102 Mr. Cooper on the Colours that enter into the 



tured to give an opinion with regard to the material cha- 

 racter of light, so decidedly opposed to the present prevailing 

 theory. I am too well aware of the ease with which a 

 plausible hypothesis may be formed to meet a limited class 

 of facts, to place any reliance upon those numerous specula- 

 tions which obtrude themselves upon the theorist, in the 

 course of his investigations, and which, from their equal 

 pretensions, frequently form one of his greatest difficulties ; 

 but, when a theory j>resents itself which enables me to trace 

 the different operations of nature with the same ease that I 

 follow the train of a well connected piece of machinery ; 

 when, assuming the principles of this theory, I am led to 

 discoveries, which so correctly correspond with the results 

 of these operations, as to convince me they are its necessary 

 consequences; when, again, after a lapse of many years, 

 during which numerous discoveries have been published, I 

 find the whole of these discoveries either previously attached 

 to it, or readily included in it without the slightest altera- 

 tion, I can no longer doubt its claim to my confidence, or 

 hesitate in giving an opinion under its sanction. 



The chief support of the undulatory theory, arises from 

 an erroneous conclusion, that the interference of light must 

 necessarily be a destructive interference. I freely admit, 

 that if the annihilation of lightweresatisfactorilyestablished, 

 the material theory must instantly fall to the ground ; but 

 something more than the gratuitous assumption of the fact 

 is required to prove it. I am prepared to show, that in 

 cases of interference, the light never arrives at the points 

 where it is supposed to be destroyed ; and that the cause of 

 this is connected with a property of light of the most exten- 

 sive utility. 



I must, observe, however, that a great part of those cases 

 of the production of colours, which have been attributed to 

 interference, may be accounted for upon the principle of 

 refraction ; and, with your permission, I propose giving 

 some instances of this, connected with other subjects, in a 

 future communication. 



In the mean time, I hope the subject of these papers will 

 not. be considered unworthy the attention of some of your 

 correspondents : There is scarcely a modern treatise on 

 optics that does not give Newton's Scale of Colours as the 

 foundation of the science ; and, perhaps, in some other part 



