Ai 



.872I 



NA TURE 



III 



comes to a stand ; and so it remains, like an inanimate corose, 

 until recalled (o activity by the renew? l of its Moving Tower. 



hut, say the Reasoners who deny thrt Force is anything else 

 than a fiction of the ''msginauon, tl e revolving shaft of the 

 Steam-engine is " Matter in Motion • " and when the con- 

 nection is estahlished between that shaft and the one that drives 

 the Machine, the Motion is communicated from the former to 

 the latter, and thence distributed to the several parts of the 

 Mechan'sm. This account of the operation is just what an 

 observer might give, who had looked on with entire ignorance 

 of every thing but what his eyes coulil see ; the moment he puts 

 his hand upon any part of the machinery, and tries to stop its 

 motion, he takes as direct cognizance, through his sense of the 

 Effort required to resist it, of the force which produces that 

 motion, as he does through his eye of the motion itself. 



Now since it is universally admitted that our notion of the 

 External World would be not only incomplete, but erroneous, if 

 our Visual perceptions were not supplemented by our Tactile, so, 

 as it seems so me, our interpretation of the Phenomena of the 

 Universe must be very inadequate, if we do not mentally co- 

 ordinate the idea of Force with that of Motion, and recognise it 

 as the ''efficient cause" of those phenomena — the "material 

 conditions" constituting (to use the old Scholastic term) only 

 "their formal cause." And I lay the greater stress on this point, 

 because the Mechanical Philosophy of the present day tends 

 more and more to express itself in terms o[ A[otiou rather than in 

 terms of Foree — to become Kinelies instead ai Dynamics. 



Thus from whatever side we look at this question — whether 

 the Common Sense of Mankind, the Logical Analysis of the 

 relation between Cause and EfTect, or the Study of the working 

 of our own Intellects in the interpretation of Nature — 

 we seem led to the same conclusion ; that the notion of 

 Force is one of those elementary Forms of Thought 

 with which we can no more dispense, than we can with the 

 notion of Space or of Succession. And I shall now, in the last 

 place, endeavour to show you that it is the substitution of the 

 Dynamical for the mere Phenomenal idea, which gives their 

 highest value to our conceptions of that Order of Nature, which 

 is worshipped as itself a God by the class of Interpreters whose 

 doctrine I call in question. 



Tlie most illustrative as well as the most illustrious example 

 of the difference between the mere Generalisation of Pheno- 

 mena and the Dynamical conception that applies to them, is 

 furnished l^y the contrast between the so-called Laws of Plane- 

 tary Motion discovered by the persevering ingenuity of Kepler, 

 and the interpretation of that Motion given us by the profound 

 insight of Newton. Kepler's three Laws were nothing more 

 than comprehensive statements of certain groups of Phenomena 

 determined by obser\ation. The first, that of the revolution 

 of the Planets in Elliptical oibits, was based on the study of 

 the observed places of Mars alone ; it might or might not be 

 true of the other Planets ; for so far as Kepler knew, there was 

 no reason why the orbits of some of them might not be the 

 excentric circles which he had first supposed that of Mars to 

 be. So Kepler's second law of the passage of the Radius 

 Vector over equal areas in equal times, so long as it was simply 

 a generalisation of facts in the case of that one Planet, carried 

 with it no reason for its applicability to other cases, except that 

 which it might derive from his eiToneous conception of a whirl- 

 ing force. And his //;m/ law was in a like manner simply an 

 expression of certain Harmonic relation which he had dis- 

 covered between the times and the distances of the Planets, 

 having no more rational value than any other of his numerous 

 hypotheses. 



Now the Newtonian " Laws " are often spoken of as if they 

 were merely higher generalisations in which Kepler's are in- 

 cluded ; to me they seem to possess an altogether different 

 character. For starting with the conception of two forces, 

 one of them tending to produce continuous uniform motion 

 in a straight bne, the other tending to produce a uniformly 

 accelerated motion towards a fixed point, Newton's wonderful 

 mastery of Geometrical reasoning enabled him to show that, if 

 these Dynamical assumptions be granted, Kepler's phenomenal 

 "Laws," being necessary consequences of them, must be uni- 

 versally true. And while that demonstration would have been 

 alone sufficient to give him an imperishable renown, it was his 

 still greater glory to-divine that the fall of the Moon towards 

 the Earth— that is, the deflection of her path from a tangential 

 line to an ellipse — is a phenomenon of the same order as the fall 

 of a stone to the ground ; and thus to show the applicability 



to the entire Universe, of those simple Dynamicil conceptions 

 which constitute the brsisof the Geomeiry of the Principia. 



