THE FORCE BEHIND NATURE. 623 



pulley, or throwing the wheel work " out of gear "; while the converse 

 movement, which restores that continuity, is followed by the renewed 

 action of the machine, which goes on until the Continuity is again 

 broken. Thus he will be led to regard its maintenance as essential to 

 the working of the machine ; but nothing that he has yet learned 

 explains to him why it is essential. He has only got at the material 

 collocation which his educated vision enables him to recognize ; and, 

 for anything he knows to the contrary, the change in that collocation 

 may be in itself adequate to determine the result. 



But let him lay hold of the band which stretches between the main 

 shaft and the axis of one machine, or attempt to stay with his hand 

 the rotation of the train of wheels which connects it with another — he 

 then at once becomes conscious, through his " force-sense," of the poxoer 

 which the band or the wheelwork is the instrument of conveying ; and 

 as he finds that the "pull" upon his hand is just the same whether the 

 machine is in motion or not, provided that the band or wheel remains 

 in mechanical connection with the main shaft, he comes to the convic- 

 tion that the source of the power is in the shaft, and that, so far from 

 any one of the machines having an inherent power of movement, its 

 motion entirely depends upon the force supplied to it from the shaft. 

 And when, under the guidance of this conception, he again examines 

 the loorMng of the several kinds of machine, he finds that, while the 

 poxcer is the same for all, the diversity in their respective products is 

 traceable to the diversity in their construction — that is, to the material 

 collocations through which the one moving force exerts itself in action. 



But, having thus acquired the notion of moving poicer, and having 

 satisfied himself of the derivation of the force that gives motion to 

 each of the entire aggregate of machines, from one main shaft, our 

 inquirer finds himself again posed. Has this shaft itself an inherent 

 power of motion ; or does it derive that power from any ulterior 

 source ? He sees the shaft apparently terminate in the two end-walls 

 of the building ; and, finding no evidence of its connection with any- 

 thing else, he may feel himself drawn toward the conclusion that it 

 moves of itself — that is, by the " potency " of its own material consti- 

 tution. But, before adopting this rationale, he sees all the machines 

 stop at once, and finds that the shaft also has ceased to revolve. Here 

 is a new and startling phenomenon. After pondering on it for an hour, 

 and carefully looking out for an explanation, he sees the shaft and its 

 connected machines resume their motion, and yet is certain that no 

 agency visible to him has had any concern in that renewal. By con- 

 tinued watching, he finds this suspension and renewal to be periodical, 

 so that he can frame a law that shall express them in terms of time. 

 Thus he might give a complete phenomenal account of the action of 

 the shaft which should be perfectly consistent with the assumption of 

 its " inherent potency," and which might be sufficiently satisfactory to 

 his mind to justify him in believing that there is no more to be learned 



