Important historic dates in science

April 30: Electron
In 1897, at the Royal Institution Friday Evening Discourse, Joseph John Thomson (1856-1940) first announced the existence of electrons (as they are now named). Thomson told his audience that earlier in the year, he had made a surprising discovery. He had found a particle of matter a thousand times smaller than the atom. He called it a corpuscle, meaning "small body." Although Thomson was director of the Cavendish Laboratory at the University of Cambridge, and one of the most respected scientists in Great Britain, the scientists present found the news hard to believe. They thought the atom was the smallest and indivisible part of matter that could exist. Nevertheless, the electron was the first elementary particle to be discovered.

April 29: X-ray research in humans
In 1998, it was revealed in Oslo that in experiments conducted for decades until 1994, Norwegian and American researchers used mentally ill or retarded Norwegians in tests of the biological and genetic effects of X-ray radiation on the body.

April 28: Wave mechanics
In 1926, the term "wave mechanics" was coined by nuclear physicist Erwin Schrödinger in a letter he sent to Einstein. The term was applied to the newly emerging branch of physics which interprets the behavior of subatomic particles according to a mathematical description in terms of a wave motion.

April 27: Maurice de Broglie
(Born April 27, 1875: Died July 14, 1960)
Maurice de Broglie was a French physicist who made many contributions to the study of X rays. While in the navy (1895-1908), he first distinguished himself by installing the first French shipboard wireless. From 1912, his chief interest was X-ray spectroscopy. His "method of the rotating crystal" was an application of Bragg's "focussing effect" to eliminate spurious spectral lines. De Broglie discovered the third L absorption edge (1916), which led to the exploration of "corpuscular spectra." During 1921-22, he worked with his brother Louis to refine Bohr's specification of the substructure of the various atomic shells. He also did pioneer work in nuclear physics and cosmic radiation.

April 26: Chernobyl nuclear plant explosion
In 1986, in Pripet, Russia, the Chernobyl nuclear plant exploded in the world's worst civil nuclear catastrophe which sent a cloud of radioactive dust over Europe. It was the result of an experiment went wrong, causing the fourth reactor to explode and melt down. Thirty-one people, mostly firemen, were killed immediately after the explosion, and several thousand more - those involved in the clean-up and children - have since died from radiation-related illnesses. Ukraine says the health of millions of its people have been affected by the disaster.

April 25: Atomoic Reactor
In 1957, an experimental sodium reactor (SRE) began operation producing about 6,000 kilowatts of electricity. It was located about 30 miles northwest of Los Angeles, in the Santa Susana Mountains, California. It was built for the Atomic Energy Commission by Atomics International, a division of North American Aviation., Inc.

April 24: Hendrik Anthony Kramers
(Born December 17, 1894: Died April 24, 1952)
Dutch physicist who, with Ralph de Laer Kronig, derived important equations relating the absorption to the dispersion of light. He also predicted (1924) the existence of the Raman effect, an inelastic scattering of light. Kramer's work covers almost the entire field of theoretical physics. He published papers dealing with mathematical formalism of quantum mechanics, and others on paramagnetism, magneto-optical rotation, ferro-magnetism, kinetic theory of gases, relativistic formalisms in particle theory, and on theory of radiation. His work shows outstanding mathematical skill and careful analysis of physical principles.

April 23: Max von Laue
(Born October 9, 1879: Died April 23, 1960)
German recipient of the Nobel Prize for Physics in 1914 for his discovery of the diffraction of X rays in crystals. This enabled scientists to study the structure of crystals and hence marked the origin of solid-state physics, an important field in the development of modern electronics.

April 22: Fritz Strassman
(Born February 22, 1902: Died April 22, 1980)
German physical chemist who, with Otto Hahn and Lise Mietner, discovered neutron-induced nuclear fission in uranium (1938) and thereby opened the field of atomic energy used both in the atomic bomb for war and in nuclear reactors to produce electricity. Strassmann's analytical chemistry techniques showed up the lighter elements produced from neutron bombardment, which were the result of the splitting of the uranium atom into two lighter atoms. Earlier in his career, Strassmann codeveloped the rubidium-strontium technique of radio-dating geological samples.

April 21: Sir Edward Appleton
(Born September 6, 1892: Died April 21, 1965)
Sir Edward (Victor) Appleton, was an English physicist, born in Bradford, who won the Nobel Prize for Physics in 1947 for his discovery of the so-called Appleton layer of the ionosphere, which is a dependable reflector of radio waves and as such is useful in communication. Other ionospheric layers reflect radio waves sporadically, depending upon temperature and time of day.

April 20: Radium
In 1902, Marie and Pierre Curie isolated one gram of radium, the first sample of the radioactive element. They had refined it from eight tons of pitchblend ore.

