Permanent Colours of Opake Bodies. ' 11 c 



no reflexion is made by Coloured Matter, but 

 by White, or Colourlefs, Particles only. 



Sernipellucid Subf^ances, which appear of one 

 colour when viewed by incident light, and of 

 another colour when viewed by tranfmicted light, 

 confift of pellucid media, throughout which 

 White, or Colourlefs, Opake Particles are dif- 

 fufed. 



The opake particles are difpofed at fuch dif- 

 tances from each other, that fome of the inci- 

 dent rays of light are capable of pafTing through 

 the intervals which intercede them, and thus 

 are tranfmitted through the femipellucid mafs. 



Some forts of rays penetrate through fuch 

 mafTcs, whilft other forts, which differ from them 

 in their refrangibility, are refleded, bv the 

 White, or Colourlefs, Particles, and from thence 

 are tranfmitted back through the pellucid part 

 of the medium, which intervenes between the 

 refleding particles and the anterior furface of 

 the mafs. 



When pellucid colourlefs glafs is melted with 

 arfenic, the arfenic is thereby divided into mi- 

 nute opake white particles, which are equably 

 diffufed throughout the glafs. If only a fmall 

 quantity of arfenic is ufed in this compound, 

 the white particles are rarely difleminated in it. ' 



When glafs, thus combined with a fmall prL 



portion of arfenic, is held between the windo^r 



and the eye, it appears Yellow or Oranae 



^"^•"- Q. . Cqjgured, 



