St 
case seems to liave the power of producing these tints in a sort of 
neutral manner, as if it only relieved tliem in their utmost purity ; 
{Tab. 3. g. It. /.) and thin or pale tints marked by dark, or black, 
still give pale colours in proportion as they are pallid or less forcible 
themselves. 
COLOURS PRODUCED BY A CERTAIN BREADTH OF LIGHT ADMITTED 
BETWEEN REGULiVR PROPORTIONS OF BLACK, 
At 5 or 6 Inches Distance from the Prism. 
Tab. 3./ is a proportion that may give a general idea of four 
colours, red, blue, green and indigo ; the yellow being just seen at 
the edge of the green. In many instances the dazzling richness of the 
tints gives them more distinctness than perhaps belongs to them, (see 
Dr. Wollaston, and Dr. Young's descriptions, with that of Prieur's,) 
but I believe the tints in all cases blend a little as in our fioures, but 
" \\\w can paint as Nature paints" must argue for the want of nicety 
m them. Tab. 4. e. will perhaps convey a tolerable hint of the 
wider proportion producing the usual idea of the seven prismatic 
tints of sir Isaac Newton, and show how they mix : 
No. 2. Red No. 4. Orange Red and Yellow. 
No. 1. Yellow No. 5. Green Yellow and Blue, 
No. 6. Indigo Blue and a little Red. 
No. 3. Blue No. 7. Violet Blue and Red. 
It is perhaps difficult to account for the rays that produce the two 
last mixtures. We, however, always see them more or less perfectly. 
I suspect that the penumbra or loose rays that always accompany a 
beam of light, produce again by refraction the red, yellow, and 
blue, in a fainter manner upon the dark ground outside the princij)al 
spectrum. Thus the indigo No. 6. is found to consist of the blue 
with a proportion of the pale edge of the red so produced, and the 
violet No. r. has a portion of the stronger red in addition to the 
blue. Tab. 3. g. h. i. show that a narrow line of black gives the 
appearance of three tints chiefly, and those pale, as it were diluted 
with white, or water, as it has been done by the artist in the ex- 
