all who
would learn aught from the recorded wisdom of mankind. And yet there
never was anything essentially absurd or insurmountable in the
invention of a method of recording speech in audible instead of
visible symbols.

The phonograph came swiftly after the telephone. The new instrument is
in a sense the complement of its predecessor. Both inventions are
based upon the same principle in science. The discovery that every
sound has its physical equivalent in a wave or agitation which affects
the particles of matter composing the material through which the sound
is transmitted led almost inevitably to the other discovery of
_catching_ and _retaining_ that physical equivalent or wave in the
surface of some body, and to the reproduction of the original sound
therefrom.

Such is the fundamental principle of the interesting but, thus far,
little useful instrument known as the phonograph. The same was
invented by Thomas A. Edison, of Menlo Park, in the year 1877. The
instrument differs considerably in structure and purpose from the
_Vibrograph_ and _Phonautograph_ which preceded it. The latter two
instruments were made simply to _write_ sound vibrations; the former,
to reproduce _audibly_ the sounds themselves.

The phonograph consists of three principal parts,--the sender or
funnel-shaped tube, with its open mouth-piece standing toward the
operator; the diaphragm and stylus connected therewith, which receives
the sound spoken into the tube; and thirdly, the revolving cylinder,
with its sheet-coating of tin-foil laid over the surface of a spiral
groove to receive the indentations of the point of the stylus. The
mode of operation is very simple. The cylinder is revolved; and the
point of the stylus, when there is no sound agitation in the funnel or
mouth-piece, makes a smooth, continuous depression in the tin-foil
over the spiral groove. But when any sound is thrown into the
mouth-piece the iron disk or diaphragm is agitated; this agitation is
carried through the stylus and written in irregular marks, dots, and
peculiar figures in the tin-foil over the groove.

When the utterance which is to be reproduced has been completed, the
instrument is stopped, the stylus thrown back from the groove, and the
cylinder revolved backward to the place of starting. The stylus is
then returned to its place in the groove, and the cylinder is revolved
forward at the same rate of rapidity as before. As the point of the
stylus plays up and