34^ ON LIGHT. 



came to be arranged, half with their poles in one direc- 

 tion (as regards the sides of the crystal), and half in a 

 direction at right angles to the former. And this is the 

 way in which Newton conceived it, as he himself dis- 

 tinctly states (Opt., Query 21); and as it necessarily must 

 be conceived if the corpuscular theory were to be 

 adopted. How it is explained on the undulatory hypo- 

 thesis, we shall presently see. 



(126.) It was while gazing one evening in 1808, through 

 such a prism of Iceland spar as we have just described, 

 from his study in the Rue d'Enfer at the windows of the 

 Luxembourg Palace in Paris, that M. Malus, at that time 

 engaged in studying the law of extraordinary refraction in 

 this body, happened to notice that the reflexion of the sun 

 on a window of the palace disappeared from one of its 

 images, in a certain position of the prism, and from the 

 other when held at right angles to that position ; while in 

 the intermediate situations, the glare was visible in both 

 images, unequally divided, however, between them, ex- 

 cept when held in a situation exactly intermediate, or at 

 45 from its first position : in a word, that the light re- 

 flected from the window had acquired precisely the pecu- 

 liarity which would have been impressed on it by pre- 

 vious transmission through a similar prism. To this 

 peculiarity he gave the name of polarization, and light 

 so affected has ever since been said to be polarized. 



(127.) Total and partial polarization of light by reflexion. 

 The angle at which a ray of light must be incident on 

 glass that the reflected ray may acquire this property is 

 56 45' from the perpendicular, or at an incHnation of 



