a sense of the people that are using Latin American research, thereby opening the door for others to see how it has touched those individuals and communities. In this context, new indicators for linguistic diversity have been proposed. Proposals include the PLOTE index and the Linguistic Diversity Index. As of 2022, however, they have had "limited traction in the scholarly anglophone literature". Comprehensive indicators of the local impact of research remain largely non-existent; "many aspects of research cannot be measured quantitatively, especially its sociocultural impact."

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=== Policies in favor of multilingualism ===
A new scientific and policy debate over linguistic diversity emerged after 2015: "in recent years, policies for Responsible Research and Innovation (RRI) and Open Science call for increasing access to research, interaction between science and society and public understanding of science". The debate initially stemmed from wider discussions about the evaluation of open science and the limitations of commercial metrics. In 2015, the Leiden Manifesto included ten principles to "guide research evaluation", which included a call to "protect excellence in locally relevant research". Building on empirical data showing the persistence of non-English research communities in Europe, Gunnar Sivertsen (in 2018) theorized the need for a balanced multilingualism "to consider all the communication purposes in all different areas of research, and all the languages needed to fulfil these purposes, in a holistic manner without exclusions or priorities." In 2016, Sivertsen contributed to the "Norwegian model" of scientific evaluation: he proposed a flat hierarchy among a few large international journals, along with a wide selection of journals that would not discriminate against local publications, and he encouraged journals in the social sciences and the humanities to favor Norwegian publications.
These local initiatives developed into a new international movement in favor of multilingualism. In 2019, 120 research organizations and several hundred individual researchers cosigned the Helsinki Initiative on Multilingualism in Scholarly Communication. The initiative includes three principles:
"Support dissemination of research results for the full benefit of the society", which implies that they should be available "in a variety of languages".
"Protect national infrastructures for publishing locally relevant research" through specific support of the non-commercial/diamond model to "make sure not-for-profit journals and book publishers have both sufficient resources". Non-commercial journals are more likely to be published in a local language.
"Promote language diversity in research assessment, evaluation, and funding systems", in line with the third recommendation of the Leiden Manifesto.
In the aftermath of the Helsinki Initiative, multilingualism has been increasingly associated with open science. This trend was accelerated during the COVID-19 pandemic, which "saw a widespread need for multilingual scholarly communication, not only between researchers, but to enable research to reach decision-makers, professionals and citizens". Multilingualism has also re-emerged as a topic of debate beyond the social sciences. In 2022, the Journal of Science Policy and Governance published a "Call to Diversify the Lingua Franca of Academic STEM Communities", which stressed that "cross-cultural solutions are necessary to prevent critical information from being missed by English-speaking researchers."
In November 2021, the UNESCO Recommendation for Open Science included multilingualism as the core of its definition of open science: "For the purpose of this Recommendation, open science is defined as an inclusive construct that combines various movements and practices aiming to make multilingual scientific knowledge openly available, accessible and reusable for everyone".
During the early 2020s, the European Union begin to officially support language diversity in science, as a continuation of its general policies in favor of multilingualism. In December 2021, the European Commission issued an important report on the future of scientific assessment in European countries. However, this report overlooked the issue of linguistic diversity: "Multilingualism is the most notable omission". In June 2022, the Council of the European Union included a detailed recommendation on the "Development of multilingualism for European scholarly publications" in its research assessment of open science. The declaration acknowledges the "important role of multilingualism in the context of science communication with society" and welcomes "initiatives to promote multilingualism, such as the Helsinki initiative on multilingualism in scholarly communication." While the declaration is not binding, it invites experiments with multilingualism "on a voluntary basis" and to assess the need for further action by the end of 2023.
== References ==
== Bibliography ==
=== Books & theses ===
Alperin, Juan Pablo (2015). The public impact of Latin America's approach to open access (Thesis). Stanford University.
Andriesse, Cornelis D. (2008-09-15). Dutch Messengers: A History of Science Publishing, 1930–1980. Leiden: Brill. ISBN 978-90-04-17084-1.
Behrens, Julia; Fischer, Lars; Minks, Karl-Heinz; Rösler, Lena (2010). Die internationale Positionierung der Geisteswissenschaften in Deutschland. Hannover: HIS:Projektbericht.{{cite book}}: CS1 maint: publisher location (link)
Bourne, Charles P.; Hahn, Trudi Bellardo (2003-08-01). A History of Online Information Services, 1963-1976. MIT Press. ISBN 978-0-262-26175-3.
Bowker, Lynne; CIro, Jairo Buitrago (2019-05-01). Machine Translation and Global Research: Towards Improved Machine Translation Literacy in the Scholarly Community. Emerald Group Publishing. ISBN 978-1-78756-721-4.
Gordin, Michael D. (2015-04-13). Scientific Babel: How Science Was Done Before and After Global English. University of Chicago Press. ISBN 978-0-226-00032-9.
Montgomery, Scott L. (2013-05-06). Does Science Need a Global Language?: English and the Future of Research. University of Chicago Press. ISBN 978-0-226-01004-5.
Moore, Samuel (2019-05-02). Common Struggles: Policy-based vs. scholar-led approaches to open access in the humanities (Thesis). Retrieved 2021-12-11.
Olechnicka, Agnieszka; Ploszaj, Adam; Celińska-Janowicz, Dorota (2018-10-08). The Geography of Scientific Collaboration. Routledge. ISBN 978-1-315-47192-1.
Poibeau, Thierry (2019-05-09). Babel 2.0: Où va la traduction automatique ?. Odile Jacob. ISBN 978-2-7381-4850-6.
Wächter, Bernd; Maiworm, Friedhelm (2014). English-taught Programmes in European Higher Education: The State of Play in 2014. Lemmens Medien GmbH. ISBN 978-3-86856-017-6.
Wouters, P. F. (1999). The citation culture (Thesis). Retrieved 2018-09-09.
=== Reports ===
Bosman, Jeroen; Frantsvåg, Jan Erik; Kramer, Bianca; Langlais, Pierre-Carl; Proudman, Vanessa (2021-03-09). OA Diamond Journals Study. Part 1: Findings (Report). doi:10.5281/zenodo.4558704.
Council of the European Union (2022-06-10). Research assessment and implementation of Open Science (PDF) (Report).
European Commission. Directorate General for Research and Innovation. (2019). Future of scholarly publishing and scholarly communication: report of the Expert Group to the European Commission (Report). LU: Publications Office. doi:10.2777/836532. ISBN 978-92-79-97238-6.
Ficarra, Victoria; Fosci, Mattia; Chiarelli, Andrea; Kramer, Bianca; Proudman, Vanessa (2020-10-30). Scoping the Open Science Infrastructure Landscape in Europe (Report). doi:10.5281/zenodo.4159838. Ficarra, Victoria; Chiarelli, Andrea (2020). "Open science, open access, open infrastructure, services, sustainability, funding, open standards, open content, good governance, open principles". Dataset: Scoping the Open Science Infrastructure Landscape in Europe (Dataset). doi:10.5281/zenodo.4153741.
Kramer, Bianca; Neylon, Cameron (2022-06-21). Language Diversity in Scholarly Publishing (Report). COKI. Retrieved 2022-06-28.
Ochsner, Michael; Kancewicz-Hoffman, Nina; Hołowiecki, Marek; Holm, Jon (April 2020). Overview of Peer Review Practices in the SSH (Report). European Network for Research Evaluation in the Social Sciences and Humanities. doi:10.6084/m9.figshare.12032589.v2. Retrieved 2020-09-24 – via figshare.
Recommendation on Open Science (Report). UNESCO. 2021-11-23. CL/4363.

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Leith AGCM is a climate model that was developed by Cecil Leith beginning in 1958; it is likely the oldest atmospheric general circulation model. Leith published videos of its model output, inspiring other scientists to do the same. Today it has been superseded by climate models developed from different base codes; as such, it is little known.
== History and development ==
Efforts to calculate the behaviour of the weather system commenced in the 1920s with a seminal paper by Lewis Fry Richardson. By the 1950s and 1960s several groups were involved in making climate models, with major efforts taking place at several US universities that eventually gave rise to the well-known GFDL, UCLA, and NCAR models. Today climate models are an important enterprise with significant impact on public policy, where hundreds of scientists and institutions participate worldwide.
