150 Dr. S. Tolver Preston on some 



first appeared in the Philosophical Magazine, Sept. 1877, 

 to replace the arbitrarily assumed atom streams of Le Sage 

 and Lord Kelvin by a motion which is exactly analogous to 

 that which belongs to the kinetic theory of gases. 



In that way the most obscure assumption of Le Sage's 

 theory finds an unforced explanation — namely, how the 

 symmetrical motion of the atoms under the continual changes 

 of their direction produced by their collisions against gross 

 matter, is kept up. 



Now it has already been mathematically demonstrated in 

 the case of ordinary gases, that an automatic correction goes 

 on in a system of bodies or particles in free collision, and such 

 a one that the particles are forced to move equally in all 

 directions : and this is the absolutely necessary condition for 

 equal pressure in all directions. The rate of establishment of 

 this automatic correction, which is chiefly brought about by 

 the oblique encounters, has, in fact, been calculated mathe- 

 matically by Prof. Ludwig JBoltzmann for ordinary gases. 

 This adjustment (or correction) is in fact of such a stable 

 character, that if the motion of the gas particles were artificially 

 disturbed, the particles would of themselves equalize the 

 motion again, so that an equal number of particles are moving 

 in any two opposite directions. The motion can also be 

 described so, that if we think of any small point situated 

 anywhere in space, the atoms are at every instant flying 

 towards and from this point, exactly as if it were a luminous 

 point. 



Hence it follows that when a system of atoms is left to 

 itself, it will, by the principles of dynamics, automatically 

 adjust the character of its motion in such a way that this 

 motion is adapted to produce the gravitation effects. The 

 motion of streams of atoms equally at all angles, which 

 Le Sage gave forth as an arbitrary postulate, is attainable 

 in a gas without any postulate. Instead of streams, each of 

 which for itself maintains a constant direction of motion, and 

 which cease to flow after a long epoch of time, we have a per- 

 manent motion of atoms correcting itself in a self-acting 

 manner ; and which fulfils the wished-for object. 



So, therefore, we have succeeded, by starting from a very 

 simple and thoroughly natural foundation, in establishing all 

 those conditions which Le Sage needs for his theory. 



Nevertheless there are certain assumptions concerning 

 quantitative relations to be added. In the first place, the 

 mean length of path of an aether atom must be assumed to be 

 exceedingly great. If, namely, the same were small in pro- 

 portion to the distance between two influencing masses, then 



