454 Mr. Owen Glynn e Jones on 



would be 



V . 



The ratio of ^- is therefore 



Pa+2 ft' 1-2600, + Sp 



Since all the quantities involved are positive, this ratio is 

 evidently greater than unity. As (3 varies from <x> to zero, 

 the value of the ratio increases from 1 to a maximum 1 4- k, 

 and then diminishes to 1 again. Thus the divergence be- 

 tween the calculated and the observed speeds does not become 

 greater as the coefficient of sliding-friction diminishes, al- 

 though this divergence is actually due to the sliding. 



Taking the value *04 centim. for the radius of the sphere, 



the maximum value of k will be jj, the divergence thus 

 amounting to about 2J per cent. The ratio -^ that gives this 

 result is rror /3=55/-t. 



If we assume ~ to have the same value for glycerine that 



Helmholtz assigns to water, the difference between the ob- 

 served and the calculated speeds will amount to about 1 in 144 

 for such spheres (a = '04 centim.) as were employed in the 

 investigation. 



Various experiments were recently made by the author to 

 test these results ; considerable difficulty was experienced in 

 keeping the temperature constant, except when this was 0° C. 

 The tests hitherto made are not regarded as final, and the 

 author would prefer to defer their publication until the series 

 of experiments is complete. But the divergences from the 

 simple law as at first assumed are in all cases within the limits 

 of experimental error, and the method of determining viscosity 

 is not shown to be defective by those test experiments. The 

 temperature difficulty is not so serious in the case of colza- 

 oil, which is one of the liquids experimented upon. The 

 error involved with speeds not exceeding 2 centim. per second 

 through that liquid did not range beyond + 0'2 per cent., 

 and it was as usual to get positive errors as to get negative. 

 Times were estimated only to the same degree of accuracy. 



It is possible that sliding may occur if the speed of the 



