784 
MR. H. TOMLINSON ON THE COEFFICIENT OF VISCOSITY OF AIR. 
On the whole it would seem that the aqueous vapour in the air used in my 
experiments would hardly influence the value of g to the extent of '1 per cent. 
The presence of carbon dioxide in the air would still less affect the result, as not 
only is the viscosity of carbon dioxide not very remote from that of air, but the 
amount of the gas present is also very minute. 
Comparison of the Results of Recent Investigations of the Coefficient of 
Viscosity of Air. 
In the beginning of this memoir I pointed out the very large discrepancies which 
existed between the results of different experimenters, but, since I entered on my 
task, not only have I acquired fresh information respecting what had already been 
done, but also quite recently fresh investigations have been made. Table III. 
contains the required information. 
Table III. 
Authority. 
Coefficient of viscosity 
of air at 0° C. 
Method. 
O. E. Meter* .... 
•0001875 
Oscillating plates. 
95 .... 
•0001727 
Transpiration. 
PtTLUJ*. 
•0001798 
SCHNEEBELlf .... 
•0001707 
55 
OBERMAYERf.... 
•0001705 
55 
In order to reduce my own observations to 0° C., I have made use of the investiga¬ 
tions of Professor Silas W. Holman on the effect of temperature on the viscosity of 
air.J According to the exceedingly careful and elaborate observations of this experi¬ 
menter, the coefficient of viscosity of dry air is not proportional to the absolute 
temperature, but 
g, = gf\ +0-00275H-0-00000034^),.(12) 
where t is the temperature in degrees Centigrade, and g t , g 0 , are the coefficients of 
viscosity at t° C. and 0° C. respectively. 
My own observations were made with too small ranges of temperature to show the 
relation between the value of g and the temperature, but the above formula expresses 
more nearly this relation as deduced from my experiments than the formula 
gz = gfl —0*00366?). 
* ‘ Phil. Mag,’ vol. 21, 1886, p. 220. 
t ‘ Archives Sci. Phys. Nat,’ vol. 14, 1885. 
t ‘ Phil. Mag,’ vol. 21, 1886. 
