PHYSICAL AND LITERARY. jy 



pothefes concerning the caufe of gravity). 

 In his Optics, he- lays down his difcoveries 

 at full length, without ever inquiring whe- 

 ther light confifts in vibrations propagated 

 thro' a fluid or of particles projeded in 

 ilraight lines from the luminous body : and, 

 in . his queries, where he touches this matr 

 ter *, he feems to be more pofitive in reje6l- 

 ing the hypothefls of vibrations, than in efta- 

 bliiliing any other. 



32, But Eukr likeways advances a new no- 

 tion with refped to the origin of colours in 

 opaque bodies, which is intirely inconfiftent 

 with the principal part of Sir Ifaac Newton^ 

 dodrine. He fuppofes, that coloured bo- 

 dies refled the:fun's incident white light from 

 their anterior furface j but, that the par.ticu- 

 lar fpecies of light, by which they appear 

 (Coloured, is properly emitted by the parts of 

 the body : for inftance, he imagines that 

 verm-ilion does not appear red by a more co- 

 pious reflexion of red than of other incident 

 rays, but by the new emiilion of red rays 

 from the particular velocity of vibration 

 which its elaflic parts are capable of concei- 

 ving by the impulfe of the incident light. 



33- It 



* i\Vw/. Opt. quer. 28. and 29. 



