i^6 Mr. Delaval on the Cauje of ihi 



preceding obfervations, it appears, that the parti- 

 cles of coloured media infleft the feveral forts of 

 rays, according to the feveral fizes, and denfitics, 

 of the particles ; and alfo, in proportion to the in~ 

 flammability, of the media which owe their colour 

 to them : and it is manifeft, that the tranfmifHon 

 of coloured rays depends upon their inflection. 



All thefe obfervations are conformable to Sir 

 Ifaac Newton's dofbrine, that the rays of light 

 are reflected, refradted, and infleded, by one and 

 the fame principle, afting varioufly in various 

 circumftances. 



I have hitherto inveftigated, and explained, the 

 powers and operations, by which the rays of light 

 are tranfmitted through coloured media ; and, 

 have Ihewn that, in Opake coloured Bodies, they 

 are refleded by the Opake particles, which arc 

 conftituent parts of fuch bodies, and, that the 

 light, thus refleded, paffes back through the 

 Tranfparerrt Colouring Matter, with which the 

 opake particles are covered. 



It appears, both from the analyfis of Opake 

 Coloured Bodies, and from feveral other experi- 

 ments and obfervations, that the matter, by which 

 they reflect the light, confifts of white particles. 



The folid parts of animals, and vegetables, are 

 principally compofed of calcareous earth, which 

 is a perfectly white fubftance. This earth alfo 

 abounds in the mineral kingdom, as well as the 

 filiceous, and argillaceous, earths, and magnefia, 



which 



