Rutherford, Ernest

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Rutherford, Ernest, 1st Baron Rutherford of Nelson and Cambridge (1871-1937), British physicist, who became a Nobel laureate for his pioneering work in nuclear physics and for his theory of the structure of the atom.

Rutherford was born in Nelson, New Zealand, and educated at the University of New Zealand and the University of Cambridge. He was professor of physics at McGill University in Montréal, Québec, Canada, from 1898 to 1907 and at the University of Manchester in England during the following 12 years. After 1919 he was professor of experimental physics and director of the Cavendish Laboratory at the University of Cambridge and also held a professorship, after 1920, at the Royal Institution of Great Britain in London.

Rutherford was one of the first and most important researchers in nuclear physics. Soon after the discovery of radioactivity in 1896 by the French physicist Antoine Henri Becquerel, Rutherford identified the three main components of radiation and named them alpha, beta, and gamma rays. He also showed that alpha particles are helium nuclei. His study of radiation led to his formulation of a theory of atomic structure, which was the first to describe the atom as a dense nucleus about which electrons circulate in orbits.

In 1919 Rutherford conducted an important experiment in nuclear physics when he bombarded nitrogen gas with alpha particles and obtained atoms of an oxygen isotope and protons. This transmutation of nitrogen into oxygen was the first artificially induced nuclear reaction. It inspired the intensive research of later scientists on other nuclear transformations and on the nature and properties of radiation. Rutherford and the British physicist Frederick Soddy developed the explanation of radioactivity that scientists accept today. The rutherford, a unit of radioactivity, was named in his honor.

Galileo

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Galileo (1564-1642), Italian physicist and astronomer, who, with the German astronomer Johannes Kepler, initiated the scientific revolution that flowered in the work of the English physicist Sir Isaac Newton. Born Galileo Galilei, his main contributions were, in astronomy, the use of the telescope in observation and the discovery of sunspots, lunar mountains and valleys, the four largest satellites of Jupiter, and the phases of Venus. In physics, he discovered the laws of falling bodies and the motions of projectiles. In the history of culture, Galileo stands as a symbol of the battle against authority for freedom of inquiry.

Galileo was born near Pisa, on February 15, 1564. His father, Vincenzo Galilei, played an important role in the musical revolution from medieval polyphony to harmonic modulation. Just as Vincenzo saw that rigid theory stifled new forms in music, so his eldest son came to see Aristotelian physical theology as limiting scientific inquiry. Galileo was taught by monks at Vallombrosa and then entered the University of Pisa in 1581 to study medicine. He soon turned to philosophy and mathematics, leaving the university without a degree in 1585. For a time he tutored privately and wrote on hydrostatics and natural motions, but he did not publish. In 1589 he became professor of mathematics at Pisa, where he is reported to have shown his students the error of Aristotle’s belief that speed of fall is proportional to weight, by dropping two objects of different weight simultaneously from the Leaning Tower. His contract was not renewed in 1592, probably because he contradicted Aristotelian professors. The same year, he was appointed to the chair of mathematics at the University of Padua, where he remained until 1610.

At Padua, Galileo invented a calculating “compass” for the practical solution of mathematical problems. He turned from speculative physics to careful measurements, discovered the law of falling bodies and of the parabolic path of projectiles, studied the motions of pendulums, and investigated mechanics and the strength of materials. He showed little interest in astronomy, although beginning in 1595 he preferred the Copernican theory—that the earth revolves around the sun—to the Aristotelian and Ptolemaic assumption that planets circle a fixed earth. Only the Copernican model supported Galileo’s tide theory, which was based on motions of the earth. In 1609 he heard that a spyglass had been invented in Holland. In August of that year he presented a telescope, about as powerful as a modern field glass, to the doge of Venice. Its value for naval and maritime operations resulted in the doubling of his salary and his assurance of lifelong tenure as a professor.

Mendeleyev, Dmitry Ivanovich

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Mendeleyev, Dmitry Ivanovich (1834-1907), Russian chemist, best known for his development of the periodic law of the properties of the chemical elements. This law states that elements show a periodicity (regular pattern) of properties when they are arranged according to atomic weight.

Mendeleyev was born in Tobol’sk, Siberia. He studied chemistry at the University of Saint Petersburg, and in 1859 he was sent to study at the University of Heidelberg. There he met the Italian chemist Stanislao Cannizzaro, whose views on atomic weight (see Atom) influenced his thinking. Mendeleyev returned to Saint Petersburg and became professor of chemistry at the Technical Institute in 1863. He became professor of general chemistry at the University of Saint Petersburg in 1866. Mendeleyev was a renowned teacher, and, because no good textbook in chemistry was available, he wrote the two-volume Principles of Chemistry (1868-1870), which became a classic.

During the writing of this book, Mendeleyev tried to classify the elements according to their chemical properties. In 1869 he published his first version of what became known as the periodic table, in which he demonstrated the periodic law. In 1871 he published an improved version of the periodic table, in which he left gaps for elements that were not yet known. His chart and theories gained increased acceptance when three predicted elements—gallium, germanium, and scandium—were subsequently discovered.

Mendeleyev's investigations also included the study of the chemical theory of solution, the thermal expansion of liquids, and the nature of petroleum. In 1887 he undertook a solo balloon flight to study a solar eclipse.

In 1890 he resigned from the university as a consequence of his progressive political views and his advocacy of social reforms. In 1893 he became director of the Bureau of Weights and Measures in Saint Petersburg and held this position until his death.

Gay-Lussac, Joseph Louis

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Gay-Lussac, Joseph Louis (1778-1850), French chemist and physicist, known for his studies on the physical properties of gases. He was born in Saint Léonard and educated at the École Polytechnique and the École des Ponts et Chaussées in Paris. After holding several professorships he became professor of physics at the Sorbonne from 1808 to 1832.

In 1804 he made balloon ascensions to study magnetic forces and to observe the composition and temperature of the air at different altitudes. In 1809 he formulated a law of gases that is still associated with his name. Gay-Lussac's law of combining volumes states that the volumes of the gases involved in a chemical reaction (both reactants and products) are in the ratio of small whole numbers. In connection with these studies he investigated, with German naturalist Baron Alexander von Humboldt, the composition of water and found it forms when two parts of hydrogen and one of oxygen unite.

In 1809 Gay-Lussac worked on the preparation of potassium and boron and investigated the properties of chlorine and hydrocyanic acid. In the field of industrial chemistry, he developed improvements in various manufacturing and assaying processes. In 1831 he was elected to the Chamber of Deputies and in 1839 to the Senate.

Hofmann, August Wilhelm von

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Hofmann, August Wilhelm von (1818-1892), German chemist, born in Giessen, and educated at the University of Giessen. From 1845 to 1864 he was director of the Royal College of Chemistry in London. In 1865 he accepted a professorship in chemistry at the University of Berlin. He founded the German Chemical Society in 1868.

Hofmann was one of the great organic chemists of his time. He worked with coal-tar products, from which he isolated benzene and aniline, and which he used in the synthesis of artificial dyes that formed the basis for a new industry. He studied and clarified the chemistry of amines, and his method for converting amides to amines is now called the Hofmann reaction. He also discovered many organic chemicals, including allyl alcohol and formaldehyde.