64 Mr. James Rice on 



which the molecule may possess by reason of the relative motion 

 of its parts to each other, i.e., its atoms, or even the electrons 

 within the atoms. Considered in that restricted light the mole- 

 cule has, as we say, three degrees of freedom, i.e., the most 

 general translatory movement can be compounded of three 

 partial movements in three defined directions, say, back to front, 

 side to side, and up and down ; this is a natural sort of division 

 in view of the three dimensional nature of our space. We also 

 say that for each degree of freedom the molecule possesses an 

 amount of energy 



2 a T ergs 



giving the total, a T ergs, as before for the three degi'ces of 

 freedom. 



Now, when we go inside the molecule, as it were, we per- 

 ceive the existence of other degrees of freedom. To a huge 

 celestial intelligent being our solar system would be as one body 

 travelling through space with apparently three degrees of freedom. 

 To us, however, it a})pears as a number of discrete bodies with 

 many degrees of freedom quite independent of its own present 

 motion towards the costellation Hercules. Similarly the com- 

 plexity of the structure of the molecule yields many more 

 degrees of freedom than the three referred to, and the accom 

 panying movements and vibrations must involve the possession 

 of kinetic energy over and above the energy of translation. The 

 theorem of Equipartition states that in so far assuchmovetnents 

 can he affected by coiiditions which alter temperature, the 



molecule, on the average, should possess - a T ergs of kinetic 



energy for each such degree of freedom. I have put in a pro- 

 visional clause, you will observe. On the grounds of pure 

 Dynamics it should not be necessary to insert it ; the movements 

 in question should be affected by changes of temperature. But 

 that is the trouble, as we shall see. This enumeration of the 

 average energy of the molecule is not exhaustive ; it refers solely 