April 19: Albert Wallace Hull
(Born April 19, 1880: Died January 22, 1966)
American physicist who independently discovered the powder method of X-ray analysis of crystals (1917), which permits the study of crystalline materials in a finely divided microcrystalline, or powder, state. His first work was on electron tubes, X-ray crystallography, and (during WW II) piezoelectricity. In the 1920's, he studied noise measurements in diodes and triodes. In the 1930's, he also took interest in metallurgy and glass science. His best-known work was done after the war, especially his classic paper on the effect of a uniform magnetic field on the motion of electrons between coaxial cylinders. He also invented the magnetron (1921) and the thyratron (1927), and other electron tubes with wide application as components in electronic circuits.

April 18: Maurice Goldhaber
Born April 18, 1911
U.S. physicist whose contributions to nuclear physics include the discovery that the nucleus of the deuterium atom consists of a proton and a neutron.

April 17: Harriet Brooks
(Born January 1, 1876: Died April 17, 1933)
Canadian nuclear physicist who was probably the first to observe the recoil of the atomic nucleus during radioactive decay as nuclear particles are emitted. She was well known in the years 1901-5 for her original contributions to the then youthful science of radioactivity. With Rutherford, she determined the rate of diffusion of the radium emanation (radon) into air and other gases, significant for they showed that the radium emanation diffused like a gas of heavy molecular weight - estimated to be at least 100. Rutherford credited her identification of radon as a vital piece of work that led him to propose the theory of the transmutation of one element into another. She died at the age of 56, from leukemia or a similar radiation-induced disease.

April 16: John Hadley
(Born April 16, 1682: Died February 14, 1744)
British mathematician and inventor who improved the reflecting telescope, producing the first such instrument of sufficient accuracy and power to be useful in astronomy.

April 15: Jean-Charles-Galinard de Marignac
(Born April 24, 1817: Died April 15, 1894)
Swiss chemist whose life work consisted of making many precise determinations of atomic weights suggested the possibility of isotopes and the packing fraction of nuclei. He began a study of the rare-earth elements in 1840, when barely 23 years old. In 1878, he heated until it decomposed some erbium nitrate obtained from gadolinite. Extracting the product with water he obtained two oxides: a red one he named erbia and a colourless one he named ytterbia. Thus he discovered ytterbium, and later was a codiscover of gadolinium (1880). By separating tantalic and columbic acids, he also proved that tantalum and colubium (niobium) were not identical.

April 14: Christiaan Huygens
(Born April 14, 1629: Died July 8, 1695)
Dutch mathematician, astronomer, and physicist, who founded the wave theory of light, and made original contributions to the science of dynamics-the study of the action of forces on bodies. Using a lens he ground for himself, Huygens detected in 1655, the first moon of Saturn. In 1656 he patented the first pendulum clock, which he developed to meet the need for an exact measure of time while observing the heavens. Huygens studied the relation of the length of a pendulum to its period of oscillation (1673). This lead him to formulate theories on the centrifugal force in circular motion which would influence Sir Issac Newton in formulating his Law of Gravity.

April 13: Stanislaw M. Ulam
(Born April 13, 1909: Died May 13, 1984)
Polish-American mathematician who played a major role in the development of the hydrogen bomb at Los Alamos. He solved the problem of how to initiate fusion in the hydrogen bomb by suggesting that compression was essential to explosion and that shock waves from a fission bomb could produce the compression needed. He further suggested that careful design could focus mechanical shock waves in such a way that they would promote rapid burning of the fusion fuel. Ulam, with J.C. Everett, also proposed the "Orion" plan for nuclear propulsion of space vehicles.

April 12: Igor Yevgenyevich Tamm
(Born July 8, 1895: Died April 12, 1971)
Soviet physicist who shared the 1958 Nobel Prize for Physics with Pavel A. Cherenkov and Ilya M. Frank for his efforts in explaining Cherenkov radiation. Tamm was an outstanding theoretical physicist, after early researches in crystallo-optics, he evolved a method for interpreting the interaction of nuclear particles. Together with I. M. Frank, he developed the theoretical interpretation of the radiation of electrons moving through matter faster than the speed of light (the Cerenkov effect), and the theory of showers in cosmic rays. He has also contributed towards methods for the control of thermonuclear reactions.

April 11: Macedonio Melloni
(Born April 11, 1798: Died August 11, 1854)
Italian physicist who was the first to extensively research of infrared radiation. After Herschel's earlier discovery of infrared radiation a generation before, suitable tools were lacking until the invention of a thermopile in 1830. That instrument was a series of strips of two different metals that produced electric current when one end was heated. Melloni improved the thermopile and used it to detect infrared radiation. In 1846, from an observation point high on Mount Vesuvius, he measured the slight heating effect of moonlight. He showed also that rock salt, being transparent to infrared, made suitable lenses and prisms to demonstrate the reflection, refractioin, polarization and interference of infrared in the same manner as visible light.

