Sir George Gabriel Stokes. 211 



become President of the Royal Society, the hardihood and impunity 

 with which he attended public dinners were matters of general admira- 

 tion. The nonsense of fools, or rash statements by men of higher 

 calibre, rarely provoked him to speech ; but if directly appealed to, he 

 would often explain his view at length with characteristic moderation 

 and lucidity. 



His experimental work was executed with the most modest 

 appliances. Many of his discoveries were made in a narrow passage 

 behind the pantry of his house, into the window of which he had a 

 shutter fixed with a slit in it and a bracket on which to place crystals 

 and prisms. It was much the same in lecture. For many years he 

 gave an annual course on Physical Optics, which was pretty generally 

 attended by candidates for mathematical honours. To some of these, 

 at any rate, it was a delight to be taught by a master of his subject, 

 who was able to introduce into his lectures matter fresh from the anvil. 

 The present writer well remembers the experiments on the spectra of 

 blood, communicated in the same year (1 864) to the Royal Society. There 

 was no elaborate apparatus of tanks and " spectroscopes." A test- 

 tube contained the liquid and was held at arm's length behind a slit. 

 The prism was a small one of 60, arid was held to the eye without the 

 intervention of lenses. The blood in a fresh condition showed the 

 characteristic double band in the green. On reduction by ferrous salt, 

 the double band gave place to a single one, to re-assert itself after 

 agitation with air. By such simple means was a fundamental reaction 

 established. The impression left upon the hearer was that Stokes felt 

 himself as much at home in chemical and botanical questions as in 

 Mathematics and Physics. 



At this time the scientific world expected from him a systematic 

 treatise on Light, and indeed a book was actually advertised as in. 

 preparation. Pressure of work, and perhaps a growing habit of pro- 

 crastination, interfered. Many years later (1884-1887) the Burnett 

 Lectures were published. Simple and accurate, these lectures are a 

 model of what such lectures should be, but they hardly take the place of 

 the treatise hoped for in the sixties. There was, however, a valuable 

 report on Double Refraction, communicated to the British Association 

 in 1862, in which are correlated the work of Cauchy, MacCullagh 

 and Green. To the theory of MacCullagh, Stokes, imbued with the 

 ideas of the elastic solid theory, did less than justice. Following 

 Green, he took too much for granted that the elasticity of aether must 

 have its origin in defamation, and was led to pronounce the incom- 

 patibility of MacCullagh's theory with the laws of Mechanics. It 

 lias recently been shown at length by Prof. Larmor that MacCullagh's 

 equations may be interpreted on the supposition that what is resisted 

 is not deformation, but rotation. It is interesting to note that Stoke? 



