1835.] Composkion of White Light, 356 



bringing the images into a position in which they exactly 

 correspond, or absorbing the whole of the colour, or colours, 

 of which they are formed. 



If we direct a common telescope to an uniform surface of 

 white light, the field of view will be surrounded with blue 

 and violet fringes ; the complementary fringes, red and 

 yellow, being gradually lost in the white centre by a system 

 of mutual compensations. But if the field of view be broken 

 by the interposition of different objects, this mutual com- 

 pensation will be interrupted, and every interruption will 

 be marked w*ith complementary colours, which will be most 

 distinctly seen upon the edges of white objects ; where they 

 will be violet and blue on one side, and yellow and red on 

 the other. 



These fringes are a necessary consequence of the diff'erent 

 refrangibility of light : the violet rays converge at a greater 

 angle than the green, and the green at a greater angle than 

 the red; of course, they arrive at a focus, so as to form 

 correct images, at different distances from the object glass. 

 Now, if it were possible to view these images through the 

 glass by which they are formed, or through any other similar 

 to it, and in the same direction, the images, notwithstanding 

 their different distances, would fall upon the retina together, 

 and form one correct picture, because these distances are 

 precisely what are required for this purpose ; the effect of 

 refraction, when the images fall on the eye, being in every 

 respect the reverse of what it is when they fall on a screen. 

 But when we view these images, as we necessarily do, in 

 an opposite direction, the eye glass, instead of correcting, 

 doubles the defect; the violet image, which, to produce 

 distinct vision of the whole, should be the nearest, is the 

 most distant ; and the red, which requires to be kept at a 

 greater distance to form a corresponding image with the 

 violet, is the nearest ; of course, the violet, which, after 

 passing the focus, is not only the most divergent, but de- 

 verges through a greater space, forms the largest image ; 

 the green, the next in size ; and the red, the smallest ; and 

 when these images are superposed, the different appear- 

 ances, as already described, are what our theory prepares us 

 to expect. 



It appears, then, from these considerations, that the re- 



2 A 2 



