21 SI ON A NATURAL SYSTEM 



cular kinds of rays be reflected ; would we en- 

 quire into the caufe of this phenomenon, we 

 mud feck it in the quality of the furface, which 

 is indeed often fu tranlk-nt, that the colour may 

 be changed, or entirely dedroyed by the heat 

 of boiling water, or even by the influence of fo- 

 lar light. 



A tranfparcnt colour arifes from tranfmittcd 

 rays, and feems to indicate a fpecies of attrac- 

 tion ; while, on the other hand, an opaque co- 

 lour implies rcpuliion. Both without doubt fug- 

 ged the idea of tome relation between the light 

 and the given body ; but which is of fuch fub- 

 tlety, that though it alone were varied, the cha- 

 racter of the matter remains altogether unalter- 

 ed ; at lead the difference is hot obvious to the 

 fc nil's. We have fccn, that tranfparency de- 

 pends upon the difpoiition of the particles ; and 

 this once didurbed, the tranfparency vanilhes, 

 and with it all the effect produced by tranfinit- 

 ted rays. Thefe fe\ eral appearances feem to a- 

 rife from the phlogiitic molecules, \\hich vary ei- 

 ther as to quantity, magnii ude, or eladicity. Ve- 

 locity even determines the difference of colours. 



5 xxvi. Internal Texture ami Form. 



WE have already touched on interim! te\ture 

 and form in the foregoing divifions, ($ xviii.) 



Determinate 



