158 Mr. Dela^val on the Cniife of thi 



ing, and fuch others as depend upon the know- 

 ledge, and management, of Colouring Materials, 



The experiments, by which the caufe of thofe 

 changes of colours was inveftigated, confided 

 chiefly of various methods of uniting the Colour- 

 ing Particles into larger, or dividing them into 

 fmaller, mafTes. 



I (hall now proceed to examine thofc proper- 

 ties of Permanently Coloured Subllance^, by 

 which they operate on the rays of light, in pro- 

 ducing colours. • 



No eflential information, relative to this fub- 

 jed, can be obtained from any optical writers, 

 who preceded Sir Ifaac Newton. For, the origin 

 and nature of light and colours were entirely 

 unknown, till they were unfolded by his re- 

 fearchcs. 



To him we owe the difcovery of the different 

 refrangibility of the rays of light; the invariable 

 colours of the differently refrangible rays; the 

 power of thin tranfparent plates, particles, and 

 fibres, to exhibit feveral colours, according to 

 their feveral thicknelTes and denfities ; as well 

 as the inveftigation and explanation of feveral 

 other properties of light. 



All thefe were refults of experiments made by 

 means of Tranfparent Colourlefs Media. But, he 

 does not appear to have examined, with equal 

 attention and fuccefs, the properties of Perma- 

 nently Coloured Bodies, and their operations on 



the 



