116 J. A. POLLOCK. 



A NOTE on A RELATION BETWEEN the THERMAL 

 CONDUCTIVITY and the VISCOSITY op GASES. 



By J. A. Pollock, f.r.s. 



[Read before the Royal Society of N. S. Wales, September 3, 1919.'] 



In a recent number of the Proceedings of the Royal Society 

 of London, Hercus and Laby 1 publish the details of an 

 accurate redetermination of the thermal conductivity of 

 air. Combining their result with those of eleven other 

 experimenters, they give as the most probable value of the 

 conductivity at 0° 0., k = 5*22 x 10-*. 



In 1913 Eucken 2 gave the results of a series of measure- 

 ments of the thermal conductivities of a number of gases 

 relative to that of air, the determinations being reduced to 

 absolute measure by considering the conductivity of air 

 as 5*66 x 10 -5 . As shown by Hercus and Laby, the new 

 determination of this latter constant is at once useful, as 

 it enables Eucken's absolute values to be put on a more 

 accurate basis. 



After reviewing the whole evidence, Hercus and Laby 

 have collected for the various gases the most probable 

 values of the following constants: — fc, the thermal conduc- 

 tivity, C P , the specific heat at constant pressure, y, the 

 ratio of the specific heats, and ^, the viscosity, and with 

 these results have calculated the values of f given by the 

 equation, , 



f = ~X- (D 



Vo <^p 



As the value of f depends on the atomicity of the mole- 

 cule, attempts have been made to find a relation between 

 f and y. Jeans 3 has suggested the formula, f = (9y-5)/4. 



1 Hercus and Laby, Proc. Roy. Sec, A, 95, p. 190, 1919. 



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



3 Jeans, The Dynamical Theory of Gases, 2nd ed., p. 317, 1916. 



