Open main menu

Popular Science Monthly/Volume 7/October 1875/Sketch of Professor Stokes

 
PSM V07 D660 George Gabriel Stokes.jpg
George Gabriel Stokes
 

SKETCH OF PROFESSOR STOKES.

THE subject of this notice, George Gabriel Stokes, was born August 13, 1819, at Skreen, in the county of Sligo, Ireland, his father being rector of the parish. At an early age he was sent to a school at Dublin, conducted by the Rev. R. H. Wall, D.D. Here he remained for about three years, when he entered a college at Bristol, as a preparation for the university. After two years spent at Bristol, young Stokes, in 1837, entered Pembroke College, University of Cambridge, and four years later graduated Bachelor of Arts, at the same time winning the highest honors of the university—the Senior Wranglership and the First Smith's Prize. In the same year he was elected to a fellowship in his college. In 1849 he was appointed to the Lucasian chair of Mathematics in the university, and thus became the successor of Newton. Mr. Stokes enjoyed the emoluments of his fellowship until 1857, when he vacated that position by taking a wife. Later, by an amendment of the statutes of Pembroke, he was reinstated in his fellowship. In 1851 he was chosen Fellow of the Royal Society, and in the following year received the Rumford medal "in recognition of his services to the cause of science by the discovery of the change of the refrangibility of light." The "Philosophical Transactions" for 1852 gives an account of this discovery. In 1854 Mr. Stokes was elected one of the secretaries of the Royal Society. He was President of the British Association for the Advancement of Science at the Exeter meeting, 1869. In 1871 the University of Edinburgh conferred upon Prof. Stokes the degree of Doctor of Laws.

It requires merit of no common order to enable a man to attain the high honor of occupying the chair of Newton, at the early age of thirty. Mr. Stokes's election to the Lucasian professorship was a surprise to the undergraduates of Cambridge, who had expected to see the place filled by some man of European fame. But the wisdom of the choice was soon made manifest, and the students of Cambridge recognized in the new professor not only an exceptionally able and learned man, but also one whose whole heart and soul were devoted to the advancement of his pupils. How Prof. Stokes won the confidence and love of the students is told by Prof. P. G. Tait, who at the time was himself an undergraduate at Cambridge. In a memoir recently published in Nature, Prof. Tait writes that, a few months after his election to the chair of Mathematics, Prof. Stokes gave public notice that he considered it part of the duties of his office to assist any member of the university in difficulties that he might encounter in his mathematical studies. Here was, thought the students, "a single knight fighting against the whole mêlée of the tournament." But they soon discovered their mistake, and felt that the undertaking was the effect of an earnest sense of duty on the conscience of a singularly modest but profoundly learned man.

As a mathematician and physicist, Stokes stands in the foremost rank, whether of his contemporaries or of his predecessors. "Newton's wonderful combination of mathematical power with experimental skill." writes Prof. Tait, "without which the natural philosopher is but a fragment of what he should be, lives again in his successor. Stokes has attacked many questions of the gravest order of difficulty in pure mathematics, and has carried out delicate and complex experimental researches of the highest originality, alike with splendid success. But several of his greatest triumphs have been won in fields where progress demands that these distinct and rarely associated powers be brought simultaneously into action. For there the mathematician has not merely to save the experimenter from the fruitless labor of pushing his inquiries in directions where he can be sure that (by the processes employed) nothing new is to be learned; he has also to guide him to the exact place at which new knowledge is felt to be both-necessary and attainable. It is on this account that few men have ever had so small a percentage of barren work, whether mathematical or experimental, as Stokes."

A partial list of Stokes's contributions to science is given in Prof. Tait's memoir. It is there stated that up to 1864 Stokes had published the results of some seventy distinct investigations. Since that year he has published but little, though it is well known that he has in retentis several optical and other papers of the very highest order, which he cannot bring himself to publish in an incomplete form. Many of the papers which have been published by Prof. Stokes are of so rigidly mathematical a character that their titles would fail to convey any idea to the non-mathematical mind. To this category belong the papers entitled "Critical Values of the Sums of Periodic Changes" and "Numerical Calculation of Definite Integrals and Infinite Series." The following incomplete list will serve to show the comprehensiveness of Prof. Stokes's researches in applied mathematics:

"On the Friction of Fluids in Motion, and the Equilibrium and Motion of Elastic Solids," 1845; "Effects of the Internal Friction of Fluids on the Motion of Pendulums," 1850.

