21b* Dr Brewster on the reflection and decomposition of 



the intensity of its light. By the application of heat p sn be- 

 comes yellowish-white, and increases greatly in intensity. It 

 now approaches at oblique incidences to the brightness of op m, 

 but is still inferior to it, while at small incidences it surpasses 

 it in intensity. 



In the preceding experiments the solid had nearly the same 

 refractive density as the balsam. We shall now take a solid, 

 namely obsidian, which has nearly the same refractive power 

 as the oil. 



When the lower prism B is obsidian, and the film C D, H G 

 balsam of capivi, the ray ji s n passes through three orders of 

 colours ; namely, 



White, 

 Yellow, 

 Red, 



Limit of red and blue at 7S°. 

 fBlue, 

 Bluish-green, 

 2d Order. ^ Yellowish white. 

 Reddish white. 

 Pink, faint. 



1st Order. 



3d Order. {SSu,e. 



These colours are by no means good, nor are they much 

 improved by heat, which approximates the refractive power of 

 the fluid to that of the solid. The heat reduces the orders to 

 two, each colour being now developed at a much smaller an- 

 gle of incidence. The first order, for example, which ended 

 at an incidence of 73°, now ends at an incidence of 52°. When 

 the heat is so great that we cannot touch the prisms with the 

 hand, all the colours are effaced. 



If we now substitute the castor oil in place of the balsam, 

 no colours are visible ; but the reflected pencil p s n is white 

 and bright, notwithstanding the coincidence between the re- 

 fractive energies of the solid and the fluid. Heat increases 

 the intensity of the pencil, but produces no colour. 



Hitherto we have considered the action of the two surfaces 

 of the film as exhibited separately in the two images displaced 

 laterally by the prismatic shape of the fluid. We shall now 