The researcher Cecil E. “Chuck” Leith (1923–2016) is well-known for his research on fluid mechanics. After an initial career on the Manhattan Project, which resulted in the invention of nuclear bombs, he joined the Lawrence Radiation Laboratory after 1946 and in 1968 the National Center for Atmospheric Research. Beginning in 1958, he began to work on a climate model that was later named the "Leith atmospheric model" or "Livermore atmospheric model". Its existence was barely reported at that time, with only several contemporary journal articles mentioning it. According to interviews with Leith, he was inspired to work on climate modelling by the noted scientist Edward Teller and by the idea to put his knowledge on nuclear explosions to use in a field that wouldn't be hindered by nuclear test bans. The model was written in assembly language, which may have given it a headstart compared to other climate model projects that were undergoing in Livermore at the time and which relied on compiler language. There appear to have been four versions, based on reports of improvement work on the code, and Leith publicized numerous videos (at the time called "movies") of the output of his model. Today, the readable presentation of the often enormous quantities of data output by climate models is a major problem in climate modelling; and Leith's example inspired other scientists to make videos as well. Leith apparently relied on a private company, Pacific Title, which worked in the entertainment industry at Hollywood, and one video displaying the output of hid model.
== The model ==
This model, which was apparently created single-handedly by Leith, included initially five, later six, elevation levels in the atmosphere and a realistic land-sea distribution, with the entire model covering the latitudes between the equator and 60° north on a 5° grid. Later its scope was broadened to the polar regions. It included parametrized drag, eddy diffusion, radiative processes but no topography. It could simulate the day-night temperature cycle but did not yield realistic precipitation distribution even after improvement work. Later versions were used to simulate the climate of Mars and the behaviour of the Arctic during the ice ages.
== Significance ==
Leith twice claimed that his model was the first to include a simulated hydrological cycle. There are other earlier models discussed in the literature, but only little evidence that they were actually operative; it is not clear when hydrological cycles began to be included in climate models but it appears that it was after the Leith model. The model was however only once used in an academic publication, specifically in a 1968 publication about atmospheric tides, as Leith's interest shifted to two dimensional turbulence, and ultimately his model proved much less influential than other climate modelling efforts.
== References ==
=== Sources ===
== External links ==
"The grandfather of today's climate models" on YouTube
Leith, C. E. (1988), Mark, Hans; Wood, Lowell (eds.), "The Computational Physics of the Global Atmosphere", Energy in Physics, War and Peace: A Festschrift Celebrating Edward Teller’s 80th Birthday, Dordrecht: Springer Netherlands, pp. 161–173, doi:10.1007/978-94-009-3031-5_11, ISBN 978-94-009-3031-5, retrieved 2023-03-25{{citation}}: CS1 maint: work parameter with ISBN (link)

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Logical positivism, also known as logical empiricism or neo-positivism, was a philosophical movement, in the empiricist tradition, that sought to formulate a scientific philosophy in which philosophical discourse would be, in the perception of its proponents, as authoritative and meaningful as empirical science.
Logical positivism's central thesis was the verification principle, also known as the "verifiability criterion of meaning", according to which a statement is cognitively meaningful only if it can be verified through empirical observation or if it is a tautology (true by virtue of its own meaning or its own logical form). The verifiability criterion thus rejected statements of metaphysics, theology, ethics and aesthetics as cognitively meaningless in terms of truth value or factual content. Despite its ambition to overhaul philosophy by mimicking the structure and process of empirical science, logical positivism became erroneously stereotyped as an agenda to regulate the scientific process and to place strict standards on it.
The movement emerged in the late 1920s among philosophers, scientists and mathematicians congregated within the Vienna Circle and Berlin Circle and flourished in several European centres through the 1930s. By the end of World War II, many of its members had settled in the English-speaking world and the project shifted to less radical goals within the philosophy of science.
By the 1950s, problems identified within logical positivism's central tenets became seen as intractable, drawing escalating criticism among leading philosophers, notably from Willard Van Orman Quine and Karl Popper, and even from within the movement, from Carl Hempel. These problems would remain unresolved, precipitating the movement's eventual decline and abandonment by the 1960s. In 1967, philosopher John Passmore pronounced logical positivism "dead, or as dead as a philosophical movement ever becomes".
== Origins ==
Logical positivism emerged in Germany and Austria amid a cultural background characterised by the dominance of Hegelian metaphysics and the work of Hegelian successors such as F. H. Bradley, whose metaphysics portrayed the world without reference to empirical observation. The late 19th century also saw the emergence of neo-Kantianism as a philosophical movement, in the rationalist tradition.
The logical positivist program established its theoretical foundations in the empiricism of David Hume, Auguste Comte and Ernst Mach, along with the positivism of Comte and Mach, defining its exemplar of science in Einstein's general theory of relativity. In accordance with Mach's phenomenalism, whereby material objects exist only as sensory stimuli rather than as observable entities in the real world, logical positivists took all scientific knowledge to be only sensory experience. Further influence came from Percy Bridgman's operationalism—whereby a concept is not knowable unless it can be measured experimentally—as well as Immanuel Kant's perspectives on aprioricity.
Ludwig Wittgenstein's Tractatus Logico-Philosophicus established the theoretical foundations for the verifiability principle. His work introduced the view of philosophy as "critique of language", discussing theoretical distinctions between intelligible and nonsensical discourse. Tractatus adhered to a correspondence theory of truth, as opposed to a coherence theory of truth. Logical positivists were also influenced by Wittgenstein's interpretation of probability though, according to Neurath, some objected to the metaphysics in Tractatus.
== History ==
=== Vienna and Berlin Circles ===
The Vienna Circle was led principally by Moritz Schlick, congregating around the University of Vienna and at the Café Central. A manifesto written by Otto Neurath, Hans Hahn and Rudolf Carnap in 1929 summarised the Vienna Circle's positions. Schlick had originally held a neo-Kantian position, but later converted, via Carnap's 1928 book Der logische Aufbau der Welt (The Logical Structure of the World). The Viennese maintained closely cooperative ties with the Berlin Circle, among whom Hans Reichenbach was pre-eminent. Carl Hempel, who studied under Reichenbach in Germany, was also to prove influential in the movement's later history. A friendly but tenacious critic of the movement was Karl Popper, whom Neurath nicknamed the "Official Opposition".
Early in the movement, Carnap, Hahn, Neurath and others recognised that the verifiability criterion was too stringent in that it rejected universal statements, which are vital to scientific hypothesis. A radical left wing emerged from the Vienna Circle, led by Neurath and Carnap, who proposed revisions to weaken the criterion, a program they referred to as the "liberalisation of empiricism". A conservative right wing, led by Schlick and Waismann, instead sought to classify universal statements as analytic truths, thereby to reconcile them with the existing criterion. Within the liberal wing Carnap emphasised fallibilism, as well as pragmatics, which he considered integral to empiricism. Neurath prescribed a move from Mach's phenomenalism to physicalism, though this would be opposed by Schlick. As Neurath and Carnap sought to pose science toward social reform, the split in the Vienna Circle also reflected political differences.
Both Schlick and Carnap had been influenced by and sought to define logical positivism versus the neo-Kantianism of Ernst Cassirer, the contemporary leading figure of the Marburg school, and against Edmund Husserl's phenomenology. Logical positivists especially opposed Martin Heidegger's obscure metaphysics, the epitome of what they had rejected through their epistemological doctrines. In the early 1930s, Carnap debated Heidegger over "metaphysical pseudosentences".

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=== Anglosphere ===
As the movement's first emissary to the New World, Moritz Schlick visited Stanford University in 1929, yet otherwise remained in Vienna and was murdered in 1936 at the University by a former student, Johann Nelböck, who was reportedly deranged. That year, A. J. Ayer, a British attendee at various Vienna Circle meetings since 1933, published Language, Truth and Logic, which imported logical positivism to the English-speaking world. In 1933, the Nazi Party's rise to power in Germany had triggered flight of intellectuals, which accelerated upon Germany's annexation of Austria in 1938. The logical positivists, many of whom were Jewish, were targeted and continued flight throughout the pre-war period. Their philosophy thus became dominant in the English-speaking world.
By the late 1930s, many in the movement had replaced phenomenalism with Neurath's physicalism, whereby material objects are not reducible to sensory stimuli but exist as publicly observable entities in the real world. Neurath settled in England, where he died in 1945. Carnap, Reichenbach and Hempel settled permanently in America.
