HOGG, — VISCOSITY OF AIR. 



to express the variation of [i with the temperature, 

 been used to reduce the above result to 0°C. 



621 



This formula has 



Ato 



0.000171 G. 



Experiment II. 



After being in use for some time, the ivory sphere and disk were 

 found to have changed in weight and shape, so that the ivory was re- 

 phvced by glass. The dimensions of the glass sphere and the requisite 

 disk have been given in the description of the apparatus. The metliod 

 of performing the experiment was the same in this case as in the pre- 

 vious one. Metal cylinders, however, were used for determining the 

 moment of inertia. The latter was found to be. from the first cylinder, 

 1.3047, from the second 1.3042, and from the third 1.3029. The mean 

 is 1.3039. The decrement for tlie sphere and disk was 0.02211, and for 

 the lead disk 0.00862. The time for the lead disk was 41.77 seconds, 

 so that no correction for time was necessary. The results are summar- 

 ized in Table II. : — 



TABLE II. 



From the data given in this table 



yuis.6 = 0.0001795. 

 When reduced to 0° C. this gives 



fxo = 0.0001708. 



Experiment III. 



In this experiment the temperature of the gas when the sphere was 

 suspended was 15°. 6 C, while \'\ hen the lead disk was suspended it was 

 14°. 8 C. The correction to be applied was obtained by getting the 

 decrement for the lead disk when the temperature was 15°. 3 C, and using 

 this as a basis for determining what it would be at 15°. 6. In this way 

 the correction was found to be 0.00004. This correction was not quite 

 as satisfactory as might have been desired, as appeared when the decre- 

 ment was deduced from the observations at 15°. 3. The results were not 



