the Cause of Coloured Concentric Rings . 177 
are produced by the contact of two plain surfaces, it would be 
an endless undertaking to follow them till they enter the 
eye. Enough has already been said upon this subject to con- 
vince every intelligent reader, that all the phenomena of 
coloured rings, which have been ascribed to the effect of cer- 
tain fits of easy reflection and easy transmission of the rays 
of light, as well as the great variety of other coloured ap- 
pearances of which I have treated, admit of a most satisfactory 
solution, by substituting the solid principle of the critical 
separation of the different colours in the room of these fits. 
