230 



INDUCTION. 



tides of the same ether in the inter- 

 stices of terrestrial bodies ; and this, 

 too, with a sufficient mechanical force 

 to throw the particles of those bodies 

 into a state of similar vibration, pro- 

 ducing the expansion of their mass, 

 and the sensation of heat in sentient 

 creatures. All this is hypothesis, 

 though of its legitimacy as hypothesis 

 I do not mean to express any doubt. 

 It would seem to follow as a conse- 

 quence from this theory, that Force 

 may and should be defined, matter 

 in motion. This definition, however, 

 will not stand, for, as has already 

 been seen, the matter needs not be 

 in actual motion. It is not necessary 

 to suppose that the motion afterwards 

 manifested is actually taking place 

 among the molecules of the coal dur- 

 ing its sojourn in the earth;* certainly 

 not in the stone which is at rest on 

 the eminence to which it has been 

 raised. The true definition of Force 

 must be, not motion, but Potentiality 

 of Motion ; and what the doctrine, 

 if established, amounts to is, not that 

 there is at all times the same quantity 

 of actual motion in the universe ; but 

 that the possibilities of motion are 

 limited to a definite quantity, which 

 cannot be added to, but which cannot 

 be exhausted ; and that all actual 

 motion which takes place in Nature is 

 a draft upon this limited stock. It 

 needs not all of it have ever existed 

 as actual motion. There is a vast 

 amount of potential motion in the 

 universe in the form of gravitation, 

 which it would be a great abuse of 

 hypothesis to suppose to have been 

 stored up by the expenditure of an 

 equal amount of actual motion in some 

 former state of the universe. Nor 



* I believe, however, the accredited 

 authorities do suppose that molecular 

 motion, equivalent in amount to that 

 which will be manifested in the combus- 

 tion of the coal, is actually taking place 

 during the whole of the long interval, if 

 not in the coal, yet in the oxygen which 

 will then combine with it. But how purely 

 hypothetical this supposition is, need 

 hardly be remarked ; I venture to say, un- 

 necessarily and extravagantly hypotheti- 

 cal. 



does the motion produced by giravity 

 take place, so far as we know, at the 

 expense of any other motion, either 

 molar or molecular. 



It is proper to consider whether the 

 adoption of this theory as a scientific 

 truth, involving as it does a change 

 in the conception hitherto entertairxed 

 of the most general physical agencies, 

 requires any modification in the view 

 I have taken of Causation as a law of 

 nature. As it appears to me, none 

 whatever. The manifestations which 

 the theory regards as modes of motion 

 are as much distinct and separate 

 phenomena when referred to a single 

 force as when attributed to several. 

 Whether the phenomenon is called a 

 transformation of force or the genera- 

 tion of one, it has its own set or sets 

 of antecedents, with which it is con- 

 nected by invariable and uncondi- 

 tional sequence ; and that set, or 

 those sets, of antecedents are its 

 cause. The relation of the Conser- 

 vation theory to the principle of 

 Causation is discussed in much de- 

 tail, and very instructively, by Pro- 

 fessor Bain, in the second volume of 

 his Logic. The chief practical con- 

 clusion drawn by ' him bearing on 

 Causation is, that we must distinguish 

 in the assemblage of conditions which 

 constitutes the Cause of a pheno- 

 menon two elements : one, the pre- 

 sence of a force ; the other, the col- 

 location or position of objects which 

 is required in order that the force 

 may undergo the particular transmu- 

 tation which constitutes the pheno- 

 menon. Now, it might always have 

 been said with acknowledged correct- 

 ness, that a force and a collocation 

 were both of them necessary to pro- 

 duce any phenomenon. The law of 

 causation is, that change can only be 

 produced by change. Along with any 

 number of stationary antecedents, 

 which are collocations, there must 

 be at least one changing antecedent, 

 which is a force. To produce a bon- 

 fire, there must not only be fuel, and 

 air, and a spark, which are colloca- 

 tions, but chemical action between 



