25 
forms distinctly, when viewed at a moderate distance or from the 
bottom of the j)hite, the orange binary ; and again, yellow No. 1 
passing among blue No 3, forms the green binary ; and lastly, 
red No. 2, at the bottom of letter a. passing among blue No. 3, 
forms the violet or purple binary: the whole sum of the proper bi- 
naries, excepting their being ligliter or darker. 
I shall now consider them combined by threes, or in Ternaries, b. 
iit the bottom of the same Tab. 4. thus; Nos. I and 3, yellow and 
blue, pass into Nos, 2 and 3, red and blue, and the yellow and red 
being inost prominent, the efTect becomes at a moderate distance, or 
from the top of the plate, orange brown, as at the bottom half; and 
where there is a double portion of blue as in the upper half, it is a 
darker brown when seen at such a distance as that the effect may 
unite the whole to our vision. We see therefore that independent 
coloured rays may become so placed as to give the sense of a perfect 
mixture, which would have been the case with these if the lines had 
not been made visible, which, however, was absolutely necessary to 
explain them to our purpose : fine dots of the primaries among each 
other would produce binaries or ternaries with a similar effect, also 
one transparent tint over another, &c. 
CHROMATOMETER. 
I now enter upon a curious subject ; and I presume that even after 
what has been said and done, it will appear at first a sort of chimaera 
for a parcel of dark unintelligible forms to give a most exact account 
of the proportion of colours. Having in the preceding part shown 
in what manner colours are produced by means of the proportions 
of black upon a white ground, or white on a black ground, this is in- 
tended to serve as a lasting means of proving the hypothesis, or as a 
test for any particular tint, under whatever impression we wish to 
form a comparison. 
I shall here denominate the black forms productors, as they ap- 
pear to produce the colours ; their proportions being told or mea-. 
E 
