l6z On the general Nature of IJight. 



the fubtileft of all vifible fubftances, renders it infinitely 

 fepfible, equally to the general attractive force and (o the 

 chemical affinities of other bodies approaching it : — for thefe 

 reafons, the fame general and chemical affinities, which pro- 

 duce the other changes on material bodies, mull appear luf- 

 iicient to decafion the different phenomena which light pre- 

 fects in its various trantitions. 



4. The true primitive colour of light, when unmixed 

 with other fubftances, when its particles exift together in 

 their natural arrangement and aggregation, when the at- 

 tractions of other bodies for it act not fo as to fcatter or de- 

 compofc its parts, is white. 



5. Its colours and its peculiar action on the optic nerve 

 depend on the peculiar forms of its elementary particles, on 

 their peculiar aggregation, on their mechanical and chemical 

 qualities, on the modes of its dvffufion. 



6. It pajjes without alteration or deflexion through tranf- 

 ■p.ifcnt Indies in winch the abfolnte vacancies are fufficientfy 

 numerous to receive its rays, in which the dilpofition of 

 thefe vacancies is perpendicular to the direction of the rays, 

 and in which the attractions of the body for the light arc 

 not fo ftrong as to act on the rays with a diflblving or a de- 

 compiling force. 



7. It is refracted )' when the vacuities iit the bodies on 

 which it falls are not difpofed throughout the tranfparent 

 medium perpendicularly to the direction of the rays 5 and 

 when the attractions, chemical and mechanical, of the 

 parts of that medium are, in refpect to light, fo powerful as 

 to occalion either a tendency to the carrying of the ray into 

 new combination, which flia.ll alter its aggregation, or even 

 a partial fixation of it in fotne new compound. 



8. It is reflected when it falls on furfaces which patent 

 no rectilinear vacancies, none but inch as are curves, 

 through which its rays cannot pal's; and when, at the fame, 

 time, thofe furfaces have no affinities for its particles of 

 hiifieient ltrength to attract thefe particles into their own 

 compofition. When thefe circumfiances concur in their 

 utmoft power tlie reflexion is complete, and all the falling 

 rays are returned from thefurface; but the required cir- 



4 curo,ftances 



