157 
also, says Newton, look of the same colour by re- 
flected light *. But the numerous experiments of 
Mr Delaval prove, that, in transparently coloured li- 
quors, the colouring matter does not reflect any light ; 
and that, if the light, which such liquors transmitted, 
be stopped, they do not vary from their former co- 
lour to any other colour, but become entirely black f. 
This conclusion he extends to transparently coloured 
solids as well as fluids J. The light, also, which 
opaquely coloured bodies, as plants, return to the 
eye, continues Mr Delaval, is reflected by their 
white opaque substance ; and the colours of vegeta- 
bles, therefore, are produced by the light reflected 
from this white matter, and transmitted from thence 
through the coloured coat, or covering, which is 
formed on its surface by the colouring particles . 
418. Admitting, then, that the permanent colours 
of natural bodies depend on the varied reflexion or 
transmission of the differently coloured rays, we have 
yet to learn why these bodies reflect or transmit some 
sorts of rays in preference to others, so as to present 
to our view that great diversity of colours which they 
exhibit. Sir Isaac Newton resolves this property of 
bodies into the varying thickness or density of their 
particles, and lays it down as a general law, that the 
forces of bodies to refract and reflect light are very 
nearly proportional to their densities ; so that nothing 
more, says he, is requisite for producing all the co* 
* Optics B. i. part 2. prop. 10* 
t Manch. Mem. vol. ii. p. 140*. 
| Ibid. p. 150. Ibid. p. 19 
