THB DYNAMICAL EVIDENCE OF THE 



For a rigid body n-6, which makes the whole energy of motion twice the 



w of translation. 



*But if the molecule is capable of changing its form under the action of 

 impressed forces, it must be capable of storing up potential energy, and if the 

 forces are such as to ensure the stability of the molecule, the average potential 



will increase when the average energy of internal motion increases. 

 Hence, as the temperature rises, the increments of the energy of translation, 

 the energy of internal motion, and the potential energy are as 3, (n-3), and e 

 respectively, where e is a positive quantity of unknown value depending on the 

 law of the force which binds together the constituents of the molecule. 



When the volume of the substance is maintained constant, the effect of 

 the application of heat is to increase the whole energy. We thus find for the 

 specific heat of a gas at constant volume 



where p t and V t are the pressure and volume of unit of mass at zero centi- 

 grade, or 273* absolute temperature, and J is the dynamic equivalent of heat. 

 The specific heat at constant pressure is 



In gases whose molecules have the same degree of complexity the value of 

 n is the same, and that of e may be the same. 



If this is the case, the specific heat is inversely as the specific gravity, 

 according to the law of Dulong and Petit, which is, to a certain degree of 

 approximation, verified by experiment. 



But if we take the actual values of the specific heat as found by Regnault 

 and compare them with this formula, we find that n + e for air and several 

 other gases cannot be more than 4 - 9. For carbonic acid and steam it is greater. 

 We obtain the same result if we compare the ratio of the calculated specific 

 heats 



2 + n + c 

 n + e 



with the ratio as determined by experiment for various gases, namely, T408. 



