462 



Prof. E. K. Rideal on the 



to the method suggested by Langmuir (Phys. Rev. viii. p. 171, 

 1916) from the equation 



K = ha 

 W 



where li is the thermal conductivity in ergs per cm. per sec, 

 a the distance between adjacent atoms, or approximately the 

 molecular diameters, and k the gas constant = l*37 . 10 -16 erg 

 per degree. 



For comparison are appended the ultra-violet vibration 

 frequencies of the elements, calculated with the aid of the 

 Lindemann melting-point equation and Haber's relationship, 



Mv 2 red = mv 2 violet, 



where M and m are the atomic and electronic masses 

 respectively. 



Metal. 



K 



Cu 



Ag 



Na 



K 



Al 



Gd 



Zn 



Mg 



Au 



Sn 



Ni 



Fe 



In the case of the non-metals where the thermal con- 

 duction is molecular and not electronic in character, the 

 reciprocal of the time of relaxation calculated in the above 

 manner is equal to the period of the natural infra-red 

 vibration, as in the case of sulohur : 



io- 14 . 



*.io- 14 



21-5 



22-9 



22-3 



19-5 



9-5 



10-8 



9-1 



6-9 



11-2 



16-7 



5-2 



13*2 



5-6 



15-1 



8-7 



15-2 



11-6 



20-4 



3-7 



10-5 



4-1 



21-5 



4-0 



26-7 



0-51 



13-2 



s 



K. 

 1-9x10- 



2-1 xlO" 12 



It will be noted that, in spite of the errors introduced in 

 the calculations of the ultra-violet vibration frequencies, the 

 time of molecular relaxation is identical with, or a few times 

 longer than, the natural period of vibration. 



It is significant to note that the time of molecular re- 

 laxation increases with the valency of the element, indicating 



