io6 Dr. Brewster on some Properties of Light, 



properties of this extraordinary mineral will be noticed in the 

 next article. 



3. On Substances with a higher refractive Power than the Diamond. 



Since the time of Sir Isaac Newton, who first measured the 

 action of the diamond upon light, its refractive power has been 

 regarded as superior to that of every other substance ; but, in 

 the course of my researches, I have found that realgar and 

 chromate of lead exceed the diamond in refractive power, and 

 that this high refraction, in both these substances, is accom- 

 panied with dispersive powers greater than those of any other 

 body. The following are the measures which I have obtained 

 for these, and a few other substances. 



Refractive Powers. 



Index of Refr. Index of Refr. 



Chromate of lead Phosphorus - - 2.224 



(gr. refr. ) - - 2,926 Sulphur, native - 2.115 



Ditto, least refraction 2.479 Cryolite - - 1 .344 



Realgar - - 2.510 Ice - - 1307 



Diamond (according to 

 Newton) - - 2.439 



Dispersive powers or values of ^^17. 



