ON THE ORIGIN OF FORCE. 465 



is necessarily and invariably destroyed. The destruction 

 may be total, or may fall short of totality in any propor- 

 tion according to the directness of the impact, and the pro- 

 portion of the moving masses ; but whenever contact oc- 

 curs between such bodies, vis viva disappears, and, once 

 lost, is gone for ever. Taking such a system in its entirety 

 (where force exists not), there is no possibility of its re- 

 production. There is therefore a necessary and unceas- 

 ing drain on the vis viva of such a system. Everything 

 which constitutes an event, whatever its nature, exhausts 

 some portion of the original stock. Such a system has 

 no vitality. It feeds upon itself, and has no restorative 

 power. All relative motion in it tends rapidly to decay, 

 or at all events to a final state, when there will occur no 

 more collision, i.e., when phenomena cease altogether ; 

 when the minimum of vis viva consistent with the con- 

 servation of momentum is attained ; and nothing remains 

 but either a single caput mortuum, journeying through 

 space, or a multitude of such, travelling different ways ; 

 having parted company never to meet again. 



(7.) It will of course be urged that this reasoning takes 

 for granted the law just mentioned of the conservation of 

 momentum estimated in any given direction : since we 

 cannot assert a priori that two inelastic bodies, after col- 

 lision, must move on with a common velocity and un- 

 changed joint momentum. Of course it does so. But 

 the object of the hypothesis we are combating is to ex- 

 hibit collision as a substitute for force; i.e., to give an 

 account of the acknowledged laws of motion without in- 

 troducing the conception of force. We are therefore 



2 G 



