126 EXPERIMENTS AND INVESTIGATIONS 



made to pass through it. But instead of making the fringes 

 by a single edge deflecting, and so casting them in the spec- 

 trum, I approach the opposite edges, so that both acting 

 together on the light, the fringes are seen in the shadow and 

 surrounding the spectrum. These fringes are no longer 

 parallel to the shadows of the edges as they were in the white 

 light, but incline towards the most refrangible and least 

 flexible rays, and away from the least refrangible and most 

 flexible. Thus the red part r of the fringes is nearest the 

 shadow of the edge a'; the orange, o, next ; then yellow, y ; 

 green, g ; blue, b ; indigo, i ; and violet, v. Moreover, the 

 fringe r v is both inclined in this manner, so that its axis is 

 inclined, and also its breadth increases gradually from v to r. 

 This is a complete refutation of the notion entertained by 

 some that Sir I. NEWTON'S experiment of measuring the 

 breadths in different coloured lights and finding the red 

 broadest, the violet narrowest, explains the colours of the 

 fringes made in white light as if these were only owing to 

 the different breadths of the fringes formed by the different 

 rays. The present experiment clearly proves, that not only 

 the fringes are broadest in the least refrangible rays, but 

 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 GP.IMALDI, the discoverer, the 

 three fringes, as well as by NE\VTON 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 per- 

 ceived, 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 



* Philosophical Transactions, 1797, part II. 



