244 
LORD brougham’s EXPERIMENTS AND OBSERVATIONS 
disposed, a second polarizes the disposed side ; and that any one flexion having 
polarized, a second flexion depolarizes and disposes the polarized side. 
Exp. 3. Another test may be applied to this subject. Instead of a rectilinear 
edge, I made use of edges formed into a curve, as in fig. 12, where C is such an edge, 
and then the figure made is g h, corresponding to the curve e b. The first edge in 
the last experiment being formed like C, instead of a straight-lined edge, we can at 
once perceive that it has acted on the rays as well as the second and third edges, 
because these being straight-lined, never could give the comb-like shape g h to the 
fringes. This completely confirmed the other observations, and made the inference 
irresistible. 
Proposition IV. 
The disposition communicated by the flexion to the rays is alternative; and after 
inflexion they cannot be again inflected on either side ; nor after deflexion can they 
be deflected. But they may be deflected after inflexion and inflected after deflexion, 
by another body acting upon the sides disposed, and not by its acting upon the sides 
polarized. 
This is gathered from the experiments in proof of the second and third proposi- 
tions. 
Proposition V. 
The disposition impressed upon the rays, whether to be easily deflected or easily 
inflected by a second bending body, is strongest nearest the first bending body, and 
decreases as the distance between the two bodies increases. ^ 
Plate XI. fig. 1 1. Let AB = a be the distance between the first bending body and a 
given point, more or less arbitrarily assumed ; P the second body; AP= 2 ’; PM=r/, 
the force exerted by the second body at P ; C= the chart ; P M=r/ is in some inverse 
proportion to AP, but not as ^ p - or because it is not infinite at A, but of an 
assignable value there; therefore ; and the curve which is the locus of P 
has an asymptote at B, when x= — a. The fringes being received on the chart at C, 
it might be supposed that the dift'erence in their breadth, by which I measure the 
force, or y, is owing to P approaching the chart C, in proportion as it recedes from A, 
and thus making the divergence less in the same proportion ; but the experiments 
are wholly at variance with this supposition. 
Exp. 1. The following table is the result of one such experiment. The first column 
contains the distances horizontally of P from A, being the sines of the angle made by 
the rays with the vertical edges ; the second column contains the real distance of the 
second from the first edge, the secant of that angle ; the third column gives the 
breadths of the fringes at the distances given in the preceding columns ; the fourth 
gives the values of^, supposing MN were a conic hyperbola. 
