457 



Comparison of tlie oxpi-ession obtained tlierc for \hv oner^} of 

 the moleculai' rotations with the expei-iniental data concerning the 

 specific heat of hydrogen shows, as far as the general course is 

 concerned, an agreement which is just as good as that found by 

 Einstein and Stern. For the ordinary and the not very low tem'pe- 

 ratures, for which Eucken's results have been confirmed by Scheel 

 and Heuse, now also deviations are found, which, just as those 

 found by Einstein and Stern cannot be ascribed to experimental 

 errors. The deviations found here differ from those found by 

 Einstein and Stern in these respects : they are all in the same 

 direction, viz. so that the experimental value is larger than the 

 calculated one ^), and they increase regularly with the temperature. 

 These points seem to be in favour of the suppositions made in § 2, 

 in so far as it seems easier to account for deviations showing this 

 course by introducing the hypothesis of the "appearance of a new 

 degree of freedom" than for deviations such as were found, by 

 Einstein and Stern. On the other hand the possible unequality of 

 the two principal moments of inertia which govern in this region 

 of temperature the contribution of the rotatory motion to the specific 

 heat of hydrogen in the supposition that the third principal moment 

 of inertia is so small that the contribution furnished by the rotation 

 round the corresponding axis is not perceivable or only very small, 

 may perhaps also have as a consequence deviations such as found 

 by Einstein and Stern in supposing those two moments of inertia 

 to be equal. 



Before introducing one of these new hypotheses it seemed to me 

 to be preferable to put the expression for the energy of the mole- 

 cular rotations derived in § 2 to the test with the aid of other 

 phenomena. As according to Langevin's theory the molecular rota- 

 tory energy has a determining influence on the magnetization of 

 paramagnetic substances, the latter can be used for the purpose. 

 Dr. OosTERHUis, who applied with good success the quantum-theory 

 with introduction of the zero-point energy following Einstein and 

 Stern for the explanation of the deviations which the susceptibility 

 of some paramagnetic substances show from Curie's law, w^as so 

 kind at my suggestion as to put to the test the expression derived 

 in § 2 also ^). He found that those deviations are not represented 

 \evy much better with the aid of that expression than with that of 

 the simpler expression given by Einstein and Stern. A clear deci- 

 sion between the two expressions was not obtained. 



1) The same in true for the deviations found by Sackur I.e. 

 i*; E. OosTERHUis. Coram. Suppl. N". 31 (June 1913), § 7, 



