1857.] on the Conservation of Force. 359 



servation principle be true, must have consumed an equivalent 

 proportion of the cause of attraction ; and yet, according to the 

 definition of gravity, the attractive force is not diminished thereby, 

 but increased four-fold, the force growing up within itself the more 

 rapidly, the more it is occupied in producing other force. On the 

 other hand, if mechanical force from without be used to separate 

 the particles to twice their distance, this force is not stored up in 

 momentum or by inertia, but disappears ; and three-fourths of the 

 attractive force at the first distance disappears with it : How can 

 this be ? 



We know not the physical condition or action from which 

 inertia results ; but inertia is always a pure case of the conser- 

 vation of force. It has a strict relation to gravity, as appears by 

 the proportionate amount of force which gravity can communicate 

 to the inert body ; but it appears to have the same strict relation 

 to other forces acting at a distance as those of magnetism or 

 electricity, when they are so applied by the tangential balance 

 as to act independent of the gravitating force. It has the like 

 strict relation to force communicated by impact, pull, or in any 

 other way. It enables a body to take up and conserve a given 

 amount of force until that force is transferred to other bodies, or 

 changed into an equivalent of some other form ; that is all that we 

 perceive in it : and we cannot find a more striking instance amongst 

 natural, or possible, phenomena of the necessity of the conservation 

 of force as a law of nature ; or one more in contrast with the 

 assumed variable condition of the gravitating force supposed to 

 reside in the particles of matter. 



Even gravity itself furnishes the strictest proof of the conser- 

 vation of force in this, that its power is unchangeable for the same 

 distance ; and is by that in striking contrast with the variation 

 which we assume in regard to the cause of gravity, to account for 

 the results at different distances. 



It will not be imagined for a moment that I am opposed to 

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

 by which all the known effects of gravity are governed ; 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 admit ; 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 utterance to the law : but that the totality of a force can be 

 employed according to that law I do not believe, either in relation 

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

 form of power. 



I might have drawn reasons for urging a continual recollection 

 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 



