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XIII
EXPERIMENTS ON THE CATHODE DISCHARGE
composed of a part which flows continuously and an alternating
part. Our bridge is only adjusted for the former; for the
latter the arm ac has apparently a vanishing resistance, for
the condenser is capable of taking in and giving out the
quantities of electricity conditioned by the alternating current
without any appreciable change of the potential difference
between its coatings. It follows that for the alternating part
the potential difference between a and c must be very small,
and that between a and b must become large enough to be
detected. It seemed advisable to test the correctness of this
conclusion by experiment. Into the external circuit was
introduced a toothed wheel having a large number of teeth,
by which the current could be broken artificially up to 2000
times per second. When the current was thus interrupted
the gold leaves still remained at rest, provided that the
condenser was not in action. When the condenser was
introduced they diverged immediately; the divergence in-
creased with the rate of interruption, and was very considerable
at the above-mentioned rate. A single opening and closing of
the current could be recognised, when the condenser was
introduced, by a slight twitching of the gold leaves. I
estimate that the number of partial discharges per second
would have to amount to many hundred thousand before the
method of testing here used would become ineffective.
course it would become ineffective if the intermittence was so
rapid that in the intervals the electric waves could only
travel along a small fraction of the lengths of the liquid
resistances used.
of
5. The leaves of a gold-leaf electroscope were connected by
a short copper wire to the negative electrode; these leaves
were suspended in a metallic case which could either be
connected to the positive electrode by a metallic wire or to the
negative electrode through a large resistance of a few million
S.U. When the current was passed through the tube and the
metal case connected to the positive electrode, the gold leaves
diverged strongly; they showed no trace of divergence when
the metal case was connected to the negative electrode through
the above-mentioned resistance. This result tells against
discontinuity of the discharge. For if the potential at the
cathode fluctuated very rapidly between that necessary for the