"7JT 



338 Aggregation and Dissociation [OH. xvm 



of 270. Indeed the molecule is in every way identical so long as we treat 

 the atoms as points, each having only three degrees of freedom ; it is merely 

 a difference of point of view whether we regard the molecule as a single 

 body of which the two components are slightly separated by centrifugal 

 force, or as two bodies describing circular orbits about one another. When 

 we regard the atoms as something more complex than mere points, a 

 distinction has to be drawn between rotation of the atoms as part of the 

 molecule and rotation of the atoms as separate systems. This distinction 

 can hardly be discussed without formulating definite views as to the internal 

 structure of the atom. 



Similar remarks apply to molecules which consist of more than two 

 atoms. The condition for no dissipation from the vibrations forced by the 

 mass motion of the atoms is that the relative distance of the atoms shall 

 remain the same, so that the molecule must rotate as a rigid body. If this 

 argument is sound, the molecule must have six degrees of freedom 

 altogether, so that if it were not for the influence of aggregation, etc., 

 we should have to have <y = 1^ for all gases other than monatomic and 

 diatomic, as suggested in 403. 



As soon, however, as we accept the view that dissipation of energy plays 

 a part of the kind explained, in the phenomenon of dissociation and recom- 

 bination, we have to give up all hope of calculating the degree of dissociation 

 from the principles of the Kinetic Theory. For the factors which are of 

 greatest importance in determining the degree of dissociation will be just 

 those which measure the dissipation of energy, and of these we know 

 nothing. We can only proceed further by introducing some simplifying 

 supposition which is altogether extraneous to the Kinetic Theory, as for 

 instance that of J. J. Thomson (I.e. ante, p. 335) that there is a definite 

 average time during which two or more atoms of known kinds remain in 

 combination. 



