12 ON THE VISCOSITY OR INTERNAL FRICTION 



It appears from the experiments of Mr. Graham that the ratio of the 

 transpiration time of hydrogen to that of air is '4855, and that of carbonic 

 acid to air '807. These numbers are both smaller than those of this paper. 

 I think that the discrepancy arises from the gases being less pure in my 

 experiments than in those of Graham, owing to the difficulty of preventing air 

 from leaking into the receiver during the preparation, desiccation, and admission 

 of the gas, which always occupied at least an hour and a half before the 

 experiment on the moving disks could be begun. 



It appears to me that for comparative estimates of viscosity, the method 

 of transpiration is the best, although the method here described is better 

 adapted to determine the absolute value of the viscosity, and is less liable to 

 the objection that in fine capillary tubes the influence of molecular action 

 between the gas and the surface of the tube may possibly have some effect. 



The actual value of the coefficient of viscosity in inch-grain-second measure, 

 as determined by these experiments, is 



00001492(461 + 0). 

 At 62* F. p. = '007802. 



Professor Stokes has deduced from the experiments of Baily on pendulums 



Vp 



which at ordinary pressures and temperatures gives 



/* = -00417, 



or not much more than half the value as here determined. I have not found 

 any means of explaining this difference. 



In metrical units and Centigrade degrees 



^ = '01878(1 + -003650). 



M. O. E. Meyer gives as the value of /x in centimetres, grammes, and 

 seconds, at 18* C., 



000360. 



This, when reduced to metre-gramme-second measure, is 



/t = -0360. 

 I make /*, at 18C., ='0200. 



