20 



a deep impression is made by the very striking realisation which 

 it gives of the mechanism imagined by Maxwell completed by the 

 conception of electrons. 



It is obvions that the subject will lead to further discussions ^) 

 and plans, but in this paper 1 maj^ be allowed to confine myself to 

 the simple description of the experiment carried out. 



Physics. — "The chemical constant and the application of the 

 quantum-theor// hy the method of the natural vibrations to the 

 equation of state of an ideal monatomic gas." By Dr. W. 

 H. Keesom. Supplement N". 36i^ to the Communications from 

 the Physical Laboratory at Leiden. (Communicated by Pi-of. 

 H. Kamerlingh Onnes). 



(Communicated in the meeting of March 28, 1914). 



§ 1. In Suppl. N". 33 (Dec. 1913) the expression for the entropy, 

 aS', of a gas was discussed, as it follows from the application of the 

 quant um-theorj" to the molecular translatory motion by the method 

 of the natural vibrations. Molecular rotations and intramolecular 

 motions were not taken into account there. As was observed, the 

 chemical constant is connected with the additive constant which 

 occurs in the development of .S' for high temperatures. The object 

 of this paper is to show that the value of the chemical constant, 

 which in that manner is deduced from the expression for the entropy 

 (an expression which had already been given by Tetrode), is in 

 satisfactory agreement with values of this constant which correspond 

 to the experimental data concerning vapour pressures of monatomic 

 gases. 



§ 2. We shall confine ourselves in this paper to the consideration 

 of monatomic gases. If for the energy distribution one of the tem- 

 perature functions is assumed which occur in the quantum-theory, 

 one may suppose that the molecular rotatory motion, particularly 

 for the molecules of a monatomic gas, is in thermal equilibrium 

 Bay with the translatory motion. If in particular tluit temperature 

 function (given by Planck) is assumed which implies a zero point 

 energ3'j the molecular rotations in a monatomic gas also, at the 

 temperatures at which they have been investigated, represent a con- 

 siderabie amou]it of eneigy in proportion to the molecular trans- 



1) Compare also Maxwell, lillectricity and Magnetism II, Gh. VI. 



