266 Mr. Delaval on the Caufe of the 



of the Opakc Coloured Body, through the Tranf- 

 parent Coloured Medium. 



When a fmall portion of colouring matter is 

 mixed with a colourlefs medium, the mafs appears 

 tinged with colour; but, when a great quantity 

 of colouring matter is added, the mafs exhibits 

 no colour, but appears black. Therefore, to at- 

 tribute to colouring matter a refledive power, is 

 to advance an inexplicable and contradiflory pro- 

 pofition : for, it is aflerting, that, in proportion 

 as more refleftive colouring matter is oppofed 

 to the incident light, lefs colour is refleded ; and 

 that, when the quantity of colouring matter is very 

 great, no colour at all is refleded, but blacknefs 

 is thereby produced. 



From thefe arguments, it might have been 

 (hewn, that the reflediVe power does not cxift in 

 colouring matter, but in Opake White Subdances 

 only. Neverthelefs, in this difquifition, I have 

 not entirely relied on arguments drawn from a 

 fewj known and obvious, appearances, but have 

 endeavoured, by numerous experiments, to afcer- 

 tain the caufe of the colours of natural, as well 

 as artificial bodies, and the manner in which they 

 sre produced. 



M. Euler obferved, * that the colours of bodies 

 pre not produced by refledion. He fuppofes that 

 the coloured rays are emitted by the colorific 

 particles. This hypothefis, however, is not agree- 

 able to experiment. For, as the colouring matter 



* Acad. Berlin. Ann. 1752. p. 262. 



36IS 



