THERMAL CONDUCTIVITY AND VISCOSITY OF GASES. 249 



A NOTE on the RELATION BETWEEN the THERMAL 

 CONDUCTIVITY and the VISCOSITY OF GASES 

 WITH REFERENCE to MOLECULAR COMPLEXITY- 



By J. A. Pollock, d.sc, 



Professor of Physics in the University of Sydney. 



[Read before the Royal Society of N. S. Wales, October 6, 1915.'] 



In the equation k = fyc v , expressing the thermal con- 

 ductivity of a gas in terms of the viscosity and specific 

 heat, the coefficient f is a numerical factor which is approx- 

 imately constant for gases of the same atomicity. Such 

 a fact suggests the probability of a relationship between f 

 and 7, the ratio of the specific heats. But long before 

 the result, just mentioned, was fully established, the prob- 

 ability of f being a function of 7 was recognised, though it 

 was not generally appreciated. As early as 1876 Boltz- 

 mann, 1 from theoretical considerations, obtained the 

 expression f = 3 f(y - 1)/2, where f is the constant for 

 monatomic gases. It has been known for some time that 

 the equation is physically inaccurate, but the matter does 

 not seem to have been followed further. 



Recently new results for the thermal conductivities of a 

 number of gases have been published by Eucken. 2 In con- 

 nection with these measures, Eucken discusses the depend- 

 ence of f, not only on the properties of the molecule, but 

 also on the temperature. As possibly lying outside the 

 main lines of his investigation, he does not consider the 

 relationship of f to 7, but, from the zero temperature 



' Boltzmann, Fogg". Ann., 157, p. 457, 1S76; see also Schleierrnacher, 

 Wied. Ann., 36, p. 346, 1889, and Chapman, Trans. Eoy. Soc, 211, A, p. 

 433, 1912. 



2 Eucken, Phys. Zeitschr., 14, p. 324, 1913. 



