George Gabriel Stokes
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George Gabriel Stokes |
Sir George Gabriel Stokes, 1st Baronet (
13 August 1819–
1 February 1903) was an
Irish mathematician and
physicist, who at
Cambridge made important contributions to
fluid dynamics (including the
Navier-Stokes equations),
optics, and mathematical physics (including
Stokes' theorem). He was secretary, then president of the
Royal Society.
George Stokes was the youngest son of the Reverend Gabriel Stokes,
rector of
Skreen,
County Sligo, 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 84th birthday, he was elected to the mastership. He did not enjoy this position for long, for he died at Cambridge on
February 1 in the following year.
In
1849, he was appointed to the
Lucasian professorship of mathematics in the university, and on
June 1,
1899 the jubilee of his appointment was celebrated at Cambridge in a brilliant ceremony, which was attended by numerous delegates from European and American universities. A commemorative gold medal was presented to him by the chancellor of the university, and marble busts of him by
Hamo Thornycroft were formally offered to Pembroke College and to the university by
Lord Kelvin. Sir George Stokes, who was made a baronet in
1889, further served his university by representing it in parliament from
1887 to
1892 as one of the two members for the
Cambridge University constituency. During a portion of this period (
1885–
1890) he was president of the
Royal Society, of which he had been one of the secretaries since
1854, and thus, being at the same time Lucasian professor, he united in himself three offices which had only once before been held by one man, Sir Isaac Newton, who, however, did not hold all three simultaneously.
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. His 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.
In content his work is distinguished by a certain definiteness and finality, and even of problems which, when he attacked them, were scarcely thought amenable to mathematical analysis, he has in many cases given solutions which once and for all settle the main principles. This fact must be ascribed to his extraordinary combination of mathematical power with experimental skill. From the time when in about
1840 he fitted up some simple physical apparatus in his rooms in Pembroke College, mathematics and experiment ever went hand in hand, aiding and checking each other. 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.
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
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 work on fluid motion and
viscosity led to his calculating the terminal velocity for a sphere falling in a viscous medium. This became known as
Stokes' law. Later the
CGS unit of viscosity was named a
Stokes after his work.
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. In
1849 he published a long paper on the dynamical theory of
diffraction, in which he showed that the plane of
polarization must be perpendicular to the direction of propagation. Two years later he discussed the colours of thick plates.
In
1852, in his famous paper on the change of
wavelength 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 radiation into radiation of longer wavelengths that are visible. The
Stokes shift, which describes this conversion, is named in Stokes' honor. A mechanical model, illustrating the dynamical principle of Stokes's explanation was shown. The offshoot of this,
Stokes line, is the basis of
Raman scattering. In
1883, during a lecture at the
Royal Institution, Lord Kelvin 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
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, 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 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 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
1840—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 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).
But large as is the tale of Stokes's published work, it by no means represents the whole of his services in the advancement of science. Many of his discoveries were not published, or at least were only touched upon in the course of his oral lectures. An excellent example is his work in the theory of
spectroscopy. In his presidential address to the British Association in
1871, Lord Kelvin (Sir William Thomson, as he was then) 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 in Cambridge 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. 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.
In another way, too, Stokes did much for the progress of mathematical physics. Soon after he was elected to the Lucasian chair he announced that he regarded it as part of his professional duties to help any member of the university in difficulties he might encounter in his mathematical studies, and the assistance rendered was so real that pupils were glad to consult him, even after they had become colleagues, on mathematical and physical problems in which they found themselves at a loss. Then during the thirty years he acted as secretary of the Royal Society he exercised an enormous if inconspicuous influence on the advancement of mathematical and physical science, not only directly by his own investigations, but indirectly by suggesting problems for inquiry and inciting men to attack them, and by his readiness to give encouragement and help.
*
Stokes' law, in
fluid dynamics*
Stokes' theorem, in
differential geometry *
Stokes line, in
Raman scattering*
Stokes relations, relating the phase of light reflected from a non-absorbing boundary
*
Stokes shift, in
fluorescence*
Navier-Stokes equations, in
fluid dynamics*
Stokes (unit), a unit of
viscosity*
Stokes parameters and
Stokes vector, used to quantify the polarisation of electromagnetic waves
*
Campbell-Stokes recorder, an instrument for recording sunshine improved by Stokes, and still widely used today
*
Stokes (lunar crater)*
Stokes (crater on Mars)In addition to the honours mentioned above:
*From the
Royal Society, of which he became a fellow in
1851, he received the
Rumford Medal in 1852 in recognition of his inquiries into the wavelength of light, and later, in
1893, the
Copley Medal.
*In
1869 he presided over the
Exeter meeting of the British Association.
*From
1883 to
1885 he was Burnett lecturer at
Aberdeen, his lectures on light, which were published in
1884–
1887, dealing with its nature, its use as a means of investigation, and its beneficial effects.
*In
1889 he was made a
baronet.
*In
1891, as
Gifford lecturer, he published a volume on Natural Theology.
*His academic distinctions included honorary degrees from many universities, together with membership of the
Prussian Order Pour le Mérite.
Sir George Stokes's mathematical and physical papers 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.
*Wilson, David B.,
Kelvin and Stokes A Comparative Study in Victorian Physics, (1987) ISBN 0-85274-526-5
*
Biography on Dublin University Web site
