136 EXPERIMENTS AND INVESTIGATIONS 



edge and disposed on their side opposite to that edge, are 

 bent in the other direction "by the second edge acting on that 

 opposite side, and are, afterwards again bent in the direction 

 of the first bending by the action of the third edge upon the 

 side which was opposite the second edge and nearest the first 

 edge. But this side is the one polarized by the first edge, 

 and therefore that side is depolarized by the action of the 

 second edge. Hence it is proved that the rays polarized by 

 one flexion are depolarized by a second ; and as it is proved 

 by repeated experiments that no body placed on the same 

 side of the rays with any of the bending bodies, whether the 

 first or the second or the third, exercises any action on 

 those rays, it is thus manifest that any one flexion having 

 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. In- 

 stead 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 

 3 formed like C, instead of a straight-lined edge, 

 * f 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 de- 

 flexion, 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 propositions. 



