214 Dr Brewster on the reflection and decomposition of 



course are seen ; but the reflected pencils have their maxima 

 and minima of intensity, like the rings of thin plates or the 

 fringes of inflected light when formed by homogeneous rays. 

 The following are the periods for red and for blue light : — 



Red Light. Blue Light. 



1st minimum, - 77° 54' 80° 27 



2d minimum, - 50 57 59 4 



If we substitute for the prism A a square prism, the tints 

 are thrown more closely together ; and if the luminous ob- 

 ject is a long stripe of bright light, we may see most of the 

 colours at one view. 



If we now apply heat to the oil so as to diminish its refrac- 

 tive power, the brightness of the colours is greatly diminish- 

 ed, and the first period is completed at a less angle of inci- 

 dence. 



Such are the phenomena which take place when the refrac- 

 tive power of the glass exceeds that of the fluid. We shall 

 now see what happens when the fluid has a greater refractive 

 energy than the solid ; a case of peculiar interest, because we 

 are able to reduce the two refractive powers to a perfect 

 equality for any given ray of the spectrum. 



The same prisms being employed, let the film C D H G be 

 now balsam of capivi. Before total reflection takes place, the 

 reflected pencil is perfectly white : it then becomes yellow, 

 and passes through the same orders of colours as in castor oil. 

 All the colours, however, are produced at less angles of inci- 

 dence, the 1st order terminating at an angle of 64° 58', as ap- 

 pears from the following Table, in which I have given only 

 the leading tints. 



