362 P. C. on the Colours that enter into the [Nov, 



stating, that the three surfaces of colours upon a white body 

 in their unrefracted state, are every wherein the proportion 

 which forms white light ; and though the quantity of light 

 may vary on different parts of the body, producing a diffe- 

 rence of intensity, every part has the essential properties of 

 white light ; but when the images are shifted by the action 

 of the prism, any difference in the intensity of the white 

 unrefracted surface must produce colours ; because the parts 

 of the images now intersect each other in different positions, 

 without any regard to the just proportion of the colours 

 which previously existed ; and as the whole of the colours 

 taken together are in the proportion which forms white 

 light, any excess in one part must be marked with a corre- 

 sponding deficiency in another. Hence, shadows, clouds, 

 and, in short, all obstructions, whether in reflected or direct 

 light, which produce inequalities in the light that falls 

 on the surface of the prism, are bounded with complemen- 

 tary colours. 



The explanation of these fringes, which is here attempted, 

 introduces no new point of theory ; it is simply the applica- 

 tion of the Newtonian theory of refraction to particular cir- 

 cumstances ; the phenomena of which, though at first view 

 they appear to be out of its usual order, are, in fact, such 

 necessary consequences of it, that if the appearances were 

 not exactly as we find them, the theory, as delivered to us 

 by its illustrious author, could not be supported. 



In a paper which I some time since addressed to the Royal 

 Society, I have extended the explanation to the fringes seen 

 in diffracted light; and, by showing the connexion be- 

 tween this light and refracted light, the most important, if 

 not the whole of the phenomena exhibited by the former, 

 are reduced to the most simple principles. 



Having, thens, explained as well as I can, in so concise a 

 form, the nature and character of these fringes, with refe- 

 rence to the theory of three primitive colours, I will now 

 endeavour to draw from them more direct evidence in sup- 

 port of this theory. 



If we look through a prism at the bars of a window, as 

 before directed ; at some little distance from the window, 

 the horizontal bar which divided the panes of glass will 

 appear to be fringed with three colours, blue, crimson and 



