and Heat- conduction in rarefied Gases, 



57 



whole the requisite flexibility. Exhaustion was produced by 

 means of a Geissler mercury air-pump. 



The following Tables show the dependence of the logarithmic 

 decrement, X, on the pressure, p. All the numbers arc reduced 

 to 15° Cels. (the mean temperature of the experiments) ; and, 

 following Maxwell, we have supposed the friction-coefficient 

 proportional to the absolute temperature. 







A 



r. 









centim. 





centim. 





centim. 





^=0*1104 





^ = 0-1967 





d 3 = 0-2802 



V- 



\. 



p- 



A. 



P- 



X. 



millim. 





millim. 





millim. 





380 



0-132 



750-380 



00583 



750-370 



00425 



20 



0131 



20-5 



0-0582 



20-5 



00424 



76 



0-129 







7-3 



00419 



2-4 



0125 



2-4 



00567 



2-4 



0-0413 



1-53 



0120 



1-53 



00554 



1-53 



00405 



Hydrc 



)gcn. 





Carbon 



ic Acid. 





380 



00652 



750-380 



0-0169 



750-380 



00341 



20 



0-0638 



20-5 



00467 







8-8 



00629 







8-8 



00338 



2-4 



0-0601 



2-4 



00461 



2-4 



00336 



1-53 



00557 



154 



0-0453 



1-48 



0331 



A glance at these Tables shows, first, that, in accordance with 

 the theory of sliding, the less the thickness of the layer of air 

 engaged in friction, the greater is the decrease per cent, of the 

 logarithmic decrement with the pressure for a given gas. Further, 

 numerically, we should have 



\= 



1 + S 



1+- 

 P 



if A is the value of \ for -.— go . 



8 should be (1) inversely proportional to the pressure; (2) in- 

 versely proportional to the thickness d of the stratum of air in 

 friction ; (3) for different gases, directly proportional to the mean 

 length of path with the pressure of an atmosphere. 



To test these laws, we calculated one set of series of experi- 

 ments from the others; and found differences only rarely reach- 

 ing 1 per cent, of the total observed value. Certainly the con- 

 stancy of the value of a . d for one gas, and consequently the 



