Tennment Colours of Opake Bodies. 249 



In a former work, I have (hewn by a feries 

 of experiments, that the changes of colour, 

 which Permanently Coloured Subllances under^ 

 go, are made in a regular order, accordingly 

 as the fizes of their colouring particles are dimU 

 nifhed, or augmented. 



I have here adduced fome examples of the 

 influence of denfity and of phlpgifton, on the 

 colours of the bodies. 



Befides thefe means, by which the colours of 

 fome fubllances are affe6led, I have frequently 

 obferved that there is another caufe, by which 

 changes are produced in Tranfparent Coloured 

 Media, not only in the degree, but alfo in the 

 fpecies of the colour. 



Thefe changes arife from the greater, or lefs 

 obflruflion which the rays meet with, in their 

 paffage through the interftices which intercede 

 the Colouring Particles i according to the thick- 

 riefles of the media, and the quantity of colouring 

 matter diffufed through them. 



Tranfparent Coloured Media ac^ upon the 

 rays of light, more fimply and uniformly, than 

 Semipcllucid Subftances : becaufe, in thefe 3 

 greater variety of phjenomena refult from the 

 different forces of the Opake Particles : by which 

 fome of the rays are reflcfted, whilll others are 

 tranfmitted. 



Although all Tranfparent Coloured Media 

 ^rapfmic a lefs quantity of the jijcident rays, 



