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XIII
EXPERIMENTS ON THE CATHODE DISCHARGE
a galvanometer and a dynamometer were simultaneously
introduced into the circuit, and the deflections produced in
both instruments were read off. The battery, gas-tube, and
liquid resistance were then separated from the two measuring
instruments, and replaced by a Daniell cell, and such a
metallic resistance as gave the same galvanometer deflection as
before. It was found that the dynamometer reading also was
precisely the same as before. But if the current sent by the
large battery through the gas-tube had been an intermittent
current, it would for a given magnetic effect have produced a
much larger dynamometric effect. Suppose, for example, that
the duration of one of the partial discharges was equal to a
fourth of the time from the beginning of such a discharge to
the beginning of the next. While this current lasted it
would be four times as strong as a continuous current capable
of exerting an equal magnetic effect. While it lasted, its
dynamometric effect would be sixteen times as great, or, on an
average over the whole time, four times as great as that of the
continuous current. Hence this experiment indicates that the
discharge is continuous.
3. The current was led to the tube through a Wheatstone
bridge arrangement. One arm of this consisted of the
secondary of a small induction-coil, having a resistance of
1700 S.U., and a coefficient of self-induction of ten earth-
quadrants. The other three arms consisted of equivalent
metallic resistances of negligible self-induction. In the actual
bridge a dynamometer was introduced, and the arrangement
was so adjusted that when a continuous current flowed
through it there was no deflection of the dynamometer.
It
was then found that no deflection was produced by the battery
current flowing through the Geissler tube, although this was
strong enough to produce a very marked effect as soon as
the equilibrium was destroyed by inserting a resistance of
100 S.U. in one of the branches. This experiment tells
against discontinuity. For we may regard an intermittent
current as composed of a part which flows continuously, and
another part which continually changes its direction. The
bridge was only adjusted for the former: to the latter the
coil, on account of its high self-induction, would certainly
offer a far higher apparent resistance than the other branches.