II 
from each other, rings of different colours appeared. To observe 
more nicely the order of the colours produced in this manner, he 
took two object-j>lasses ; one of them a plano-convex one belonging 
to a fourteen-feet refracting telescope, and the other a large double 
convex one for a telescope of about fifty feet; and laying the former 
of them upon the latter with its plane side downwards, he pressed 
them slowly together ; by which means the colours very soon 
emerged, and appeared distinct to a considerable distance. Next to 
the pellucid central spot, made by the contact of the glasses, suc- 
ceeded blue, white, yellow and red. The blue was very little in 
quantity, nor could he discern any violet in it ; but the yellow and 
red were very copious, extending about as far as the white, and four 
or five times as far as the blue. The next circuit immediately sur- 
rounding these consisted of violet, blue, green, yellow and red : all 
these were copious and vivid, except the green, which was very little 
in quantity, and seemed more faint and dilute than the other colours: 
of the other four, the violet or purple was the least in extent, and 
the blue les.s than the yellow or red. The third circle of colours 
was pur}>le, blue, green, yellow, and red : in this the purple seemed 
more reddish than the violet in the former circle; and the green was 
more conspicuous, being as brisk and copious as any of the former, 
except the yellow; but the red began to be a little faded, inclining 
much to purple. The fourth circle consisted of green and red ; and 
of these the green was very copious, inclining on the one side to 
blue, and on the other to yellow : but in this fourth circle there was 
neither blue, violet, nor yellow, and the red was very imperiect 
and dirty. All the succeeding colours grew more and more im- 
perfect and dilute, till after three or four revolutions they ended in 
perfect whiteness*. It is perhaps now to be wondered that sir Isaac 
Newton did not take more particular notice of the fading of the 
violet and red, or of their becoming more of a diluted cast, and of 
* Probably brownish first. I have not the means of trying his glasses, but it seems a 
general law that has been overlooked, as a sign of obscurity perhaps. 
c 2 
