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LORD brougham’s EXPERIMENTS AND OBSERVATIONS 
those rays are bent most out of their course, because both the axis of the fringes is 
inclined, and also their breadths are various. 
Exp. 3. Though called by Grimaldi, the discoverer, the three fringes, as well as 
by Newton and others who followed him, they are seen to be almost innumerable, if 
viewed through a prism to refract away the scattered light that obscures them. I 
stated this fact many years ago*. 
Exp. 4. That the fringes are images may be at once perceived, not when formed 
in the light disc as in some of the foregoing experiments, but when formed in 
the shadow. Thus when the opposite edges are moved so near one another as to 
form fringes bordering the luminous body’s image, they are formed like the disc they 
surround. When you view a candle through the interval of the opposite edges, you 
perceive that the fringes are images of its flame, with the wiek, and that they move 
as the flame moves to and fro. When you observe the half-moon in like manner, you 
perceive that the side of the fringes answering to the rectilinear side of the moon, are 
rectilinear, and the other side circular ; and when the full moon is thus viewed, the 
fringes on both sides are circular. The circular disc of the moon is, indeed, drawn 
or elongated as well as coloured. It is, that is to say, the fringe or image is exactly 
a spectrum by flexion. Like the prismatic spectrum, it is oblong, not circular, and 
it is coloured ; only that its colours are much less vivid than those of the prismatic 
spectrum. 
Proposition II. 
The rays of light, when inflected by bodies near which they pass, are thrown into a 
condition or state which disposes them to be on one of their sides more easily de- 
flected than they were before the first flexion ; and disposes them on the other side 
to be less easily deflected : and when deflected by bodies, they are thrown into a 
condition or state which disposes them on one side to be more easily inflected, and 
on the other side to be less easily inflected than they were before the first flexion. 
Let RA (fig. 4) be a ray of light whose opposite sides are R A, R' A', and let A be 
a bending edge near which the ray passes, the side R' A' acquires by A’s inflexion, 
a disposition to be more easily deflected by another body placed between A and the 
chart C, and the side RA acquires a disposition to be less easily deflected than 
before its first flexion ; and in like manner R' A' aequires a disposition to be more 
easily inflected, and RA a disposition to be less easily inflected by a body placed be- 
tween A and C. 
Exp. 1. Place A' (fig. 5) in any position between A and vr, the image made on C 
by A’s influence, as at A' or A", or close to A at A'". If it is placed on the same side 
of the ray with A, no diflFerence whatever can be perceived to be made on the breadth 
of rv, or on its distance v R' from the direct ray RR'. In like manner the image by 
deflexion r' v' is not affected at all, either in its breadth, or in its removal from RR' 
by any object, a, a', placed on the same side with A of the deflected ray A v'. 
* Philosophical Transactions, 1797, Part II. 
