482 HISTORY OF OPTICS. 



the compression is most intense, he obtained two 

 distinct images. This evidence of the dependence 

 of dipolarizing structure upon a doubly-refracting 

 state of particles, thus excogitated out of the general 

 theory, and verified by trial, may well be considered, 

 as he says, "as a new occasion of proving the in- 

 fallibility of the principle of interferences." 



2. Circular Polarization. Fresnel then turned 

 his attention to another set of experiments, related 

 to this indeed, but by a tie so recondite that no- 

 thing less than his clearness and acuteness of view 

 could have detected any connexion. The optical 

 properties of quartz had been perceived to be pecu- 

 liar, from the period of the discovery of dipolarized 

 colours by MM. Arago and Biot. At the end of 

 the notice just quoted, Fresnel says 2 , "As soon as 

 my occupations permit me, I propose to employ 

 a pile of prisms similar to that which I have 

 described, in order to study the double refraction 

 of the rays which traverse crystals of quartz in the 

 direction of the axis." He then ventures, without 

 hesitation, to describe beforehand what the phe- 

 nomena will be. In the Bulletin des Sciences* for 

 December 1822, it is stated that experiment had 

 confirmed what he had thus announced. 



The phenomena are those which have since 

 been spoken of as circular polarization ; and the 

 term first occurs in this notice 4 . They are very 



* Ann. de Chint. 1822, torn. xx. p. 382. 

 3 Ib. p. 191. 4 Ib. p. 194. 



