1^1 Mr. Delaval oh the Cauje of the 



and tranfmit the lefs refrangible rays. Such 

 media, for the moft part, aft upon the rays in a 

 fimilar manner. 



The refleftion, and tranfmifTion, of the more 

 or lefs refrangible rays, depend upon the powers 

 of the refleclive particles. The reflective, as 

 well as the refractive, power of bodies being in 

 a great meafurc proportionable to their fpecific 

 gravity. 



Inftances rarely occur either of natural, or 

 faftitious femipellucid fubftances, in which the 

 refleflive particles are of lb great a fpecific 

 gravity, as qualifies them to refle6l the lefs 

 refrangible rays, fuch as red, or orange ; and, 

 which at the fame time are fo minute, and fo 

 rarely diffufed, that intervals are left between 

 them, fufficient to admit the paflage of the 



rays. 



The fpecific gravity of gold is much greater 

 than that of any other known fubftance, by 

 which glafs can be equably tinged. I therefore, 



*' jacent air exhibited rings of colours, as well by tranf- 

 *' mitting light, as by reflecting it. 



•• I found that white was oppofite to black, red to blue, 

 ' *' yellow to violet, and green to a compound of red and 

 '**' violet. That is, thofe parts of the glafs were black 

 *' when looked through, which when looked upon appeared 

 " white, and on the contrary. And fo thofe which in one 

 •' cafe exhibited blue, did in the other cafe exhibit red, 

 ** and the like of the other colours." 



judged 



