the Cause of Coloured Concentric Rings . 175 
is not well founded, because the modification of the subjacent 
reflecting surface, so essential to the formation of the phe- 
nomena under consideration, has not been attended to. In 
addition to this, the inference I have drawn from a foregoing 
experiment proves, that not only the modification of the re- 
flecting surface, but also that through which the rays are 
transmitted and radiate upon the subjacent one, must be 
equally taken into consideration. 
It remains therefore established, that by combination, the 
figure of either of the surfaces in contact, be it the reflecting 
or the radiating one, will make these appearances visible 
over an extended space, in the shape of rings, ellipses, lenti- 
cular figures, and all sorts of irregular configurations, except 
in the only case, where both reflection and radiation, happen 
between two plain surfaces in contact, and where consequently 
no change in the angle of seeing the critically separated rays 
can take place. The uniformity of this modification will then 
produce streaks, only visible in the bow place. 
If the objection should now assume the second form, which 
is, that unless I can show how the rays of the critical separa- 
tion thus modified can reach the eye, the rings must arise 
from some other cause, I may then fairly say, it is sufficient 
to have proved two very essential points, the first of which 
is, that these rings are formed from the colours of the critical 
separation, modified by the subjacent reflecting surface ; and 
the next, that when this modification is caused by subjacent, 
or even by incumbent surfaces of any curvature whatsoever, 
that can be brought into proper contact, their modification of 
reflection or radiation will then increase the field of visibility 
of all the various coloured phenomena that can be produced, 
A a 3 
