g02 Dr. Herschei/s Experiments , &c. 
those that have been recited will surely be sufficient to show 
that the same operations, which will produce these prismatic 
phenomena, will equally account for those that are formed by 
the lens ; now, as it has been clearly proved, that the critical 
separation of the colours, which takes place at certain angles 
of incidence, occasions all the phenomena of the blue and red 
bows, and of the streaks, rings, and other regular or irregular 
appearances, that may be seen in a prism, there cannot remain 
a doubt but that the Newtonian rings observed between object 
glasses, are owing to the same cause. 
53. Remarks relating to the Newtonian alternate Fits of easy 
Reflection and easy Transmission. 
In attempting to rescue the science of optics, from what has 
been so long considered as unsatisfactory for explaining the 
great question about the cause of the coloured rings, I have 
made use of a principle, the effects of which have so near a 
resemblance to those of the suppositious fits of easy reflection 
and easy transmission, that the author of them might easily 
be misled by appearances. But although the principle of a 
critical separation of the colours substituted for these fits, ad- 
mits the reflection of some rays at the same angles of inci- 
dence at which others are transmitted, yet since the New- 
tonian different refrangibility of light will account for these 
critical reflections within glass, and the equally critical intro- 
missions from without, we can have no longer any reason to 
ascribe original fits to the rays of light, which in the first part 
of this paper, they have already been proved not to possess, 
and which now, in all prismatic experiments, I have shown are 
not necessary for explaining appearances that may be accounted 
for without them. 
Slough near Windsor, 
Dec. 9, 1808. 
