366 Dr. G. J. Stoney on the 



those which are consequences of such general facts as that 

 the molecules spend most of their time in travelling about 

 in straight lines like missiles, without a preponderance of 

 the kinetic energy of the motions in any one direction ; and 

 the further fact that the interchange of energy which occurs 

 during the encounters, and the immense number of these 

 encounters, lead to a rapid distribution to other motions of 

 any excess of energy which any one motion of any one 

 molecule may possess, and thus both equalize the pressure 

 throughout the gas and establish the prevalence of a con- 

 stant average ratio between that portion of the energy which 

 manifests itself in the journeyings of the molecules, and that 

 which is occupied in internal motions of the Ba class. 



In order to make this language intelligible, it is necessary 

 to explain that in treating of gases it is convenient to use the 

 word motions in a generalized sense, so as to include both 

 motions proper and all other events which are brought about 

 by imparting energy to the gas, and which thereby become 

 depositories of energy. These motions or events may be first 

 divided into the two classes A and B, external and internal 

 events. The A or external events are simply the motions of 

 the centres of inertia of the molecules between their en- 

 counters ; the B events are rotations or other motions, or 

 changes of configuration, of the parts of a molecule relatively 

 to one another, or electrical or other events ; any events, in 

 fact, which can be brought about by an expenditure of energy. 

 These may all be spoken of either as motions or events, using 

 the term motions in its generalized sense. 



Again, the B events require to be subdivided into three 

 classes : Ba events, which readily exchange energy with the 

 A events, i. e., which are affected by the speed with which 

 two molecules plunge into one another when an encounter 

 takes place, and which in turn contribute in a marked degree 

 towards determining with what velocities they shall separate 

 when the encounter is over. In contrast to these, the Be 

 events (if any such exist, as is perhaps probable if the vortex 

 theory of matter is true) are such as are completely isolated 

 from the A and Ba events, and therefore neither gain nor 

 lose energy in the encounters. Between the Ba and Be 

 events stand B6 events, which seem to be a conspicuous part 

 of what is actually going on in all the real gases of nature. 

 These Bb events are not wholly unaffected by the encounters, 

 but in any one encounter gain or lose but little energy ; while 

 after millions of encounters, the transference of energy, 

 perhaps chiefly in one direction — from them to other events — 

 may be appreciable. Events of this kind may produce even 



