244
XIII
EXPERIMENTS ON THE CATHODE DISCHARGE
In these a denotes the blue cathode light, B the positive
striæ; the curved lines are equidistant equipotential lines.
In a and c the pressure amounted to one-tenth of a millimetre ;
FIG. 32, a (nat. size).
hence in
in these the
cathode rays have free
ends. In b the pressure
was reduced so much
that the battery could
only barely keep up a
continuous discharge;
hence in this the cathode
raysend perpendicularly
upon the opposite side.
With regard to these
equipotential curves we
have to remark: (1)
That in constructing
each figure some fifty
to sixty deflections

were used; these were not distributed uniformly over the
whole surface, but were mostly taken in the places which
seemed most important.
(2) The uncertainty
which remained is in-
dicated by the number
of equipotential curves
drawn. For just so
many were drawn that
the uncertainty as to
the position of any
single one was equal
to the interval between
two neighbouring ones.
(3) In order to obtain
the actual current-lines
from the equipotential
lines here drawn, we

Fio. 32, b (nat. size).
must imagine the end-points of the latter joined to the electrodes,
and the lines themselves compressed somewhat more together
towards those places in which they are closest. It is clear