2S 
help of a prism, will appear like (/. 1, having the five prismatic tints, 
as Tab. 3. /; d. 1 being distant like c. 1 from c. 2, it does not interfere 
with d. 2, but c. 2 is so near c. 3, as to allow one portion of yellow, 
as in d. 2, which does not diminish in breadth, to reach the blue of 
c. 3, forming a green binary, that may be distinctly seen, without 
mixing with the other colours ; and so of the rest, which by their 
construction give deeper mixtures of greens; and finally they become 
triple compounds, as may be seen at c. 4 and 5, the red of 4 being 
mixed with the blue of 5, the j'ellow of which passes as it were over 
the violet and purplish red of 5, causing blue, red, or yellow browns, 
in many degrees, where it passes over the red, the browns becoming 
warmer, &c. No. 5 is narrow, like Tab. 3. g. that it may as it were 
admit of the colours produced from the black of 4 above it 
being effective. Thus we have a means of producing browns, 
and different proportions may be made use of for different pur- 
poses of measure, &c., as these are portioned in divisions of about 
the 10th of an inch in width, to show what is the proportion mixed 
or causing the mixture. Thus the four examples of black, each about 
-■Lths of an inch wide, approach nearer by -pirthj ^^ich producing, in 
conjunction with its proportion of white, a broad set of colours, and 
this is made distinct even in the narrow line, 5, which is only ^^^ths 
of an inch wide, and ^'^th is left of white, (see c. 4 and 5, and d. 4 and 
5,) which just allows of an almost imperceptible penumbra to join 
the brown in the latter example. 
OF GRADUATING TINTS, &c. BY WEDGES. 
If two wedges are placed opposite each other, they may be so 
arranged that the space between shall allow the colours produced to 
form a green mixture, and the green thus formed will be blue green 
prism, to put as few figures of reference as possible, as in such examination each figure 
will give a certain quantity of colour. We therefore request the reader will understand 
that c. 1 means the black mark nearest the letter c ; and d. 1 the first range of colours 
nearest d, reckoning downwards cord. 1, 2, 3, 4, 5. 
