156 Mr. S. T. Preston on the Continuance of 



would not be thus definitely limited. We are, however, deal- 

 ing here with a fundamental matter of principle, not with sub- 

 sidiary details*. It appears difficult to see where we are to limit 

 the scale in the application of a principle, or how ? if the ki- 

 netic theory be applicable to the case of a compound gas con- 

 sisting of small masses (molecular clusters) of, say, as many as 

 50 to 60 molecules aggregated about a common centre, it should 

 not apply when the number of molecules aggregated about a 

 centre is increased (so as to form a visible mass). It might 

 be said that the cases are different, inasmuch as the compound 

 molecules of a gas rebound from each other as elastic bodies, 

 whereas in the case of the masses of the universe they would 

 generally be broken up and scattered at the encounters. This 

 objection could only arise, however, from a superficial view of 

 the case. For it is a known fact that the compound molecules 

 of a gas often acquire in the accidents of collisions very great 

 velocities, and they are thus broken up and their parts scat- 

 tered at their encounters. There is, however, on the whole no 

 work done (or loss of energy) in this breaking-up of the mi- 

 nute masses (compound molecules) of the gas ; for the disso- 

 ciated molecules unite again in another region of the gas; and 

 so long as the mean state of aggregation (per unit of volume) 

 in the gas remains unchanged, there is on the whole no work 

 done. So in the case of the universe, if the mean state of ag- 

 gregation remain the same, there would be on the whole no 

 work performed by the occasional breaking-up of matter. 

 But it may be said that at every such collision of two masses 

 of the universe there would be a dissipation of energy in the 

 aether attendant on the heat developed at the encounter, and 

 this energy would be unavoidably lost. But if we regard the 

 matter of the universe as (in the mean) uniformly diffused, as 

 it would necessarily be under the kinetic theory, there would 

 be no such actual loss of energy^ — merely a radiation back- 

 wards and forwards from one region to another. Thus in the 

 smaller scale case of a gas, there is undoubtedly a dissipation 

 of energy in the sether at every encounter of the small-scale 

 masses (molecular clusters) in translatory motion; but this 

 energy is (as is known) not lost, but only radiated to another 



go on increasing indefinitely by the imaginary continual piling-up of mat- 

 ter, but would attain a final maximum. We allude to this last point as a 

 possible detail of interest, without thereby implying that it essentially 

 affects the main principle we have been developing in this paper. 



* We merely apply in principle the same general mechanical considera- 

 tions to molecules aggregated into clusters (lumps) under chemical action, 

 as to molecules aggregated into lumps under gravific action (stellar 

 masses). 



