244 KINETIC THEORIES OF GRAVITATION. 



treating molecalar physics initiated by those great leaders, that the 

 iuefficieucy and inconsistency of this modo of inquiry with the mechani- 

 cal theory of heat seems as yet not to be fully appreciated by some even 

 of the most zealous upholders of that theory. With this im[)ression, it 

 seems desirable that every effort should be made to arrive at a clear 

 understanding of fundamental points, and the principle of physical 

 causation, which the mechanical theory supplies.'-* 



As this is the usual point of departure with kinematists, {not " brought 

 up in the statical method,") it may be well here to afQrm with some 

 positiveness that without the ceaseless co-operation of two antagoniz- 

 ing or reciprocating statical tensions, a " mechanical theory of heat " is 

 rationally impossible. Matter possessing only inertia and motion (whose 

 product is momentum) would very speedily arrive at a state of stable 

 and inert equilibrium, without having ever exhibited a single phenome- 

 non of force, and without the possibility of any dynamic potential. 

 xVu abstract system of kinematics, under any geometrical arrangement 

 or conception, is indeed quite irreconcilable with the actual system of 

 dynamics fountl in nature and subject to our observation. All gases 

 would under the operation of the first law of motion, tend to infinite 

 and equable diffusion ; and liquids and solids would quickly follow in 

 their wake. Heat, whether considered as a vibration or a revolution, 

 (or preferably as both a rectilinear and au orbital movement,) could of 

 course have no existence, since there could be neither recoil nor con- 

 straining bond ; and the very first step toward an oscillation would 

 also be the last one. Even the principle itself of "conservation of 

 force'' is absolutely dependent on the existence of primordial static po- 

 tentiality. So much for a " clear understanding of fundamental points." 



" Section 1. The integral of gravitation is a function of space. Sup- 

 pose a central homogeueous globe to augment in bulk by the descent 

 of similar matter from au infinite distance in radial directions all around ; 

 each descending element, on arriving at tbe surface of the globe, pre- 

 sents itself charged with a certain amount of mechanical force equiva- 

 lent to the square velocity with which it impinges. If we confine our 

 attention to tbe centripetal iutiueuce of the original central globe only, 

 the square velocity of the descending element diminishes in the inverse 

 ratio of the radius of th e augmenting globular mass ; for it is upon the 

 surface of this that impact takes place, and the matter that has been 

 added to the original globe is assumed not to augment the centripetal 

 force acting upon the descending matter." t This established ratio of 

 final velocity does not appear in any way to substantiate the general 

 proposition ; nor is it seen to receive support from any of the succeed- 

 ing illustrations. Gravitation, as a fact of observation, is always found 

 to be rigorously relative to two posited elements ; and its integral is by 

 such observation a function of the distance between these elements. If 



* L. E. D. Phil. Ma«., May, 1«58, vol. xv, p. •^29. 

 t Loco cilat., p. 330. 



