382 THE CONSERVATION OF FORCE. 



position that such are necessary : it is simply, as it appears 

 to me, to deny the conservation of force. 



As to the gravitating force, I do not presume to say that I 

 have the least idea of what occurs in two particles when their 

 power of mutually approaching each other is changed by 

 their being placed at different distances ; but I have a strong 

 conviction, through the influence on my mind of the doctrine 

 of conservation, that there is a change ; and that the phe- 

 nomena resulting from the change will probably appear some 

 day as the result of careful research. If it be said that 

 " 'twere to consider too curiously to consider so," then I 

 must dissent : to refrain to consider would be to ignore the 

 principle of the conservation of force, and to stop the inquiry 

 which it suggests whereas to admit the proper logical force 

 of the principle in our hypotheses and considerations, and to 

 permit its guidance in a cautious yet courageous course of in- 

 vestigation, may give us power to enlarge the generalities we 

 already possess in respect of heat, motion, electricity, mag- 

 netism, &c., to associate gravity with them, and perhaps 

 enable us to know whether the essential force of gravitation 

 (and other attractions) is internal or external as respects the 

 attracted bodies. 



Returning once more to the definition of the gravitating 

 power as " a simple attractive force exerted between any two or 

 all the particles or masses of matter at every sensible distance, 

 but with a STRENGTH VARYING inversely as the square of the 

 distance" I ought perhaps to suppose there are many who 

 accept this as a true and sufficient description of the force, and 

 who therefore , in relation to it, deny the principle of conser- 

 vation. If both are accepted and are thought to be consist- 

 ent with each other, it cannot be difficult to add words 

 which shall make "varying strength" and "conservation" 

 agree together. It cannot be said that the definition merely 

 applies to the effects of gravitation as far as we know them. 

 So understood, it would form no barrier to progress ; for, 



