use very high frequencies, the return wire becomes unnecessary, and
all the appliances are simplified. By the use of obvious means the
same result is obtained as though the return wire were used. It is
sufficient for this purpose to bring in contact with the bulb, or
merely in the vicinity of the same, an insulated body of some surface.
The surface need, of course, be the smaller, the higher the frequency
and potential used, and necessarily, also, the higher the economy of
the lamp or other device.
This plan of working has been resorted to on several occasions this
evening. So, for instance, when the incandescence of a button was
produced by grasping the bulb with the hand, the body of the
experimenter merely served to intensify the action. The bulb used was
similar to that illustrated in Fig. 19, and the coil was excited to a
small potential, not sufficient to bring the button to incandescence
when the bulb was hanging from the wire; and incidentally, in order to
perform the experiment in a more suitable manner, the button was taken
so large that a perceptible time had to elapse before, upon grasping
the bulb, it could be rendered incandescent. The contact with the bulb
was, of course, quite unnecessary. It is easy, by using a rather large
bulb with an exceedingly small electrode, to adjust the conditions so
that the latter is brought to bright incandescence by the mere
approach of the experimenter within a few feet of the bulb, and that
the incandescence subsides upon his receding.
[Illustration: FIG. 24.--BULB WITHOUT LEADING-IN WIRE, SHOWING EFFECT
OF PROJECTED MATTER.]
In another experiment, when phosphorescence was excited, a similar
bulb was used. Here again, originally, the potential was not
sufficient to excite phosphorescence until the action was
intensified--in this case, however, to present a different feature, by
touching the socket with a metallic object held in the hand. The
electrode in the bulb was a carbon button so large that it could not
be brought to incandescence, and thereby spoil the effect produced by
phosphorescence.
[Illustration: FIG. 25.--IMPROVED EXPERIMENTAL BULB.]
Again, in another of the early experiments, a bulb was used as
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