be the reverse of
those above indicated, but the end sought--namely, the relaying of
messages--would be attained with the same certainty.

While the principal object of this invention was to accomplish the
repetition of signals without the aid of an electromagnetic relay, the
instrument devised by Edison was capable of use as a recorder also, by
employing a small wheel inked by a fountain wheel and attached to the
vibrating arm through suitable mechanism. By means of this adjunct the
dashes and dots of the transmitted impulses could be recorded upon a
paper ribbon passing continuously over the drum.

The electromotograph is shown diagrammatically in Figs. 1 and 2, in plan
and vertical section respectively. The reference letters in each case
indicate identical parts: A being the chalk drum, B the paper tape, C
the auxiliary cylinder, D the vibrating arm, E the frictional pad, F the
spring, G and H the two contacts, I and J the two wires leading to local
circuit, K a battery, and L an ordinary telegraph key. The two last
named, K and L, are shown to make the sketch complete but in practice
would be at the transmitting end, which might be hundreds of miles
away. It will be understood, of course, that the electromotograph is a
receiving and relaying instrument.

Another notable use of the electromotograph principle was in its
adaptation to the receiver in Edison's loud-speaking telephone, on which
United States Patent No. 221,957 was issued November 25, 1879. A chalk
cylinder moistened with a chemical solution was revolved by hand or
a small motor. Resting on the cylinder was a palladium-faced pen or
spring, which was attached to a mica diaphragm in a resonator. The
current passed from the main line through the pen to the chalk and to
the battery. The sound-waves impinging upon the distant transmitter
varied the resistance of the carbon button therein, thus causing
corresponding variations in the strength of the battery current. These
variations, passing through the chalk cylinder produced more or less
electrochemical decomposition, which in turn caused differences of
adhesion between the pen and cylinder and hence gave rise to mechanical
vibrations of the diaphragm by reason of which the speaker's words were
reproduced. Telephones so operated repeated speaking and singing in
very loud tones. In one instance, spoken words and the singing of songs
originating at a distance were heard perfectly by an audience of over
five