1295 
Physics. “Contributions to the kinetic theory of solids. 
II. The unimpeded spreading of heat even in case of deviations 
from Hooke's law’. By Prof. L. S. Ornstein and Dr. 
F. ZeRNIKE. (Communicated by Prof. H. A. Lorentz). 
(Communicated in the meeting of March 25, 1916.) 
1. In a supplement to his lecture on the equation of state of 
the solid body, Depie*) has endeavoured to “make a qualitative 
theoretical calculation of the coefficient of conduction of heat.” There 
the author points out repeatedly that his estimations are only to be 
taken very approximately and should serve as a first orientation 
only. So, as we tried to obtain an accurate calculation of the 
conduction of heat, it did not seem desirable to us to deal with the 
problem in exactly the same way and to carry out only bere and 
there some corrections and completions. 
Now DeBije's principle, which we therefore intended to work 
out otherwise, runs as follows. In an ideal solid body, i.e. a solid 
for which the elastic equations would be linear, various progressive 
waves may exist independently of each other, like the electromag- 
netic waves in a field of radiation. This implies that a heat-motion 
occurring on one side of the solid spreads unimpededly through the 
solid, so that the density of energy becomes equal in all parts of 
the solid. If the solid is in a stationary state, the temperature will 
thus be everywhere the same, even if continually a current of energy 
moves through the solid in a definite direction. Hence DeBije empha- 
sizes this dictum: the coefficient of heat conduction of the ideal solid 
body is infinitely great (le. § 7, ef. the statement given there). Now in 
several regards it is preferable to formulate the rule in this way: 
the ideal solid body does not show any resistance of heat. 
That a real solid body does show resistance of heat DegiJe ascribes 
to the fact that the elastic equations are not perfectly linear. Therefore 
various normal vibrations strietly cannot be superposed and it 
is conceivable that waves running in different directions so to say 
oppose each other. Derije has indeed succeeded in deducing indirectly 
a scattering and consequently a suppression of the running waves. 
Our endeavours to state more directly the connection between 
resistance of heat and non-linear terms of the elastic equations of 
motion have failed. Therefore we will not report our considerations 
1) Mathematische Vorlesungen an der Universität Göttingen VI (WoOLFSKEHL- 
Vorträge) pg. 19. 
