1289 
mit den durch Fermente hervorgerufenen Wirkungen vergleichbar, 
dass wir mit einiger Bestimmtheit annehmen, dass die Fähigkeiten 
einiger Erbeinheiten im wesentlichen in der Bildung bestimmter 
Substanzen bestehen, welche in der Art von Fermenten wirken’’. 
Although the observations on which this statement is based are 
in accordance with the enzyme theory, it is clear that Barrson’s 
view is quite different from mine. 
Physics. — “Contributions to the kinetic theory of solids. 1. The 
thermal pressure of isotropic solids. By Prof. L. S. Ornstein 
and Dr. F. Zernike. (Communicated by Prof. H. A. Lorentz). 
(Communicated in the meeting of February 26, 1916). 
P. Desise*) has in his Wolfskehl-lecture developed a theory of 
the equation of state of solid matter which has been elaborated by 
Dr. M. I. M. yan EvERDINGEN °). Depise assumes as a physical principle 
that the forces between the molecules in solid matter are not quasi- 
elastic, but depend also on higher powers of the deformations. He 
points out that only this principle enables us to understand the 
expansion of solid matter which gains energy under constant pressure. 
This assumption enables him to give a deduction of the GRÜNRISEN- 
theorem about the connection between the coefficient of expansion 
and the specific heat. 
Degije calculates the free energy of a solid body with the help 
of a canonical ensemble, using the method of normal vibrations, 
and introducing from the beginning the hypothesis of energy-quanta. 
We shall indicate in this paper another way to find the equation 
of state with the aid of the physical principles of Degijr. The 
quantum-theory will be applied to our final result if we wish to 
use it for low temperatures. DepiJe has taught us to replace in the 
calculations the space-lattice of molecules by a continuum, Born *) 
has shown this artifice to be right. Therefore, in considering the 
isotropic body, we shall use a continuum as a limiting case. For 
explanation we shall treat the case of a row of points and for this 
case we shall perform the transition to a continuous bar. Our method 
consists ‘in determining the thermal pressure, i.e. the pressure that 
1) Vorträge über die kinetische Theorie der Materie, Leipzig 1914. “Zustandsgleichung 
und Quantenhypothese u. s. w.”. 
2) De toestandsvergelijkingen van het isotrope vaste lichaam. Diss. Utrecht 1914, 
5) M, Born. Dynamik der Krystallgitter. Teubner. 1915, 
