Notes on some Points in the Theory of Light. 195 



the Proceedings, but also " deposited in the Archives " of that 

 body* he gave a precise statement of his more extended views, 

 informing the Academy that he had submitted his new theory 

 to calculation, and that, among other remarkable results, he had 

 obtained (with a slight variation or correction) the laws of cir- 

 cular polarization, discovered by Arago, Biot, and Fresnel. Re- 

 ferring to his Memoir on Dispersion, published at Prague, under 

 the title of Nouveaux Exercices de Mathematiques, he observes, that 

 the results therein contained may be generalized, by " ceasing to 

 neglect " in the equations of motion [the equations marked (24) 

 in 2 of that memoir] certain terms which vanish in the case of 

 a symmetrical distribution of the ether. He then goes on to 

 say 



"Nos formules ainsi generalisees representent les phe- 

 nomenes de 1'absorption de la lumiere ou de certains rayons, 

 produite par les verres colores, la tourmaline, &c., le phe- 

 nomene de la polarisation circulaire produite par le cristal 

 de roche, 1'huile de terebenthine, &c. (Voir les experiences 

 de MM. Arago, Biot, Fresnel). Elles servent meme a de- 

 terminer les conditions et les lois de ces phenomenes; elles 

 montrent que generalement, dans un rayon de lumiere po- 

 larisee, une molecule d' ether decrit une ellipse. Mais dans 

 certains cas particuliers, cette ellipse se change en une droite, 

 et alors on obtient la polarisation reetiligne." " Enfin le cal- 

 cul prouve que, dans le cristal de roche, 1'huile de tereben- 

 thine, &c., la polarisation, des rayons transmis parallelement 

 a 1'axe (s'il s'agit du cristal de roche) n'est pas rigoureusement 

 circulaire, mais qu' alors 1'ellipse differe tres peu du cercle." 



Thus, fco say nothing for the present of the questions of 

 dispersion and absorption, it appears that M. Cauchy conceived 

 he had completely accounted for the facts of circular and 

 elliptic polarization, and that he had deduced the formulas 

 "which serve to determine the conditions and laws of these 

 phenomena." But neither in this letter, nor in any subse- 



See the Comptes Rcndus des Seances de V Academic des Sciences, torn. ii. p. 182. 



o2 



