450 



The corrections are calculated by means of Knudsen's formulae ^). 

 In the previous communication it was shown that witli the degree 

 of accuracy of our measurements these formulae may be considered 



X 



as correct, if the region where approximately 1 <^ — - <C 10 is exclu- 



ded. If Breitenbach's observations on the viscosity of carbon dioxide 

 are extrapolated b}^ means of Sutherland's formula ^) it may be 

 concluded that the corrections cannot be computed in the range 

 between 25 and 3 baryes for the wide tube and between 75 and 8 

 baryes for the nari-ow tube. Supposing that the mean free- path is 

 known with sufficient accuracy it will be seen that between 25 and 

 8 baryes there is a range for which the correction cannot be cal- 

 culated. An additional tube of say 1 mm. diameter ought to have 

 been used. 



It appears further that below 3 baryes there is a range of pres- 

 sures, where the correction can be found for botli tubes. With the 

 formula which holds for this range the mean free path may be 

 determined by eliminating the unknown vapour pressure. The result 

 of this calculation is found to agree within the limits of accuracy 

 of the observations with the mean free path as calculated with 

 Sutherland's formula. In table II this shows by the close agreement 

 between the vapour pressures under I corr. and II corr. 



The conclusion seems therefore justified that the mean free path 

 of carbon dioxide is known with sufficient accuracy at these tem- 

 peratures, and that the corrections may be deduced by means of 

 Knudsen's formulae with the exception of the range between 25 

 and 8 baryes. 



Leaving this range out of account in the mean time we will now 

 discuss the formulae for those ranges where in our opinion they 

 are still applicable. 



2R 



[!). — > 10. 



In this range we use the following formula theoretically deduced 

 by Knudsen. 



1) Martin Knudsen. Ann. der Phys. 31 (1910\ p. 205, 633 ; 33 (1910), p. 1435. 



*) The exirapolation by means of Sutherland's formula is probably allowable 

 in this case, as the range of reduced temperature is comparatively small. Over 

 larger ranges of reduced temperature Sutherland's formula does not appear 

 to 1)6 applicable {U. Kamerlingh Onnes C. Dorsman and Sophus Weber. Comm. 

 N'. 134a March l'JlÖ). 



