1922 Encyclopædia Britannica/Moseley, Henry Gwyn Jeffreys

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MOSELEY, HENRY GWYN JEFFREYS (1887-1915), British physicist, was born Nov. 23 1887. He was educated at Eton, where he entered as a King's scholar, and at Trinity College, Oxford, from which he graduated in 1910 with honours in natural science. His earliest research work was undertaken in Rutherford's laboratory in Manchester, whither he went as lecturer in physics after leaving Oxford. He at once gave evidence of unusual ability both as an original thinker and skilful experimenter. After two years he resigned his lectureship in order to devote more time to research work, and was elected John Harling fellow. The researches with which his name is specially associated were those made shortly before his death. Rutherford had announced the nuclear theory of atomic structure which required each atom to consist of a minute positively charged nucleus about which negative electrons were distributed. It seems also that the charge would increase with the atomic weight of the element. It had been suggested, and Bohr had adopted this view, that the nuclear charge was equal to the atomic number, i.e. to the number of the element in a complete series of the elements arranged in ascending order, but hitherto no atomic property had been discovered which could be definitely represented by this number. Moseley, shortly after the discovery of the diffraction of X-rays by crystals, set to work to examine the X-ray spectrum of a number of elements each of which he made in turn the target of an X-ray tube. He found that his crystal-grating gave a spectrum of two lines for each element and that their frequency increased by definite steps as he passed from one element to the next; indeed, the frequency of vibration associated with each element was a simple function of a number which he found to be identical with the atomic number. It is now generally accepted that this number, experimentally determined by Moseley for a number of elements, defines the physical and chemical properties of the particular element. This number is probably to be identified with the electric charge upon the nucleus of the atom. From the regular progression of the lines in the X-ray spectra of different elements Moseley was able tc indicate the number of elements yet to be discovered, and he cleared up certain anomalies in the periodic tables of the elements. He laid the foundation of what will probably prove to be a new and more precise form of chemistry (see Chemistry, and Matter, Constitution of). Moseley was in Australia with the British Association in 1914 when the World War broke out; he returned to England, obtained a commission in the Royal Engineers, and was killed by a Turkish bullet on the Gallipoli peninsula on Aug. 10 1915. (W. G. D.)