else the volume of the condenser is too great. Some dielectrics 0.2
mm. thick can be made to stand up to 8,000 volts when in small pieces,
but in complete condensers a much greater margin must be allowed.
Another difficulty arises from absorption, and whenever this occurs,
the apparent capacity is greater than the calculated. Supposing the
fibers of paper in a paper condenser to be conductors embedded in
insulating hydrocarbon, then every time the condenser is charged the
fibers have their ends at different potentials, so a current passes to
equalize them and energy is lost. This current increases the capacity.
One condenser made of paper boiled in ozokerite took an abnormally
large current and heated rapidly. At a high temperature it gave off
water, and the power wasted and current taken gradually decreased.

When a thin plate of mica is put between tin foils, it heats
excessively; and the fall of potential over the air films separating
the mica and foil is great enough to cause disruptive discharge to the
surface of the mica. There appears to be a luminous layer of minute
sparks under the foils, and there is a strong smell of ozone. In a
dielectric which heats, there may be three kinds of conduction, viz.,
metallic, when an ordinary conductor is embedded in an insulator;
disruptive, as probably occurs in the case of mica; and electrolytic,
which might occur in glass. In a transparent dielectric the conduction
must be either electrolytic or disruptive, otherwise light vibrations
would be damped. The dielectric loss in a cable may be serious.
Calculating from the waste in a condenser made of paper soaked in hot
ozokerite, the loss in one of the Deptford mains came out 7,000 watts.
Another effect observed at Deptford is a rise of pressure in the
mains. There is as yet no authoritative statement as to exactly what
happens, and it is generally assumed that the effect depends on the
relation of capacity to self-induction, and is a sort of resonator