XII
ON A PHENOMENON WHICH ACCOMPANIES THE
ELECTRIC DISCHARGE
(Wiedemann's Annalen, 19, pp. 78-86, 1883.)
IN the following a phenomenon is described which often
accompanies the electric discharge, and in particular the
Leyden jar spark, in air and other gases, when the density
is not too small. It is true that in most circumstances it is
so trivial as not to have appeared worthy of mention, but the
first time I noticed it its appearance was so striking
as to induce me to make several investigations as
to its nature. I remark at once that in the experi-
ments a somewhat large induction coil was used,
which in the open air gave sparks 4 to 5 cm. long;
the Leyden jar mentioned had a coating of some
two square feet in area, and it was simply joined
up with one coating connected to each pole of the
induction coil, without making any other alteration
whatever in the circuit.
1. Fig. 25 represents a discharging apparatus,
which consists of a glass tube, not too finely drawn
out, and of two electrodes, one inside the tube, the
other attached to it outside near the opening.
When this apparatus is placed under the receiver
of an air pump, the receiver filled with well-dried
air and exhausted down to 30 to 50 mm. pressure,
and the discharge from the induction coil then sent
through, the following phenomenon is observed:
Near the cathode is the blue glow; it is succeeded towards
FIG. 25.