158 BEVIEWS— EESEAfiCHES ON COLOUE-BLINDKESS. 



very volume, stand in direct contradiction to this view. The "beauty" of 

 the hypothesis is a matter of opinion, (and we certainly differ from Dr. 

 "Wilson in this point,) but of the unreality of it, Ave think there is small 

 doubt ; and hold confidently to the belief that the simple and elegant 

 explanation of our great Newton stands unimpeached in its integrity. 

 In an altogether different category stands the hypothesis first sug- 

 gested by Newton and adopted with modification by others, such as 

 Young, Mayer, Lambert, Herschel, and lastly by Mr. Maxwell ; 

 namely, that all possible tints can be produced by proper combination 

 of three standard tints, (which may be designated as principal or 

 primary,) and that c.;uj three tints may thus be assumed, provided 

 they are capable in certain proportions of producing white, an exten- 

 sion due to Sir John Herschel, which Dr. Wilson erroneously attri- 

 butes to Mr. Maxwell. AVe regret that we have not yet seen the in- 

 vestigations of this latter gentleman in cxtenso, the volume of the 

 B*. S. E. Transactions, in which they are published, not having yet 

 reached this country ; and we hesitate at pronouncing an opinion 

 derived only from the letter of Mr. Maxwell, in the volume before us, 

 giving an outline of his system neither over full nor sharply defined. 

 Mr. Maxwell assumes three tints (or as he calls them, three pure 

 sensations of colour,) as his primaries; he supposes these to be 

 placed in the corners of a triangle, and then by a simple geometrical 

 construction, namely, finding the centre of gravity of three weights 

 placed at these points proportional to the respective intensities of 

 the tints used in forming any required tint, — he assigns to every 

 possible colour its position relative to them, and also the numerical 

 measure of its intensity. Undoubtedly this construction is extremely 

 beautiful, and the numerical expression of it is in effect little different 

 from that of Mayer, as extended by Herschel. The only question is 

 whether Mr. Maxwell' 8 formula will express all the colours that exist 

 in nature, a question that can only be answered by observation ; Mr. 

 Maxwell indeed has drawn some conclusions regarding colour-blind- 

 ness, which would furnish an experimentum cruris of his hypothesis, 

 but we do not find that Dr. Wilson has yet submitted it to this test. 

 Meanwhile we cannot help suspecting that the formula may break 

 down, at the same point as that of Mayer, in assigning the position 

 of the browns, and indeed of all colours in which, in our opinion, black 

 enters as a positive element, and not as a mere negation. Be this as 

 it mav, we must protest against any hypothesis of this kind, indis- 

 pensable though it must be as a means of measurement and classifi- 

 cation of colours, being designated as a theory of colour ; nor can we 

 asseut to the conclusion drawn both by Mr. Maxwell and our author, 