Thus, then, whilst no ' Law " which is s'nip'y a generalisatiott 

 0/ Phenomena c^n be considered as having any coercive ^Q[\or\, 

 we may assign that value to Laws which express the universal 

 eoniiHioiis of the action of a Force, the existence of which we 

 learn from the testimony of our own consciousness. The assur- 

 ance we feel that the Attraction of Gravitation must act under 

 all circumstances according to its one simple Law, is of a very 

 different order from that which we have in regard (for example) 

 to the Laws of Chemical Attraction, which are as yet only 

 generalisations of phenomena. And yet even in that strong 

 assurance, we are required by our examination of the basis on 

 which it rests, to admit a resci-ie of the possihility of something 

 different ; a reserve which we may well believe that Newton 

 himself must have entertained. 



A most valuable lesson as to the allowance we ought always 

 to make for the unknown "possibilities of Nature," is taught 

 us by an exceptional phenomenon so familiar that it does not 

 attract the notice it has a right to claim. Next to the Law of 

 the Universal Attraction of Masses of ^fatter, there is none that 

 has a wider range than that of the Expansion of Bodies by Heat. 

 Excluding Water and one or two other substances, the fact of 

 such expansion might be said to be inz'ariahle ', and, as regards 

 bodies whose Gaseous condition is known, the Law of Expansion 

 can be stated in a form no less simple and deiinite than the Law 

 of Gravitation. Supposing those exceptions, then, to be un- 

 known, the Law would be universal in its range But it comes 

 to be discovered that Water, whilst conforming to it in its 

 expansion from 39^° up^oards to its boiling-point, as also, when 

 it passes into Steam, to the special law of Expansion of Vapours, 

 is exceptional in its expansion also from 39;° doionuiards to its 

 Freezing-point ; and of this faUure in the Universality of the 

 Law, no rationale can be given. Still more strange is it, that 

 by dissolving a little salt in water, we should remove this ex- 

 ceptional peculiarity ; for .t<vj-water continues to contract from 

 39j° downwards to its Freezing-point 12' or 14° lower, just as 

 it doe5 with reduction of temperature at higher ranges. 



Thus from our study of the mode in whicli we arrive at those 

 conceptions of the Orderly Sequence observable in tiie Phenomena 

 of Nature which we call " Laws," we are led to the conclusion 

 that they are Human conceptions, subject to Human fallibility ; 

 and that they may or may not express the Ideas of the Great 

 Author of Nature. To set up these Laws as self-acting, and as 

 either excluding or rendering unnecessary the Power which alone 

 can give them effect, appears to me as arrogant as it is unphilo- 

 sophical. To speak of <!«!' Lawas "regulating" or "governing" 

 phenomena, is only permissible on the assumption that the Law 

 is the expression of the modus operandi of a Governing Power. 

 I was once in a great City which for two days was in the hands 

 of a lawless mob. Magisterial authority was suspended by 

 timidity and doubt ; the force at its command was paralysed by 

 want of resolute direction. The "Laws" were on the Statute 

 book, but there was no Power to enforce them. And so the 

 Powers of evil did their terrible work ; and fire and rapine con- 

 tinued to destroy life and property without check, until new 

 Power came in, when the Reign of Law was restored. 



And thus we are led to the culminating point of Man's Intel- 

 lectual Interpretation of Nature— his recognition of the Unity 

 of the Power, of which her Phenomena are the diversified mani- 

 festations. Towards this point all Scientific inquiry now tends. 

 The Convertibility of the Physical Forces, the Correlation of 

 these with the Vital, and the intimacy of that nexus between 

 Mental and Bodily activity, which, explain it as we may, cannot 

 be denied, all lead upward towards one and the same conclusion ; 

 and the pyiamid of which that Philosophical conclusion is the 

 apex, has its foundation in the Primitive Instincts of Humanity. 



By our own remote Progenitors, as by the untutored Savage 

 of the present day, every change in which Human agency was 

 not apparent was referred to a particular Animating Intelligence. 

 And thus they attributed not only the movement of the Heavenly 

 bodies, but all the phenomena of Nature, each to its own Deity. 

 These Deities were invested with more than Human power ; but 

 they were also supposed capable of Human passions, and subject 

 to Human capriciousness. As the Uniformities of Nature came 

 to be more distinctly recognised, some of these Deities were in- 

 vested with a dominant control, while others were supposed to 

 be their subordinate ministers. A serene Majesty was attributed 

 to the greater Gods who sit above the clouds ; whilst their inferiors 

 might "comedown to Earth in the likeness of Men." With 



