Dictionary of National Biography, 1912 supplement/Stokes, George Gabriel

STOKES, Sir GEORGE GABRIEL, first baronet (1819–1903), mathematician and physicist, born at Skreen, co. Sligo, 13 Aug. 1819, was youngest son of Gabriel Stokes, rector of Skreen, by his wife Elizabeth, daughter of John Haughton, rector of Kilrea, co. Derry. First educated at Dr. Wall's school in Dublin from 1831, he proceeded in 1835 to Bristol college under Dr. Jerrard, the mathematician, and entered Pembroke College, Cambridge, in 1837, becoming senior wrangler, first Smith's prizeman, and fellow of his college in 1841.

In his early Cambridge years he established a close scientific friendship with William Thomson (afterwards Lord Kelvin) [q. v. Suppl. II], which gathered force throughout their long lives. Both were impelled by the keenest interest in the advance of scientific discovery, but their endowments were in some respects complementary. Stokes remained a student throughout has life, closely pondering over mathematical questions and the causes of natural phenomena, perhaps over-cautious in drawing conclusions and in publication of his work, remarkable for his silence and abstraction even in crowded assemblies, but an excellent man of affairs, inspiring universal confidence for directness and impartiality in such administration as came to him. Thomson, during all his career, took Stokes as his mentor in the problems of pure science which he could not find leisure to probe fully for himself; and, though their opinions sometimes clashed, yet in the main no authority was with him more decisive or more venerated than that of his friend. In 1845, at the end of his undergraduate course, Thomson took over the editorship of the 'Cambridge Mathematical Journal' from Robert Leslie Ellis [q. v.], and for the following ten years his own contributions and those which he obtained from Stokes made that journal a classic. In 1849 Stokes was appointed Lucasian professor of mathematics at Cambridge, and he held the post till his death.

In his early years of residence as a graduate Stokes promoted most conspicuously the development of advanced mathematical knowledge at Cambridge. His own earliest work was mainly on the science of the motion of fluids, which he found in the preliminary stage in which it had been left by Lagrange, notwithstanding some sporadic work done by George Green [q. v.], then resident at Cambridge; in a few years he developed it into an ordered mathematical and experimental theory. To this end, in addition to a very complete discussion of the phenomena of waves on water, he created, in two great memoirs of dates 1845 and 1850, the modern theory of the motion of viscous fluids, a subject in which some beginnings had been made by Navier. In the later of these memoirs the practical applications, especially to the important subject of the correction of standard pendulum observations for aerial friction, led him into refined extensions of mathematical procedure, necessary for the discussion of fluid motion around spheres and cylinders; these, though now included under wider developments in pure analysis, have remained models for physical discussion, and have been since extensively applied to acoustics and other branches of physical science.

In the science of optics he had already in 1849 published two memoirs on Newton's coloured rings, treated always with dynamical implications; one appeared in 1851 establishing on a firm physical basis the explanation of Newton's colours of thick plates; and he had elucidated the principles of interference and polarisation in many directions. In 1849 a new path was opened in the great memoir on 'The Dynamical Theory of Diffraction,' which deals with the general problem of propagation of disturbances spreading from vibrating centres through an elastic æther, and in which mathematical expressions were developed wide enough to include the Hertzian theory of electrical vibrations and other more recent extensions of the theory of radiation. A side problem was the experimental investigation of the displacement of the plane of polarisation of light by diffraction, in order, by comparison with the theory, to ascertain the relation of the plane of its vibration to that of its polarisation. Such a determination, though fundamental for a purely dynamical view, is not essential to the construction of an adequate formal account of the phenomena of radiation, and the workers in the modern electric theory have been content in the main to stop short of it.

The calculations relating to corrections for pendulums had led him into pure analysis connected with Bessel functions and other harmonic expansions; in various subsequent memoirs he established and justified the semi-convergent series necessary to their arithmetical use over the whole range of the argument, thus making practical advances that were assimilated only in later years into general analysis. Likewise the discrepancies which he encountered in practical applications of Fourier's theory led him as early as 1847 to a reasoned exposition of doctrines, now fundamental, relating to complete and limited convergence in infinite series. Here and elsewhere, however, his work developed rather along the path of advance of physical science than on the lines of formal pure analysis; and the recognition of its mathematical completeness was in consequence delayed.

