264 KINETIC THEORIES OF GRAVITATION. 



ing stone ; and that as the latter is an example of kinetic energy, capa- 

 ble of transmuting itself into heat, so gravity must be in essence also 

 a kinetic energy capable of similar transformation. On this " hypo- 

 thesis " all the consequences so incongruous with experience, as above 

 indicated, would result. The ascending stone would have its energy 

 "transformed into attraction," and the latter would be correspondingly 

 increased. It would then be truly " said to consume the motion " of the 

 stone. And when the stone was falling there would be " a certain 

 amount of the attractive force converted into motion, and so the 

 attractive force should be so far reduced." The reasoning is undoubt- 

 edly correct. " But instead of this, it is actually increased. There is 

 therefore, [by the kinetic hypothesis, J no account given of what becomes 

 of the motion externally imparted to the stone when thrown upward.'* 

 And the undisputed facts of observation therefore, show us that if the 

 kinetic hypothesis "be correct, then there is a destruction of force in 

 the one case and a creation of force in the other." The conclusion is 

 incontrovertible. 



Seeing then the incongruity and inadmissibility .of the assumed 

 hypothesis, let us try a new departure. Let us, recurring to that only 

 safe guide experience, recall as the necessary outcome of the fourth, 

 fifth, and sixth propositions, that " gravitation is a property im- 

 mutable and inconvertible." Let us, to avoid confusion of idea by 

 the unconscious double entendre of the word " force," limit the term for 

 the present to that innate and primitive tendency or tension which 

 appears as the last result of dynamic analysis, and which obviously 

 differs as much from the action of the falling stone, as the flying arrow 

 differs in function from the elasticity of the bow which has impelled it. 

 "We shall thus have a term comparable in derivation and use to the 

 "element" or the "atom" of the chemist, designating simply that 

 which as a matter of fact, has not yet been further resolved. If now we 

 deny (for the present purpose) the application of this term " force," to< 

 the dynamic action of the falling stone, and call the latter " energy," a 

 term which conversely we deny to the primitive vis motrix, all confu- 

 sion and inconsistency will disappear. Obviously, "conservation" can 

 be intelligently applicable only to that which is capable of expenditure,, 

 transformation, or dissipation ; as to matter, or to energy. To speak of 

 the conservation of immutable gravitation is as unmeaning as to speak 

 of the conservation of the equally immutable molecular cohesion or 

 atomic elasticity. As a fact of daily observation, motion' is a variable 

 function, and like heat, color, form, or density, is not conserved. 



When a stone is thrown upward therefore, it loses tension, because- 

 this has been found empirically to be the inflexible law of distance-ratio- 

 for the gravitative force, and for no other human reason. It gains in 

 potential energy by the ascent, because there has been a corresponding 

 expenditure of kinetic energy in effecting the ascent ; and all experi- 

 mental research proves the absolute constancy of the sum of these two 



