XIII
251
EXPERIMENTS ON THE CATHODE DISCHARGE
discharge, began to vibrate through ten or twenty scale-
divisions from its position of rest. When the induction coil
was stopped, the needle remained at rest in its zero-position,
and again began to vibrate as above when the current was
started. As far as the accuracy of the experiment allows, we
can conclude with certainty that no electrostatic effect due to
the cathode rays can be perceived; and that if they consist of
streams of electrified particles, the potential on their outer
surface is at most one-hundredth of that of the cathode. And
this conclusion remains correct even if we now find that there
are complications in the part of the tube beyond the wire-
gauze, viz. that this part of it is by no means unelectrified.
If we start the induction coil after the apparatus has been
long at rest, and is therefore free from electricity, a consider-
able deflection (150 to 200 scale-divisions), showing a negative
charge on the tube, is produced in the electrometer. But this
charge and deflection remain constant, however often the coil
is put in and out of action. They remain for an hour after the
discharge has been stopped. But while the discharge is on, the
position of the needle changes instantaneously when a magnet
is brought near the tube, and the needle remains constant in
its new position so long as the magnet is not moved.
As a
matter of fact, then, electricity does penetrate through the
wire-gauze into the protected part of the tube until its
entrance is prevented by the rise of potential. We shall not
here establish the laws which underlie this penetration of the
electricity; it is enough that it has nothing to do with the
cathode rays.
For the passage of these latter is in no way
influenced when the further penetration of the electricity is
prevented; nor, as the first experiment shows, is the amount
of electricity in the tube appreciably increased when the
cathode rays again begin to enter it.
B. In order to find out whether pure cathode rays are
affected by electrostatic forces, the following experiments were
made. The rays were produced in a glass tube 26 cm. long,
provided with a circular aluminium cathode 5 mm. in
diameter. As in the preceding experiments, the cathode was
almost completely surrounded by the anode, and the cathode
rays had to pass out through the wire-gauze. Further on in
their path was a fine wire; the sharp shadow of this, appear-