PHYSICAL and' literary, 3:^: 



lie acknowledges to be incident light pro- 

 perly refleded ; but the other, he fuppofes, is 

 properly emitted from the colorific parts of 5 

 the body. But what neceffity is there of re- 

 curring to this fuppojQtion, when we know, 

 flrevioully, thait the component parts * of all 

 opaque bodies are tranfparent j that, from' 

 every tranfparent body, there is at double re- ■ 

 flexion ; part of the incident light being re-' 

 fledted at the firft furface, and apart of what' 

 pafTes thro' the firft, refleded at the fecond ?' 

 and when we krtow, further, that very thm 

 bodies, (as foap-bubbles, Mi/fco'Vy- gh{s, and; 

 air in a fradure of glafs or ice, or between 

 two kfifesj while they refled fome rays of all 

 colour from the firft furface, refled only 

 particular colours at the fecond -f- ? Do not 

 thefe fads lead us naturally to fuppofe the 

 firft fort of hght to be only a part of the in- 

 cident light refleded from the firft furface 

 of the body ; and the fecond, a part of what 

 had pafTed on, refleded from the pofterior 

 furfaces of the fuperficial particles ? 



SECT, 



* AW/. Opt. book. 2. part 2. prop. 2. 

 f Ibid, book 2. part 3. prop. 12. 



