COMPOSITION OP CAUSES. 411 



it. The law of definite proportions, first discovered in its full 

 generality by Dalton, is a complete solution of this problem 

 in one, though but a secondary aspect, that of quantity : and 

 in respect to quality, we have already some partial generaliza- 

 tions sufficient to indicate the possibility of ultimately pro- 

 ceeding farther. We can predicate some common properties 

 of the kind of compounds which result from the combination, 

 in each of the small number of possible proportions, of any 

 acid whatever with any base. We have also the curious law, 

 discovered by Berthollet, that two soluble salts mutually 

 decompose one another whenever the new combinations which 

 result produce an insoluble compound, or one less soluble than 

 the two former. Another uniformity is that called the law 

 of isomorphism ; the identity of the crystalline forms of sub- 

 stances which possess in common certain peculiarities of 

 chemical composition. Thus it appears that even heteropathic 

 laws, such laws of combined agency as are not compounded 

 of the laws of the separate agencies, are yet, at least in some 

 cases, derived from them according to a fixed principle. There 

 may, therefore, be laws of the generation of laws from others 

 dissimilar to them ; and in chemistry, these undiscovered 

 laws of the dependence of the properties of the compound 

 on the properties of its elements, may, together with the 

 laws of the elements themselves, furnish the premises by 

 which the science is perhaps destined one day to be rendered 

 deductive. 



It would seem, therefore, that there is no class of pheno- 

 mena in which the Composition of Causes does not obtain : 

 that as a general rule, causes in combination produce exactly 

 the same effects as when acting singly : but that this rule, 

 though general, is not universal : that in some instances, at 

 some particular points in the transition from separate to 

 united action, the laws change, and an entirely new set of 

 effects are either added to, or take the place of, those which 

 arise from the separate agency of the same causes: the 

 laws of these new effects being again susceptible of com- 

 position, to an indefinite extent, like the laws which they 

 superseded. 



