156 
4 1 '. Having thus examined the several properties 
of the primary rays, this great philosopher proceeded 
to apply his discoveries to the explanation of the per- 
manent colours of natural bodies. These colours, 
says he, arise from hence ; that some bodies reflect 
some sorts of rays ; others, other sorts more copious- 
ly than the rest. Every body reflects the rays of its 
own colour most copiously, and from the excess or 
predominance of these rays in the reflected light de^ 
rives its colour. And while bodies become coloured 
by thus reflecting this or that sort of rays, it is to be 
considered, he adds, that they stop and stifle in them- 
selves those rays which they do not reflect *. Hence 
it appears that Newton considered all coloured mat- 
ter to reflect light j and this reflexion he supposed to 
be made by some power of the body which is evenly 
diffused all over its surface, and by which it acts on 
the body without immediate contact f. 
416. According to Dr Wells, however, both Kep- 
jfer and Zucchius had previously shewn, by experi- 
ment, that light is reflected without colour from- the 
surfaces of bodies ; and that the colours of bodies 
depend, therefore, not'on the light reflected by their 
anterior surfaces, but upon that portion which has 
entered their internal parts, and is from thence sent 
back through those surfaces J. 
417. Beside the colours which are thus exhibited 
by reflexion, bodies appear coloured by the light that 
is transmitted through them ; and the bodies which 
thus appear of any colour by transmitted light, may, 
* Optics B. i. prop. 10. prob. 5. f Ibid. B. i\. prop. 8. 
J Phil. Transact, an. 1797, p. 418, 
