HYPOTHESES. U 



Now although, as M. Comte elsewhere observes, a 

 colour must always remain a different thing from a 

 weight or a sound, it ought not to be forgotten, and 

 notwithstanding these expressions, cannot possibly 

 be forgotten by M. Comte, that varieties of colour 

 might nevertheless follow, or correspond to, given 

 varieties of weight, or sound, or some other phe- 

 nomenon as different as these are from colour itself. 

 It is one question what a thing is, and another 

 what it depends upon ; and although to ascertain the 

 conditions of an elementary phenomenon is not to 

 obtain any new insight into the nature of the pheno- 

 menon itself, that is no reason against attempting to 

 discover the conditions. M. Comte's interdict against 

 endeavouring to reduce distinctions of colour to any 

 common principle, would have held equally good 

 against a like attempt on the subject of distinctions of 

 sound ; which nevertheless have been found to be 

 immediately preceded and caused by distinguishable 

 varieties in the vibrations of elastic bodies : although 

 a sound, no doubt, is quite as different as a colour is 

 from any motion of particles, vibratory or otherwise. 

 We might add, that, in the case of colours, there are 

 strong positive indications that they are not ultimate 

 properties of the different kinds of substances, but 

 depend upon conditions capable of being superinduced 

 upon all substances; since there is no substance 

 which cannot, according to the kind of light thrown 

 upon it, be made to assume any colour we think fit; 

 and since almost every change in the mode of aggre- 

 gation of the particles of the same substance, is 

 attended with alterations in its colour^ and in its 

 optical properties generally. 



The real defect in the attempts which have been 

 made to account for colours by the vibrations of a 



