Events in Science & History
20th Century
(Still under Construction)
1900s
1900: Planck
produced quantum theory of radiation
***** The
quantum of energy is discovered.
To explain the colors of hot,
glowing matter, the German physicist Max Planck assumes that emission and absorption
of radiation occur in discrete, quantized amounts of energy. His idea initiates
the quantum theory of matter and of light.
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1901:
Electromagnetic waves cross an ocean.
Guglielmo Marconi, an Italian
inventor, generates radio waves that are detected across the Atlantic Ocean.
Within a few years, radio is widely used by ships at sea.
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1902: Marconi transmitted
by radio across Atlantic
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1903: The first
detailed design of a spacecraft is made.
After building his nation's
first aeronautical wind tunnel, the Russian physicist Konstantin Eduardovich
Tsiolkovsky introduces important ideas about space travel, such as the multi-stage
rocket.
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1904:
Fleming devised valve for reception of radio signals
***** The neural network is discovered.
By carefully examining the retina
of the eye, the Spanish neuroanatomist Santiago Ramón y Cajal shows that
the nervous system consists of discrete cells linked into a network.
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1905: The Theory
of Relativity redefines time and space.
Albert Einstein publishes his
Special Theory of Relativity, which postulates that nothing can move faster
than light, that time and space are not absolute, and that matter and energy
are equivalent (e=mc2).
***** The wave-particle duality
of light is formulated.
Albert Einstein proposes that
light, which has wavelike properties, also consists of discrete, quantized bundles
of energy which are later called photons. This model explains the photoelectric
effect, in which light ejects electrons from a metal pla
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1906:
The British seismologist Richard Dixon Oldham notes that earthquake waves travel
more slowly when they pass through the center of Earth, and suggests that our
planet has a dense core
***** A theory of magnetism is
developed.
The French physicist Pierre
Weiss proposes a theory for the magnetism of iron, which explains its disappearance
at a high temperature.
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1907: The age
of Earth is determined.
By measuring the radioactive
disintegration of uranium, the American chemist and physicist Bertram Boltwood
estimates Earth's age to be 2109 years, far greater than previous value
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1908: A cosmic
distance scale is established.
Henrietta Leavitt identifies
a class of variable stars with similar physical properties. Their differing
apparent brightnesses reveal their distances which Edwin Hubble later uses to
determine the scale of the universe.
1910s
1910 Geiger invented counter
1911: Superconductivity
is discovered.
***** The
Dutch physicist Heike Kamerlingh Onnes finds that mercury loses its electrical
resistance at temperatures near absolute zero. This low temperature effect is
observed in other materials as well.
*****
The atomic nucleus is found. To explain the recoil of alpha particles
from thin gold foils, New Zealand-born physicist Ernest Rutherford, working
in England, proposes the nuclear model of the atom.
***** Inherited
factors are shown to be determined by structure. After experimenting with
fruit flies, the American geneticist Thomas Morgan shows that inherited factors
are represented by genes placed at specific sites along a chromosome, revealing
the role of physical structure in biological function. (Left, false-color micrograph
of a fruit fly.)
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1911 - 1912:
The atomic structure of crystals is revealed.
The technique of X-ray crystallography,
developed by the father-son team of William Henry & William Lawrence Bragg
in Great Britain, & Max von Laue in Germany, shows that the pleasing symmetries
of solid crystals reveal the underlying arrangement of atoms.
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1913:
Quantum theory explains the spectrum of hydrogen.
The Danish physicist Niels Bohr
uses the idea of the quantum to predict the wavelengths of light emitted by
glowing hydrogen, which classical physics could not do. (Taking a spin, 1931.)
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1914: Earth's inner
details emerge.
The German seismologist Beno
Gutenberg studies earthquake waves and finds evidence for structure inside Earth,
as he locates the boundary between two internal layers.
***** Experimental rocketry begins.
To study the upper atmosphere, the American physicist Robert Goddard begins a
series of rocket launchings. (With liquid fuel rocket, 1926.)
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1915: The General
Theory of Relativity describes gravity.
Albert Einstein extends his
Special Theory to describe gravity as an inherent property of four-dimensional
spacetime. The theory correctly explains a gradual shift in the orbit of the
planet Mercury
***** The
origin of the continents is described. Noting that the coastlines of continents
match like jigsaw-puzzle pieces, the German scientist Alfred Wegener suggests
that the continents once formed a single land mass he calls Pangaea, then split
off and drifted apart to become the world as we know it.