=== Post-war period ===
Following the Second World War, logical positivism—now referred to by some as logical empiricism—turned to less radical objectives in the philosophy of science. Led by Carl Hempel, who expounded the covering law model of scientific explanation, the movement became a major underpinning of analytic philosophy in the English-speaking world and its influence extended beyond philosophy into the social sciences. At the same time, the movement drew intensifying scrutiny over its central problems and its doctrines were increasingly criticised, most trenchantly by Willard Van Orman Quine, Norwood Hanson, Karl Popper, Thomas Kuhn and Carl Hempel.
== Principles ==
=== Verification and Confirmation ===
==== Verifiability Criterion of Meaning ====
According to the verifiability criterion of meaning, a statement is cognitively meaningful only if it is either verifiable by empirical observation or is an analytic truth (i.e. true by virtue of its own meaning or its own logical form). Cognitive meaningfulness was defined variably: possessing truth value; or corresponding to a possible state of affairs; or intelligible or understandable as are scientific statements. Other types of meaning—for instance, emotive, expressive or figurative—were dismissed from further review.
Metaphysics, theology, as well as much of ethics and aesthetics failed this criterion, and so were found cognitively meaningless and only emotively meaningful (though, notably, Schlick considered ethical and aesthetic statements cognitively meaningful). Ethics and aesthetics were considered subjective preferences, while theology and metaphysics contained "pseudostatements" that were neither true nor false. Thus, logical positivism indirectly asserted Hume's law, the principle that factual statements cannot justify evaluative statements, and that the two are separated by an unbridgeable gap. A. J. Ayer's Language, Truth and Logic (1936) presented an extreme version of this principle—the boo/hooray doctrine—whereby all evaluative judgments are merely emotional reactions.
==== Revisions to the criterion ====
Logical positivists in the Vienna Circle recognised quickly that the verifiability criterion was too restrictive. Specifically, universal statements were noted to be empirically unverifiable, rendering vital domains of science and reason, such as scientific hypothesis, cognitively meaningless under verificationism. This would pose significant problems for the logical positivist program, absent revisions to its criterion of meaning.
In his 1936 and 1937 papers, Testability and Meaning, Carnap proposed confirmation in place of verification, determining that, though universal laws cannot be verified, they can be confirmed. Carnap employed abundant logical and mathematical tools to research an inductive logic that would account for probability according to degrees of confirmation. However, he was never able to formulate a model. In Carnap's inductive logic, a universal law's degree of confirmation was always zero. The formulation of what eventually came to be called the "criterion of cognitive significance", stemming from this research, took three decades (Hempel 1950, Carnap 1956, Carnap 1961). Carl Hempel, who became a prominent critic of the logical positivist movement, elucidated the paradox of confirmation.
In his 1936 book, Language, Truth and Logic, A. J. Ayer distinguished strong and weak verification. He stipulated that, "A proposition is said to be verifiable, in the strong sense of the term, if, and only if, its truth could be conclusively established by experience", but is verifiable in the weak sense "if it is possible for experience to render it probable". He would add that, "no proposition, other than a tautology, can possibly be anything more than a probable hypothesis". Thus, he would conclude that all are open to weak verification.
=== Analytic-synthetic distinction ===

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In theories of justification, a priori statements are those that can be known independently of observation, contrasting with a posteriori statements, which are dependent on observation. Statements may also be categorised into analytic and synthetic: Analytic statements are true by virtue of their own meaning or their own logical form, therefore are tautologies that are true by necessity but uninformative about the world. Synthetic statements, in comparison, are contingent propositions that refer to a state of facts concerning the world.
David Hume proposed an unambiguous distinction between analytic and synthetic, categorising knowledge exclusively as either "relations of ideas" (which are a priori, analytic and abstract) or "matters of fact and real existence" (a posteriori, synthetic and concrete), a classification referred to as Hume's fork. Immanuel Kant identified a further category of knowledge: Synthetic a priori statements, which are informative about the world, but known without observation. This principle is encapsulated in Kant's transcendental idealism, which attributes the mind a constructive role in phenomena whereby intuitive truths—including synthetic a priori conceptions of space and time—function as an interpretative filter for an observer's experience of the world. His thesis would serve to rescue Newton's law of universal gravitation from Hume's problem of induction by determining uniformity of nature to be in the category of a priori knowledge.
The Vienna Circle rejected Kant's conception of synthetic a priori knowledge given its incompatibility with the verifiability criterion. Yet, they adopted the Kantian position of defining mathematics and logic—ordinarily considered synthetic truths—as a priori. Carnap's solution to this discrepancy would be to reinterpret logical truths as tautologies, redefining logic as analytic, building upon theoretical foundations established in Wittgenstein's Tractatus. Mathematics, in turn, would be reduced to logic through the logicist approach proposed by Gottlob Frege. In effect, Carnap's reconstruction of analyticity expounded Hume's fork, affirming its analytic-synthetic distinction. This would be critically important in rendering the verification principle compatible with mathematics and logic.
=== Observation-theory distinction ===
Carnap devoted much of his career to the cornerstone doctrine of rational reconstruction, whereby scientific theories can be formalised into predicate logic and the components of a theory categorised into observation terms and theoretical terms. Observation terms are specified by direct observation and thus assumed to have fixed empirical definitions, whereas theoretical terms refer to the unobservables of a theory, including abstract conceptions such as mathematical formulas. The two categories of primitive terms would be interconnected in meaning via a deductive interpretative framework, referred to as correspondence rules.
Early in his research, Carnap postulated that correspondence rules could be used to define theoretical terms from observation terms, contending that scientific knowledge could be unified by reducing theoretical laws to "protocol sentences" grounded in observable facts. He would soon abandon this model of reconstruction, suggesting instead that theoretical terms could be defined implicitly by the axioms of a theory. Furthermore, that observation terms could, in some cases, garner meaning from theoretical terms via correspondence rules. Here, definition is said to be 'implicit' in that the axioms serve to exclude those interpretations that falsify the theory. Thus, axioms define theoretical terms indirectly by restricting the set of possible interpretations to those that are true interpretations.
By reconstructing the semantics of scientific language, Carnap's thesis builds upon earlier research in the reconstruction of syntax, referring to Bertrand Russell's logical atomism—the view that statements in natural language can be converted to standardised subunits of meaning assembled via a logical syntax. Rational reconstruction is sometimes referred to as the received view or syntactic view of theories in the context of subsequent work by Carl Hempel, Ernest Nagel and Herbert Feigl.
=== Logicism ===
By reducing mathematics to logic, Bertrand Russell sought to convert the mathematical formulas of physics to symbolic logic. Gottlob Frege began this program of logicism, continuing it with Russell, but eventually lost interest. Russell then continued it with Alfred North Whitehead in their Principia Mathematica, inspiring some of the more mathematical logical positivists, such as Hans Hahn and Rudolf Carnap.
Carnap's early anti-metaphysical works employed Russell's theory of types. Like Russell, Carnap envisioned a universal language that could reconstruct mathematics and thereby encode physics. Yet Kurt Gödel's incompleteness theorem showed this to be impossible, except in trivial cases, and Alfred Tarski's undefinability theorem finally undermined all hopes of reducing mathematics to logic. Thus, a universal language failed to stem from Carnap's 1934 work Logische Syntax der Sprache (Logical Syntax of Language). Still, some logical positivists, including Carl Hempel, continued support of logicism.
== Philosophy of science ==
The logical positivist movement shed much of its revolutionary zeal following the defeat of Nazism and the decline of rival philosophies that sought radical reform, notably Marburg neo-Kantianism, Husserlian phenomenology and Heidegger's existential hermeneutics. Hosted in the climate of American pragmatism and common sense empiricism, its proponents no longer crusaded to revise traditional philosophy into a radical scientific philosophy, but became respectable members of a new philosophical subdiscipline, philosophy of science. Receiving support from Ernest Nagel, they were especially influential in the social sciences.
=== Scientific explanation ===

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Carl Hempel was prominent in the development of the deductive-nomological (DN) model, then the foremost model of scientific explanation defended even among critics of neo-positivism such as Popper. According to the DN model, a scientific explanation is valid only if it takes the form of a deductive inference from a set of explanatory premises (explanans) to the observation or theory to be explained (explanandum). The model stipulates that the premises must refer to at least one law, which it defines as an unrestricted generalization of the conditional form: "If A, then B". Laws therefore differ from mere regularities ("George always carries only $1 bills in his wallet") which do not necessarily support counterfactual claims. Furthermore, laws must be empirically verifiable in compliance with the verification principle.
