156 MALUS. 



glass, at angles greater or less than that of complete 

 polarization, are partially polarized, and in a greater 

 degree, as their inclination to the reflecting surface 

 approaches nearer to 35° or 36° respectively. 



Mains conceived that rays reflected from metals are 

 not polarized even partially ; but this was a slight error 

 which was soon after rectified. 



After his first researches, Malus believed that re- 

 flexion from certain transparent and opaque substances, 

 besides double refraction, was the sole means of polariz- 

 ing light. About the end of the year 1809, his views on 

 this subject underwent a great extension ; he, in fact, 

 recognized, experimentally, that light which has passed 

 through a plate of glass, shows at certain inclinations 

 evident traces of partial polarization ; and that if we 

 form a pile of glasses, the natural ray which traverses 

 them emerges completely polarized. 



He did not fail to remark, that the polarization of the 

 ray, in this case, was the opposite to that with which the 

 reflected ray under the same circumstances Avas aflPected ; 

 so that if the latter were identified with the ordinary 

 ray, emerging from a crystal placed in a given position, 

 the former, i. e. the ray passing through the pile of glass 

 plates, would be similar to the extraordinary ray of the 

 same crystal. 



It does not enter into our plan to point out either the 

 detailed and very curious consequences which Malus 

 deduced from his experiments, or the further improve- 

 ments they have received. I shall content myself by 

 here saying that whenever we find a substance which 

 alone, at the angle of complete polarization, reflects one 

 half of the incident light, the ray transmitted through a 

 single plate will also be completely, instead of partially, 



