582 
ON THE BOUNDARY OF A LIQUID IN MOTION. 
Tempei’ature. 
Time of swing. 
Logarithmic 
decrement. 
(6) and (7). 
127.5 
9'893 
•I9S68 
(11). 
1275 
9-922 
•19867 
The ratio of the frictions is 1‘00288 : 1, the change being less than 0‘3 per cent, 
greater for glass. Thus within the limits of experimental error the friction on silver 
is the same as the friction on glass, and this part of Piotrowskt’s j^aper is certainly 
misleading. 
It is evident that the oscillation method is much inferior to that in which the flow 
of water through tubes is observed. The experiments described in the early part of 
this paper show that the difference in the time of flow for a glass and silver tube is 
less than one-half per cent., in a case wdrere the existence of a slipping coefficient of 
only one-half the magnitude of that deduced by Helmholtz for gold, would make 
the time of flow for the silver tube about twelve times less than the time of flow for 
the glass tube. 
The arguments sometimes used in favour of the contact theory of electromotive 
force, based on the differences in friction of a liquid on different solid surfaces, must 
now be admitted to be without value. It is certain that no slip occurs, at any rate 
in the case of substances which are wetted by the liquid. 
In conclusion I must offer my most sincere thanks to Professor J. J. Thomson and 
to Mr. Glazebrook for the help they have given me, and the many valuable sugges¬ 
tions they have made. 
