244 



INDUCTION. 



There are thus two different modes 

 of the conjunct action of causes, from 

 which arise two modes of conflict, or 

 mutual interference, between laws of 

 nature. Suppose, at a given point of 

 time and space, two or more causes, 

 which, if they acted separately, would 

 produce effects contrary, or at least 

 conflicting with each other, one of 

 them tending to undo, wholly or 

 partially, what the other tends to do. 

 Thus, the expansive force of the gases 

 generated by the ignition of gun- 

 powder tends to project a bullet 

 towards the sky, while its gravity 

 tends to make it fall to the ground. 

 A stream running into a reservoir at 

 one end tends to fill it higher and 

 higher, while a drain at the other 

 extremity tends to empty it. Now, 

 in such cases as these, even if the 

 two causes which are in joint action 

 exactly annul one another, still the 

 laws of both are fulfilled : the effect 

 is the same as if the drain had been 

 open for half an hour first,* and the 

 stream had flowed in for as long 

 afterwards. Each agent produced 

 the same amotmt of effect as if it had 

 acted separately, though the contrary 

 effect which was taking place during 

 the same time obliterated it as fast 

 as it was produced. Here then are 

 two causes, producing by their joint 

 operation an effect which at first 

 seems quite dissimilar to those which 

 they produce separately, but which on 

 examination proves to be really the 

 sum of those separate effects. It will 

 be noticed that we here enlarge the 

 idea of the sum of two effects, so as 

 to include what is commonly called 

 their difference, but which is in reality 

 the result of the addition of opposites ; 

 a conception to which mankind are 

 indebted for that admirable extension 



* I omit, for simplicity," to take into 

 account the effect iu this latter case of the 

 diminution of pressure, in diminishing the 

 flow of water through the drain ; which 

 evidently in no way affects the truth or 

 applicabiUty of the principle, since when 

 the two causes act simultaneously the con- 

 ditions of that diminution of pressure do 

 Mot arise. 



of the algebraical calculus which has 

 so vastly increased its powers as an 

 instrument of discovery, by introduc- 

 ing into its reasonings (with the sign 

 of subtraction prefixed, and under the 

 name of Negative Quantities) every 

 description whatever of positive phe- 

 nomena, provided they are of such a 

 quality in reference to those previ- 

 ously introduced, that to add the one 

 is equivalent to subtracting an equal 

 quantity of the other. 



There is, then, one mode of the 

 mutual interference of laws of nature, 

 in which, even when the concurrent 

 causes annihilate each other's effects, 

 each exerts its full efficacy according 

 to its own law — its law as a separate 

 agent. But in the other description 

 of cases, the agencies which are 

 brought together cease entirely, and 

 a totally different set of phenomena 

 arise : as in the experiment of two 

 liquids which, when mixed in certain 

 proportions, instantly become, not a 

 larger amount of liquid, but a solid 



§ 2. This difference between the 

 case in which the joint effect of causes 

 is the sum of their separate effects, 

 and the case in which it is hetero- 

 geneous to them ; between laws which 

 work together without alteration, and 

 laws which, when called upon to work 

 together, cease and give place to 

 others ; is one of the fundamental 

 distinctions in nature. The former 

 case, that of the Composition of 

 Causes, is the general one ; the other 

 is always special and exceptional. 

 There are no objects which do not, as 

 to some of their phenomena, obey the 

 principle of the Composition of Causes; 

 none that have not some laws which 

 are rigidly fulfilled in every combina- 

 tion into which the objects enter. 

 The weight of a body, for instance, 

 is a property which it retains in all 

 the combinations in which it is placed. 

 The weight of a chemical compound, 

 or of an organised body, is equal to 

 the sum of the weights of the ele- 

 ments which compose it. The weight 



