24 ON THK VISCOSITY OB INTERNAL FRICTION 



TABLE V. Results. 



Coefficient of viscosity in dry air. Units the inch, grain, and second, and 

 Fahrenheit temperature, 



ft, = -00001 492 (461 + 6) = '006876 + '00001490. 



At 60* F." the mean temperature of the experiments, p = '007763. Taking 

 the foot as unit instead of the inch, /t = '000179 (461 +6). In metrical units 

 (metre, gramme, second, and Centigrade temperature), 



,t = -01878(1 + -003650). 



The coefficient of viscosity of other gases is to be found from that of air 

 by multiplying /t by the ratio of the transpiration time of the gas to that of 

 air as determined by Graham*. 



f POSTSCRIPT. Received December 7, 1865. 



Since the above paper was communicated to the Royal Society, Professor 

 Stokes has directed my attention to a more recent memoir of M. O. E. Meyer, 

 "Ueber die innere Reibung der Gase," in Poggendorffs Anncden, cxxv. (1865). 

 M. Meyer has compared the values of the coefficient of viscosity deduced from 

 the experiments of Baily by Stokes, with those deduced from the experiments 

 of Bessel and of Girault. These values are '000104, '000275, and -000384 

 respectively, the units being the centimetre, the gramme, and the second. 

 M. Meyer's own experiments were made by swinging three disks on a vertical 

 axis in an air-tight vessel. The disks were sometimes placed in contact, and 

 sometimes separate, so as to expose either two or six surfaces to the action 

 of the air. The difference of the logarithmic decrement of oscillation in these 

 two arrangements was employed to determine the viscosity of the air. 



The effects of the resistance of the air on the axis, mirror, &c., and of 

 the viscosity of the suspending wires are thus eliminated. 



The calculations are made on the supposition that the moving disks are 

 so far from each other and from the surface of the receiver which contains 

 them, that the effect of the air upon each is the same as if it were in an 

 infinite space. 



At the distance of 30 millims., and with a period of oscillation of fourteen 

 seconds, the mutual effect of the disks would be very small in air at the 



* Philosophical Transactions, 1849. 



