128 EXPERIMENTS AND INVESTIGATIONS 



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 

 Rg.5. the same side of the ray with 



A, no difference whatever can 

 be perceived to be made on the 

 breadth of rv, or on its dis- 



tance v~R' from the direct ray BE'. In like manner the 

 image by deflexion r' v' is not affected at all, either in its 

 breadth, or in its removal from E R' by any object, a, a', 

 placed on the same side with A of the deflected ray A v'. 



Y 6 But (fig. 6) place B anywhere 



_ between A and v r on the side 



of the ray opposite to A, and 

 the breadth of rv is increased, 

 and also its distance from the direct ray E E', as v' r' ; and in 

 like manner (fig. 7) the deflected rays A v, A r are both more 



separated, making a broader 

 image at r" v", and are further 

 removed from E E' by B's in- 

 flexion. 



Exp. 2. If you bend the rays either by a single edge, or by 

 the joint action of two edges, it makes not the least difference 

 either in the breadth or in the distance from the direct rays 

 of the images, or in the distension or elongation of the lumi- 

 nous body's disc, whether the bending body is a perfectly 

 sharp edge (which in regard to the rays of light is a surface, 

 though a narrow one), or is a plane (that is, a broader sur- 

 face), or is a curve surface of a very small, or of a very large 

 radius of curvature. 



In fig. 8, a e is an instrument composed of four pieces of 

 different forms, but all in a perfectly straight line ; a & is an 

 extremely sharp edge ; b c a flat surface ; c d a cylindrical or 

 circular surface of a great radius of curvature ; de one of a 

 small radius of curvature. But all these pieces are so placed 

 that E 3 y is a tangent to ed, d c, and is a continuation of 

 y ft K, that is, of c b, b a. So the light passing by the whole 

 abode, passes by one straight line E K, uniting or joining 



