eries of very minute
indentations, not exceeding 1/1000th of an inch in depth.[33] Seen under
a microscope, the surface of the record is a succession of hills and
valleys, some much larger than others (Fig. 151, _a_). A loud sound
causes the stylus to give a vigorous dig, while low sounds scarcely move
it at all. The wonderful thing about this sound-recording is, that not
only are the fundamental tones of musical notes impressed, but also the
harmonics, which enable us to decide at once whether the record is one
of a cornet, violin, or banjo performance. Furthermore, if several
instruments are playing simultaneously near the recorder's horn, the
stylus catches all the different shades of tone of every note of a
chord. There are, so to speak, minor hills and valleys cut in the slopes
of the main hills and valleys.

[Illustration: FIG. 149.--Section of the reproducer of an Edison Bell
phonograph.]

[Illustration: FIG. 150.--Perspective view of a phonograph reproducer.]

The _reproducer_ (Fig. 149) is somewhat more complicated than the
recorder. As before, we have a circular box communicating with the horn
of the instrument. A thin glass disc forms a bottom to the box. It is
held in position between rubber rings, R R, by a screw collar, C. To the
centre is attached a little eye, from which hangs a link, L. Pivoted at
P from one edge of the box is a _floating weight_, having a circular
opening immediately under the eye. The link passes through this to the
left end of a tiny lever, which rocks on a pivot projecting from the
weight. To the right end of the lever is affixed a sapphire bar, or
stylus, with a ball end of a diameter equal to that of the cutting point
of the recorder. The floating weight presses the stylus against the
record, and also keeps the link between the rocking lever of the glass
diaphragm in a state of tension. Every blow given to the stylus is
therefore transmitted by the link to the diaphragm, which vibrates and
sends an air-impulse into the horn. As the impulses are given at the
same rate as those which agitated the diaphragm of the recorder, the
sounds which they represent are accurately reproduced, even to the
harmonics of a musical note.

THE GRAMOPHONE.

This effects the same purpose as the phonograph, but in a somewhat
different manner. The phonograph recorder digs vertically downwards into
the surface of the record, whereas the stylus of the gramophone wags
from side to side and describes