2x8 Mr. Delaval on the Cauje of the 



When particles of air, or of the rarer matter, 

 occupy the interftices of any denfe 'Tranjparent 

 Coloured Body, the White Light refleded from 

 thofe rare fubftances fhines through the Tranf- 

 parent Coloured Medium which the particles 

 intercede, and is tinged by it, according to 

 the colour which it tranfmits. 



Thus, an infufion of cochineal tranfmits a 

 jed colour, and its furface is blacky when viewed 

 by incident light. But, if this liquor be agi- 

 tated, its furface is thereby covered with a red 

 froth, whofe colour is occafioned by the light, 

 fefieded from the globules of air inclofed in 

 each of the bubbles, and tranfmitted back, 

 through the tranfparent films of red liquor, 

 which cover them. 



I tinged feveral mafies of glafs with metals 

 io intenfely, that they appeared blacky except 

 in fuch parts as, from their thinncfs, tranfmitted 

 the Coloured Light. Pieces of thefe glafles 

 were pulverized feparately, and each of the 

 powders, thus prepared, exhibited the refpec- 

 tive colours, with which the feveral maffes of 

 glafs had been tinged. 



The aftion of fuch powders, on the rays of 

 light, arifcs from the difcontinuity of their parts, 

 whereby the air is admitted into their interftices, 

 and, by its refledive power, produces thofe 

 appearances, which refult from rare media con- 

 tained 