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1916:
The magnitude of the quantum constant is determined.
The photoelectric effect that
Einstein explained in 1905 is used by the American Robert Millikan to measure
h, the mathematical constant introduced by Max Planck to define his quantum
of energy.
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1917:
The Mount Wilson telescope begins operations.
A telescope with a 100-inch
mirror (the world's largest for thirty years) is installed atop Mount Wilson
in California, chosen for the calmness and clarity of its atmosphere. (Hubble
at the controls.)
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1919: Infrared light
probes the size and structure of molecules.
The American physicist Elmer
Samuel Imes, at Fisk University, makes the first accurate measurement of distances
between atoms in a molecule. His infrared spectra of HCl, HBr, and HF support
quantum theory and reveal that chlorine occurs in two forms with different atomic
masses.
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1919: General Relativity
is confirmed during an eclipse of the sun.
According to Einstein's General
Relativity, gravity warps space and deflects light beams. An expedition mounted
by the Royal Astronomical Society sees the predicted effect under the ideal
conditions of a solar eclipse. The confirmation makes Einstein famous. (Left,
composite photo of a total solar eclipse, 1991.)
***** The origin of weather patterns
is found. The Norwegian meteorologist Jacob Bjerknes extends his father
Vilhelm's physical analysis of atmospheric conditions, and relates weather patterns
to fronts, the sharp boundaries between cold and warm air masses.
***** Superheterodyne radio receivers
become widely available. In the early days of radio, good reception required
luck and delicate tuning. That changes with the superheterodyne receiver, invented
by the American engineer Edwin Armstrong, which allows uniform reception of a
wide range of stations.
1920s
1922:
General Relativity predicts an expanding universe.
Although Einstein at first rejects
the result, his General Relativity predicts that all spacetime expands, as pointed
out by the Soviet mathematician and meteorologist Aleksander Friedmann.
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1923:
The nature of galaxies is discovered.
The American astronomer Edwin
Hubble, using the Mount Wilson telescope, determines that the Andromeda Galaxy
is a million light years away (later corrected to two million light years).
This resolves a long-standing debate about cosmic dista
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1923:
The particle nature of light is confirmed.
The American physicist Arthur
Holly Compton observes that in their interactions with electrons, X rays behave
like miniature billiard balls, further evidence for the reality of the photon.
***** Matter
is proposed to be wave-like. Inspired in part by his World War I experience
with radio waves, the French physicist Louis de Broglie generalizes wave-particle
duality by suggesting that particles of matter are also wave-like.
***** Zworykin
developed electronic scanning
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1924: "The Rocket
into Interplanetary Space" is published. The German rocket pioneer Hermann Oberth
shows how a rocket could develop enough thrust to overcome Earth's gravitational
pull.
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1925: New foundations
are laid for quantum mechanics.
The German physicist Werner
Heisenberg invents matrix mechanics to account for the discrete quanta of light
emitted and absorbed by atoms. His idea provides a framework for the new quantum
physics. In 1927 Heisenberg states his quantum Uncertainty Principle, that it
is impossible to exactly measure the position and momentum of a particle at
the same time.
***** The study of stellar structure
is launched. The English astrophysicist Arthur Eddington finds a simple
relation between the mass of a star and the energy it radiates. (Left, the surface
of our nearest star, the Sun.)
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1926:
An equation for matter waves is invented.
The Austrian physicist Erwin
Schrödinger describes the wave nature of matter by a formula called the
Schrödinger equation, which becomes a cornerstone of quantum mechanics.
***** Baird
demonstrated Television
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1926 - 1928:
Television is developed, and sent across an ocean.
The British electrical engineer
John Baird transmits the first television image of moving objects. In
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1928:
T he sendsa picture by wireless across the Atlantic Ocean. (Above, a digital
restoration of Baird's image of a face.)
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1927:
Matter is proved to be wave-like.
Clinton Davisson (left) &
Lester Germer, working at the Bell Telephone Laboratories, show that electrons
rebound from the rows of atoms in a crystal of nickel the way light waves are
reflected and diffracted from a corrugated surface.
