^ l>i' !Brewster on a new series of 



Fine blue - - ^5° of incidence. 



Purple. 



Bed. 



Orange. 



Yellow - - vet'tical incidence. 



Another specimen frbm the same steel pkte gave, when 

 soft and newly taken off, a bright purple at a perpendicular 

 incidence, which passed through pink and blue at greater in- 

 cidences. But in the process of induration, the vertical purple 

 became red, orange, and yellow. In a third impression the 

 perpendicular tint was a bright pink when soft, which descend- 

 ed to yellow when drier. 



In order to observe the relation between the reflected and 

 transmitted tints, I took a fresh impression on very transpa- 

 rent isinglass, and obtained the following results : 



90 







The comparison of these tints affords the most satisfactory 

 evidence that they are not complementary to each other. The 

 transmitted tints of the ordinary prismatic images always in- 

 crease in brightness as the angle of incidence diminishes, while 

 the reflected tints become fainter. 



As I had preserved the different specimens of isinglass with 

 which these experiments were made, it became interesting to 

 observe the changes which their colours had undergone after 

 a lapse of six years. The following was the result : — 



