COMPOSITION OP CAUSES. 433 



and in respect to quality, we have already some par- 

 tial generalizations sufficient to indicate the possibility 

 of ultimately proceeding further. We can predicate 

 many 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 very 

 curious law, discovered by Berthollet, that two 

 soluble salts mutually decompose one another when- 

 ever the new combinations which result produce an 

 insoluble compound; or one less soluble than the two 

 former. Another uniformity has been observed, com- 

 monly called the law of isomorphism ; the identity of 

 the crystalline forms of substances 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 gene- 

 ration 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 ele- 

 ments themselves, furnish the premisses by which the 

 science is destined one day to be rendered deductive. 



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

 phenomena in which the Composition of Causes does 

 not obtain : that as a general rule, causes in combina- 

 tion 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 



VOL. i. 2 F 



