LAWS OF MOTION. 413 



the motion produced precisely in the direction 

 of that force. 



4th. Admitting, however, by hypothesis, 

 what is false in fact, that external resistance 

 can be abstracted and removed, by the annihi- 

 lation of all the matter which filled the medium 

 through which the moving body was to pass, 

 I contend that no body whatever, which had 

 been excited to move, would move for ever, 

 that is " persevere in its state of motion." A 

 proposition such as this, is false in fact; be- 

 cause obstacles constantly exist to retard, and 

 ultimately to destroy, that motion ; these obsta- 

 cles not only reside in the medium, but in the 

 essential attributes of inertness, and of immo- 

 bility, which inheres in the solid matter which 

 is intended to be moved ; and these attributes 

 of inertness and immobility, constantly tend to 

 weaken, and to destroy, the energy of this mov- 

 ing power. It is to the nature, and to the 

 efficacy, of the moving power, that is to be 

 ascribed the motion which is accomplished ; 

 in order that motion be produced, it is abso- 

 lutely necessary that the power should be 

 active, and that the thing moved should be pas- 

 sive. And, finally, to produce motion perpe- 

 tual, (i. e. perseverance in a state of motion,) the 

 power must not only be active, but active infi- 

 nitely ; and the matter moved not passive only, 

 but passive infinitely. 



