227 



high. We are uncertain as to the oaiise of this diflferencc -. most 

 probably it is due to an uncertainty in the temperature with tlie 

 absolute manometer. 



It is of special interest to compare these observations with Nernst's 

 formula. The fourth cohimn of Table II contains the pressures accord- 

 ing to this formula, calculated with the constants which Falck ') 

 has determined with the data at his disposal. Falck found the following 

 expression 



6000 1 0,009983 



loqp = . y l.lhloqT r + 3,1700 



^'^ 4,571 T ^ '' 4,571 ^ 



where p is the pressure in atmospheres. 



The correspondence will be seen to be satisfactory considering the 

 degree of accuracy of the observations. It does not look as if the 

 constants could be materially improved. 



Physics. — "On the equation of state of an ideal monatomic gas 

 according to the quantum-theory.'" By Dr. W. H. Keesom. Supple- 

 ment N". 30<2 to the Communications from the Physical Labora- 

 tory at Leiden. Communicated by Prof. H. Kameklingh Onnes. 



(Communicated in the meeting of May 31, 1913). 



§ 1. Introduction. Sumniari/. Debije*) has shown that agreement 

 with the observations concerning the specific heat of solid substances 

 can be obtained by modifying the theory of Elnstein ^) in this sense, 

 that the formula^) which PLA^CK has given for the mean energy at 

 the temperature T of a linear electrical oscillator is applied to the 

 different principal modes of vibration of a solid. 



It seems natural to apply the same principle to other material 

 systems which can behave as an oscillator and hence to investigate 

 the correctness of the consequences which follow from the hypothesis 



1) Falck: Physik. Zeits. 1908, p. 433. 



2) P. Debije. Ann. d. Phys. (4) 39 (1912), p. 789. 



3) For the literature see : H. Kamerlingh Onnes and W. H. Keesom. Math. 

 Enz. V 10, Leiden Gomm. Suppl. N». 23, § 74c. 



*) Debije makes use of the original formula of Planck, VViirmestrahlung, Isto 

 Aufl., p. 157. The more recent formula, Warmestrahlung, 2te Aufl., p. 140, which 

 differs from the first by the introduction of a zero point energy, leads to the same 

 results as regards the specific heal as long as the frequencies do not depend upon 

 the temperature. For processes in which the frequencies change, cf. P. Debije, 

 Programme for the Wolfskkhl lecture, Physik. Z S. 14 (1913), p. 239, it can 

 give diverging results for solids too. 



J 5* 



