LAWS OF DOUBLE REFRACTION. 403 



he gives a rule for the extraordinary refraction of 

 Iceland spar which is altogether erroneous, without 

 assigning any reason for rejecting the law published 

 by Huyghens ; and, so far as appears, without having 

 made any experiments of his own. The Huyghenian 

 doctrine of double refraction fell, along with his 

 theory of undulations, into temporary neglect, of 

 which we shall have hereafter to speak. But in 

 1788, Haiiy showed that Huyghens' rule agreed 

 much better than Newton's with the phenomena: 

 and in 1802, Wollaston, applying a method of his 

 own for measuring refraction, came to ihe same 

 result. "He made," says Young 4 , "a number of 

 accurate experiments with an apparatus singularly 

 well calculated to examine the phenomena, but 

 could find no general principle to correct them 

 until the work of Huyghens was pointed out to 

 him." In 1808, the subject of double refraction 

 was proposed as a prize-question by the French 

 Institute; and Malus, whose Memoir obtained the 

 prize, says, " I began by observing and measuring a 

 long series of phenomena on natural and artificial 

 faces of Iceland spar. Then, testing by means of 

 these observations the different laws proposed up to 

 the present time by physical writers, I was struck 

 with the admirable agreement of the law of Huy- 

 ghens with the phenomena, and I was soon con- 

 vinced that it is really the law of nature." Pursuing 

 the consequences of the law, he found that it satis- 

 4 Quart. Rev. 1809, Nov. p. 338. 



DD2 



