instance, I have found that a musical tone proceeds from a piece of
plumbago or retort carbon when an intermittent current of electricity is
passed through it, and I have observed the most curious audible effects
produced by the passage of reversed intermittent currents through the
human body. A breaker was placed in circuit with the primary wires of an
induction coil, and the fine wires were connected with two strips of
brass. One of these strips was held closely against the ear, and a loud
sound proceeded from it whenever the other slip was touched with the
other hand. The strips of brass were next held one in each hand. The
induced currents occasioned a muscular tremor in the fingers. Upon
placing my forefinger to my ear a loud crackling noise was audible,
seemingly proceeding from the finger itself. A friend who was present
placed my finger to his ear, but heard nothing. I requested him to hold
the strips himself. He was then distinctly conscious of a noise (which I
was unable to perceive) proceeding from his finger. In this case a
portion of the induced current passed through the head of the observer
when he placed his ear against his own finger, and it is possible that
the sound was occasioned by a vibration of the surfaces of the ear and
finger in contact.

When two persons receive a shock from a Ruhmkorff's coil by clasping
hands, each taking hold of one wire of the coil with the free hand, a
sound proceeds from the clasped hands. The effect is not produced when
the hands are moist. When either of the two touches the body of the
other a loud sound comes from the parts in contact. When the arm of one
is placed against the arm of the other, the noise produced can be heard
at a distance of several feet. In all these cases a slight shock is
experienced so long as the contact is preserved. The introduction of a
piece of paper between the parts in contact does not materially
interfere with the production of the sounds, but the unpleasant effects
of the shock are avoided.

[Illustration: Fig. 12]

When an intermittent current from a Ruhmkorff's coil is passed through
the arms a musical note can be perceived when the ear is closely applied
to the arm of the person experimented upon. The sound seems to proceed
from the muscles of the fore-arm and from the biceps muscle. Mr. Elisha
Gray has also produced audible effects by the passage of electricity
through the human body.

An extremely loud musical note is occasioned