The DN model ignores causal mechanisms beyond the principle of constant conjunction ("first event A and then always event B") in accordance with the Humean empiricist postulate that, though sequences of events are observable, the underpinning causal principles are not. Hempel stated that well-formulated natural laws (empirically confirmed regularities) are satisfactory in approximating causal explanation.
Hempel later proposed a probabilistic model of scientific explanation: The inductive-statistical (IS) model. Derivation of statistical laws from other statistical laws would further be designated as the deductive-statistical (DS) model. The DN and IS models are collectively referred to as the "covering law model" or "subsumption theory", the latter referring to the movement's stated goals of "theory reduction".
=== Unity of science ===
Logical positivists were committed to the vision of a unified science encompassing all scientific fields (including the special sciences, such as biology, anthropology, sociology and economics, and the fundamental science, or fundamental physics) which would be synthesised into a singular epistemic entity. Key to this concept was the doctrine of theory reduction, according to which the covering law model would be used to interconnect the special sciences and, thereupon, to reduce all laws in the special sciences to fundamental physics.
The movement envisioned a universal scientific language that could express statements with common meaning intelligible to all scientific fields. Carnap sought to realise this goal through the systematic reduction of the linguistic terms of more specialised fields to those of more fundamental fields. Various methods of reduction were proposed, referring to the use of set theory to manipulate logically primitive concepts (as in Carnap's Logical Structure of the World, 1928) or via analytic and a priori deductive operations (as described in Testability and Meaning, 1936, 1937). A number of publications over a period of thirty years would attempt to elucidate this concept.
== Criticism ==
In the post-war period, key tenets of logical positivism, including the verifiability criterion, analytic-synthetic distinction and observation-theory distinction, drew escalated criticism. This would become sustained from various directions by the 1950s, so that, even among fractious philosophers who disagreed on the general objectives of epistemology, most would concur that the logical positivist program had become untenable. Notable critics included Karl Popper, W. V. O. Quine, Norwood Hanson, Thomas Kuhn, Hilary Putnam, as well as J. L. Austin, Peter Strawson, Nelson Goodman and Richard Rorty. Hempel himself became a major critic from within the movement, denouncing the positivist thesis that empirical knowledge is restricted to basic statements, observation statements or protocol statements.
=== Karl Popper ===
Karl Popper, a graduate of the University of Vienna, was an outspoken critic of the logical positivist movement from its inception. In Logik der Forschung (1934, published in English in 1959 as The Logic of Scientific Discovery) he attacked verificationism directly, contending that the problem of induction renders it impossible for scientific hypotheses and other universal statements to be verified conclusively. Any attempt to do so, he argued, would commit the fallacy of affirming the consequent, given that verification cannot—in itself—exclude alternative valid explanations for a specific phenomenon or instance of observation. He would later affirm that the content of the verifiability criterion cannot be empirically verified, thus is meaningless by its own proposition and ultimately self-defeating as a principle.
In the same book, Popper proposed falsifiability, which he presented, not as a criterion of cognitive meaning like verificationism (as commonly misunderstood), but as a criterion to distinguish scientific from non-scientific statements, thereby to demarcate the boundaries of science. Popper observed that, though universal statements cannot be verified, they can be falsified, and that the most productive scientific theories were apparently those that carried the greatest 'predictive risks' of being falsified by observation. He would conclude that the scientific method should be a hypothetico-deductive model, wherein scientific hypotheses must be falsifiable (per his criterion), held as provisionally true until proven false by observation, and are corroborated by supporting evidence rather than verified or confirmed.
In rejecting neo-positivist views of cognitive meaningfulness, Popper considered metaphysics to be rich in meaning and important in the origination of scientific theories and value systems to be integral to science's quest for truth. At the same time, he disparaged pseudoscience, referring to the confirmation biases that embolden support for unfalsifiable conjectures (notably those in psychology and psychoanalysis) and ad hoc arguments used to entrench predictive theories that have been proven conclusively false.
=== Willard V. O. Quine ===
In his influential 1951 paper Two Dogmas of Empiricism, American philosopher and logicist Willard Van Orman Quine challenged the analytic-synthetic distinction. Specifically, Quine examined the concept of analyticity, determining that all attempts to explain the idea reduce ultimately to circular reasoning. He would conclude that, if analyticity is untenable, so too is the neo-positivist proposition to redefine its boundaries. Yet Carnap's reconstruction of analyticity was necessary for logic and mathematics to be deemed meaningful under verificationism. Quine's arguments encompassed numerous criticisms on this topic he had articulated to Carnap since 1933. His work effectively pronounced the verifiability criterion untenable, threatening to uproot the broader logical positivist project.

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=== Norwood Hanson ===
In 1958, Norwood Hanson's Patterns of Discovery characterised the concept of theory-ladenness. Hanson and Thomas Kuhn held that even direct observations are never truly neutral in that they are laden with theory, i.e. influenced by a system of theoretical presuppositions that function as an interpretative framework for the senses. Accordingly, individuals subscribed to different theories might report radically different observations even as they investigate the same phenomena. Hanson's thesis attacked the observation-theory distinction, which draws a dividing line between observational and non-observational (theoretical) language. More broadly, its findings challenged the central-most tenets of empiricism in questioning the infallibility and objectivity of empirical observation.
=== Thomas Kuhn ===
Thomas Kuhn's landmark book of 1962, The Structure of Scientific Revolutions—which discussed paradigm shifts in fundamental physics—critically undermined confidence in scientific foundationalism. Kuhn proposed in its place a coherentist model of science, whereby scientific progress revolves around cores of established, coherent ideas which periodically undergo abrupt revolutionary changes.
Though foundationalism was often considered a constituent doctrine of logical positivism (and Kuhn's thesis an epistemological criticism of the movement) such views were simplistic: In the 1930s, Neurath had argued for the adoption of coherentism, famously comparing the progress of science to reconstruction of a boat at sea. Carnap had entertained foundationalism from 1929 to 1930, but he, Hans Hahn and others would later join Neurath in converting to a coherentist philosophy. The conservative wing of the Vienna Circle under Moritz Schlick subscribed to a form of foundationalism, but its principles were defined unconventionally or ambiguously.
In some sense, Kuhn's book unified science, but through historical and social assessment rather than by networking the scientific specialties using epistemological or linguistic models. His ideas were adopted quickly by scholars in non-scientific disciplines, such as the social sciences in which neo-positivists were dominant, ushering academia into postpositivism or postempiricism.
=== Hilary Putnam ===
In his critique of the received view in 1962, Hilary Putnam attacked the observation-theory distinction. Putnam proposed that the division between "observation terms" and "theoretical terms" was untenable, determining that both categories have the potential to be theory-laden. Accordingly, he remarked that observational reports frequently refer to theoretical terms in practice. He illustrated cases in which observation terms can be applied to entities that Carnap would classify as unobservables. For example, in Newton's corpuscular theory of light, observation concepts can be applied to the consideration of both sub-microscopic and macroscopic objects.
Putnam advocated scientific realism, whereby scientific theory describes a real world existing independently of the senses. He rejected positivism, which he dismissed as a form of metaphysical idealism, in that it precluded any possibility to acquire knowledge of the unobservable aspects of nature. He also spurned instrumentalism, according to which a scientific theory is judged, not by whether it corresponds to reality, but by the extent to which it allows empirical predictions or resolves conceptual problems.
== Decline and legacy ==
In 1967, John Passmore wrote, "Logical positivism is dead, or as dead as a philosophical movement ever becomes". His opinions concurred with widespread sentiment in academic circles that the movement had run its course by the late 1960s. Logical positivism's fall heralded postpositivism, distinguished by Popper's critical rationalism—which characterised human knowledge as continuously evolving via conjectures and refutations—and Kuhn's historical and social perspectives on the saltatory course of scientific progress.
In a 1976 interview, A. J. Ayer, who had introduced logical positivism to the English-speaking world in the 1930s, was asked what he saw as its main defects and answered that, "nearly all of it was false". Yet, he maintained that it was "true in spirit", referring to the principles of empiricism and reductionism whereby mental phenomena resolve to the material or physical and philosophical questions largely resolve to ones of language and meaning. Despite its problems, logical positivism helped to anchor analytic philosophy in the English-speaking world and its influence extended beyond philosophy in shaping the course of psychology and the social sciences. In the post-war period, Carl Hempel's contributions were vitally important in establishing the subdiscipline of the philosophy of science.
