906 
ease 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 Ampére directly, but inelegantly. 
M. Cauchy, Mr Archibald Smith, and Professors 
Sir W. R. Hamilton and Maccullagh gave more 
complete and elegant solutions. 
MATHEMATICAL AND PHYSICAL SCIENCE. 
[Diss. Mi 
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- 
(494.) Fresnel submitted his theory (as usual) to experi- ford medal from the same body. This recognition of 
oles: ment. He found that in topaz, which is a biaxial his merits was due, as we learn on the authority of 
ment. 
fraction. The plane of polarization (which is always Royal Society) to the influence of Sir John Herschel, 
perpendicular in the two rays) follows very nearly at that time and afterwards a zealous supporter of 
indeed, by theory, the law which M. Biot had as- the undulatory theory of light, and by whom it be- 
signed by experiment, Fresnel thus stated the came first generally known in England through the 
ground of his conviction of the truth of his theory, medium of his admirable Essay on Light. Dr 
and it would be difficult to express more appropri- Young, though present, was silent; “from being,” 
ately the characteristics of a just hypothesis:— as he himself tells us, “too much interested in the 
“The theory which we have adopted, and the simple subject” on account ef his personal share in the 
construction which we have deduced from it, present matter. In announcing this distinction officially to 
this remarkable character, that all the unknown Fresnel (then in the last stage of consumption), 
quantities are at once determined by the solution of Young characteristically observed, “I too should 
the problem ;—the velocity of the ordinary and ex- claim some right to participate in the compliment 
traordinary rays, and their respective planes of polar- which is tacitly paid to myself in common with you 
ization. Physicists who have studied with attention by this adjudication; but considering that more 
the laws of nature, will admit that this simplicity than a quarter of a century is past since my prin- 
and these intimate relations between different parts cipal experiments were made, I can only feel it a 
of the same phenomenon present a great probability in sort of anticipation of posthumous fame which I have 
favour of the theory by which they are established.” never particularly coveted.”* 
(495.) The memoir on double refraction was received 
wre th with much incredulity and partial applause. It was I have stated in the opening of the section that (496.) 
theory;  20t to be supposed that a theory in opposition to Fresnel, who was attached to the Bourbon cause, had acon ‘ 
that imagined by Newton, and received with almost retired to Normandy near the close of Napoleon’s j?hthouse 
general assent for more than a century and a half, career, On the re-establishment of the monarchy in illumina- 
would not meet with many opponents; but in the 1815 he was recalled from his retreat and appointed tion. 
case of double refraction and polarization it was also _ to an office in the departments connected with his pro- 
essentially coupled with the idea of transverse vibra- fession as an engineer ; but in 1817 he was brought 
tions, whose exact mechanism was admitted on all to Paris with the express view of giving him more 
hands to be extremely obscure, Laplace, now more facility in his researches. In 1819 he was placed 
in France, tHaH seventy years of age, opposed the new opinion on the Commission for the Management of the 
’ to the last. His reason for doing so was eminently Lighthouses of France (of which he afterwards be- 
characteristic of the great geometer—* it was one to came Secretary), and he entered with ardour on the 
which analysis could not*be applied without much application of his favourite science of optics to the 
difficulty ;” to which Fresnel replied, ‘‘that it was duties of his profession and the benefit of man- 
still harder to believe that the laws of nature were kind, 
arrested by such obstacles.” Poisson, as might have The use of lenses in place of reflectors for prevent- (497.) 
been expected, was equally opposed to the undula- ing the indefinite dispersion of the light employed, 
tory doctrine, for he was still less of. physicist than and the effectual concentration of it in the direction 
Laplace. His standing argument against it was its where it will be most useful, was not altogether new. 
inability to explain dispersion. M. Biot, alsoakeen ‘The construction of immense lenses of glass of no 
supporter of Laplace, was still more strongly com- great thickness, formed by grinding out a series of 
promised to the theory of emission. The inertia of concentric refracting surfaces having a common focus, 
such authorities at the Institute retarded of course had also been proposed by Buffor, and the idea of 
the growth of Fresnel’s reputation at home, notwith- constructing these rings or échélons separately and 
inEng- Standing the great weight of his friend Arago’s opi- then uniting them had been suggested by Condorcet 
land. nion, It was in factin England that the merits of in his éloge of Buffon, as well as at a later period 
erystal, neither ray follows the law of common re- 
Dr Young (who was then Foreign Secretary of the 
2 Peacock’s Life of Young, p. 401, 
7 
