258 ME, CLEEK MAXWELL ON THE VISC08ITT 



tubes the influence of molecular action between the gas and the surface of the tube may 

 possibly have some effiect. 



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

 mined by these experiments, is •00001492('461°-f ^) 

 At62°F. (x= -007802. 



Professor Stokes has deduced from the experiments of Baily on pendulums 



x/f 



116, 



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 difllerence. 



In metrical units and Centigrade degrees 



,u,= -01878(1 + -00365^). 

 M. O. E. Meter gives as the value of /k. in centimetres, grammes, and seconds, at 18° C, 



•000360. 

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



j«,=-0360. 



I make u,, at 18° C, 



^ =-0200. 



Hence the value given by Meyer is 1-8 times greater than that adopted in this paper. 



M. Meyer, however, has a different method of taking account of the disturbance of 

 the air near the edge of the disk from that given in this paper. He supposes that when 

 the disk is very thin the effect due to the edge is proportional to the thickness, and he 

 has given in Crelle's 'Journal' a vindication of this supposition. 1 have not been able 

 to obtain a mathematical solution of the case of a disk oscillating in a large extent of 

 fluid, but it can easily be shown that there will be a finite increase of friction near the 

 edge of the disk due to the want of continuity, even if the disk were infinitely thin. 

 I think therefore that the difference between M. Meyer's result and mine is to be 

 accounted for, at least in part, by his having under-estimated the effect of the edge of 

 the disk. The effect of the edge will be much less in water than in air, so that any 

 deficiency in the correction will have less influence on the results for liquids which are 

 given in M. Meyer's very valuable paper. 



Mathematical Tlieory of the Experiment. 



A disk oscillates in its own plane about a vertical axis between two fixed horizontal 

 disks, the amplitude of oscillation diminishing in geometrical progression, to find what 

 part of the retardation is due to the viscosity of the air between it and the fixed disks. 



