490 DR. J. HOPKINS ON ON THE RESIDUAL CHARGE OE THE LEYDEN JAR. 
are constants for the material, and A and B are constants dependent on the state of the 
dielectric previous to insulation. It should be remarked that X does not depend alone 
on the conductivity and specific inductive capacity, as ordinarily determined, of the 
material, but also on the constants connecting polarization with electric force. Indeed if 
the above view really represent the facts, the conductivity of a dielectric determined 
from the steady flow of electricity through it measured by the galvanometer will differ 
from that determined by the rate of loss of charge of the condenser when insulated. 
2. A Florence flask nearly 4 inches in diameter was carefully cleansed, filled with 
strong sulphuric acid, and immersed in water to the shoulder. Platinum wires were 
dipped in the two fluids, and were also connected with the two principal electrodes of 
the quadrant electrometer. The jar was slightly charged and insulated, and the poten- 
tials read off from time to time. It was found (1) that even after twenty-four hours the 
percentage of loss per hour continued to decrease, (2) that the potential could not be 
expressed as a function of the time by two exponential terms. But the latter fact was 
more clearly shown by the rate of development of the residual charge after different 
periods of discharge, which put it beyond doubt that if the potential is properly expressed 
by a series of exponential terms at all, several such terms will be required. 
The following roughly illustrates how such terms could arise. Glass may be regarded 
as a mixture of a variety of different silicates ; each of these may behave differently 
under electric force, some rapidly approaching the limiting polarity corresponding 
to the force, others more slowly. If these polarities be assumed to be n in number, 
they and E may be connected with the time by n -\- 1 linear differential equations. Hence 
uring insulation E would be expressed in the form A r s “V. Suppose now a condenser 
be charged positively for a long time, the polarization of all the substances will be fully 
developed ; let the charge be next negative for a shorter time, the rapidly changing 
polarities will change their sign, but the time is insufficient to reverse those which are 
more sluggish. Let the condenser be then discharged and insulated, the rapid polari- 
zations will decay, first liberating a negative charge ; but after a time the effect of the 
slow terms will make itself felt and the residual charge becomes positive, rises to a 
maximum, and then decays by conduction. This inference from these hypotheses and 
the form of the curve connecting E with i for a simple case of return charge is verified in 
the following experiments. 
3. A flask was immersed* in and filled with acid to the shoulder. Platinum electrodes 
communicated with the electrometer as before. The flask was strongly charged positive 
at 5.30 and kept charged till 6.30, then discharged till 7.8 and negatively charged till 
7.15, when it was discharged and insulated. The potential was read off at intervals till 
8.20. The abscissae of curve A (Plate 44) represent the time from insulation, the ordinates 
the corresponding potentials, positive potentials being measured upwards. It will be seen 
that a considerable negative charge first appeared, attaining a maximum in about five 
* Acid on both sides of the dielectric, that there might be no electromotive force from the action of acid on 
water either through or over the surface of the glass. 
