427 
f. If we combine the results obtained in d and e with those given 
in c we reach the conclusion that, as far as B is concerned, between 
—100° C. and —180°C. the thermal behaviour of hydrogen, which, 
between — 100° C. and + 100° C. is that of a system of rigid 
spheres of central structure each with an electric doublet of constant 
moment at its centre, and acting upon each other according to the 
ordinary laws of mechanics and of the electromagnetic field, now 
changes to that which characterises a monatomic substance, and that 
between — 180° C. to at least — 230° C. this behaviour is completely 
followed '). On this account we shall postpone further considerations 
of the second virial coefficient for hydrogen in this region until 
monatomic gases are discussed in a subsequent communication. 
From the above it is accordingly evident that the thermal behaviour 
of hydrogen exhibits a strict parallelism with its calorie behaviour 
as deduced from Kuckrn’s measurements of the specific heat at constant 
volume. As we suspect, in accordance with the theories of Nernst ’) 
and EinsreiN®), that the decrease in the specific heat at lower 
temperatures will find an explanation in the application of the 
hypothesis of finite elements of action to the rotations of the mole- 
cule, the parallelism here observed at once leads to the question 
as to whether the explanation of the pecularities of the thermal 
equation of state for hydrogen obtained in the present paper may 
not profitably be sought in the same direction. For instance, one can 
imagine that the hypothesis in question would lead to the assumption 
that, on approaching one another, the molecules have not such 
orientations and are not so distributed with respect to their mutual 
distances, as is required by the laws of statistical mechanics according 
to ordinary dynamics and electrodynamics, and that therefore the 
mean attraction would be smaller at lower temperatures *) than would 
be the case if these laws were obeyed at these temperatures as well. 
From the fact that B is negative at those temperatures at which the 
di-atomic hydrogen begins to behave as a monatomic substance, and 
that there is consequently some attraction still left which does not 
decrease much more even with the temperature (ef. 0), it follows 
that the quantum hypothesis applied to this region would not have 
1) The temperature regions here given are not to be regarded as sharply bounded, 
still less are they to be considered as sharply defined by the observations at 
present available. 
2) W. Nernst. ZS. f. Elektrochem. 17 (1911), p. 265. 
3) A. Einstein. Discussions of the Sotvay Congress, Nov. 1911. 
4) A similar diminution of the attraction was assumed in Comm. No. 119 in 
order to explain the maximum observed in the density of helium, 
