KINETIC THEORIES OF GRAVITATION. 233 



primitive iunate tension, exclusive of all motion, although the parent of 

 all motion. So that while one would limit the word to desiguate a 

 purely kinetic condition of matter, another would limit it on the opposite 

 side to designate a purely static quality in matter. 



Elasticity is a natural force, having always an entirely different space- 

 potential from gravity, and yet is equally removed in every case from 

 that ratio of uniformity supposed to be the true representation of con- 

 servation. In the case of tensile elasticity, (as of a rubber baud or of a 

 long spiral spring,) the tension increases directly with the distance of 

 elongation. 



Professor Faraday thus proceeds to illustrate the difficulty he finds 

 in the ordinary definition of gravity : " Assume two particles of matter, 

 A and B, in free space. . . . Then at the distance of 10 the force 

 may be estimated at 1, whilst at the distance of 1, i. e., one-tenth of the 

 former, the force will be 100 ; and if we suppose an elastic spring to be- 

 in troduced between the two as a measure of the attractive force, the 

 power compressing it will be a hundred times as much in the latter case 

 as in the former. But from whence can this enormous increase of the 

 power come?" The answer is, that this increase of "power" comes 

 from either particle being so much nearer the source of the influence. 

 Why this increase should be just one hundred-fold in the case supposed, 

 the present state of science does not furnish any explanation. The re- 

 sult is accepted simply as a very rigorously verified " fact." 



" Suppose the two particles A and B removed back to the greater 

 distance of 10, then the force of attraction would be only a hundredth 

 part of that they previously possessed ; this, according to the statement 

 that the force varies inversely as the square of the distance, would 

 double the strangeness of the above results ; it would be an annihilation 

 of force." Here again, the law of intensity, as a function of distance, 

 is confounded with absolute quantity in the agent. Such a confusion 

 could hardly have occurred in discussing the action of a permanent 

 magnet. The actually existing gravity decrement no more involves 

 any "annihilation of force," than would an equality of ratio irrespective 

 of distance involve a creation of force, were it found in any case to be 

 true. So far from there being any destruction or loss of force in the 

 crucial case supposed, the doctrine of "conservation" teaches us that 

 the separation of the two particles could be effected only by the expendi- 

 ture of an adequate amount of energy; and that at their greater dis- 

 tance of 10, these particles would possess a potential of position precisely 

 equivalent thereto. 



Faraday continues : "According to the definition, the force depends 

 upon both particles ; and if the particle A or B were by itself, it could 

 not gravitate, i. e. it could have no attraction, no force of gravity. . . . 

 As the particles can be separated, we can easily conceive of the particle 

 B being removed to an infinite distance from A, and then the power in 

 A will be infinitely diminished. Such removal of B will be as if it were 



