PHOSPHORESCENCE. 71 



a greenish-yellow phosphorescence. Dolomite, 

 Aragonite, and some specimens of diamond, shine 

 with a brilliant, white, phosphoric light. 



In the same manner, the colour of a flame de- 

 pends upon the nature of the body that burns. 

 Thus, carburetted hydrogen and sodium burn with 

 a yellow flame, oxide of carbone with a blue 

 flame, potassium and cyanogen with a purple 

 flame, etc. 



Pearsall, Brewster, Dessaignes, and Becquerel 

 have studied this subject. It appears to me very 

 evident that the same substance may slightly 

 differ in the colour of its phosphorescence, ac- 

 cording to the manner in which the latter is 

 prepared or excited. 



Concerning colours and tints, we should, in 

 general, be careful in admitting them too exclu- 

 sively, for there are scarcely two persons who will 

 entirely agree upon the denomination of any tint 

 that is not one of the striking colours of the solar 

 spectrum. 



