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DR. BREWSTER ON REFLECTED LIGHT. 



disappointments which it occasioned, I was led to the results which I shall now 

 proceed to describe. 



The solids which I employed were two prisms of plate gl^ss, which I shall 

 call A and B. The prism A, whose section was an isosceles right-angled tri- 

 angle, had its base polished at the plate glass manufactory where it was made. 

 The prism B was executed for me by Dollond, and very finely polished, having 

 also its section a right-angled isosceles triangle. The refractive indices were 



^ In A ... w = 1.508 



InB . . . w = 1.510 



The fluids which I employed were castor oil and balsam of capivi, the latter 

 having a greater and the former a less refractive power than the glass prisms. 

 The refractive indices were 



In castor oil m = 1.490 



In balsam of capivi . . . m = 1.528 



Fig. 1. 



The prisms A, B were now fixed 

 together as in fig. 1, and a film C D 

 of castor oil interposed between 

 them. A ray of light R r will after 

 refraction at r be reflected in the di- 

 rection oqm from the surface C o D 

 which separates the prism A and 

 the oil ; and another portion of it 

 will be reflected in the direction ;> .s m from the surface Gpli which separates 

 the prism B and the oil. In order that the two rays qm,sn may be suffi- 

 ciently separated, the common sections of the faces which contain the right 

 angle are slightly inclined to each other. 



When the angle of incidence R r E is very great, the light suffers total re- 

 flection at the surface C o D. Within the limit of total reflection the light o q m 

 is yellow ; and by diminishing the angle of incidence gradually, the pencil 

 oqm passes through all the tints of nearly three orders of colours, as shown in 

 the following Table. 