Logical positivism's fall reopened the debate over the metaphysical merit of scientific theory, whether it can offer knowledge of the world beyond human experience (scientific realism) or whether it is simply an instrument to predict human experience (instrumentalism). Philosophers increasingly critiqued the movement's doctrine and history, often misrepresenting it without thorough examination, sometimes reducing it to oversimplifications and stereotypes, such as its association with foundationalism.
== See also ==
=== People ===
Ernst Mach – Austrian physicist, philosopher and university educator (1838–1916)
Gottlob Frege – German philosopher, logician, and mathematician (1848–1925)
Friedrich Waismann – Austrian mathematician, physicist and philosopher (1896–1959)
Gustav Bergmann – Austrian-born American philosopher (1906–1987)
Herbert Feigl – Austrian-American philosopher
Kurt Grelling – German logician and philosopher (1886–1942)
R. B. Braithwaite – English philosopher and ethicist (1900–1990)
== References ==
== Further reading ==
== External links ==
Media related to Logical positivism at Wikimedia Commons
Articles by logical positivists
The Scientific Conception of the World: The Vienna Circle
Carnap, Rudolf. 'The Elimination of Metaphysics Through Logical Analysis of Language'
Carnap, Rudolf. 'Empiricism, Semantics, and Ontology.'
Excerpt from Carnap, Rudolf. Philosophy and Logical Syntax.
Feigl, Herbert. 'Positivism in the Twentieth Century (Logical Empiricism)', Dictionary of the History of Ideas, 1974, Gale Group (Electronic Edition)
Articles on logical positivism
Kemerling, Garth. 'Logical Positivism', Philosophy Pages
Murzi, Mauro. 'The Philosophy of Logical Positivism.'

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The materialism controversy (German: Materialismusstreit) was a public debate in the mid-19th century about how new developments in the natural sciences might affect existing worldviews. During the 1840s, a new form of materialism emerged, shaped by advances in biology and the decline of idealistic philosophy. This form of materialism sought to explain human beings and their behavior through scientific methods. The central question of the debate was whether scientific discoveries were compatible with traditional ideas such as the existence of an immaterial soul, a personal God, and human free will. The discussion also touched on deeper philosophical issues, such as what kind of knowledge a materialist or mechanical view of the world could offer.
In his Physiologische Briefe from 1846, zoologist Carl Vogt argued that mental processes were entirely physical, famously stating that "thoughts stand in the same relation to the brain as bile does to the liver or urine to the kidneys." In 1854, the physiologist Rudolf Wagner criticized this view in a speech to the Göttingen Naturalists' Assembly. He argued that religious belief and science belonged to separate areas of understanding, and that natural science could not answer questions about God, the soul, or free will.
Wagner’s comments were strongly worded, accusing materialists of trying to undermine spiritual values. His attacks sparked sharp responses from Vogt and others. The materialist position was later defended by figures such as physiologist Jakob Moleschott and physician Ludwig Büchner, brother of writer Georg Büchner. Supporters of materialism saw themselves as opposing what they viewed as outdated philosophical, religious, and political ideas. While their approaches varied, they found growing support among the middle classes. The idea of a scientific worldview became an important feature in the broader cultural debates of the late 19th and early 20th centuries.
== Development of natural scientific materialism ==
=== Emancipation of biology ===
The rise of popular materialism in the mid-19th century was partly driven by growing criticism of romantic and idealist natural philosophy. This critique became widespread after 1830 and influenced science, philosophy, and politics alike.
One major scientific development that supported this shift was the emergence of cell theory, founded by botanist Matthias Jacob Schleiden. In 1838, Schleiden published a study on plant development in which he identified the cell as the basic unit of all plant life and emphasized the role of the cell nucleus, discovered in 1831, in plant growth. This theory marked a turning point in botany, which had previously focused mainly on describing the external forms of plants. Schleiden combined his scientific findings with a strong critique of idealist natural philosophy. He argued that scientific knowledge must be based on direct observation, unlike the speculative systems of earlier philosophers. According to him, abstract theorizing not grounded in evidence had to be rejected.
Schleiden’s call for a more scientific and observation-based approach soon influenced other areas of biology. In 1839, Theodor Schwann published Microscopic Investigations on the Similarity in Structure and Growth of Animals and Plants, extending Schleiden’s ideas to animals. Schwann proposed that all living things are made of cells and that tissues and organs develop through cell growth and reproduction. Building on this, physician Rudolf Virchow later summarized the idea by stating: “Life is essentially cellular activity". These insights laid the foundation for a scientific understanding of life, which materialist thinkers would build upon in the following years.
=== Turning away from idealistic philosophy ===
At the same time, a broader critique of German idealism began to take shape, especially in the years before the 1848 revolutions (the Vormärz period). While many scientists still opposed materialism, criticism of idealist philosophy became more common, particularly among younger intellectuals.
One of the most influential figures in this movement was Ludwig Feuerbach, whose 1841 work The Essence of Christianity had a major impact. Feuerbach had studied under Georg Wilhelm Friedrich Hegel in Berlin and initially followed the idealist tradition. However, by the late 1830s, he began to reject it. Like other young Hegelians, he grew dissatisfied with idealism's abstract systems and its alignment with conservative politics. In 1839, Feuerbach openly criticized Hegel's philosophy. While he acknowledged its internal logic, he argued it was too far removed from the natural world and human experience. Feuerbach believed that philosophy should be grounded in the senses and in the physical reality of nature and humanity. As he put it: “All speculation that seeks to go beyond nature and man is vain. Although Feuerbach was not a scientist, his ideas about grounding knowledge in human experience and nature echoed the goals of the new biology. He promoted a type of anthropology—a theory of humanity based on lived experience—rather than a speculative or purely scientific approach.
Feuerbach’s most controversial ideas came from his critique of religion. He argued that religion was not a reflection of divine truth, but a projection of human hopes and needs. God, he claimed, was not an external being, but a creation of the human mind. While he did not reject religion entirely, he believed its value lay in its psychological and emotional function, not in metaphysical truth. Religious doctrines, he argued, could not be proven through reason or science—they were, in his view, products of imagination rather than reality.
== Carl Vogt and the political opposition ==

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The materialism controversy was sparked in part by the writings of physiologist Carl Vogt, beginning in 1847. His commitment to materialism was shaped by the scientific and political reform movements of the time, as well as his own personal and political development. Vogt was born in Giessen in 1817, into a family with both scientific and revolutionary traditions. His father, Philipp Friedrich Wilhelm Vogt, was a professor of medicine who moved to Bern in 1834 after facing political persecution. On his mother’s side, political activism was also a strong influence: Louise Follen’s three brothers—Adolf, Karl, and Paul Follen—were all involved in nationalist and democratic causes and eventually went into exile.
In 1817 Adolf Follen drafted a proposal for a future German constitution and was later arrested for his political activities. He avoided a 10-year prison sentence by fleeing to Switzerland. Karl Follen was suspected of encouraging the assassination of conservative writer August von Kotzebue and escaped to the United States, where he became a professor at Harvard University. The youngest brother, Paul Follen, helped found the Gießener Auswanderungsgesellschaft in 1833, which aimed to establish a German republic in the U.S. Though the plan failed, Paul settled in Missouri as a farmer.
Carl Vogt began studying medicine at the University of Giessen in 1833, but soon switched to chemistry under the influence of Justus Liebig, a pioneer of organic chemistry. Liebig’s experimental approach, which rejected the traditional divide between living and non-living matter, helped lay the groundwork for Vogt’s later materialist views. In 1835, however, Vogt had to leave Giessen after helping a politically persecuted student escape. He fled to Switzerland and completed his medical degree in 1839.
In the early 1840s, Vogt became active in both scientific and political reform circles, though he had not yet fully adopted a materialist worldview. His ideological shift took place during a three-year stay in Paris, where he came into contact with anarchist thinkers like Mikhail Bakunin and Pierre-Joseph Proudhon. These interactions significantly influenced his political ideas. Starting in 1845, Vogt published the Physiological Letters (Physiologische Briefe), which aimed to make physiology more accessible to the public. Inspired by Liebig’s Chemical Letters, the early volumes were written in clear, popular language. While the first letters avoided strong ideological claims, the 1846 letter on the nervous system marked a turning point. In it, Vogt argued that consciousness, will, and thought originate solely in the brain, a direct challenge to spiritual or dualist explanations of the mind.
