XIV
257
RESIDUAL CHARGE
FIG. 35.
ST
24.
M. P.
the residual charge the outer coating
was disconnected by the key ẞ from
the battery, and connected by y with
the earth; just a second after closing
γ the current was broken at a. The
residual charge present then pro-
duced a negative deflection of the
electrometer; this rapidly increased,
reached a maximum, and then, owing to loss
of charge by conduction, slowly fell off. An
exact measure of the residual charge could
only be deduced by complicated calculations
from the course of the deflections; but an
estimate of its magnitude can be obtained
directly from the maximum deflection.
2. The canister was filled with com-
mercial benzene, and the current was closed,
excepting when the resistance and residual
charge were from time to time tested. The
results were as follows. At first the resist-
ance was so small that in a few moments
after opening a the scale moved quite out of
the field of view. The residual charge was
fairly considerable; its maximum value was
more than 10 per cent of the original charge,
but in consequence of the high conductivity
it soon disappeared. Twenty to thirty minutes
later the resistance was found to have in-
creased to a conveniently measurable value;¹
at the same time the residual charge had
become much smaller. The same changes
went on without interruption; after twenty-
four hours the benzene had become almost a
perfect insulator, and scarcely any residual
charge could be detected. Fig. 35 represents
correctly the numerical results of one of the
experiments. The abscissæ give the time in
hours and minutes from the beginning of the
experiment. The vertical ordinates give the
1 It had increased for both directions of the current.
S