body to be set in motion
by them, and thus reproduce the motions of the first vibrating body."

It will be at once obvious that these words describe perfectly the
basic principle of every modern phonograph or other talking-machine,
irrespective of its manufacture or trade name.

Edison's first model of the phonograph is shown in the following
illustration.

It consisted of a metallic cylinder having a helical indenting groove
cut upon it from end to end. This cylinder was mounted on a shaft
supported on two standards. This shaft at one end was fitted with a
handle, by means of which the cylinder was rotated. There were two
diaphragms, one on each side of the cylinder, one being for recording
and the other for reproducing speech or other sounds. Each diaphragm
had attached to it a needle. By means of the needle attached to the
recording diaphragm, indentations were made in a sheet of tin-foil
stretched over the peripheral surface of the cylinder when the diaphragm
was vibrated by reason of speech or other sounds. The needle on
the other diaphragm subsequently followed these indentations, thus
reproducing the original sounds.

Crude as this first model appears in comparison with machines of later
development and refinement, it embodied their fundamental essentials,
and was in fact a complete, practical phonograph from the first moment
of its operation.

The next step toward the evolution of the improved phonograph of to-day
was another form of tin-foil machine, as seen in the illustration.

It will be noted that this was merely an elaborated form of the first
model, and embodied several mechanical modifications, among which was
the employment of only one diaphragm for recording and reproducing.
Such was the general type of phonograph used for exhibition purposes
in America and other countries in the three or four years immediately
succeeding the date of this invention.

In operating the machine the recording diaphragm was advanced nearly
to the cylinder, so that as the diaphragm was vibrated by the voice the
needle would prick or indent a wave-like record in the tin-foil that
was on the cylinder. The cylinder was constantly turned during the
recording, and in turning, was simultaneously moved forward. Thus the
record would be formed on the tin-foil in a continuous spiral line.
To reproduce this record it was only necessary to again start at the
beginning and cause the needle to retrace its path in the spiral line