***** The
universe is postulated to have started from a single event. Georges Lemaître,
Belgian astronomer and cleric, concludes that the universe began its expansion
from a small, hot "cosmic egg." This is the origin of the Big Bang Theory.
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1928: A new interaction
of light with matter is discovered.
The Indian physicist Chandrasekhara
Venkata Raman finds that a beam of light changes its wavelength as it is deflected
by matter. With the later advent of lasers, Raman scattering becomes a major
tool to study inorganic and organic materials.
***** Antiparticles
are predicted. Combining special relativity with quantum mechanics, the
British physicist Paul Dirac derives an equation for the behavior of electrons,
which also unexpectedly predicts the existence of new particles with similar
properties, but opposite charge, called antiparticles.
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1929: The expansion
of the universe is established.
Edwin Hubble discovers that
the farther a galaxy is from us, the more its light is shifted toward the red
and the faster it recedes from us. This suggests that the universe is expanding,
as predicted in 1922.
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1929 - 1932:
Neural cells are shown to exhibit electrical activity.
The British neurophysiologist
Edgar Adrian uses electronic instruments such as the oscilloscope to detect
electrical events in nerves and brain cells. Later he studies how such electrical
activity relates to epilepsy.
1930s
1930:
The geological time scale is set.
The British geologist Arthur
Holmes relates the ages of rocks as obtained from fossil evidence to their ages
as determined by radioactive analysis, giving an absolute scale for geological
time.
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1930 - 1935:
Plastics are invented.
The German chemist Hermann Staudinger
shows how small molecules form chainlike polymers, and suggests how to make
polymers. At E.I. du Pont de Nemours & Company, the American chemist Wallace
Hume Carothers develops nylon and syn-thetic rubber, which he demonstrates above.
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1930: The jet engine
is invented.
Frank Whittle, a British aircraft
engineer, patents the first turbojet engine which would be testflown in 1941.
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1932: A mechanism
is proposed for the collapse of stars.
Starting from General Relativity,
the German astronomer Karl Schwarzschild showed in 1916 that a dense body can
produce gravity so strong that light cannot escape: a black hole. In 1932, the
Indian-born American astrophysicist Subrahmanyan Chandrasekhar (left) calculates
that a star of a certain mass collapses under its own gravity, becoming a white
dwarf. For a larger mass the collapse can lead to a neutron star, and finally
a black hole.
***** The
first antiparticle is found. The American physicist Carl D. Anderson (left)
examines the trails left by cosmic ray particles in a cloud chamber. He discovers
the track of a positive electron, or positron, whose existence was predicted
in 1928.
***** The cyclotron is invented.
The American physicists Ernest O. Lawrence & his student M. Stanley Livingston
construct an ingenious device to study atomic nuclei by probing them with energetic
sub-atomic particles. Their cyclotron accelerates these particles by repeatedly
cycling them through an electric field and produces particles with extremely high
energy. The design inspires generations of particle accelerators that examine
nuclei and elementary particles.
***** The neutron is discovered.
The British physicist James Chadwick bombards beryllium with helium nuclei, and
finds the neutron, the second constituent of atomic nuclei along with the proton.
This electrically neutral particle can be used to penetrate and probe nuclei.
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1933
- 1934: A quantum method is developed to calculate
the mechanical properties of metal. The Hungarian-born American physicist
Eugene Wigner, and his graduate student, the American physicist Frederick Seitz,
develop a calculational method that uses quantum physics to find the energies
of electrons in a metal. The Wigner-Seitz technique is instrumental in opening
up matter in the solid state to further study.
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1933: The problem
of dark matter is posed.
Fritz Zwicky, a Swiss astronomer
in California, examines the rotation of galaxies, concludes that they must contain
more mass than we can see, and calls the unexplained material "dark matter
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1934: Artificial radioactive
isotopes are produced.
Irène Joliot-Curie (daughter
of Pierre & Marie Curie) & her husband Frédéric Joliot-Curie
bombard aluminum with helium nuclei to make an artificial radioactive isotope,
phosphorus-30. Radioactive isotopes are soon used to examine biological processes
such as the uptake of iodine by the thyroid gland.
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1935: A theory for
the nuclear force is proposed.
