108 



MATHEMATICAL AND PHYSICAL SCIENCE. 



[Diss. VI. 



(494.) 

 confirmed 

 by experi- 

 ment. 



(495.) 

 Reception 

 of Presnel's 

 theory ; 



in France, 



in Eng- 

 land. 



case in Iceland spar and similar crystals. At 

 the same time the wave surface degenerates into 

 the united sphere and spheroid. The equation to 

 the wave surface was deduced by Fresnel in an in- 

 direct and somewhat tentative manner. It was 

 demonstrated by Ampere directly, but inelegantly. 

 M. Cauchy, Mr Archibald Smith, and Professors 

 Sir W. R. Hamilton and Maccullagh gave more 

 complete and elegant solutions. 



Fresnel submitted his theory (as usual) to experi- 

 ment. He found that in topaz, which is a biaxial 

 crystal, neither ray follows the law of common re- 

 fraction. The plane of polarization (which is always 

 perpendicular in the two rays) follows very nearly 

 indeed, by theory, the law which M. Biot had as- 

 signed by experiment. Fresnel thus stated the 

 ground of his conviction of the truth of his theory, 

 and it would be difficult to express more appropri- 

 ately the characteristics of a just hypothesis : 

 " The theory which we have adopted, and the simple 

 construction which we have deduced from it, present 

 this remarkable character, that all the unknown 

 quantities are at once determined by the solution of 

 the problem ; the velocity of the ordinary and ex- 

 traordinary rays, and their respective planes of polar- 

 ization. Physicists who have studied with attention 

 the laws of nature, will admit that this simplicity 

 and these intimate relations between different parts 

 of the same phenomenon present a great probability in 

 favour of the theory by which they are established." 



The memoir on double refraction was received 

 with much incredulity and partial applause. It was 

 not to be supposed that a theory in opposition to 

 that imagined by Newton, and received with almost 

 general assent for more than a century and a half, 

 would not meet with many opponents ; but in the 

 case of double refraction and polarization it was also 

 essentially coupled with the idea of transverse vibra- 

 tions, whose exact mechanism was admitted on all 

 hands to be extremely obscure. Laplace, now more 

 than seventy years of age, opposed the new opinion 

 to the last. His reason for doing so was eminently 

 characteristic of the great geometer " it was one to 

 which analysis could not be applied without much 

 difficulty;" to which Fresnel replied, " that it was 

 still harder to believe that the laws of nature were 

 arrested by such obstacles." Poisson, as might have 

 been expected, was equally opposed to the undula- 

 tory doctrine, for he was still less of a physicist than 

 Laplace. His standing argument against it was its 

 inability to explain dispersion. M. Biot, also a keen 

 supporter of Laplace, was still more strongly com- 

 promised to the theory of emission. The inertia of 

 such authorities at the Institute retarded of course 

 the growth of Fresnel's reputation at home, notwith- 

 standing the great weight of his friend Arago's opi- 

 nion. It was in fact in England that the merits of 



Fresnel were first most generally and liberally ac- 

 knowledged; as, singularly enough, Young had re- 

 ceived almost the first expression of sympathy in his 

 optical discoveries from France. In 1825 Fresnel 

 received the distinguished honour of being elected 

 a foreign member of the Royal Society of London, only 

 two years subsequent to his election into the Insti- 

 tute, and whilst his greatest paper was as yet known 

 only by an abstract. In 1827 he received the Rum- 

 ford medal from the same body. This recognition of 

 his merits was due, as we learn on the authority of 

 Dr Young (who was then Foreign Secretary of the 

 Royal Society) to the influence of Sir John Herschel, 

 at that time and afterwards a zealous supporter of 

 the undulatory theory of light, and by whom it be- 

 came first generally known in England through the 

 medium of his admirable Essay on Light. Dr 

 Young, though present, was silent ; " from being," 

 as he himself tells us, " too much interested in the 

 subject " on account of his personal share in the 

 matter. In announcing this distinction officially to 

 Fresnel (then in the last stage of consumption), 

 Young characteristically observed, " I too should 

 claim some right to participate in the compliment 

 which is tacitly paid to myself in "common with you 

 by this adjudication ; but considering that more 

 than a quarter of a century is past since my prin- 

 cipal experiments were made, I can only feel it a 

 sort of anticipation of posthumous fame which I have 

 never particularly coveted." 2 



I have stated in the opening of the section that (496.) 

 Fresnel, who -was attached to the Bourbon cause, had Fresn el 

 retired to Normandy near the close of Napoleon's ifg h t s 

 career. On the re-establishment of the monarchy in iiiumina- 

 1815 he was recalled from his retreat and appointed tion - 

 to an office in the departments connected with his pro- 

 fession as an engineer ; but in 1817 he was brought 

 to Paris with the express view of giving him more 

 facility in his researches. In 1819 he was placed 

 on the Commission for the Management of the 

 Lighthouses of France (of which he afterwards be- 

 came Secretary), and he entered with ardour on the 

 application of his favourite science cf optics to the 

 duties of his profession and the benefit of man- 

 kind. 



The use of lenses in place of reflectors for prevent- 

 ing the indefinite dispersion of the light employed, 

 and the effectual concentration of it in the direction 

 where it will be most useful, was not altogether new. 

 The construction of immense lenses of glass of no 

 great thickness, formed by grinding out a series of 

 concentric refracting sui'faces having a common focus, 

 had also been proposed by Buffon, and the idea of 

 constructing these rings or echelons separately and 

 then uniting them had been suggested by Condorcet 

 in his eloge of Buffon, as well as at a later period 



(497.) 



2 Peacock's Life of Young, p. 401. 



