ELEMENTARY PROPERTIES 



is received, it becomes, as usual, subdivided 

 into seven different parts ; each of which, pos- 

 sessing different degrees of refrangibility, be- 

 comes, consequently, separated from each other ; 

 and the several colors, which are known by the 

 appellation of prismatic colors, are made visi- 

 ble. Dr. Herschel found, that by placing a 

 very sensible thermometer beyond the colored 

 spectrum, external to the boundary of the red 

 ray, but still in the line of the spectrum, the 

 mercury rose much higher, than when it was 

 exposed to the immediate action of the red ray; 

 and, on shifting the thermometer still further 

 from the colored image, the mercury continued 

 to rise, and did not reach its maximum, until 

 it was placed half an inch beyond the utmost 

 extent of the red-colored ray. 



By the power of this invisible ray, as it has 

 been called, but which I shall denominate 

 colorless, the metallic oxydes were reduced ; and 

 Dr. WOLLASTON, w 7 ho has since made a num- 

 ber of experiments on the same subject, found, 

 that the muriate of silver was blackened more 

 rapidly, when exposed to its influence alone, 

 entirely beyond the reach of the prismatic 

 spectrum ; and, finally, that this change was 

 accomplished without the production of any 

 sensible increase of heat. Had it not been, 

 indeed, for the sensible phenomena produced 

 on the thermometer and other bodies, exposed 



