XIII
235
EXPERIMENTS ON THE CATHODE DISCHARGE
of the cathode could not have exceeded 10 of a Daniell;
for there was a perceptible deflection when the mean potential
difference of the terminals of the dynamometer attained this
value. Thus in order that the successive discharges should be
equivalent to a current of Daniell/S.U., they must have
amounted to two billions per second. This mode of estimat-
ing is open to criticism, and I do not wish to insist strongly
on the large number to which it leads. But I would ask
whether it is likely that an electric current could traverse a
gas-tube 20 cm. long as a fully formed partial discharge with
all its striæ, in a time which would not allow of its traversing
as a steady current 8 cm. of a metallic conductor?
7. I have not discovered any more decisive methods of
testing. But a few further experiments may be mentioned
which, although not in themselves decisive, tend in the same
direction as those already described.
(a) If the observer closes the circuit, containing the gas-
tube and a sufficient liquid resistance, through his own body,
he feels a shock on closing and a much weaker shock on open-
ing. By frequent opening and closing, the sensation can be
heightened until it becomes unbearable. But while the tube
glows uniformly nothing is perceived beyond a burning at the
points where the current enters and leaves.
(b) The battery-discharge never gives rise to the auxiliary
phenomenon of oscillatory currents, even under conditions which
are very favourable for their production, and under which
the Ruhmkorff discharge produces very powerful currents of
this kind.
(c) The following phenomena have already been mentioned
by Hittorf: When a sufficiently large resistance is introduced,
the discharge is certainly discontinuous. The tube then fre-
quently gives out a note, the pitch of which indicates the rate
at which the discharges succeed each other. When the
resistance is diminished, the note becomes higher and the
tube less bright. But it does not gradually pass over
into the quiet indifferent discharge; when the resistance is
reduced to a certain value the note stops suddenly, the tube
becomes three times as bright, and no further indications
whatever of discontinuity can be obtained. The sudden
change is still more striking when the electrodes of the tube