produced by Collisions of Atoms or Molecules. 321 



left 'at rest after its collision with C. The initial distances 

 must be such that the collision between A and B precedes the 

 collision between B and 0. Amounts of energy equal to I and 



V are carried away into infinite space in the pulses produced 

 by the two collisions. In the arrangement now described, the 

 suddennesses of the starting and stopping of B are not pre- 

 cisely equal and similar ; and, because of their difference, 



V might generally be somewhat less than I : but the law of 

 force between the atoms might be such as to render V equal 

 to, or greater than, Z, for certain ranges of values of q. 



Take an analogous case of collisions between three ideal 

 billiard balls, each perfectly elastic. The clicks of A on B, 

 and of B on C, cause losses of energy, I and I', to be carried 

 off through air by sound-waves. 



§ 13. Consider now the collisions in a non-electrified 

 monatomic gas, that is to say, an assemblage of single atoms, 

 each having within it its neutralizing quantum of electrions; 

 except a small proportion, from or to which electrions may have 

 been temporarily taken or given. For simplicity we shall 

 first take the case in which a single electrion is the electric 

 neutralizing quantum for each ponderable atom. The collisions 

 will keep the electrions continually in a state of vibration within 

 the atoms ; except, in the comparatively rare case of an elec- 

 trion being knocked out of an atom, or in the infinitely rare 

 case of the relative motion of an atom and electrion being 

 reduced exactly to zero, by a collision. 



§ 14. The law of force between the electrion and atom 

 may be such that the centre of the atom is the only position 

 of stable equilibrium for an electrion within it. 



§ 15. Or the law of force may be such that there are any 

 number, i, of concentric spherical surfaces within the atom, on 

 each of which an electrion may rest in equilibrium radially 

 stable; and others, on each of which an electrion would be 

 in equilibrium radially unstable *. In the statistical average 

 of collisions, the electrion may, immediately after a particular 

 collision, be ranging, in non-sinusoidal vibration, across 

 several spherical surfaces of stable and unstable equilibrium, 

 and losing energy by sending out irregularly reciprocating 

 waves through ether. Before the next collision, the electrion 

 may probably have settled down into very approximately 

 sinusoidal vibrations in and out across any one of the surfaces 

 of radial stability. 



§ 16. This last condition we may suppose to. be generally 

 prevalent during the greater part of the free path between 



* " Plan of an Atom to be capable of storing an Electrion with Enor- 

 mous Energy for Radio-activity,'' by Lord Kelvin, Phil. Mag. Dec. 1905. 



