270 INDUCTION. 



which result produce an insoluble compound, or one less soluble than the 

 two former. Another uniformity is that called tlie 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 generation of laws from others dissimilar to them ; and in chemis- 

 try, 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 per- 

 haps 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 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 composition, to an 

 indefinite extent, like the laws which they superseded. 



§ 3, That effects are proportional to their causes is laid down by some 

 writers as an axiom in the theory of causation ; and great use is sometimes 

 made of this principle in reasonings respecting the laws of nature, though it 

 is encumbered with many difficulties and apparent exceptions, which much 

 ingenuity has been expended in showing not to be real ones. This propo- 

 sition, in so far as it is true, enters as a particular case into the general 

 principle of the Composition of Causes; the causes compounded being, in 

 this instance, homogeneous ; in which case, if in any, their joint effect might 

 be expected to be identical with the sum of their separate effects. If a 

 force equal to one hundred weight will raise a certain body along an in- 

 clined plane, a force equal to two hundred weight will raise two bodies ex- 

 actly similar, and thus the effect is proportional to the cause. But does 

 not a force equal to two hundred weight actually contain in itself two forces 

 each equal to one hundred weight, which, if employed apart, would sepa- 

 rately raise the two bodies in question? The fact, therefore, that when ex- 

 erted jointly they raise both bodies at once, results from the Composition 

 of Causes, and is a mere instance of the general fact that mechanical forces 

 are subject to the law of Composition. And so in every other case which 

 can be supposed. For the doctrine of the proportionality of effects to their 

 causes can not of course be applicable to cases in which the augmentation 

 of the cause alters the kind of effect ; that is, in which the surplus quanti- 

 ty superadded to the cause does not become compounded with it, but the 

 two together generate an altogether new phenomenon. Suppose that the 

 application of a certain quantity of heat to a body merely increases its 

 bulk, that a double quantity melts it, and a triple quantity decomposes it : 

 these three effects being heterogeneous, no ratio, whether corresponding 



* Professor Bain adds several other well-established chemical generalizations: "The laws 

 that simple substances exhibit the strongest affinities ; that compounds are more fusible than 

 their elements; that combination tends to a lower state of matter from gas down to solid;" 

 and some general propositions concerning the circumstances which facilitate or resist chem- 

 ical combination. (Logic, ii., 254.) 



