352 Mr. P. Cooper on the Connexion between 



them, however, will so interfere with each other, in conse- 

 quence of the very gradual difference of refraction, that, 

 while their continuity is uninterrupted, they will form a 

 surface of white light by superposition. 



In order to observe the different phenomena of diffracted 

 light, let a lens L L, of very short focus, be fixed in the 

 window shutter, M N, of a dark room ; and let R L L be a 

 beam of the sun's light transmitted through the lens. 

 This light will be collected in the focus F, from which it 

 will diverge in lines F C, F D, &c, and form a circular 

 image of diffracted light on the screen, C D. 



" The shadows of all bodies whatever held in this light, 

 will be found to be surrounded with three fringes of the 

 following colours, reckoning from the shadow : 



First fringe. — Violet, indigo, pale-blue, green, yellow, 

 red. 



Second fringe. — Blue, yellow, red. 



Third fringe.— Pale-blue, pale-yellow, pale-red." 



" Let a body B be now placed at the distance B F from 

 the focus, and let its shadow be received on the screen 

 C D, at a fixed distance from the body B, and the follow- 

 ing phenomena will be observed : — 



1. Whatever be the nature of the body B with regard to 

 its density or refractive power, whether it is platina or the 

 pith of a rush, whether it is tabasheer or chromate of lead, 

 the fringes surrounding its shadows will be the same in 

 magnitude and in colour, and the colours will be those 

 given above. 



If the light R L is homogeneous light of the different 

 colours in the spectrum, the fringe will be of the same 

 colour as the light R L, and they will be broadest in red 



