two cylinders are
placed on the far side of the vessel, but out of the direct line of
fire of the rays. When the rays go straight through the slit there is
only a very small negative charge communicated to the inner cylinder,
but when they are deflected by a magnet so that the phosphorescent
patch falls on the slit in the outer cylinder the inner cylinder
receives a very large negative charge, the increase coinciding very
sharply with the appearance of the phosphorescent patch on the slit.
When the patch is so much deflected by the magnet that it falls below
the slit, the negative charge in the cylinder again disappears. This
experiment shows that the cathode rays are accompanied by a stream of
negative electrification. The same apparatus can be used to show that
the passage of cathode rays through a gas makes it a conductor of
electricity. For if the induction coil is kept running and a stream of
the rays kept steadily going into the inner cylinder, the potential
of the inner cylinder reaches a definite negative value below which it
does not fall, however long the rays may be kept going. The cylinder
reaches a steady state in which the gain of negative electricity from
the cathode rays is equal to the loss by leakage through the
conducting gas, the conductivity being produced by the passage of the
rays through it. If the inner cylinder is charged up initially with a
greater negative charge than corresponds to the steady state, on
turning the rays on to the cylinder the negative charge will decrease
and not increase until it reaches the steady state. The conductivity
produced by the passage of cathode rays through a gas diminishes
rapidly with the pressure. When rays pass through a gas at a low
pressure, they are deflected by an electric field; when the pressure
of the gas is higher the conductivity it acquires when the cathode
rays pass through it is so large that the potential gradient cannot
reach a sufficiently high value to produce an appreciable deflection.

Thus the cathode rays carry a charge of negative electricity; the
experiment described on page 875 (fig. 13) shows that they are deflected
by an electric field as if they were negatively electrified, and are
acted on by a magnetic force in just the way this force would act on a
negatively electrified body moving along the path of the rays. There is
therefore every reason for believing that they are char