4°90 A new Theory of Light. 
conclusive, especially when opposed to those direct ones 
on which [ found my opinion. t 
In my last paper sent to Nicholson’s Journal, I men- 
tidned my having formed a perfect black, by mixing the 
seven different colours of the rainbow in different propor 
tions; and that after drawing lines with this composition, 
on white paper, I analysed them by means of a powerful 
plano-convex Jens or prism into indigo and orange, which 
two colours contain the three primary rays, red, yellow, 
and blue, from which all the others might be formed. 
SirIsaac Newton, in looking through a telescope at a 
black body, observed those colours ; but he was so impressed 
with his own beautiful theory, that he superficially ex- 
amined the circumstance: he says, ‘* If a black object be 
surrounded with a white one, the colours which appear 
through the prism are to be derived from the light of the 
illuminated one spreading into the regions of the black ; and 
therefore they appear in a contrary order to that in which 
they are seen when a white object is surrounded with a 
black one*.”” To show the fallacy of this reasoning, I made 
the following experiments: 
Experiment 1.—I drew a line with a perfect black ink 
on a sheet of red paper, and, on applying my prism, ana- 
lysed it into a beautiful deep blue and orange. The red 
rays reflected from the illuminated paper added to the bril- 
liancy of the orange. Whence was the indigo derived? 
Certainly not from the red paper. If Sir Isaac Newton’s 
theory were correct, nothing but red, which is a primary 
colour, spreading into the regions of the black, should have 
met the eye. 
Experiment 2.—I drew a line with black ink on a sheet 
of yellow paper, and, on analysing it in a similar manner, 
perceived an indigo, orange, and a beautiful green; the yel- 
low rays of the illuminated paper had blended with the 
blue of the indigo, and formed a green. 
Experiment 3.—I drew a line with black ink on a blue 
paper, and obtained only indigo and orange. 
Experiment 4.—Having clung two pieces of transparent 
white paper, of a similar size, on a large pane of glass at 
the window, I applied my prism, and perceived a fringe 
of blue, red, and yellow, forming a beautiful artificial rains 
bow of a light tinge. If Sir Isaac Newton’s theory of 
light avere correct, it is obvious that, as I increased the 
* Newton's Optics, p, 141. 
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