256 THE DIRECTION OF MOTION. 



tion, or the line of least resistance, or the resultant of the 

 two, is a necessary deduction from that primordial truth 

 which transcends proof. 



Reduce the proposition to its simplest form, and it be- 

 comes still more obviously consequent on the persistence of 

 force. Suppose two weights suspended over a pulley or 

 from the ends of an equal-armed lever; or better still — sup- 

 pose two men pulling against each other. In such cases we 

 say that the heavier weight will descend, and that the 

 stronger man will draw the Aveaker towards him. But now, 

 if we are asked how w T e know T which is the heavier weight or 

 the stronger man; we can only reply that it is the one pro- 

 ducing motion in the direction of its pull. Our only evi- 

 dence of excess of force is the movement it produces. But if 

 of two opposing tractions we can know one as greater than 

 the other only by the motion it generates in its own direc- 

 tion, then the assertion that motion occurs in the direction 

 of greatest traction is a truism. ' "When, going a step further 

 back, we seek a warrant for the assumption that of the two 

 conflicting forces, that is the greater which produces mo- 

 tion in its own direction, we find no other than the con- 

 sciousness that such part of the greater force as is unneutral- 

 ized by the lesser, must produce its effect — the consciousness 

 that this residuary force cannot disappear, but must mani- 

 fest itself in some equivalent change — the consciousness 

 that force is persistent. Here too, as before, it may 



be remarked that no amount of varied illustrations, like 

 those of which this chapter mainly consists, can give greater 

 certainty to the conclusion thus immediately drawn from 

 the ultimate datum of consciousness. For in all cases, as in 

 the simpler ones just given, we can identify the greatest 

 force only by the resulting motion. It is impossible for us 

 ever to get evidence of the occurrence of motion in any 

 other direction than that of the greatest force; since our 

 measure of relative greatness among forces is their relative 

 power of generating motion. And clearly, while the com- 



