NATURAL PHILOSOPHY. 133 



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 continual mechanical action, 

 as is most probable, or assume some other idea, as that of electricity, or 

 action of a heat-fluid, still they hold to the principle of conservation, by ad- 

 mitting that the sum of force, that is, 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 phe- 

 nomena respectiA'ely. All that they are limited by in their various investi- 

 gations, whatever directions they may take, is the necessity of making no 

 assumption directly contradictory of the conservation of force applied to the 

 sum of all the forces concerned, and to endeavor 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 

 particles 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 inversely 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 

 supposition 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 approach- 

 ing 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 phenomena 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 prin- 

 ciple of the conservation of force, and to stop the inquiry which it suggests; 

 whereas, to admit the proper logical force of Vhe principle in our hypoihescs 

 and considerations, and to permit its guidance in a cautious yet courageous 

 course of investigation, may give us power to enlarge the generalises wo 

 already possess in respect of heat, mo' ion, electricity, magnetism, etc., 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 sim- 

 ple attractive force exerted between any two or all the panicles or masses of 

 master at every sensible distance, bnt 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, there- 

 fore, in relation to it, deny the principle of conservation. If both are ac- 

 cepted, and are thought to be consistent with each other, it cannot be difficult 

 to add words which shall make "varying strength" and " conservation" 

 a-iree 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 



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