Stokes GG
FULL NAME: Stokes, Sir George Gabriel
DATE OF BIRTH: 13 August 1819
PLACE OF BIRTH: County Sligo, Ireland
DATE OF DEATH: 1 February 1903
PLACE OF DEATH: Cambridge, England
DISCIPLINE: Natural science
FIELD: Mathematical physics, mathematics
ASSESSMENT: A fixture at Cambridge for six decades, Stokes ranks with Kelvin, Maxwell, and Rayleigh in the history of 19th-century British physics
LANGUAGE/S: English
EDUCATION: Bristol College, 1835-1837; University of Cambridge, 1837-1841 (senior wrangler, 1841).
ACHIEVEMENTS: Formulated Stokes' law and the Navier-Stokes equations in hydrodynamics; explained stellar aberration, diffraction, double refraction and other optical phenomena in the context of the so-called luminiferous ether; noted the Stokes shift and other properties of fluorescence; proposed Stokes' theorem in vector calculus
MAJOR WORK/S: 'Mathematical and Physical Papers', 5 volumes, 1880-1905
LIFE AND TIMES:
At the age of sixteen Stokes entered Bristol College to prepare for university. The curriculum at Bristol stressed the importance of mathematics, and Stokes studied under Francis Newman, brother of Cardinal Newman. In 1837 Stokes enrolled at Pembroke College, University of Cambridge, where he was tutored by William Hopkins in preparation for the Cambridge mathematical tripos, the final examination in mathematics and mathematical physics. Graduating in 1841 (and scoring highest on the tripos), Stokes remained at Cambridge as a fellow of Pembroke College.
In 1849 he was appointed the Lucasian professor of mathematics, a prestigious Cambridge chair once held by Isaac Newton. Stokes occupied this position until his death, although he supplemented his income in the 1850s by teaching at the Government School of Mines in London. In 1851 he was elected to the Royal Society FRS* and later received two of the society's highest honors: the Rumford medal in 1852 and the Copley medal in 1893. Stokes served as President of the Royal Society from 1885 to 1890. He also represented the University of Cambridge in Parliament from 1887 to 1891. Stokes was knighted in 1889.
In the first three decades of the 19th century, French physicists led the way in applying new mathematical techniques to the study of complex physical phenomena. Foremost among these achievements were Laplace's calculations of the perturbations in planetary motions, Poisson's treatment of electrostatics and magnetism, Ampere's work in electrodynamics, Fourier's analysis of heat conduction, and Fresnel's wave (or undulatory) theory of light. The French advances in mathematical physics were soon known in the British universities. The wave theory of light, for instance, was well established in the Cambridge curriculum by the time Stokes arrived. The wave theory postulated the existence of 'luminiferous ether' as the medium through which light propagated, and it provided precise predictions of diffraction and other optical phenomena.
Stokes would spend much of his career investigating the subtleties of the ether and its optical consequences. However, his first research after graduating concerned hydrodynamics. Stokes' initial work on hydrodynamics in the early 1840s was influenced by French mathematical physics in two ways. First, his treatment of simple fluid flow was based on an analogy with heat flow. As Stokes would later write to his lifelong friend, William Thomson, the future Kelvin*: 'What an intimate relation there is between the mathematical considerations which are applicable to heat, fluid motion, and attraction!'
Second, when Stokes introduced the internal friction of fluids (i.e., viscosity) as a complicating factor, he built on the previous work by Poisson* and Navier. Unlike these French physicists, however, Stokes did not base his mathematical derivations on a specific molecular theory. Instead, he treated internal friction as an 'emergent' property of fluid flow, for practical purposes independent of the underlying molecular reality. His analogy was 'an Indian rubber bag, in tension, filled with smooth marbles', in which the individual marbles and their interactions were hidden from view. In this model the only observable phenomenon of consequence would be the distortion of the bag, representing fluid flow.
The general equations of fluid flow are now known as the Navier-Stokes equations, in recognition of the contributions of both men. Stokes' law describes the limiting case of a solid sphere settling in a viscous fluid.
Stokes went a step further, however, by denying a sharp distinction between viscous fluids and elastic solids. Appealing to the so-called law of continuity, he adapted the equations of fluid flow to elastic deformation and introduced two independent constants (now known as the moduli of compression and rigidity) superseding Poisson's treatment of elasticity.
By the late 1840s Stokes had extended his mathematical analysis to the luminiferous ether, concluding that it must behave elastically for disturbances of short duration (to transmit light waves) but viscously for disturbances of longer duration (to permit passage of the earth). With this model of jelly-like ether in hand, he challenged Fresnel*'s prediction of an 'ether wind' at the surface of the moving earth. Instead, Stokes envisioned a 'halo' of ether being dragged along with the earth, thus eliminating the sharp velocity contrast at the surface. This distinction was critical for explaining stellar aberration, the apparent shift in the positions of stars due to the motion of earth-bound observers.
The Michelson-Morley experiment of 1881, perhaps the most famous negative experiment in the history of science, was initially conceived as a crucial test for the Fresnel and Stokes models of ether-matter interaction. Stokes also applied his analysis to sound and ocean waves, but he is known more for his studies of optical phenomena: diffraction, double refraction, and fluorescence.
In the 1860s Stokes turned his attention away from research to concentrate on administration and teaching at Cambridge, along with his duties as secretary and president of the Royal Society. His students at Cambridge included a long list of future luminaries: Maxwell*, JW Strutt, (known as Lord Rayleigh*), and Pearson*, among others. In 1871 Stokes urged Maxwell to accept the newly created Cavendish chair of experimental physics at Cambridge (even though Stokes would never fully embrace Maxwell's electromagnetic theory of light).
Stokes maintained a large correspondence with Lord Kelvin, Lord Rayleigh, Challis*, Crookes*, Sorby*, and dozens of others. Stokes and Kelvin, for example, used each other as sounding boards for decades. On the other hand, Stokes frequently clashed with Challis over hydrodynamics, theories of sound, the nature of luminiferous ether, and stellar aberration. Stokes used correspondence to encourage others, such as Crookes (in the study of cathode rays) and Sorby (in the applications of spectrum analysis). In view of his wide-ranging influence, Kelvin eulogized Stokes: 'The world is poorer through his death, and we who knew him feel the sorrow of bereavement.'
EXTRA CONNECTIONS:
Stokes met Hertz*, the discoverer of radio waves.
He was a friend of Herapath*
ONELINER: GG Stokes, major 19th-century hydrodynamicist
BIBLIOGRAPHY:
Dictionary of Scientific Biography.
Kelvin, [Lord], ‘The Scientific Work of Sir George Stokes’, Nature 67 (1903): 337-338.
R[ayleigh, Lord], 'Sir George Gabriel Stokes, Bart. 1819-1903', Proceedings of the Royal Society of London 75 (1905): 199-216.
Wilson, D.B., Kelvin and Stokes: A Comparative Study in Victorian Physics, Adam Hilger, Bristol, 1987.
PARENTS: Father, Gabriel Stokes; mother, Elizabeth Haughton
SPOUSE: Mary Susanna Robinson
SIBLINGS: Three brothers, two sisters
CHILDREN: Not known