Discovery of his Theory of Colors. 255 
in a similar form in his own works; and this by no less a 
mathematician than Leonard Euler, whose system of light, as 
far as it is worthy of notice, either was, or might have been, 
wholly borrowed from Newton, Hooke, Huyghens and Male- 
branche. 
‘Those who are attached, as they may be with the great- 
est justice, to every doctrine which is stamped with the New- 
tonian approbation, will probably be disposed to bestow on 
these considerations so much the more of their attention as they 
shall appear to coincide more nearly with Newton’s opinion. 
For this reason, after having briefly stated each particular posi- 
tion of my theory, I shall collect, from Newton's various writ- 
ings, such passages as seem to be the most favorable to its admis- 
sion; and although I shall quote some papers which may be 
thought to have been partly retracted at the publication of the 
optics, yet I shall borrow nothing from them that can be sup- 
posed to militate against his maturer ju 
The fact that Young, the founder of the undulatory theory of 
hight, in this Bakerian Lecture, in which it has been said that 
he laid the foundations of that doctrine, should set forth his 
views in a series of postulates followed by citations from the 
writings of Newton, to give them weight and proof, may justly 
surprise those who have trusted to the second-hand information 
derived from carelessly-complied text books and from. hastily- 
propane popular lectures. But then, where would be the pugi- 
istic charm of the popular lecturer on the undulatory theory of 
light, if Newton, his champion, the violent defender of the ema- 
nation cause, should decline to enter as a contestant 
Under the heading of Hypothesis III, of this paper, we first 
meet Young’s theory of color-sensation. 
“ Hypothesis IIL Zhe Sensation of different Colours depends on 
the different frequency of Vibrations, excited by Light in the Retina. 
Passages from Newton. 
_ “The objector’s hypothesis, as to the fundamental part of it, 
is not against me. That fundamental supposition is, that the 
parts of bodies, when briskly agitated, do excite vibrations in 
the ether, which are propagated every way from those bodies in 
straight lines, and cause a sensation of light, by beating and 
dashing against the bottom of the eye, something after the 
manner that vibrations in the air cause a sensation of sound, by 
beating against the organs of hearing. Now, the most free 
and natural application of this hypothesis to the solution of 
phenomena I take to be this : that the agitated parts of bodies, ac- 
cording to their several sizes, figures i a do excite vibra- 
tions in the ether of various depths or bignesses, which being pro- 
miscuously propagated through that medium to our eyes, etfect 
