12 
the three primitive tints mixing as the circles became narrower, 
which was the cause of the green in the third ring. As the colours 
were found to vary according to difi'erent distances of the glass plates 
from each other, our author showed that they proceeded from the 
different thicknesses of the plates of air intercepted between the 
glasses. But to return to the order in which he so naturally found 
the colours in the circles. — First, the three primitives and the seven 
prismatic tints naturally mixed from them, which I wish he had 
been aware of, as it would have accounted for the other rings or re- 
volutions. I have therefore produced an example of the order of 
his tints in Plate 1. figures 1, 2, 3, &c. in which it will appear that 
the rings which are called revolutions begin in a natural order, al- 
though reverse to what I have begun with, viz. first blue, whereas 
I have begun with yellow. This however is because his instruments 
were reversed, two opposite convex surfaces producing them in his 
scheme, and two concave opposites producing my past example. 
Thus, No. 1 is Blue 
2 — White* 
3 — Yellow 
4 — Red 
5 — Violet 
6 — Blue 
7 — Green 
8 — Yellow 
9 — Red 
10 — Purple 
1 1 — Blue 
12 — Green 
13 — Yellow 
1 4 — Red 
15 — - Greenish 
16 — Dirty ish Red, &c. 
* White is light, dependent upon the distance of the rings or revolutions which begin 
or end the series, as Red or Blue, which in these cases come back to back as it were, 
