Sir George Stokes, 1st Baronet

George Stokes was the youngest son of the Reverend Gabriel Stokes, rector of Skreen, County Sligo, Ireland, where he was born and brought up in an evangelical Protestant family. After attending schools in Skreen, Dublin, and Bristol, he matriculated in 1837 at Pembroke College, Cambridge, where four years later, on graduating as senior wrangler and first Smith's prizeman, he was elected to a fellowship. In accordance with the college statutes, he had to resign the fellowship when he married in 1857, but twelve years later, under new statutes, he was re-elected. He retained his place on the foundation until 1902, when on the day before his 83rd birthday, he was elected to the mastership. He did not hold this position for long, for he died at Cambridge on 1 February the following year, and was buried in the Mill Road cemetery.

Stokes was the oldest of the trio of natural Philosophers, James 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. Stokes's original work began about 1840, and from that date onwards the great extent of his output was only less remarkable than the brilliance of its quality. The Royal Society's catalogue of scientific papers gives the titles of over a hundred memoirs by him published down to 1883. Some of these are only brief notes, others are short controversial or corrective statements, but many are long and elaborate treatises.

His first published papers, which appeared in 1842 and 1843, were on the steady motion 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 1850 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 produced. These inquiries together put the science of fluid dynamics 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.

Perhaps his best-known researches are those which deal with the wave theory of light. His optical work began at an early period in his scientific career. His first papers on the aberration of light appeared in 1845 and 1846, and were followed in 1848 by one on the theory of certain bands seen in the spectrum.

Stokes was involved in several investigations into railway accidents, especially the Dee bridge disaster in May 1847, and he served as a member of the subsequent Royal Commission into the use of cast iron in railway structures. He contributed to the calculation of the forces exerted by moving engines on bridges. The bridge failed because a cast iron beam was used to support the loads of passing trains. Cast iron is brittle in tension or bending, and many other similar bridges had to be demolished or reinforced.

In 1849 he published a long paper on the dynamical theory of diffraction, in which he showed that the plane of polarisation must be perpendicular to the direction of propagation. Two years later he discussed the colours of thick plates.

In other departments of physics may be mentioned his paper on the conduction of heat in crystals (1851) and his inquiries in connection with Crookes radiometer; 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 x-rays, which he suggested might be transverse waves travelling as innumerable 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 (1849)—also demand notice, as do his mathematical memoirs on the critical values of sums of periodic series (1847) and on the numerical calculation of a class of definite integrals and infinite series (1850) and his discussion of a differential equation relating to the breaking of railway bridges (1849), research related to his evidence given to the Royal Commission on the Use of Iron in Railway structures after the Dee bridge disaster of 1847.

In the same year, 1852, there appeared the paper on the composition and resolution of streams of polarised light from different sources, and in 1853 an investigation of the metallic reflection exhibited by certain non-metallic substances. The research was to highlight the phenomenon of light polarisation. About 1860 he was engaged in an inquiry on the intensity of light reflected from, or transmitted through, a pile of plates; and in 1862 he prepared for the British Association a valuable report on double refraction, a phenomenon where certain crystals show different refractive indices along different axes. Perhaps the best known crystal is Iceland spar, transparent calcite crystals.

He married, on 4 July 1857 at St Patrick's Cathedral, Armagh, Mary Susanna Robinson, daughter of the Rev Thomas Romney Robinson. They had five children: Arthur Romney, who inherited the baronetcy; Susanna Elizabeth, who died in infancy; Isabella Lucy (Mrs Laurence Humphry) who contributed the personal memoir of her father in "Memoir and Scientific Correspondence of the Late George Gabriel Stokes, Bart"; Dr william George Gabriel, physician, a troubled man who committed suicide aged 30 whilst temporarily insane; and Dora Susanna, who died in infancy.

The chemical identification of organic bodies by their optical properties was treated in 1864; and later, in conjunction with the Rev. william Vernon Harcourt, he investigated the relation between the chemical composition 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 microscope objectives.

In his presidential address to the British Association in 1871, Lord Kelvin stated his belief that the application of the prismatic analysis of light to solar and stellar chemistry had never been suggested directly or indirectly by anyone else when Stokes taught it to him at Cambridge University some time prior to the summer of 1852, and he set forth the conclusions, theoretical and practical, which he learnt from Stokes at that time, and which he afterwards gave regularly in his public lectures at Glasgow.

He appeared as an expert witness at the Tay Bridge disaster, where he gave evidence about the effects of wind loads on the bridge. The centre section of the bridge (known as the High Girders) was completely destroyed during a storm on 28 December 1879, while an express train was in the section, and everyone aboard died (more than 75 victims). The Board of Inquiry listened to many expert witnesses, and concluded that the bridge was "badly designed, badly built and badly maintained".

Stokes's mathematical and physical papers (see external links) were published in a collected form in five volumes; the first three (Cambridge, 1880, 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 held conservative religious values and beliefs. In 1886, he became President of the Victoria Institute, which had been founded to defend evangelical Christian principles against challenges from the new sciences, especially the Darwinian theory of biological evolution. He gave the 1891 Gifford lecture on natural theology. He was also the vice-president of the British and Foreign Bible Society and was actively involved in doctrinal debates concerning missionary work.

In scope, his work covered a wide range of physical inquiry but, as Marie Alfred Cornu remarked in his Rede lecture of 1899, the greater part of it was concerned with waves and the transformations imposed on them during their passage through various media.

These statements, containing as they do the physical basis on which spectroscopy rests, and the way in which it is applicable to the identification of substances existing in the sun and stars, make it appear that Stokes anticipated Kirchhoff by at least seven or eight years. Stokes, however, in a letter published some years after the delivery of this address, stated that he had failed to take one essential step in the argument—not perceiving that emission of light of definite wavelength not merely permitted, but necessitated, absorption of light of the same wavelength. He modestly disclaimed "any part of Kirchhoff's admirable discovery," adding that he felt some of his friends had been over-zealous in his cause. It must be said, however, that English men of science have not accepted this disclaimer in all its fullness, and still attribute to Stokes the credit of having first enunciated the fundamental principles of spectroscopy.