In 1859 great interest was excited by the announcement of the discovery and development of spectrum analysis by Kirchhoff and Bunsen, and its promised revelations regarding the sun and stars by means of the Fraunhofer lines, an advance which was introduced to English readers by Stokes's translation of their earlier papers. It was soon claimed by William Thomson (Lord Kelvin) that he had been familiar with the scientific possibilities in this direction since before 1852, having been taught by Stokes the dynamical connection between the opacity of a substance to special radiation and its own power of emitting radiation of the same type. The theoretical insight thus displayed, on the basis of the interpretation of isolated observations, was, of course, no detraction from the merit of the practical establishment of the great modern science of spectrum analysis by the former workers: yet the feeling in some circles, that such a claim for Stokes was not quite warranted, was only set at rest by the posthumous discovery, among his papers, of a detailed correspondence with Lord Kelvin on this subject, mainly of date 1854, which is now printed in vol. iv. of his 'Collected Papers' (cf. pp. 126–36 and 367–76).

But in fact it was hardly necessary to wait for this evidence: for the same general considerations had already entered essentially into Stokes's discussion of one of his most refined and significant experimental discoveries. Shortly after he entered on the study of optics as a subject for his activity in the Lucasian chair at Cambridge, his attention was attracted to the blue shimmer exhibited by quinine in strong illumination, which had been investigated by Sir John Herschel [q. v.] in 1845. He soon found (1852) that the phenomenon was at variance with the Newtonian principle of the definite prismatic analysis of light, as the blue colour appeared when it was not a constituent of the exciting radiation. He discovered that this emission of light, called by him fluorescence from its occurrence in fluor-spar, was provoked mainly by rays beyond the violet end of the visible spectrum; and as a bye-product he thus discovered and explored the great range of the invisible ultra-violet spectrum, having found that quartz prisms could be used for its examination, though glass was opaque. Discussion of the exceptional nature of this illumination, created by immersion of the substance in radiation of a different kind, necessarily led him into close scrutiny of the dynamics of ordinary absorption and radiation; and the idea of a medium absorbing specially the same vibrations which it could itself spontaneously emit was thus fully before him (cf. § 237 of the memoir).

Another mathematical memoir (1878), suggested by the feeble communication of sound from a bell to hydrogen gas, elucidated the circumstances which regulate the closeness of the grip that a vibrating body gets with the atmosphere; and its ideas have also wider application, to the facility for emission and absorption of radiations of all kinds from and into the vibrating bodies which are their sources. In two memoirs of date 1849 (Papers, ii. 104–121), on the variation of gravity over the earth's surface, he became virtually the founder of the modern and more precise science of geodesy. The fundamental proposition was there established, as the foundation of the subject, that the form of the ocean level determines by itself the distribution of the earth's attraction everywhere outside it, without requiring any reference to the internal constitution of the earth, which in this regard must remain entirely unknown.

His earlier scientific work, with that of Helmholtz and Lord Kelvin, may be said to mark the breaking away of physical science from the à priori method depending on laws of attraction, which was inherited from the astronomers ; for this there was substituted a combination of the powerful analysis by partial differentials, already cultivated by Laplace and Fourier, with close attention to the improvement of physical ideas and modes of expression of natural phenomena. The way was thereby prepared for Clerk Maxwell's interpretation of Faraday, and for the modern wide expansion of ideas.

