Discovery of his Theory of Colors. 259 
tions of the sympathetic fibers of the retina; substituting red, 
green, and violet, for red, yellow, and blue, and the numbers 7, 
6, and 5, for 8, 7, and 6.” 
It thus appears that Young changed his three elementary 
color-sensations from red, yellow, and blue, to red, green, an 
violet, “‘in consequence of Dr. Wollaston 
nificance. 
‘“‘T cannot conclude these observations on dispersion with- 
out remarking that the colours into which a beam of white light 
is separable by refraction, appear to me to be neither 7, as they 
usually are seen in the rainbow, nor reducible by any means 
(that I can find) to 8, as some persons have conceived ; but that, 
by employing a very narrow pencil of light, four primary divi- 
sions of the prismatic spectrum may be seen, with a degree of 
distinctness that, I believe, has not been described nor observed 
efore. 
‘Tf a beam of daylight be admitted into a dark room by a 
crevice ,'; of an inch broad, and received by the eye at the dis- 
tance of 10 to 12 feet through a prism of flint glass, free from 
veins, held near the eye, the beam is seen to be separated into. 
the four following colours only, red, yellowish green, blue and 
violet ; in the proportions represented in fig. 2. 
“The line A that bounds the red side of the spectrum is 
somewhat confused, which seems in part owing to want of power 
mM the eye to converge red light. The line B, between red 
nd green, in a certain position of the prism, is perfectly dis- 
tinct; so also are D and H, the two limits of violet. But ©, 