At this stage, however, Vogt prioritized political activism over theory. In 1847, he was appointed professor of zoology in Giessen with the help of Liebig and Alexander von Humboldt. But shortly afterward, the Revolutions of 1848 broke out across Europe. When the uprising reached Giessen, Vogt led the local militia and was elected to represent Hesse-Darmstadt in the Frankfurt Parliament (1848–1849), a democratic assembly aiming to unify Germany. After the Prussian King Frederick William IV refused the crown offered by the parliament and conservative forces regained control, Vogt joined the remaining 158 deputies in Stuttgart to form the so-called rump parliament. This assembly was short-lived, and on 18 June 1849, troops from Württemberg forcibly shut it down. Vogt fled once again to Switzerland and took refuge at his family home.
With his political career in ruins and his academic post lost, Vogt returned to scientific work. His research from this point onward took on a more openly ideological tone, as he began to interpret biological processes through the lens of materialist philosophy.
== Progression of the debate ==
=== Materialism controversy until 1854 ===
In 1850, Vogt travelled to Nice to continue his zoological research, as his academic prospects in Germany remained uncertain. A year later, he published a book on animal societies, which combined zoological observations with a sharp political critique of the German state. In the book, Vogt argued in favor of anarchism, claiming that all forms of government and law were signs that humanity had not yet returned to its natural state. Vogt’s argument for anarchism was rooted in his biological and materialist worldview. He believed that humans, like animals, are entirely material beings and part of the natural world. Therefore, biology not only supported materialism but also challenged existing social and political structures.
Despite—or because of—its controversial content, the book attracted public attention in Germany. In 1852, Vogt published Bilder aus dem Thierleben (Images from Animal Life), which further developed his materialist views and strongly criticized German academic circles. He argued that any biologist who thinks clearly must recognize the truth of materialism, especially given the evidence from animal experiments. From this, he concluded that if mental functions depend on brain functions, then the soul cannot exist independently of the body or survive after death. Furthermore, if the brain operates according to natural laws, then so must the soul—leaving no room for free will:
Thus the door would be opened to simple materialism – man, as well as the animal, would be only a machine, his thinking the result of a certain organisation – free will therefore abolished? ... Truly, that is so. It really is so.
Vogt argued that those who rejected these conclusions misunderstood the implications of physiological science. His criticism was partly aimed at Rudolf Wagner, an anatomist and physiologist from Göttingen, who had attacked Vogt in an 1851 article in the Augsburger Allgemeine Zeitung. Wagner accused Vogt of replacing God with “blind, unconscious necessity". Wagner also proposed that a child’s soul was composed of equal parts from the mother’s and father’s souls. Vogt responded sarcastically, pointing out that such an idea contradicted the theological principle of the soul’s indivisibility and was scientifically implausible. Instead, he argued, character traits—like physical features—are inherited from parents through the brain, and therefore the idea of a "composite soul" could be explained in purely materialist terms.
=== Göttingen Naturalists' Meeting ===

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During the summer of 1854, the 31st Naturalists' Meeting was held in Göttingen. A major topic of discussion was the existence of the soul and its compatibility with emerging materialist views in science. During the event, physiologist Rudolf Wagner gave a prominent lecture on human creation and the nature of the soul, in which he sharply criticized materialism. He argued that denying the existence of a soul created by God—and especially the rejection of free will—would undermine the moral foundations of society.
Wagner claimed that materialist theories, such as those proposed by Carl Vogt, reduced human beings to passive machines without responsibility, which conflicted with the ethical duties of scientists. Later that year, Wagner published a second paper that expanded on his criticisms. He argued that science and faith occupy separate domains, and that science alone could neither prove nor disprove religious beliefs.
He explained that while physiologists can describe the structure and function of physical organs, their findings can be interpreted in different ways. Materialists use these observations to argue that mental functions are based on physical processes, while dualists believe the body interacts with an immaterial soul. Wagner maintained that physiology cannot determine which interpretation is correct. He stated: "There is not a single point in the biblical]doctrine of the soul ... that would contradict any doctrine of modern physiology and natural science."
=== Charcoal burning faith and science ===
Wagner’s public criticism brought the materialism debate into the spotlight. In response, Carl Vogt published a strongly worded counterattack titled Köhlerglaube und Wissenschaft (Charcoal-Burner's Faith and Science), directly aimed at Hofrat Rudolf Wagner. The first part of the text consisted largely of personal attacks. Vogt accused Wagner of lacking scientific originality, claiming that he relied on the work of others while presenting himself as a leading scholar. He also alleged that Wagner had tried to silence materialist thinkers by using political influence and state power. Wagner had linked the denial of free will with the revolutionary upheavals of 1848, suggesting that materialist ideas posed a risk to political and social stability. Vogt, angered by this accusation, turned the discussion into a broader attack on Wagner’s attempt to reconcile religion and science.
In the second part of the pamphlet, Vogt took aim at Wagner’s claim that simple religious belief—referred to sarcastically as Köhlerglaube (the "faith of a charcoal burner")—could coexist with modern science. Vogt argued that if someone places the soul beyond the reach of scientific investigation, that belief cannot be tested or disproven. However, he insisted that such an assumption was scientifically meaningless. Vogt argued that the growing understanding of how mental functions depend on the brain supported a materialist interpretation. He pointed out that Wagner himself accepted that all organs, such as the kidneys or muscles, follow biological laws. Yet when it came to the brain, Wagner made an exception by invoking an immaterial soul. According to Vogt, this selective reasoning showed that belief in an immaterial soul was a holdover from theology, not a conclusion supported by science. He concluded that materialism offered a more consistent and evidence-based framework for understanding human nature.
=== Food, strength and substance ===
By 1855, materialism had become an increasingly influential intellectual movement, even though the ideas promoted by Carl Vogt continued to face resistance in academic and political circles. Vogt was supported by two younger scientists, Jakob Moleschott and Ludwig Büchner, who also advanced materialist ideas through widely read popular science publications. Together, the three were seen as prominent advocates of materialism, which many at the time considered a compelling and coherent worldview. The controversy surrounding materialism sparked wider public debates about the relationship between science and society. These discussions also played a key role in the popularisation of science, paving the way for the reception of Charles Darwin’s theory of evolution in the late 1850s.
Jakob Moleschott was born in 's-Hertogenbosch, the Netherlands, in 1822. He encountered Hegelian philosophy early in his life but went on to study medicine at the University of Heidelberg. Influenced by Ludwig Feuerbach, Moleschott developed a materialist perspective focused on metabolism and nutrition. In his book Die Lehre der Nahrungsmittel: Für das Volk (The Science of Food: For the People), Moleschott argued that nutrition was the foundation of both physical and mental functions. This reflected his belief that humans are entirely material beings. His aim was not only to deny the existence of an immaterial soul or God, but also to use scientific knowledge to improve people's lives, especially the poor, by offering practical dietary advice.
In 1850, Moleschott sent a copy of the book to Feuerbach, who responded with a widely read review titled Die Naturwissenschaft und die Revolution (Science and the Revolution). While Feuerbach had previously positioned his philosophy beyond both idealism and materialism, this publication marked his explicit support for the materialist movement. He argued that while philosophers continued to debate the nature of body and soul, the natural sciences had already resolved the question in favor of materialism.
Ludwig Büchner, born in Darmstadt in 1824, played an even more prominent public role than Moleschott. As a student, he met Carl Vogt, and in 1848 joined Vogt’s citizen militia during the revolutionary uprisings. After an unsatisfying academic career—including a brief assistantship at the University of Tübingen—Büchner decided to publish a concise and accessible overview of the materialist worldview. His book, Kraft und Stoff (Force and Matter), became a major success: it went through 12 editions in 17 years and was translated into 16 languages. Unlike Vogt and Moleschott, who framed their materialism through their own scientific research, Büchner presented it as a general scientific summary, written for readers without a background in philosophy or science. The central idea was the unity of force and matter—a concept Moleschott had also emphasized. Büchner argued that forces cannot exist without matter, and matter cannot exist without forces. Therefore, the idea of an immaterial soul was inconsistent with scientific understanding, since it would require a force without a material base.

