THE LAWS OF MOTION 325 



The Newtonian laws of motion form the starting-point 

 of most modern treatises on dynamics, and it seems to me 

 that physical science, thus started, resembles the might}^ 

 genius of an Arabian tale emerging amid metaphysical 

 exhalations from the bottle in which for long centuries it 

 has been corked down. When the mists have quite 

 cleared off we shall see more clearly its proportions, and 

 there is special need for a strong breeze to clear away our 

 confused notions as to matter, mass, and force. The 

 writer is far from imagining that he can accomplish this 

 clearance, but he is convinced that a firm basis for physics 

 will only be found when scientists recognise that mechanism 

 is no reality of the phenomenal world — that it is solely 

 the mode by which we conceptually mimic the routine of 

 our perceptions. The semblance is, indeed, so striking 

 that we are able with astonishing accuracy to predict in 

 vast ranges of phenomena what will be the exact sequence 

 of our future sense-impressions. If, however, the scientist 

 projects the whole of his conceptual machinery into the 

 perceptual world he throws himself open to the charge of 

 being as dogmatic as either theologian or metaphysician. 

 On the other hand, when he simply postulates the con- 

 ceptual value of his symbols as a mode of describing past 

 and predicting future perceptual experience, then his 

 position is unassailable, for he asserts nothing as to the 

 why of phenomena. But as soon as he does this, matter 

 as that which moves, and force as the cause of change in 

 motion, disappear into the limbo of self- contradictory 

 notions. What moves is only a geometrical ideal, and it 

 moves only in conception. Why things move thus 

 becomes an idle question, and hozv things are to be con- 

 ceived as moving the true problem of physical science.^ 



In this field we know much, but our account of the 

 laws of motion has been specially intended to emphasise 

 how great is the room both for further investigation and 



1 " Such demonstrations, however, only show how all these things may be 

 ingeniously made out and disentangled, not how they may truly subsist in 

 nature ; and indicate the apparent motions only, and a system of machinery 

 arbitrarily devised and arranged to produce them — not the very causes and 

 truth of things" (Bacon, Dc Auffmeiitls, bk. iii. chap. iv.). 



