107 CONDUCTION OF HEAT 291 



Smoluchowski von Smolan l and Brush 2 have essenti- 

 ally contributed. 



Winkelmann similarly tested the constancy of the 

 internal conductivity by determining the logarithmic decre- 

 ment of the series of observed readings of his air ther- 

 mometer, which decreased with the time in geometrical 

 progression. The following are some of the values found by 

 him : 



Air . . Apparatus I . . p = 750 mm. 0-000509 



138 501 



3 480 



Apparatus II . p = 750 0-000277 



43-3 260 



13-1 260 



1 259 



Hydrogen Apparatus I . . p = 750 0-00294 



91-9 290 



4-7 258 



3 245 



1-92 216 





Winkelmann examined other gases, too, especially ethy- 

 lene, and found a similar confirmation of the law. But the 

 examples we have given will suffice to prove the accuracy of 

 the theoretical law and to show us to what low pressures 

 the conductivity remains constant. 



108. Calculation of the Heat- conductivity from 

 the Coefficient of Viscosity 



But the theory requires more than that the value of 

 the conductivity should not vary with the density of the 

 gas ; it furnishes also the law of the variation of the con- 

 ductivity with the temperature, and even suggests the 

 possibility of calculating the value of the conductivity 

 itself in absolute units for those gases whose viscosity and 



1 Wied. Ann. 1898, Ixiv. p. 101 ; Phil. Mag. [5] xlvi. p. 192 ; Wien. Akad. 

 Anzeiger, 36. Jahrg. 1899, p. 1, and Sitsungsber. 1899. 

 3 Phil. Mag. 1898 [5] xlv. p. 31. 



TJ 2 