The copious early output of Stokes's own original investigation slackened towards middle life. In 1851 he had been elected F.R.S., and next year was awarded the Rumford medal for his discovery of the nature of fluorescence. In 1854 he became secretary of the Royal Society, and the thirty-one years of his tenure of this office (1854-5) were devoted largely to the advancement of science in England and the improvement of the publications of the Royal Society. There were few of the memoirs on physical science that passed to press through his hands that did not include valuable extensions and improvements arising from his suggestions. When the Indian geodetic survey was established, he was for many years its informal but laborious scientific adviser and guide. The observatory for solar physics, which was founded in 1878, was indebted to him in a similar manner. His scientific initiative as a member of the meteorological council, who managed from J1871 the British weather service, was a dominant feature of their activity. During these years the imperfect endowment of his chair at Cambridge made it necessary for him to supplement his income from other sources : thus he was for some time lecturer at the School of Mines, and a secretary of the Cambridge University Commission of 1877-81. He had vacated his fellowship at Pembroke on his marriage in 1857, but was re-elected under a new statute in 1869.

In 1883 Stokes was appointed, under a new scheme, Burnett lecturer at Aberdeen, and delivered three courses of lectures on 'Light' (1883-5), which were published in three small volumes (1884-7). In 1891 he became Gifford lecturer at Edinburgh, and delivered other three courses on the same general subject (1891-3). The theme in all these courses was treated from the point of view of natural theology, as the terms of the foundations required. His interests as a churchman and theologian were strong through life, and found occasional expression in print. He often took part in the proceedings of the Victoria Institute in London, which was founded for inquiry into Christian evidences. Stokes received in his later years nearly all the honours that are open to men of science. He was president of the British Association at the Exeter meeting in 1869. In 1885 he succeeded Professor Huxley as president of the Royal Society, holding the office till 1890, when he was himself succeeded by his friend Lord Kelvin ; he remained on the council as vice-president two years longer, and on his retirement he was immediately awarded in 1893 the society's Copley medal. On the death of Beresford-Hope in 1887, he was elected without opposition, in the conservative interest, one of the members of parliament for Cambridge University, and he sat in the House of Commons till 1891. He was a royal commissioner for the reform of the University of London (1888-9). In 1889 he was created a baronet (6 July). In 1899 the jubilee of his tenure of the Lucasian chair was celebrated at Cambridge by a notable international assembly. Through the friendship of Hofmann, Hehnholtz, Comu, Becquerel, and other distinguished men, he became in his later years widely known abroad ; and the Prussian order pour le mérite and the foreign associateship of the Institute of France were conferred on him. At his jubilee celebration the Institute of France sent him the special Arago medal ; and he was one of the early recipients of the Hehnholtz medal from Berlin. He received honorary doctor's degrees from Edinburgh, Dublin, Glasgow, and Aberdeen, as well as from Oxford and Cambridge. In October 1902 his colleagues of Pembroke College, of which he had long been fellow and of late years president, elected him Master. He died at Cambridge on 1 Feb. 1903, and was buried there at the Mill Road cemetery.

Stokes married on 4 July 1857 Mary (d. 30 Dec. 1899), daughter of Thomas Romney Robinson, the astronomer [q. v.], and left issue two sons and one daughter. His elder son, Arthur Romney Stokes succeeded him as second baronet.

Stokes's writings have been collected into five volumes of 'Mathematical and Physical Papers' (Cambridge, 1880-1905) of which the first three were carefully edited by himself, and the other two were prepared posthumously by Sir Joseph Larmor, his successor in the Lucasian chair. Two volumes of his very important 'Scientific Correspondence' were published in 1907 under the same editorship, and include a biographical memoir (pp. 1–90) prepared mainly by his daughter, Mrs. Laurence Humphry.

There is a portrait by G. Lowes Dickinson in Pembroke College, and one by Sir Hubert von Herkomer at the Royal Society; marble busts by Hamo Thomycroft were presented to the Fitzwilliam Museum and to Pembroke College on the celebration of his jubilee as Lucasian professor in 1899, and a memorial medallion bust by the same sculptor is in Westminster Abbey.

[Mrs. Humphry's memoir mentioned above; notice by Lord Rayleigh in Proc. Royal Soc. 1903, and reprinted in Papers, vol. v. pp. ix-xxv; cf. also Silvanus Thompson's Life of Lord Kelvin, 1910.]

J. L.