the Inflection, Reflection, and Colours of Light. 261 
that, upon the whole, there appears every reason to believe 
that the rings are formed by the first surface, out of the light 
which, after reflection from the second surface, is scattered, 
and passes on to the chart. It will follow, 1. that a plane 
mirror makes them not, for the regularly reflected light, not 
being thrown to a focus, mixes with the decompounded scat- 
tered light, and dilutes it. 2. That the nearer to the perpen- 
dicular the rays are incident, the more light will be reflected 
to the focus, and consequently the less will dilute and weaken 
the rings. 3. That the thinner the mirror is, or the nearer 
the two surfaces are, the broader will the rings be. 4. That 
the rings farther from the focus will be broader. And lastly, 
that when homogeneous light is reflected, the fringes or images 
will be larger, and farther from one another, in red than in 
any other primary colour. All which is perfectly consistent 
with the experiments of Newton and Chaujlnes. There is 
only one difficulty that may be started to this explanation : 
how happens it that the colours (made by the mirror) are al- 
ways circular ? We answer, it is owing to the manner of po- 
lishing the concave mirror, which is laid between a convex 
and concave plate, and then turned round (with putty or 
melted pitch) in the very direction in which the rings are. If 
it should be asked, why does the thickness of the mirror in- 
fluence the breadth of the rings exactly in the inverse -subdu- 
plicate ratio ? We answer, that to a certain distance from the 
point of incidence (and the rays are never scattered far from 
it) this is demonstrable, to hold as a property of mathematical 
lines in general. 
Having found that the fringes by flexion are images of the 
