370 THE CONSERVATION OF FOECE. 



to what may be called the law of gravitating action, that is, 

 the law by which all the known effects of gravity are gov- 

 erned ; what I am considering is the definition of the force of 

 gravitation. That the result of one exercise of a power may 

 be inversely as the square of the distance, I believe and ad- 

 mit ; and I know that it is so in the case of gravity, and has 

 been verified to an extent that could hardly have been within 

 the conception even of Newton himself when he gave utter- 

 ance to the law ; but that the totality of a force can be em- 

 ployed according to that law I do not believe, either in rela- 

 tion to gravitation, or electricity, or magnetism, or any other 

 supposed form of power. 



I might have drawn reasons for urging a continual recol- 

 lection of, and reference to, the principle of the conservation 

 of force from other forms of power than that of gravitation ; 

 but I think that when founded on gravitating phenomena, 

 they appear in their greatest simplicity ; and precisely for this 

 reason, that gravitation has not yet been connected by any 

 degree of convertibility with the other forms of force. If I 

 refer for a few minutes to these other forms, it is only to 

 point in their variations, to the proofs of the value of the 

 principle laid down, the consistency of the known phenomena 

 with it, and the suggestions of research and discovery which 

 arise from it. Heat, for instance, is a mighty form of power, 

 and its effects have been greatly developed ; therefore, assump- 

 tions regarding its nature become useful and necessary, and 

 philosophers try to define it. The most probable assumption 

 is, that it is a motion of the particles of matter ; but a view, 

 at one time very popular, is, that it consists of a particular 

 fluid of heat. Whether it be viewed in one way or the other, 

 the principle of conservation is admitted, I believe, with all its 

 force. When transferred from one portion to another portion 

 of like matter, the full amount of heat appears. When trans- 

 ferred to matter of another kind an apparent excess or defi- 

 ciency often results ; the word " capacity" is then introduced, 