April 10: Giovanni Battista Amici
(Born March 25, 1786: Died April 10, 1863)
Astronomer and optician who made important improvements in the mirrors of reflecting telescopes and also developed prisms for use in refracting spectroscopes (instruments used to separate light into its spectral components).

April 9: William Prout
(Born January 15, 1785: Died April 9, 1850)
English chemist best known for formulating Prout's hypothesis (1815) which states that the atomic weights of all elements are exact multiples of the atomic weight of hydrogen. At that time the atomic weight of hydrogen was taken to be 1.0, the hypothesis implied that all atomic weights would be whole numbers. In 1920, Rutherford named the proton after Prout.

April 8: Harold Delos Babcock
(Born January 24, 1882: Died April 8, 1968)
American astronomer who with his son, Horace, invented the solar magnetograph (1951), for detailed observation of the Sun's magnetic field. With their magnetograph the Babcocks measured the distribution of magnetic fields over the solar surface to unprecedented precision and discovered magnetically variable stars. In 1959 Harold Babcock announced that the Sun reverses its magnetic polarity periodically. Babcock's precise laboratory studies of atomic spectra allowed others to identify the first "forbidden" lines in the laboratory and to discover the rare isotopes of oxygen. With C.E. St. John he greatly improved the precision of the wavelengths of some 22,000 lines in the solar spectrum, referring them to newly-determined standards.

April 7: Atomic Electricity
In 1959, the first atomic generated electricity is produced at Los Alamos Scientific Laboratory, New Mexico. The experimental model used a "plasma thermocouple" in the reactor instead of a fullscale turbine, and produced merely enough electrical power for a light bulb.

April 6: Russian nuclear accident
In 1993, in Russia, a huge radioactive cloud was released from an explosion of a tank of radioactive waste at the secret military facility at Tomsk 7. Located in the Russian wilderness, 1700 miles east of Moscow, it was the worse nuclear accident, thought not the only one, since the incident at Chernobyl in Apr 1986. A week later, delegates at a meeting in Tokyo from the world's richest nations, agreed to give urgent help to Russia for problems with nuclear waste, obsolete nuclear missile warheads, and aging nuclear reactors.

April 5: Robert Oppenheimer
In 1963, the U.S. Atomic Energy Commission gave the Fermi Award to J. Robert Oppenheimer for research in nuclear energy. Oppenheimer was the chief scientist of the Manhattan Project during WWII that created the atomic bomb. Later, he opposed the more destructive hydrogen bomb development and his security clearance was revoked (1954). Nine years later, a wiser U.S. government awarded Oppenheimer the prestigious Fermi Award, "For contributions to theoretical physics as a teacher and originator of ideas, and for leadership of the Los Alamos Laboratory and the atomic energy program during critical years." The actual presentation of the medal and $50,000 was made 2 Dec 1963 by President Lyndon B. Johnson.

April 4: Sir William Crookes
(Born June 17, 1832: Died April 4, 1919)
British chemist and physicist noted for his discovery of the element thallium and for his cathode-ray studies, fundamental in the development of atomic physics.

April 3: Space nuclear power
In 1965, SNAP 10A, the first nuclear reactor in space, was launched from Vanden berg Air Force Base, Calif. It was activated by a signal from scientists on earth about four hours later, and generated 500 kilowatt-hours of power during its life, providing electrical power for a 1 kgf ion engine. While its ground version lasted 10,000 hours without problems, the orbiting reactor was shut down by an electrical failure in another of the satellite's systems after 45 days in operation. It is still orbiting the earth. SNAP stands for Systems for Nuclear Auxiliary Power. Although the Soviet Union has flown many nuclear reactors in space, the SNAP-10A is the only one flown by the United States.

April 2: Theodore William Richards
(Born January 31, 1868: Died April 2, 1928)
American chemist whose research on the atomic weights of approximately 60 elements indicated the existence of isotopes and earned him the 1914 Nobel Prize for Chemistry.

April 1: Dame Kathleen Lonsdale
(Born January 28, 1903: Died April 1, 1971)
British crystallographer who developed several X-ray techniques for the study of crystal structure. Her experimental determination of the structure of the benzene ring by x-ray diffraction, which showed that all the ring C-C bonds were of the same length and all the internal C-C-C bond angles were 120 degrees, had an enormous impact on organic chemistry. She was the first woman to be elected (1945) to the Royal Society of London.

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