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. 
Malus 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 was affected ; 
so that if the latter were identified with the ordinary 
ray, emerging from a crystal placed in a given position, 
the former, ¢. 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, 
