RELATION OF GRAVITY. 363 



either of the phenomena or of the results to be dealt with, 

 should stop our exertions to ascertain, by the use of the prin 

 ciple, that something remains to be discovered, and to trace 

 in what direction that discovery may lie. 



I will endeavour to illustrate some of the points which 

 have been urged, by reference, in the first instance, to a case 

 of power, which has long had great attractions for me, be 

 cause of its extreme simplicity, its promising nature, its uni 

 versal presence, and in its invariability under like circum 

 stances ; on which, though I have experimented * and as yet 

 failed, I think experiment would be well bestowed, I mean the 

 force of gravitation. I believe I represent the received idea 

 of the gravitating force aright in saying that it is a simple at 

 tractive 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. The usual 

 idea of the force implies direct action at a distance ; and such 

 a view appears to present little difficulty except to Newton, 

 and a few, including myself, who in that respect may be of 

 like mind with him. 



This idea of gravity appears to me to ignore entirely the 

 principle of the conservation of force ; and by the terms of 

 its definition, if taken in an absolute sense, &quot; varying inversely 

 as the square of the distance,&quot; to be in direct opposition to it, 

 and it becomes my duty now to point out where -this contra 

 diction occurs, and to use it in illustration of the principle of 

 conservation. Assume two particles of matter, A and B, in 

 free space, and a force in each or in both by which they gravi 

 tate towards each other, the force being unalterable for an 

 unchanging distance, but varying inversely as the square of 

 the distance when the latter varies. Then, at the distance of 

 ten, the force may be estimated as one ; whilst at the distance 

 of one, that is, one-tenth of the former, the force will be one 



* Philosophical Transactions, 1851, p. 1. 



