233 Prof. Faraday on the Conservation of Force. 



but constantly in them and all space. I have already put 

 forth considerations regarding gravity which partake of this 

 idea*, and it seems to have been unhesitatingly accepted by 



Newton t- 



There is one wonderful condition of matter, perhaps its only 

 true indication, namely inertia; but in relation to the ordinary 

 definition of gravity, it only adds to the difficulty. For if we 

 consider two particles of matter at a certain distance apart, 

 attracting each other under the power of gravity and free to 

 approach, they will approach ; and when at only half the distance 

 each will have had stored up in it, because of its inei-tia, a certain 

 amount of mechanical force. This must be due to the force 

 exerted ; and, if the conservation 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 fourfold, 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 communi- 

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

 relation to other forces acting at a distance as those of magnet- 

 ism 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 commiinicated 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 phfenomena of the necessity 

 of the conservation of force as a law of nature, or one more in 



* Proceedings of the Royal Institution, 1855, vol. ii. p. 10, &e. 



t " That gravity should be innate, inherent, and essential to matter, so 

 that one body may act upon another at a distance, through a vacuum, with- 

 out the mediation of anything else, by and through -nhich their action and 

 force may be conveyed from one to another, is to me so gi'eat an absurdity 

 that I believe no man who has in philosophical matters a competent faculty 

 of thinking, can ever fall into it. Gravity must be caused by an agent act- 

 ing constantly according to certain laws ; but whether this agent be mate- 

 rial or immaterial I have left to the consideration of my readers." — See New- 

 ion's Third Letter to Bentley. 