As part of his theory of the
force that holds nuclei together, the Japanese physicist Hideki Yukawa predicts
the existence of mesons, particles of nuclear glue with a mass between those
of protons and electrons.
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1935 - 1938: Xerography
is invented.
The American inventor Chester
Carlson invents a copying method based on the fact that selenium becomes a good
electrical conductor when illuminated. The first automatic copier is produced
under the Xerox name in 1959.
1936:
Sound is recorded on magnetic tape.
The "Magnetophone" device uses
magnetic tape -- first made from magnetic powder applied to a strip of paper
-- to record a concert conducted by Sir Thomas Beecham.
***** Earth's core is examined
in detail. The Danish seismologist Inge Lehmann analyzes the speed of earthquake
waves near the center of the Earth, and distinguishes between a central inner
core and a surrounding outer core.
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1937:
A "heavy electron" i found.
Among the cosmic rays they examine
in cloud chambers, the American physicists Carl D. Anderson & Seth Neddermeyer
find the muon, an elementary particle 200 times more massive than an electron.
***** Radar is invented and put
into operation. Radar (RAdio Detection And Ranging), a method to detect
distant objects by illuminating them with radio waves and measuring the reflected
signal, is developed for use in air defense by Robert Watson-Watt & other
British engineers.
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1938:
The mechanism for energy production in stars is discovered.
Classical physics cannot account
for the enormous energy output of an average-sized star like our Sun. The German-born
American physicist Hans Bethe explains it in terms of the theory of nuclear
reactions. He calculates that the high temperature inside a star causes hydrogen
nuclei to fuse into helium, releasing tremendous power for billions of years.
(In the tunnel of the Cornell accelerator, 1968.)
***** A new kind of fluid behavior
is found. The Soviet physicist Pyotr Kapitsa, working at temperatures near
absolute zero, finds that liquefied helium has superfluid properties; it flows
with almost no internal friction, displaying bizarre behavior such as a tendency
to climb spontaneously out of its container.
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1938 - 1939:
Nuclear fission is observed in uranium.
The German chemists Otto Hahn
(above right) & Fritz Strassmann detect light elements in uranium irradiated
with neutrons; the Austrian physicist Lise Meitner (in flight from the Nazis)
and her nephew Otto Frisch explain this result as nuclear fission.
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1939:
The first helicopter designed for mass production flies.
After his failure to build a
workable helicopter in 1909-1910, the Russian-born aeronautical engineer Igor
Sikorsky uses new aerodynamic knowledge to build and successfully fly his VS-300
helicopter.
***** The first FM (frequency modulation)
radio station is built. FM station WKCR introduces static-free radio to
New York City. In 1941 the station is put into regularly scheduled operation by
the Radio Club at Columbia Universit
1940s
1940: The
Radiation Laboratory is established.
The "Rad Lab" is established
at MIT to develop military radar using the magnetron, a British invention that
improves performance by producing microwaves
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1942:
The United States begins to build an atomic bomb.
President Franklin D. Roosevelt
approves a full-scale effort to build an atomic bomb, the massive Manhattan
Project under General Leslie Groves of the Army Corps of Engineers.
***** The element plutonium is
produced, and uranium-235 is isolated. Two fundamental discoveries made
in the United States support military technology. Glenn Seaborg and colleagues
bombard uranium in a cyclotron and produce the fissionable element plutonium,
one of nine new elements heavier than uranium that Seaborg would help discover.
John Dunning and co-workers show that uranium-235 is a fissionable form of uranium
and develop a method to isolate this isotope. Plutonium-239 & uranium-235
become essential for the atomic bomb.
***** The electron microscope is
used to examine a virus. Since particles are also wave-like, an electron
has an associated wavelength. In the electron microscope, invented by the German
engineer Ernst Ruska, a beam of short-wavelength electrons examines a specimen
with a higher resolution than can be obtained with an optical microscope. In
***** Salvador
Edward Luria, an Italian-born American biologist, uses the device to make
mages of a virus 10-7 meters in siz
***** The
first nuclear reactor becomes operational. Beneath the west stands of
the football stadium at the University of Chicago, a team led by the Italian-born
physicist Enrico Fermi initiates the first controlled nuclear fission chain
reaction in an "atomic pile" containing uranium and graphite.
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1942 - 1944:
The V-2 rocket is tested and used in warfare.
