1304 
case certainly not so.*) The correct deviations of density in the 
solid are much smaller and have another dependence of temperature 
than that which DeBijE used. 
In connection with what we found above in point 4, at last it 
remains to be said that especially the use of statical deviations of 
density instead of the dynamic ones is a great mistake. In some simple 
cases we have been able to demonstrate that also in three dimensions 
the latter do not produce any scattering. Our conclusion therefore 
is that the molecular theory of the heat-resistance still remains 
entirely open. 
Physics. — “Contributions to the kinetic theory of solids. IN. The 
equation of state of the isotropic sold.’ By Prof. L. S. 
ORNsTEIN and Dr. F. ZeRNIKE. (Communicated by Prof. H. A. 
LORENTZ.) 
(Communicated in the meeting of June 24, 1916.) 
In this contribution we shall use the method we developed in 
our first contribution for the determination of the expansion in 
order to deduce the equation of state, i.e. the connection between 
the strain and the stress in its dependence on the temperature. In 
contribution I we have treated only the simple case that the 
strains are zero, and have determined the stress resulting from 
heating (thermal pressure). A quite analogous deduction can be 
used in order to find the stresses of a solid, which has been 
deformed at the absolute zero (equation of state). The only difference 
with the former case lies in the fact, that by this strain the solid 
generally departs from exact isotropy. Hence a more ample calcu- 
lation is necessary in the case of shearing. 
Further we shall mention the terms which present themselves if 
we take into account the remark of the note on p. 1293. 
Finally we shall show how the equation of state is also to be 
found with the aid of thermodynamic relations from the specific 
heat of solid bodies, which may be calculated from the formulae 
given by Born. This method, for the present only mentioned in 
principle, is more analogous to that of Drsyx-Everpincen than to 
our first deduction, which is purely dynamical. 
1. Now we will calculate the force necessary to give the solid 
1) See Epstein, Physik. Zeitschr. XV, 
