Composition of White Light. 101 



produced by its own colour, that the white light appears 

 wholly converted to it : it is, in fact, no longer white light, 

 but the complementary colour, diluted with white light in 

 proportion to the state of sensibility in which the previously 

 employed parts of the eye meet the primary colour ; 

 white light in this, and in every other instance, is formed 

 not in proportion to the quantity of light of the different 

 colours present, but in proportion to the sensations pro- 

 duced by them. 



Now, if a distinct means of communication be necessary 

 for each colour, in every point of the retina upon which a 

 ray of white light falls, which, from various considerations, 

 appears to me to be very evident, how is it possible such an 

 arrangement could be made if the colours, instead of being 

 limited to three, were innumerable ? 



But, what renders the doctrine still more suspicious, is, 

 that it is unnecessary ; for, according to this hypothesis, 

 all these simple colours may be imitated by a composition 

 of neighbouring colours ; so that, it would appear, nature 

 has provided two causes, or distinct methods, to produce 

 one and the same effect; a prodigality of which, I believe, 

 we have no other instance. 



In conclusion, I beg, Sir, to apologize for having occupied 

 so many of your valuable pages ; the title I have chosen for 

 my paper has given me such an ample scope, that, though 

 I fear I have already been tiresome, I might have greatly 

 extended the subject without passing its boundaries. The 

 character of light, in its most extended sense, would include 

 almost every branch of Science ; great and admirable as are 

 the properties by which it is made the medium of our com- 

 munication with distant objects, I have no hesitation in say- 

 ing, that its application to other purposes, is of even higher 

 importance ; the whole system of nature seems to be depen- 

 dant upon it ; and its material cpualities, which modern 

 philosophers, from having confined their attention to a very 

 limited part of the subject, have dismissed as useless, will 

 be found essential in every part of her economy. 



The theory upon which these views are founded, claims 

 my confidence, by connecting, upon the most simple princi- 

 ples, the whole phenomena of nature ; whether displayed 

 by her ordinary means, or elicited by the aid of experiment. 



It is not, therefore, upon light grounds, that I have ven- 



