298 Mr. S. T. Preston on the Kinetic Theory of Gravitation. 



gravity in two masses immersed in the gas within the range 

 of free path. For since it has been proved from the kinetic 

 theory that the particles of a gas adjust their motions so as to 

 move uniformly or equally in all directions, and since the 

 particles within the range of free path are moving in unbroken 

 streams, it follows that two masses immersed in the gas at a 

 distance apart within this range will (owing to the one 

 sheltering the other) be struck with more particles on their 

 remote (unsheltered) sides than on their adjacent (sheltered) 

 sides, so that the two masses will be urged together. This, 

 therefore, fulfils Le Sage's fundamental idea without the 

 necessity for accepting any of his postulates. We need not 

 accept the scarcely realizable postulates of streams of particles 

 coming from indefinite distances in space (at uniform angles), 

 each stream moving continuously in one direction ; but we 

 can substitute for this the natural conception of the normal 

 motion of the particles of a gas within the range of free path, 

 where, although each particle is continually changing the 

 direction of its motion, yet the general character of the motion 

 of the system as a whole remains unchanged ; or the system 

 of particles automatically correct their motions so as to con- 

 tinue to move uniformly or equally in all directions, as demon- 

 strated in connexion with the kinetic theory of gases. This 

 movement of the particles equally in all directions is the con- 

 dition required to produce equal gravific effect in all directions. 

 Thus all we require to admit in order to produce all the effects 

 of gravity as necessary results, is the existence of a gas in 

 space. This gas differs from an ordinary gas only as to scale, 

 i. e. in the proximity, velocity, and extreme minuteness of its 

 particles, whereby a length of free path commensurate with 

 the greatest observed range of gravity is insured, the extreme 

 minuteness of the particles being at the same time adapted to 

 that high velocity which the effects of gravity require, and 

 which also necessarily renders the medium itself impalpable 

 or concealed from the senses. The range of free path, though 

 great in one sense, may be considered small and suitable for 

 a gas that pervades the vast range of the visible universe. 



2. In applying these principles to cohesion, or the approach 

 of molecules in chemical reactions, it is so far easy to see that 

 when two molecules of matter come very close together, or if 

 we suppose them actually to come into contact, then they will 

 cut off the entire stream of particles of the gravific medium 

 from between the parts in contact ; and therefore, as the gravific 

 particles now only strike against the remote sides of the two 

 molecules, the latter will be urged together with very great 



