[ 38 ] 
has obferved that, when vegetables wither y feme 
“ of them turn to a greenifi yelloWy and others to 
“ a more perfect or orangey or perhaps to redy 
“ pafling firfl through the aforefaid intermediate 
“ colours : which changes feem to be effedted by 
the exhaling of the moiflure, which may leave 
** the tinging corpufcles more denfe and fomething 
“ augmented by the accretion of the oily and earthy 
‘‘ parts of that moifture.” Newton’s Optics, lib. ii. 
prop. 7. 
This is the only palTage in Newton, in which he 
inftances any permanent colour of a natural body as 
arifing from a change of denfity : and though he 
has not any where at large delivere'd his opinion 
on thisfubjedt; it appears that, in this cafe, he 
conlidered the lefs refrangible colours in withered 
vegetables as ariling from their increafe of denfity ^ 
which is what I endeavoured in the beginning 
of this paper to prove deducible from his doc- 
trines. 
I am. 
My Lord, 
Your Lordlhip’s 
moft obedient 
and moft humble fervant. 
Old Palace Yard, 
Jan. 17, 1765. 
Edward Delaval. 
IV. An 
