130 JAMES CLEHK MAXWELL 



the consequences of supposing the particles not to bo 

 spherical. In this case the impacts would tend to set 

 up a motion of rotation in the particles. The direction 

 of the force acting on any particle at impact would 

 not necessarily pass through its centre; thus by impact 

 the velocity of its centre would be changed, and in 

 addition the particles would bo made to spin. Some 

 part, therefore, of the energy of the particles will 

 appear in the form of tho translational energy 

 of their centres, whilo tho rest will take tho 

 form of rotational energy of each particle about 

 its centre. 



It follows from Max well's work that for each par- 

 ticle the average value of these two portions of energy 

 would be equal. Tho total energy will be half trans- 

 latioual and half rotational. 



This theorem, in a more general form which was 

 afterwards given to it, has led to much discussion, 

 and will be again considered later. For the present 

 we will assume it to bo true. Clausius had already 

 called attention to tho fact that some of tho energy 

 must be rotational unless tho molecules be smooth 

 spheres, and had given some reasons for supposing 

 that the ratio of tho whole energy to the energy 

 of translation is in a steady state a constant. Max- 

 well shows that for rigid bodies this constant is 2. 

 Let us denote it for the present by the symbol (3. 

 Thus, if tho translational energy of a molecule is 

 i m v 2 , its whole energy is A ft n\ v\ 



The temperature is still measured by tho trans- 

 lational energy, or \ m r 2 ; tho heat depends on tho 

 whole energy. Hence if 11 represent the amount of 



