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227
EXPERIMENTS ON THE CATHODE DISCHARGE
and as the inner end of the wire lay lower than the level of
the mercury in the cups, the mercury flowed along the
amalgamated wire just as if it were a siphon, and emptied
each newly-filled cup in a few hours. This emptying could
be prevented by heating the wires to redness and coating them
for some distance with melted shellac; but the destruction of
the copper wires went on, and after four or five months a
number of them broke off at the soldered joints. A few of
the wires remained quite unattacked, probably because they
happened to have been tinned for some distance from the joint.
The general nature of the battery discharge in gases under
diminished pressure is now sufficiently well known; I shall,
therefore, pass this by and proceed to the description of
certain special experiments.
I. IS THE BATTERY DISCHARGE IN GASES UNDER DIMINISHED
PRESSURE CONTINUOUS OR DISCONTINUOUS ?
When Gassiot first produced the cathode discharge by
means of a large battery, and examined its appearance-
apparently quite continuous-in a rotating mirror, he found
that it could be decomposed into a number of partial dis-
charges following each other very rapidly. On this result is
based the view held by physicists, that the cathode discharge
is of a disruptive nature, and that every apparently continuous
discharge must consist of a series of separate disruptive
discharges. Most physicists approved of this view until
Hittorf, in 1879, showed that Gassiot's experiments do not
warrant any such general conclusions; that with a battery
of sufficiently small resistance a cathode discharge can be
produced which cannot be decomposed into partial discharges,
at any rate by a rotating mirror; and that various circum-
stances indicate that a mirror, however rapidly rotated, could
not effect such a resolution. On the other hand, according to
a calculation made by E. Wiedemann,' the rotating mirror
would fail to perform its function if the number of successive
discharges in a second were to attain to even a hundred
thousand. Hence certain physicists, who for other reasons
1 Wied. Ann. 10, p. 244, 1880.