4 
(111 ) 
We see that Hrrmann’s theory gives far too high values of w;; 
with the above mentioned four capillary electrometers 11 to 25 
times greater than is to be calculated from the dimensions of the 
apparatus !). 
The value adopted for the length of the sulphuric acid thread in 
the calculations was one never exceeded in recording the curves, 
hence the figures in the last column of our table are maximum 
values. It seems difficult to misinterpret the results described above 
and they are certainly sufficient to refute HerMann’s theory. 
That really the mechanical friction neglected by HeRMANN is of 
primary importance with most capillary electrometers, will be clear 
from a series of experiments of entirely different character, in which 
the mechanical friction in the capillary was measured in a direct 
manner. 
A capillary tube, after having been used for the recording of 
normal curves, is placed above a small glass vessel filled with mer- 
cury in such a manner that the end of the capillary is below the 
surface of the mercury. 
For a short time the air above the mercury in the tube is highly 
compressed so that it flows in the vessel, the free air being admitted 
however immediately again. The mercury continues flowing if there has 
been but once a direct mercury connection between the interior of the 
tube and the vessel. The total quantity of the flow in a given time 
varies according to POISEUILLE’s law directly as the pressure, in 
our case the difference of level between the mercury in the tube 
and the mercury in the vessel. 
The flow is continued during some hours and the vessel is weighed 
before and after the experiment. From the difference of weight, q 
grams, the duration of the flow, 7 seconds, the mean difference of 
level, D centimetres, can be calculated how many grams of mercury 
G are pressed through the capillary tube under a pressure of 1 cm. 
in one second, 
Let the radius of the capillary tube at its point be = r cm., 
then the mean velocity in a section near the end is 
1) In this communication a short account of our results must suffice, more parti- 
eulars concerning the mentioned and yet to be given measurements and calculations 
will be published elsewhere. 
