Kinetic Theory of Gases to Gravitation. 1 25 



off the entire stream of particles*. Secondly, the shapes of 

 diverse molecules (which would have no particular influence 

 while the molecules were at a distance) would, when the mo- 

 lecules are in contact, have a great influence, according to 

 whether the solid parts (or interstices) fitted over each other, 

 so as to afford more or less shelter from the streams of particles. 

 Possibly this might account for (or at least throw some light 

 upon) the extraordinary varied behaviour of chemical "affi- 

 nity." If this were justified, it would certainly be a remarkably 

 simple cause. It is just possible that a thing may be missed 

 sometimes by looking too deep. The processes of nature are 

 as a rule recognized to be simple, this being the necessary 

 condition for order. " Simplicity is the soul of mechanics." 

 This view, if well founded, would have the advantage of cor- 

 relating all molecular actions (including " gravity ") under 

 one cause. We have thought it just as well to mention these 

 views in passing (without attaching the same defmiteness to 

 them as we attach to gravitation). 



15. We would in conclusion make a few remarks upon a 

 matter of principle connected with this subject. It must be 

 evident that under a dynamical theory of gravitation, when a 

 mass is lifted, the energy expended in lifting cannot be con- 

 verted into " potential " energy, but must be converted into 

 kinetic energy, in imparting motion to the particles impinging 

 upon the upper side of the mass, and which tend to urge it 

 downwards. Conversely, when the mass falls, kinetic energy 

 is transferred from the particles of the medium to the mass. 

 As a general principle, therefore, by the abandonment of the 

 theory of " action at a distance" there can be no such entity 

 as " potential " energy at all. We cannot avoid thinking that 

 the very necessity to put forward a theory, that energy can 

 possess, as it were, a double nature (kinetic, and not kinetic), 

 in order to harmonize with the theory of " action at a distance" 

 is by itself a sufficient logical condemnation of this latter 

 theory. The idea of " potential" energy (i. e. an energy 

 which is not kinetic) involves the inconceivable idea of an 

 energy without motion, i. e. a kind of spiritual energy, whose 

 existence or non-existence leaves matter in the same physical 

 state. Already serious doubts have been cast upon its validity 

 as a logical principle by some of the most eminent minds. 

 From the prevalent use of the term "potential " energy, and 

 at the same time the common repudiation of the theory of 

 "action at a distance," one would be inclined to draw the in- 

 ference that there was an idea to a certain extent prevalent 



* We believe Le Sage called attention to this in its application to 

 " cohesion? 



