SUPEEMACY OF THE PEINCIPLE. 381 



servation, apply that principle to the sum total of the force. 

 Though the amount of mechanical force (using habitual lan- 

 guage for convenience sake) may remain unchanged and 

 definite in its character for a long time, yet when, as in the 

 collision of two equal inelastic bodies, it appears to be lost, 

 they find it in the form of heat ; and whether they admit that 

 heat to be a continued mechanical action (as is most proba- 

 ble), or assume some other idea, as that of electricity, or 

 action of a heat-fluid, still they hold to the principle of con- 

 servation by admitting that the sum of force, i. e. of the 

 " cause of action," is the same, whatever character the effects 

 assume. With them the convertibility of heat, electricity, 

 magnetism, chemical action and motion, is a familiar thought ; 

 neither can I perceive any reason why they should be led to 

 exclude, a priori, the cause of gravitation from association 

 with the cause of these other phenomena respectively. All 

 that they are limited by in their various investigations, 

 whatever directions they may take, is the necessity of mak- 

 ing no assumption directly contradictory of the conservation 

 of force applied to the sum of all the forces concerned, and to 

 endeavour to discover the different directions in which the 

 various parts of the total force have been exerted. 



Those who admit separate forces inter-unchangeable, 

 have to show that each of these forces is separately subject 

 to the principle of conservation. If gravitation be such a 

 separate force, and yet its power in the action of two par- 

 ticles be supposed to be diminished fourfold by doubling the 

 distance, surely some new action, having true gravitation 

 character, and that alone, ought to appear, for how else can 

 the totality of the force remain unchanged? To define the 

 force as " a simple attractive force exerted between any two 

 or all the particles of matter, with* a strength varying in- 

 versely as the square of the distance," is not to answer the 

 question ; nor does it indicate or even assume what are the 

 other complementary results which occur ; or allow the sup- 



