424 Mr. P. Cooper on the Connexion beta-ecu 



prism with the refracting angle downward. In the former 

 case, the light, and of course any object illuminated by it, 

 appears elevated, and in the latter case depressed, as it 

 would in passing through a prism, held as we have de- 

 scribed ; and the different images being differently ele- 

 vated or depressed, exhibit fringes, where the colours are 

 separated. 



The action of bodies upon light, which passes within the 

 sphere of their refractive force, being proved, not only by 

 the formation of diffracted light, but also by other experi- 

 ments, we cannot suppose that bodies when interposed in 

 such light, are divested of this influence as it regards the 

 general direction of the rays, though it may not otherwise 

 be necessary to the developement of the fringes. 



This action and its character is exhibited in the follow- 

 ing experiment: — 



If we place the edge of an object near the eye, and look 

 past it to a candle at some distance, so as to cut off a nar- 

 row vertical line of light, the light will be variously 

 refracted at different distances from the object, until they 

 are lost in the surrounding light. If we remove the ob- 

 ject to a greater distance from the eye, the images will be 

 reduced in breadth, so as at length to be scarcely distin- 

 guishable ; and if, when they are thus reduced, we bring 

 the edge of another object into such a position, that the 

 light, after passing the first object, must pass within the 

 refractive sphere of the second, and between the two 

 objects ; the images will again appear on the edge of the 

 first object broader, and more distinct than at first, and 

 there will be a very evident inclination of the light towards 

 the second object. 



In this experiment, the light diffracted by the first object, 

 passes the edge of the second, which acts upon it in the 

 same manner as when an object is interposed in light, dif- 

 fracted by the usual process ; and we have thus ocular 

 demonstration of the action of the interposed object, with 

 an evident proof that it draws the light which passes within 

 the sphere of its refractive influence towards itself. 



When light is diffracted by passing near the edge of 

 one body, and then passes near the edge of another 

 body, in an opposite direction, in the manner we have 



