350 Mr. P. Cooper on the Connexion between 



The best method of preparing white refracted light, for 

 the purpose of experiment, is to receive the light of the 

 sun, refracted by a prism of considerable breadth, upon a 

 screen placed at a short distance from the prism. It will 

 be found that all objects placed in this light will form 

 shadows on the screen fringed with complimentary colours, 

 which will increase in breadth by increasing the distance ' 

 of the object from the screen. The edges of the interposed 

 object have nothing to do with the production of these 

 coloured fringes ; they arise simply from the different 

 direction of the rays of different colours, and the conse- 

 quent difference in the position of their shadows. 



We may increase the surface of white refracted light to 

 any extent by a proportional increase of the breadth of the 

 prism; and, if the divergent light could be made to occupy 

 the whole of the circle of which the prism is the centre, 

 no distance whatever would produce the least appearace of 

 of colour ; for, although the differently coloured rays would 

 diverge at different angles, they would intersect each other 

 at every point in the proportion required to form white 

 light. Colours make their appearance in this light merely 

 from the want of continuity ; and it will be found, in every 

 case, that by bringing the two fringes towards each other, 

 a distance equal to the breadth of the interposed object, by 

 means of which the continuity is interrupted, the white 

 surface will resume its original purity by the superposition 

 of complimentary colours. 



Having given my views of the character of refracted 

 light in my papers on the number and character of the 

 colours that enter into the composition of white light, it 

 will be unnecessary for me to enlarge upon the subject 

 here ; there is, however, one part of its character that I 

 had no occasion to notice in the former inquiry, which is 

 of importance in the present ; and I shall make a few ob- 

 servations upon it before I proceed to my principal object. 



If we form surfaces of white refracted light with prisms 

 of the same materials, but with different refracting angles, 

 upon screens placed Pt equal distances from the prism, we 

 shall find that the breadth of the fringes by which these 

 surfaces are bounded will vary with the angle of the prism ; 

 and that the fringes upon the shadows of objects, at the 



