THE FORCE BEHIND NATURE. 361 



that the axes of the several machines are all in mechanical rela- 

 tion with one great longitudinal shaft, being connected with it 

 either by continuous bands passing round pulleys, or by trains 

 of wheelwork : and at last he discovers the important fact, that 

 the movement of the handle which stops the machine breaks the 

 continuity of that relation, shifting a strap from a "fast" to a 

 "loose" pulley, or throwing the wheelwork "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 collocaiioti 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 power 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 conviction 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 working of the several kinds of machine, he 

 finds that while the p07ver is the same for all, the diversity in 

 their respective products is traceable to the diversity in their 

 ^;onstruction— that is, to the material collocaiions through which 

 the one moving force exerts itself in action. 



But having thus acquired the notion of moving po7ver, 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 



