60 Mr. Cooper on the Colours that enter into the 



so that one colour, according to this hypothesis, ought to 

 run imperceptibly into another. 



These views have, I believe, been adopted, both by the 

 advocates of the material and the undulatory theories of 

 light ; and I am not aware that any question has arisen as 

 to their correctness. But notwithstanding the high autho- 

 rity upon which these opinions rest, and the general con- 

 sent with which they have been received, there does not 

 appear to me to be any sufficient foundation for them; 

 with the exception of the continuous form of the spectrum, 

 which may be otherwise accounted for, they derive no sup- 

 port from the phenomena they are intended to explain ; and 

 some of Newton's experiments are so directly opposed to 

 them, that I shall emote two of these experiments as the 

 foundation of opinions precisely the reverse. 



He says, " Homogeneal light is refracted regularly with- 

 out any dilation, splitting or shattering of the rays, and the 

 confused vision of objects seen through refracting bodies by 

 hetrogeneal light, arises from the different refrangibility 

 of several sorts of rays. This will appear by the experi- 

 ments which follow. In the middle of a black paper I made 

 a round hole about a fifth or a sixth of an inch in diameter. 

 Upon this paper I caused the spectrum of homogeneal light 

 described in the former article, so to fall that some part of 

 the light might pass through the hole in the paper. This 

 transmitted part of the light I refracted with a prism placed 

 behind the paper, letting this refracted light fall perpen- 

 dicularly upon a white paper two or three feet distant 

 from the prism, I found that the spectrum formed on the 

 paper by this light was not oblong, as when it is made by 

 refracting the sun's compound light, but was, (so far as I 

 could judge by my eye) perfectly circular, the length being 

 nowhere greater than the breadth ; which shews that this 

 light is refracted regularly without any dilation of the rays ; 

 and is an ocular demonstration of the mathematical proposi- 

 tion before mentioned.'' — (Newton's Optics, p. 62.) See 

 Smith's Optics, Art. 176. 



The following experiment, mentioned by Newton, is still 

 more decisive : 



" A circular piece of white paper A, {Fig. 2) about one 

 inch in diameter, was placed before a black wall, and using 