Of Stokes's papers stating the results of his researches on the "Undulatory Theory of Light," three are cited by Prof. Tait, viz.: "Dynamical Theory of Diffraction," 1849; "On the Colors of Thick Plates," 1851; "On the Formation of the Central Spot of Newton's Rings beyond the Critical Angle," 1848.

The "Report on Double Refraction," in the "British Association Reports for 1862," was drawn up by Prof. Stokes.

"On the Variation of Gravity at the Surface of the Earth," 1849.

"On the Change of the Refrangibility of Light," 1852. This paper contains his famous experimental explanation of fluorescence, which earned for its author his fellowship in the Royal Society.

Among the papers published by Stokes since the year 1864, two are specially worthy of mention, viz.: "On the Long Spectrum of Electric Light," and "On the Absorption Spectrum of Blood."

In conjunction with the late Mr. Vernon Harcourt, Stokes made a highly-valuable experimental inquiry into what is called Irrationality of Dispersion, chiefly with a view to the improvement of achromatic telescopes.

"There can be no doubt," writes Prof. Tait, "as was well shown by Sir W. Thomson in his presidential Address to the British Association at Edinburgh in 1871, that Stokes (at least as early as 1852) had fully apprehended the physical basis of spectrum analysis, and had pointed out how it should be applied to the detection of the constituents of the atmospheres of the suns and stars. Balfour Stewart's experiments and reasoning date from 1858 only, and those of Kirchhoff from 1859."

Prof. Stokes, however, gives due credit to Kirchhoff. Thus, in his Presidential Address to the British Association, in speaking of the applications of the spectroscope, he says:

"But how shall we find in such distant objects as the stars an analogue of the bell which we have assumed in the illustration drawn from sound? What evidence can we ever obtain, even if an examination of their light should present us with rays of definite refrangibility, of the existence in those remote bodies of ponderable matter vibrating in known periods not identical with those corresponding to the refrangibilities of the definite rays which we observe? The answer to this question will involve a reference, which I will endeavor to make as brief as I can, to the splendid researches of Prof. Kirchhoff. The exact coincidence of certain dark lines in the solar spectrum, with bright lines in certain artificial sources of light, had previously been, in one or two instances, observed; but it is to Kirchhoff we owe the inference, from an extension of Prevost's theory of exchanges, that a glowing medium which emits bright light of any particular refrangibility necessarily (at that temperature at least) acts as an absorbing medium, extinguishing light of the same refrangibility. In saying this, it is but just to mention that, in relation to radiant heat (whence the transition to light is easy), Kirchhoff was preceded, though unconsciously, by our own countryman, Mr. Balfour Stewart. The inference which Kirchhoff drew from Prevost's theory thus extended, led him to make a careful comparison of the places of the dark lines of the solar spectrum with those of bright lines produced by the incandescent gas or vapor of known elements; and the coincidences were in many cases so remarkable as to establish almost to a certainty the existence of several of the known elements in the solar atmosphere, producing by their absorbing action the dark lines coinciding with the bright lines observed. Among other elements may be mentioned, in particular, hydrogen, the spectrum of which, when traversed by an electric discharge, shows a bright line or band exactly coinciding with the dark line C, and another with the line F.
"Now, Mr. Huggins found that several of the stars show in their spectra dark lines coinciding in position with and F; and what strengthens the belief that this coincidence, or apparent coincidence, is not merely fortuitous, but is due to a common cause, is, that the two lines are found associated together, both present or both absent. And Kirchhoff's theory suggests that the common cause is the existence of hydrogen in the atmospheres of the sun and certain stars, and its exercise of an absorbing action on the light emitted from beneath."