ON POLARIZED LIGHT. 189 



be a circle, like A, B, C, D, Fig. 59, and we shall distinguish 

 the section of a beam of common light by a circle with two 

 diameters, A B, CD, at right angles to each other. 



" If we now allow the same beam of light to fall upon a 

 rhomb of Iceland spar, as in Fig. 60, and examine the two 



circular beams, o } E e, formed by double refraction, we shall 

 find, 



" 1. That the beams o, E e, have different properties on dif- 

 ferent sides ; so that each of them differs, in this respest, from 

 the beams of common light. 



" 2. That the beam o differs from E e in nothing, excepting 

 that the former has the same properties at the sides A' and B' 

 that the latter has at the sides C' and D', as shown in Fig. 59 ; 

 or, in general, that the diameters of the beam, at the extremi- 

 ties of which the beam has similar properties, are at right 

 angles to each other. 



" These two beams, o, E e, Fig. 60, are therefore said to 

 be polarized, or to be beams of polarized light, because they 

 have sides or poles of different properties. 



" Now it is a curious fact, that if we cause the two polarized 

 beams, O o, E e, Fig. 60, to be united into one, we obtain a 

 beam which has exactly the sajme properties as the beam A, B, 



