268 ON THE VISCOSITY OE INTEENAL FEICTION OF AIE AND OTHEE GASES. 



In M. Meyer's experiments the time of vibration is shorter than in most of mine. 

 This will diminish the effect of the edge in comparison with the total effect, but in rare- 

 fied air both the mutual action and the effect of the edge are much increased. In his 

 calculations, however, the effect of the three edges of the disks is supposed to be the 

 same, whether they are in contact or separated. This, I think, will account for the large 

 value which he has obtained for the viscosity, and for the fact that with the brass disks 

 which vibrate in 14 seconds, he finds the apparent viscosity diminish as the pressure dimi- 

 nishes, while with the glass disks which vibrate in 8 seconds it first increases and then 

 diminishes. 



M. Meyee concludes that the viscosity varies much less than the pressure, and that it 

 increases slightly with increase of temperature. He finds the value of /* in metrical 

 units (centimetre-gramme-second) at various temperatures, 



Temperature. Viscosity. 



8°-3 C. -000333 



2r-5 C. -000323 



34°-4 C. -000366 



In my experiments, in which fixed disks are interposed between the moving ones, the 

 calculation is not involved in so great difficulties ; and the value of /^ is deduced directly 

 from the observations, whereas the experiments of M. Meyer give only the value of •\/jM'§, 

 from which [ju must be determined. For these reasons I prefer the results deduced from 

 experiments with fixed disks interposed between the moving ones. 



M. Meyer has also given a mathematical theory of the internal friction of gases, 

 founded on the dynamical theory of gases. I shall not say anything of this part of his 

 paper, as I wish to confine myself to the results of experiment. 