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== Reactions in the 19th century ==
=== Philosophy of neo-Kantianism ===
Materialism, as promoted by scientists like Carl Vogt, Jakob Moleschott, and Ludwig Büchner, was presented as a direct consequence of empirical scientific research. Following the decline of German idealism, many saw academic philosophy—especially as taught in universities—as disconnected from reality and reduced to speculative thought. Even philosopher Ludwig Feuerbach, once aligned with idealist traditions, placed his trust in the natural sciences to answer longstanding philosophical questions such as the relationship between body and soul.
However, a strong philosophical critique of materialism did not emerge until the 1860s, with the rise of Neo-Kantianism. In 1865, Otto Liebmann published Kant und die Epigonen (Kant and His Followers), a work that sharply criticized major post-Kantian thinkers—from German idealists to Arthur Schopenhauer. Liebmann famously ended each chapter with the refrain: "So we must go back to Kant!". The following year,Friedrich Albert Lange published Geschichte des Materialismus (History of Materialism), in which he aligned himself with the Neo-Kantian position. Lange accused the scientific materialists of “philosophical dilettantism”, claiming that they overlooked central insights of Kantian thought.
At the core of Kant’s philosophy, particularly in the Critique of Pure Reason, is the question: What are the conditions for the possibility of knowledge? Kant argued that human beings do not perceive the world as it truly is, but rather through cognitive structures shaped by the mind. Concepts such as cause and effect, unity, and multiplicity are not features of the external world itself but mental categories we impose on our experiences. Similarly, space and time are not absolute properties of reality but forms of human perception. Since all experience is already filtered through these mental structures, Kant concluded that we can never know things-in-themselves—that is, reality as it exists independently of human perception. As a result, Kant held that it is impossible to scientifically prove or disprove the existence of free will, a personal God, or an immaterial soul. These ideas lie outside the scope of empirical investigation.
Friedrich Albert Lange used Kant’s theory to argue that materialism made a fundamental mistake: it claimed that only matter exists, but failed to recognize that even scientific descriptions of matter are shaped by human perception. Therefore, science cannot claim to describe absolute reality; it only describes how reality appears to us through our cognitive framework. This argument was supported by physicist and physiologist Hermann von Helmholtz, who had studied the physiology of perception in the 1850s. In his 1855 lecture, Über das Sehen des Menschen (On Human Vision), Helmholtz explained that vision does not offer a faithful copy of the external world. Instead, visual perception is constructed by the brain based on incomplete sensory input. Helmholtz’s work echoed Kant’s view: every act of perception involves interpretation, and this interpretation is shaped by human cognitive faculties. Because of this, direct access to objective reality—the “thing-in-itself”—is not possible.
=== Ignoramus et ignorabimus ===
The scientific materialists did not engage with the arguments of the Neo-Kantians, as they saw the reference to Kant as just another speculative attack on the results of the natural sciences. A more serious challenge came from Emil Heinrich Du Bois-Reymond, a prominent physiologist, whose 1872 lecture Über die Grenzen des Naturerkennens (On the Limits of Understanding Nature) posed a direct challenge to the foundations of materialist thought. In this lecture, Du Bois-Reymond famously declared that certain aspects of nature, particularly consciousness, would always remain beyond scientific explanation. He summed this up with the Latin phrase: "Ignoramus et ignorabimus" (Latin for "We do not know and we will never know"). This statement sparked the Ignorabimus controversy, a long-running public and scientific debate over whether science could ever fully explain the human mind and consciousness. The intensity of the debate rivalled—and in some circles exceeded—that of the earlier Vogt–Wagner controversy of the 1850s. However, by this point, materialists found themselves increasingly on the defensive.
Du Bois-Reymond criticized the materialist position for failing to explain how consciousness arises from the physical processes of the brain. While Vogt, Moleschott, and Büchner pointed to the observable dependence of mental functions on brain activity—especially demonstrated through brain injuries and animal experiments—this, he argued, did not address the deeper issue. However, for Du Bois-Reymond, this approach was insufficient. He argued that demonstrating a correlation between brain activity and mental states does not explain why or how subjective experience—pain, desire, colors, sounds, and so on—emerges from physical processes.
Du Bois-Reymond concluded that there was no intelligible link between the objective facts of physics and the subjective nature of conscious experience. As such, consciousness represented a fundamental limit to what science could explain.
The Ignorabimus speech revealed a major weakness in the materialist worldview. While the materialists insisted that consciousness was a product of the brain, they conceded that science could not yet—and might never—explain it. This gap contributed to a broader shift in the scientific worldview during the late 19th century, from strict materialism to monism. Ernst Haeckel, one of the most influential scientists of the time, became the leading advocate of this monistic worldview. Like the materialists, he rejected dualism, idealism, and the immortal soul, but he also moved away from the materialist claim that only matter was real.
Unlike materialism, monism held that mind and matter were equally fundamental and inseparable aspects of a single underlying reality. In this way, spirit was no longer something that had to be explained in terms of matter alone, potentially resolving the issue raised by Du Bois-Reymond.

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Even Ludwig Büchner, initially one of the most prominent advocates of materialism, eventually distanced himself from the term. In a letter to Haeckel dated 1875, he wrote:I ... have therefore never used the term 'materialism', which evokes a completely one-sided idea, for my school of thought and only accepted it here and there later out of necessity because the general public knew no other word for the whole movement ... . The term 'monism' that you suggest is very good in itself, but it is very doubtful whether it will be accepted by the general public.
=== Political and ideological impact ===
Although scientific materialism gained considerable popularity among the general public in 19th-century Germany, its proponents—Carl Vogt, Jakob Moleschott, and Ludwig Büchner—faced significant political opposition. All three lost their academic positions largely because of their outspoken advocacy of materialism. Vogt’s revolutionary materialism, in particular, failed to gain traction in the reactionary political climate following the revolutions of 1848. Scientific materialism also struggled to influence broader political movements, in part due to ideological conflicts with Karl Marx and Friedrich Engels. Marx disparaged Vogt as a “small-university beer bouncer and misguided Barrot of the Reich", and personal denunciations escalated between the two camps. Marx’s circle even accused Vogt of espionage for France.
The shifting political context was reflected in the work of Ernst Haeckel, who adopted the materialists’ scientific worldview but infused it with new political meaning. Seventeen years Vogt’s junior, Haeckel became a prominent advocate of Darwinism in Germany during the 1860s. His polemical rejection of “church-wisdom and ... after-philosophy", echoed the earlier scientific materialists’ critiques. Where Vogt emphasized physiology as the foundation of a scientific worldview, Haeckel placed Darwin’s theory of evolution at the center. He famously framed the cultural conflict as:
In this spiritual battle, which now moves the whole of thinking humanity and which prepares a humane existence in the future, on the one side under the bright banner of science stand: freedom of thought and truth, reason and culture, development and progress; on the other side under the black banner of hierarchy: spiritual bondage and lies, irrationality and crudeness, superstition and regression.For Haeckel, the idea of “progress” was chiefly anti-clerical, targeting the church rather than the state. The Kulturkampf, initiated by Chancellor Otto von Bismarck in 1871, gave Haeckel a political platform to align his anti-clerical monism with Prussian government efforts to curb ecclesiastical influence.
== Reception in the 20th century ==
In the 19th century, scientific materialism played a significant role in ideological debates, especially through discussions surrounding Darwin's theory of evolution and Ernst Haeckel's monism, which gained prominence in the 1860s. Büchner’s Kraft und Stoff remained a bestseller, reflecting enduring popular interest. However, the question of a unified scientific worldview continued to provoke controversy.
The First World War and Haeckel’s death in 1919 marked critical turning points. In the subsequent Weimar Republic, the debates of the mid-19th century lost much of their relevance. Philosophical trends in the interwar period consistently criticized materialism despite differing viewpoints. This included the rise of logical positivism, which upheld the ideal of a scientific worldview but framed it in an anti-metaphysical way. Logical positivists held that only empirically verifiable propositions were meaningful, thereby dismissing materialism, monism, idealism, and dualism as speculative and philosophically misguided. Materialist theories of consciousness were largely abandoned until their revival in Anglo-Saxon philosophy in the 1950s, by which time the 19th-century materialists—Vogt, Moleschott, and Büchner—had been largely forgotten. Post-war materialist philosophy instead focused on advances in contemporary neuroscience.
