508 THE CONSEKVATION OF ENERGY, ETC. 



On the theory of action by contact — 



( d ) The principle of conservation of actual energy depends on the 

 nature of the atoms. 



( (? ) The conservation of relative motion after impact can only hold 

 in the collision of rigid bodies. 



{f) The assumption of rigid atoms is therefore necessary to the con- 

 servation of actual energy, which assumption may be made, as 

 it involves nothing inconsistent with nature ; but, on the 

 contrary, makes possible the explanation of a wide range of 

 natural phenomena, otherwise inexplicable. 



( g ) There is no such thing as dead pressure. All forces, pulls, 

 thrusts, frictions, attractions, repulsions, etc., etc., consist of 

 collisions. That there should be action between two bodies 

 without relative motion is inconceivable. 



( h ) The use of the term potential energy, even when the forces are 

 of the above kind, is inadmissible, since it implies results 

 with regard to which the principle of conservation makes no 

 assertion, and thus leads to false ideas regarding the principle- 



