90 LIGHT. 



that the raj, like a magnetic bar, has sides in which reside pecu- 

 liar powers. One of these new properties is, that when it falls 

 upon a second glass plate, it is not reflected in the same way as 

 common light. If the plane of the second reflector is perpendi- 

 cular to the first, and the ray fall at an angle of 56, it is not 

 reflected at all, it vanishes ; but if parallel, it is entirely reflected. 

 Polarized light appears to possess some most extraordinary 

 properties, in regard to vision, of useful application. It is 

 said that a body which is quite transparent to the eye, 

 and which appears upon examination to be as homogeneous 

 in its structure as it is in its aspect, will yet exhibit, under 

 polarized light, the most exquisite organization. As an 

 example of the utility of this agent in exploring mineral, 

 vegetable and animal structures, Sir D. Brewster refers to the 

 extraordinary structure of the minerals apophylite and anal- 

 cime ; to the symmetrical and figurate disposition of siliceous 

 crystals in the epidermis of equisetaceous plants, and to the 

 wonderful variations of density in the crystalline lenses, and the 

 integuments of the eyes of animals, which polarized light ren- 

 ders visible.* 



6. Decomposition of light. When a beam of light from the 



sun is admitted into a dark room, by a small aperture r in a 

 window shutter, and is intercepted in its passage by a wedge 

 or solid angle of glass a b c, it is refracted as it enters, and a 

 second time as it issues from the glass ; and instead of forming 

 a round spot of white light, as it would have done if allowed to 

 proceed in its original direction r t, it illuminates with several 



* Reports of the British Association, vol. i. Report upon Optics, by Sir D, 

 Brewster, 



