1894.] MaxiuelVs Lmu of Partition of Energy. 255 



five of the six degrees of freedom, the ratio of the two specific 

 heats 



in o 



agreeing closely with the value found for air and most gases*. 



10. Another exceptional case is that in which the molecules 

 are regarded as smooth spheres or as centrobaric bodies repelling 

 one another according to any law of force which is a function of 

 the distance between their centres of inertia. Here, even if the 

 bodies are not dynamically symmetrical about their centres of 

 inertia, (as may be exemplified by smooth spheres containing 

 hollow concentric ellipsoidal cavities,) the forces between them in 

 a collision or encounter always pass through their centres of 

 inertia and cannot affect their angular velocities about their 

 principal axes. It is therefore not necessary in such cases that 

 the mean kinetic energies of rotation about the principal axes 

 should be equal to one another or to the kinetic energies of the 

 components of translation. 



* Sitz. der k. Wiener Akad., lxxiv, (ii.), 1876. Phil. Mag., March, 1893. 



