STOKES, SIR GEORGE GABRIEL, BART. ‘ ( _19-19o3), British mathematician and physicist, son of the rector of Skreen, Co. Sligo, Ireland, was born on Aug. 13, 1819. In 1837 he entered Pembroke college, Cambridge, where he became a fellow in 1841. He lost his fellowship when he married in 1857, but twelve years later, under new statutes, he was re-elected. In 1902, he was elected Master. As Lucasian professor, secretary and presi dent of the Royal Society, he held three offices, which had only once before been held by one man, Sir Isaac Newton. He was member of parliament for the University from 1887 to 1892, was created baronet in 1889 and died on Feb. 1, 1903.
Stokes was the oldest of the trio of physicists, Clerk Maxwell and Lord Kelvin being the other two, who especially contributed to the fame of the Cambridge school of mathematical physics in the middle of the 19th century. The Royal Society's catalogue of scientific papers gives the titles of over a hundred memoirs by him published down to 1883. The greater part of his work was concerned with waves and the transformations imposed on them during their passage through various media. His first published papers, which appeared in 1842 and 1843, were on the steady mo tion of incompressible fluids and some cases of fluid motion; these were followed in 1845 by one on the friction of fluids in motion and the equilibrium and motion of elastic solids, and in 185o by another on the effects of the internal friction of fluids on the motion of pendulums. To the theory of sound he made several contributions, including a discussion of the effect of wind on the intensity of sound and an explanation of how the intensity is influenced by the nature of the gas in which the sound is pro duced. These inquiries together put the science of hydrodynamics on a new footing, and provided a key not only to the explanation of many natural phenomena, such as the suspension of clouds in air, and the subsidence of ripples and waves in water, but also to the solution of practical problems, such as the flow of water in rivers and channels, and the skin resistance of ships.
His best-known researches are perhaps those on the undulatory theory of light. His first papers on the aberration of light ap peared in 1845 and 1846, and were followed in 1848 by one on the theory of certain bands seen in the spectrum. In 1849 his paper on the dynamical theory of diffraction showed that the plane of polarization must be perpendicular to the direction of vibration. Two years later he discussed the colours of thick plates; and in 1852, in his famous paper on the change of re frangibility of light, he described the phenomenon of fluorescence, as exhibited by fluorspar and uranium glass, materials which he viewed as having the power to convert invisible ultra-violet rays into rays of wave lengths which are visible. A mechanical model, illustrating the dynamical principle of Stokes's explanation was shown in 1883, during a lecture at the Royal Institution, by Lord Kelvin, who said he had heard an account of it from Stokes many years before, and had repeatedly but vainly begged him to publish it. In the same year, 1852, there appeared the paper on the composition and resolution of streams of polarized light from different sources, and in 1853 an investigation of the metallic reflection exhibited by certain non-metallic substances. About
186o he was engaged in an inquiry on the intensity of light re flected from, or transmitted through, a pile of plates; and in 1862 he prepared for the British Association a valuable report on double refraction, which marks a period in the history of the subject in England. A paper on the long spectrum of the electric light bears the same date, and was followed by an inquiry into the absorption spectrum of blood.
The discrimination of organic bodies by their optical properties was treated in 1864; and later, in conjunction with the Rev. W. Vernon Harcourt, he investigated the relation between the chem ical constitution and the optical properties of various glasses, with reference to the conditions of transparency and the improvement of achromatic telescopes. A still later paper connected with the construction of optical instruments discussed the theoretical limits to the aperture of microscopical objectives. In other departments of physics may be mentioned his paper on the conduction of heal in crystals 0850 and his inquiries in connection with the radio meter; his explanation of the light border frequently noticed in photographs just outside the outline of a dark body seen against the sky (1883) ; and, still later, his theory of the Röntgen rays, which he suggested might be transverse waves travelling as innu merable solitary waves, not in regular trains. Two long papers published in 1849--one on attractions and Clairaut's theorem, and the other on the variation of gravity at the surface of the earth— also demand notice, as do his mathematical memoirs on the crit ical values of the sums of periodic series (1847) and on the nu merical calculation of a class of definite integrals and infinite series (1850) and his valuable discussion of a differential equation relating to the strains, stresses and other factors involved in the breaking of railway bridges Many of his discoveries were only touched upon in lectures. An instance is his work in the theory of spectrum analysis. Some of Stokes's friends and pupils claimed that he had anticipated Kirchhoff but Stokes maintained that he had failed to see an essential step in the argument and disclaimed priority. As Luca sian professor, Stokes announced that he wished to help any member of the university in his mathematical studies, and pupils were glad to consult him, even after they had become colleagues.
During the thirty years of his secretaryship to the Royal Society he advanced the cause of mathematical and physical science, not only by his own investigations, but by suggesting problems for inquiry and inciting men to attack them.
He received the Rumford medal in 1852 and in 1893, the Copley medal. His numerous other honours included the Prussian Ordre pour le Merite. In 1869 he presided over the Exeter meet ing of the British Association.
Sir George Stokes's mathematical and physical papers were pub lished in a collected form in five volumes; the first three (Cambridge, 188o, 1883, and 1901) under his own editorship, and the two last (Cambridge, 1904 and 1905) under that of Sir Joseph Larmor, who also selected and arranged the Memoir and Scientific Correspondence of Stokes published at Cambridge in 1907. Stokes was the author of Light (1884-87) and Natural Theology (1891).