. 
into the prismatic Colours. 195 
you perceive a fringe of reflected red and yellow: paste another 
similar strip parallel to this, at about four inches distance, on 
looking through the prism you perceive the north to be fringed 
with blue. Thus we have three primary colours nearly in contact. 
The yellow rays of the upper paper, being the most refrangible, 
come nearest to the blue of the lower paper; and if we approach 
them, a green is formed by their mixture, so that we can now 
without any difficulty account for five of Sir Isaac Newton’s co- 
lours, red, orange, yellow, green, and blue. By making a small 
hole in his window-shutter, he brought the northern and southern 
fringes into contact or mixture, and produced five colours with 
three. It now remains to account for the indigo and violet; and 
here I must again refer my reader to my last communication, in 
which I have shown that blackness arises from the refiection of 
blue, red, and yellow ; which being granted, the solution of this 
otherwise difficult question becomes easy. The red and yellow of 
the lower cloth or paper, being more refrangible than the blue, 
were brought down by passing through the prism, leaving the 
upper part of the lower edge (when illuminated by the undecom- 
posed light coming through) blue. Under the blue appeared in- 
digo, which, as I shall hereafter show, is composed of blue, red, 
and yellow, in a different state of condensation from black. And 
at the bottom of all appeared violet, arising from a great quan- 
tity of yellow and red, which had been brought down, mixed with 
the black rays. From this experiment we might conclude, that 
Sir Isaac Newton by mixing three primary colours made seven. 
But I am aware, it might be objected, that Sir H. Englefield 
and others decomposed, or thought they decomposed, incident 
light coming immediately from the sun, by passing it through a 
prism placed at an open window. So far however from refuting, 
this experiment confirms my opinion, that incident light was 
never yet decomposed, as I shall now endeavour to prove. The 
prism, being a semitransparent substance, when turned in such 
a manner on its axis as partly to reflect and partly to transmit 
the rays of light, (for it will never decompose if turned at right 
angles to the sun,) condenses and reflects fringes of blue, red, and 
yellow, from each of its angles; and these fringes of reflected light, 
being carried forward through the prismatic planes by the inci+ 
dent and undecomposed light, intermix by their different refran- 
gibilities, and form a spectrum of seven colours ; and as there are 
three angles in every prism, so there are two spectra always 
formed, in the same manner as three strips of paper, pasted pa 
rallel to one another on the window, will also form two spectra. 
As I am well aware that my experiments and opinions are in 
opposition to authorities of the ve respectability in science ; and 
2% 4 as 
