286 PHENOMENA DEPENDENT ON MOLECULAR PATHS 105 



important fundamental theorem of the kinetic theory. As 

 has been mentioned in 53, Clausius has established the 

 proposition that in a perfect gas the kinetic energy of the 

 molecules bears an always constant ratio to the whole 

 energy contained in the gas ; and this theoretical proposi- 

 tion is experimentally confirmed by the experiments that 

 have been made for the measurement of the specific heats. 

 If now a greater amount of molecular energy were brought 

 to a point in a gas in consequence of the assumed better 

 conductivity for it, the necessary consequence would, accord- 

 ing to this proposition of Clausius, be. that a compensation 

 would at once result by the atomic energy gaining at the 

 expense of the molecular until the proper ratio was again 

 restored. By this the untenability of that hypothesis might 

 be established, at least for perfect gases. 



Now, there are certainly many gases and vapours for 

 which Clausius' proposition cannot hold in all strictness, 

 because their specific heats are not constant, but are highly 

 variable with the temperature. For such cases a different 

 consideration would be in place, which rests on the proposi- 

 tion of the conservation of energy alone. According to this 

 law the discussion of considerations respecting the condi- 

 tions during an encounter has no bearing on the resolution 

 of our doubt. If a particle has flown from one place to 

 another, it has carried over with it to its new place the 

 whole amount of its energy not its kinetic energy only, 

 but also the whole of its internal or atomic energy and 

 it is an entirely unimportant question whether and how this 

 energy is transformed by the collisions that afterwards 

 occur. 



Hence it follows that the conductivity of a gas for every 

 kind of energy is the same, and that if the formula 



f = 1-6027 TJC 



holds for the conduction of the molecular kinetic energy, it 

 must also hold for the conduction of heat generally. 



