XIII
237
EXPERIMENTS ON THE CATHODE DISCHARGE
which lies close to the cathode B. If there is a difference of
potential between A and B, a will be attracted by B. But
a is prevented from coming directly into contact with B by
an under layer ẞ of relatively high resistance r. Between A
and B there may exist any number more of these spring-
carriers, only differing from the first in that the resistance
corresponding to B is for each very large. A certain potential
difference must exist between A and B in order to bring the
weight a of the first spring-carrier up against B, and so for
all the other spring-carriers. Suppose this potential difference
to be very nearly the same for all of them, and equal to p.
The whole arrangement may now replace a gas-tube as follows.
It does not allow any current to pass unless the potential
difference between A and B attains the value p. It allows
an intermittent current to pass when A and B are connected
with a source of electricity which can produce a potential
difference P, but is not at the same time able to produce a
current of strength p/r. If, however, the source is capable of
yielding such a current, then a and B remain permanently in
contact and the current flows continuously. Whatever the
strength of the current may be, the potential difference cannot
exceed P, for more and more of the spring-carriers would come
into action. The whole heating effect would therefore be
proportional to the current itself, and not to its square. This
proves our point.
Another circumstance seems to have influenced the
opinions of previous writers. The position and develop-
ment of each stria of the glow-light depends upon the
preceding stria (in the direction of the cathode): upon this
is founded the legitimate view that from the cathode out-
wards there must be a time-development from one stria to
the next. But such a time-development is not conceivable,
if the discharge in all parts persists continuously. Per-
haps we shall form a correct conception of the circumstances
in question if we admit that the discharge as a whole is
continuous, but assume that its course along the separate
current-lines (Stromfäden) is a function of the time. For
example, if the contact of a gas-molecule with the cathode
gave rise to an electric disturbance travelling in waves
through the medium, the successive production of striæ