AXD MODERN PHYSICS. 137 



In this caso the kinetic energy of the molecule 

 consists of the energy of its centre of gravity, together 

 with the energy of its component parts, relative to its 

 centre of gravity.* 



Now Clausius had, as wo have seen, given reasons 

 for believing that the ratio of the whole energy of a 

 molecule to the energy of translation of its centre of 

 gravity tends to become constant We have already 

 used ft to denote this constant Thus, while the tem- 

 perature is measured by the average kinetic energy 

 of translation of the centre of gravity of each mole- 

 cule, the heat contained in a molecule is its whole 

 energy, and is ft times this quantity. Thus the con- 

 clusions as to specific heat, etc., already given on page 

 130, apply in this case, and in particular we have the 

 result that if 7 be the ratio of the specific heat at 

 constant pressure to that at constant volume, then 



2 1 

 **" 3 y -l 



Maxwell's theorem of the distribution of kinetic 

 energy among a system of molecules applied, as ho 

 gave it in 18CG, to the kinetic energy of translation of 

 the centre of gravity of each molecule. Two years 

 later Dr. lioltzmann, in the paper we have already 



Another supposition which might be made, and which is necessary 

 in order to explain various actions observed in u compound gas under 

 electric force, is that the parts of which a molecule b composed are 

 continually changing. Thus a molecule of steam consists of two 

 parts of hydrogen, one of oxygen, but a given molecule of oxygen is 

 not always combined with the (unto two molecules of hydrogen ; the 

 juirtirlcn are continually changed. In Maxwell's paper an hypothcsi* 

 of this kind U not dealt with. 



