Here, for instance, I have two plates, RR, of hard rubber (Fig. 9),
upon which I have glued two very thin wires ww, so as to form a name.
The wires may be bare or covered with the best insulation--it is
immaterial for the success of the experiment. Well insulated wires, if
anything, are preferable. On the back of each plate, indicated by the
shaded portion, is a tinfoil coating tt. The plates are placed in line
at a sufficient distance to prevent a spark passing from one to the
other wire. The two tinfoil coatings I have joined by a conductor C,
and the two wires I presently connect to the terminals of the coil. It
is now easy, by varying the strength and frequency of the currents
through the primary, to find a point at which, the capacity of the
system is best suited to the conditions, and the wires become so
strongly luminous that, when the light in the room is turned off the
name formed by them appears in brilliant letters.

[Illustration: FIG. 9.--WIRES RENDERED INTENSELY LUMINOUS.]

It is perhaps preferable to perform this experiment with a coil
operated from an alternator of high frequency, as then, owing to the
harmonic rise and fall, the streams are very uniform, though they are
less abundant then when produced with such a coil as the present. This
experiment, however, may be performed with low frequencies, but much
less satisfactorily.

[Illustration: FIG. 10.--LUMINOUS DISCS.]

When two wires, attached to the terminals of the coil, are set at the
proper distance, the streams between them may be so intense as to
produce a continuous luminous sheet. To show this phenomenon I have