Scientific materialism remained largely neglected in the histories of science and philosophy until the 1970s. In the German Democratic Republic (GDR), Dieter Wittich was an early scholar to revisit the movement; his 1960 doctoral thesis examined the scientific materialists in detail. Wittich later edited a 1971 collection of their writings, Vogt, Moleschott, Büchner: Schriften zum kleinbürgerlichen Materialismus in Deutschland, published by Akademie Verlag. In his introduction, Wittich praised the materialists’ political, scientific, and religious critiques but also highlighted their philosophical limitations, describing them as “petty-bourgeois materialists” who clung to metaphysical materialism even as dialectical materialism had become a prevailing reality.
In 1977, Frederick Gregory, an American historian of science, published Scientific Materialism in Nineteenth Century Germany, now a standard reference. Gregory contended that the significance of Vogt, Moleschott, and Büchner lay less in their specific materialist doctrines than in their socially impactful critique of religion, philosophy, and politics. He characterized their hallmark not as materialism, but as a form of atheism grounded in a "humanistic religion."
Modern scholarship generally recognizes the role of scientific materialism in the secularization processes of the 19th century, while its philosophical rigor remains debated. Renate Wahsner, for example, argues that it is untenable to deny these thinkers "sharpness and depth of thought". it is untenable to deny these thinkers "sharpness and depth of thought." Conversely, Kurt Bayertz defends their enduring relevance, noting that Vogt, Moleschott, and Büchner developed “the first fully developed form of modern materialism” — a form that, though only one variant of materialism, remains the most influential and effective in modernity. Thus, contemporary analyses of materialism’s philosophical controversies often trace their origins back to the 19th-century scientific materialists.
== References ==
== Bibliography ==

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=== Primary literature ===
Beiser, Frederick C. (2014). After Hegel: German philosophy 1840-1900. Princeton, NJ Oxford: Princeton University Press. ISBN 978-0-691-17371-9.
Büchner, Ludwig (1932). Kraft und Stoff (in German) (Pocket ed.). Leipzig: Kröner Verlag.
Du Bois-Reymond, Emil; Wollgast, Siegfried (1974). Vorträge über Philosophie und Gesellschaft. Philosophische Bibliothek. Hamburg: F. Meiner. ISBN 978-3-7873-0320-5.
Daum, Andreas W. (2002). Wissenschaftspopularisierung im 19. Jahrhundert. Bürgerliche Kultur, naturwissenschaftliche Bildung und die deutsche Öffentlichkeit 1848–1914 (in German) (2 ed.). Munich: Oldenbourg.
Feuerbach, Ludwig (1967). Gesammelte Werke (in German). Vol. 3. Berlin: Akademie Verlag.
Haeckel, Ernst (1908). Die Welträthsel (in German). Leipzig: Kröner.
Helmholtz, Hermann (2003). "Ueber das Sehen des Menschen". Gesammelte Schriften (in German). Vol. 1. Hildesheim: Olms.
Lange, Friedrich Albert (1920) [1866]. Geschichte des Materialismus und Kritik seiner Bedeutung in der Gegenwart (in German). J. Baedeker.
Marx, Karl (1961). Herr Vogt. Marx-Engels-Werke (in German). Vol. 14. Berlin: Dietz.
Vogt, Carl (1856). Köhlerglaube und Wissenschaft. Eine Streitschrift gegen Hofrasth Rudolph Wagner in Göttingen (in German) (4th ed.). Gießen: Rickersche Buchhandlung.
Vogt, Carl (1874). Physiologische Briefe (in German) (14 ed.). Gießen: Rickersche Buchhandlung.
Wagner, Rudolf (1854a). Menschenschöpfung und Seelensubstanz. Ein anthropologischer Vortrag (in German). Göttingen: G.H. Wigand.
Wagner, Rudolf (1854b). Ueber Wissen und Glauben. Mit besonderer Beziehung zur Zukunft der Seelen. Fortsetzung der Betrachtung über "Menschenschöpfung und Seelensubstanz" (in German). Göttingen: G.H. Wigand.
Wittich, Dieter (1971). Vogt, Moleschott, Büchner. Schriften zum kleinbürgerlichen Materialismus in Deutschland (in German). Berlin: Akademie-Verlag.
=== Secondary literature ===
Bayertz, Kurt; Gerhard, Myriam; Jaeschke, Walter, eds. (2007). Der Materialismus-Streit. Weltanschauung, Philosophie und Naturwissenschaft im 19. Jahrhundert / hrsg. von Kurt Bayertz, Myriam Gerhard und Walter Jaeschke. Hamburg: Meiner. ISBN 978-3-7873-2010-3.
Brock, Wilhelm (1999). Justus von Liebig (in German). Wiesbaden: Vieweg.
Aschoff, Ludwig; Diepgen, P.; Goerke, H. (1960) [1898]. Kurze Übersichtstabelle zur Geschichte der Medizin (in German). Springer Berlin Heidelberg.
Gregory, Frederick (1977a). Scientific materialism in nineteenth century Germany. Studies in the history of modern science. Dordrecht, Holland and Boston: D. Reidel Pub. Co. ISBN 978-90-277-0760-4.
Gregory, Frederick (1977b). "Scientific versus Dialectical Materialism. A Clash of Ideologies in Nineteenth-Century German Radicalism". Isis. 68 (2): 206–223. doi:10.1086/351768.
Haeckel, Ernst (1874). Anthropogenie (in German). Leipzig: Wilhelm Engelmann.
Broszat, Martin; Hardtwig, Wolfgang, eds. (1997). Deutsche Geschichte der neuesten Zeit vom 19. Jahrhundert bis zur Gegenwart. Vormärz: der monarchische Staat und das Bürgertum / Wolfgang Hardtwig. dtv (Orig.-Ausg., 4., aktualisierte Aufl ed.). Erscheinungsort nicht ermittelbar: dtv Verlagsgesellschaft. ISBN 978-3-423-04502-5.
Pauen, Michael; Stephan, Achim, eds. (2002). Phänomenales Bewusstsein: Rückkehr zur Identitätstheorie? (in German). Paderborn: Mentis. pp. 43–70. ISBN 978-3-89785-094-1. OCLC 53369599.
Jaeschke, Walter (1998). Philosophie und Literatur im Vormärz. Der Streit um die Romantik (1820–1854) (in German). Hamburg: Meiner.
Kockerbeck, Christoph, ed. (1999). Carl Vogt, Jacob Moleschott, Ludwig Büchner, Ernst Haeckel: Briefwechsel. Acta biohistorica. Marburg: Basilisken-Presse. ISBN 978-3-925347-50-4.
Liebmann, Otto (1865). Kant und die Epigonen: eine kritische Abhandlung (in German). C. Schober.
Lübbe, Hermann (2009) [1963]. Politische Philosophie in Deutschland: Studien zu ihrer Geschichte (in German). B. Schwabe. ISBN 978-3-423-04154-6.
Misteli, Hermann (1938). Carl Vogt : seine Entwicklung vom angehenden naturwissenschaftlichen Materialisten zum idealen Politiker der Paulskirche; 1817 - 1849. Schweizer Studien zur Geschichtswissenschaft. Zürich [u.a.] : Leemann.
Place, Ullin (1956). "Is Consciousness a Brain Process?". British Journal of Psychology. 47 (1): 44–50. doi:10.1111/j.2044-8295.1956.tb00560.x. PMID 13304279.
Schnädelbach, Herbert (1983). Philosophie in Deutschland 1831–1933 (in German). Frankfurt a. M.: Suhrkamp.
Smart, John J.C. (1959). "Sensations and Brain Processes". The Philosophical Review. 68 (2): 141–156. doi:10.2307/2182164. JSTOR 2182164.
Vogt, Carl (1851). Untersuchungen über Thierstaaten (in German). Frankfurt a. M.: Literarische Anstalt.
Vogt, Carl (1852). Bilder aus dem Thierleben (in German). Frankfurt a. M.: Literarische Anstalt.
Wittkau-Horgby, Annette (1998). Materialismus: Entstehung und Wirkung in den Wissenschaften des 19. Jahrhunderts. Göttingen: Vandenhoeck & Ruprecht. ISBN 3525013752.
== External links ==
Digitised works of the scientific materialists in the Internet Archive
Ernst Krause (1896). "Vogt, Carl" . Allgemeine Deutsche Biographie (in German). Vol. 40. Leipzig: Duncker & Humblot. pp. 181–189.
Zeno. "Lexikoneintrag zu »Materialismus«. Eisler, Rudolf: Wörterbuch der philosophischen ..." www.zeno.org (in German). Retrieved 2024-04-11.
Article on the materialism controversy in the German Medical Journal, 2006 (in German)