The liquid-fueled V-2 rocket
is tested at Peenemünde in Germany, under the technical direction of the
German engineers Wernher von Braun & Walter Dornberger. It is first used
in warfare in 1944.
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1943:
The Los Alamos laboratory is established.
As part of the Manhattan Project,
the Los Alamos weapons laboratory is built in New Mexico, under the scientific
direction of the American physicist Robert Oppenheimer. Other laboratories produce
fissionable material for atomic bombs.
1944: A basic
problem in magnetism is solved.
The Norwegian-born American
chemist Lars Onsager develops an ingenious mathematical description of the Ising
model, a two-dimensional simulation of a magnet composed of many small atomic
magnets. This work later proves useful in analyzing other complex systems, such
as gases sticking to solid surfaces, and hemoglobin molecules that absorb oxygen.
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1945: A radioactive
element is used to examine photosynthesis.
The American biochemist Melvin
Calvin examines photosynthesis, the basis of life, by following radioactive
carbon-14 (discovered in 1940) through the steps of the process
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1947: The pion
is discovered.
The British physicist Cecil
Frank Powell, using photographic methods, finds evidence in cosmic rays studies
for the pi meson or pion, a particle predicted by Yukawa in 1935.
***** The transistor was invented
by John Bardeen, Walter Brattain, and William Shockley, ho were awarded
the 1956 Nobel prize in physics for this work. The name transistor originally
was a contraction of transfer resistor.
***** The
transistor is invented. The American physicists John Bardeen, (counterclockwise
from the top) William Shockley & Walter Brattain invent the transistor,
an electronic amplifier made from a small piece of semiconducting material.
It is the forerunner of integrated circuits and memory chips.
***** The first large radio telescope
is completed. Drawing on the pioneering work of the American engineer Karl
Jansky, and radio technology developed during World War II, Bernard Lovell and
colleagues construct a radio telescope with a 218-foot diameter at Jodrell Bank,
England.
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1948:
The modern theory of light and electrons is formulated.
The American physicists Richard
Feynman & Julian Schwinger, and the Japanese physicist Sin-Itiro Tomonaga
develop quantum electro-dynamics (QED), the first complete theory of the interaction
of photons and electrons.
***** Carbon dating is invented.
The American chemist Willard Frank Libby shows how to find the date of death of
living organisms by measuring the decay of radioactive carbon-14. Radiocarbon
dating is accurate back to 50,000 years ago, and is widely used by archeologists,
anthropologists, and earth scientists.
***** The
first programmable electronic digital computer is completed. The ENIAC
(Electronic Numerical Integrator and Comparator) computer, based on vacuum tubes,
goes into service at the University of Pennsylvania. It is electronic, digital,
and programmable -- features that are still essential in modern computers.
***** The
world's largest otical telescope is installed. A telescope with a 200-inch
mirror begins operations on Palomar Mountain in Califor
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1949:
X-ray analysis yields the structure of penicillin.
The British X-ray crystallographer
Dorothy Crowfoot Hodgkin determines the molecular structure of penicillin, one
of the first antibiotics. Later she finds the structure of the complex compound
Vitamin B12 which prevents anemia.
***** The
magnetic core computer memory is invented. The American engineer Jay Forrester,
working for the U.S. Navy, conceives of using small rings that can be magnetized
north or south to represent binary "1" or "0." His high-speed three-dimensional
ferrite core memory becomes a landmark in computer design.
***** The atomic nucleus is modeled.
The German-American physicist Maria Goeppert Mayer, & Hans Jensen in Germany,
describe the atomic nucleus as made of spherical shells of neutrons and protons.
This xplains the special stability of certain nuclei.
***** Murphy's Law is discovered.
After a technician installs acceleration sensors backwards on a rocket sled that
will carry U. S. Army Major John Stapp, Stapp & Captain Aloysius Murphy announce
Murphy's Law: "If anything can go wrong, it will."
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1949 - 1957:
Neutron scattering reveals the structure and dynamics and materials.
The technique of neutron scattering,
developed in the early 1950's by the American Clifford T. Shull and the Canadian
Bertram Brockhouse, provides information on the atomic structure of solids and
liquids, atomic vibrations in crystals, and magnetism.
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- Compiled by D. Brewer - April 2000