KINETIC OK MECHANICAL VIEW OF NA'ITKK. 2 



~ I 



have sides, the phenomena of " laterality " (niLsleacUngly 

 called polarisation). The believers in the emission theory 

 studied them wiih predilection, l>iot at their head. Al- 

 though to Yoinig their explanati<jns were unconvincing, 

 their results were so perplexing that he wrote to l^rewster 

 in September 1815, "With respect to my own funda- 

 mental hypotheses respecting the nature of light, 1 be- 

 come less and less fond of dwelling on them, as 1 learn 

 more and more facts like those which j\lr Malus dis- 

 covered ; because, although they may not Ite incompat- 

 il)le with these facts, they certainly give us no assistance 

 in explaining them." ^ "When Young wrote this, Fresnel 

 had not yet presented his first memoir on DiHraction to 

 the Institute ; his own labours on that matter were more 

 than ten years old ; the phenomena of polarisation had 

 meantime absorbed the attention of opticians. In the 

 summer of 1816 Arago and Gay-Lussac paid a visit to 



mediately after the reading of fraction, ils font disiKiraitre une 



Arago's report, Laplace, " who had ^ difficulte qui ne pouvait luauquer de 



thought for a long time that his rcsulter de toute dtudetaut soit ])eu 



analysis had made the phenomena approfondie de ses ecrits imprimos. 



of double refraction depend on his ... Un a vu au contraire que cette 



emission theory," proclaimed the loi s'est manifesto Ji Fresnel coniiue 



great importance of the memoir, , le rdsultatd'une generalisation toute 



and declared that he placed these semblable aux g(?n<5ralisations iiui 



researches above anything that had ont ameue la plupart dcs grandes 



for a long time been communicated , ducouvertes. Lorsqu'il a voulu 



to the Academy ( 'Qiuvres de Fres- ensuite se renclre compte de la loi 



nel', vol. i. p. Lxxxvi., and vol. ii. par une thdorie mecanique, il n'e.st 



p. 459). We are indebted to M. 

 Verdet for having shown that the 

 discovery of this law by Fresnel is 

 independent of the theoretical con- 

 siderations by which he tried 



pas etonnant qu'il ait, [leut-ctre h 

 son insu, conduit cette thoorie vers 

 le but qu'il couuaissj\it il'avance, 

 et qu'il ait itc determine, dans le 

 choix dcs hyp<'th^ses au.viliaiies 



synthetically to prove it. On this moins par leur vraisemblance intriu- 



point he says : " En r(5vdlant la suque tiue par leur accord avec ce 



sdrie de generalisations et de con- qu'il utait en droit de considiVer 



jectures par lesquelles Fresnel est comme la verito " (ibid., vol. ii, p. 



arrive peu ii j)eu a la ducouverte 327. Cf. vol. i. p. Ixxxiv. ) 

 dea lois g(5n(jrales de la double re- ' Works, vol. i. p. 36 L 



