magnifying glass can the undulations caused by the vibrating
stylus be distinguished. This tube of wax is filed upon a metal barrel
like a sleeve, and the barrel, which forms part of a horizontal spindle,
is rotated by means of a silent electro-motor, controlled by a very
sensitive governor. A motion of translation is also given to the barrel
as it revolves, so that the marking stylus held over it describes
a spiral path upon its surface. In front of the wax two small metal
tympanums are supported, each carrying a fine needle point or stylus on
its under centre. One of these is the recording diaphragm, which prints
the sounds in the first place; the other is the reproducing diaphragm,
which emits the sounds recorded on the wax. They are used, one at a
time, as the machine is required, to take down or to render back a
phonographic message.

The recording tympanum, which is about the size of a crown-piece, is
fitted with a mouthpiece, and when it is desired to record a sentence
the spindle is started, and you speak into the mouthpiece. The tympanum
vibrates under your voice, and the stylus, partaking of its motion, digs
into the yielding surface of the wax which moves beneath, and leaves a
tiny furrow to mark its passage. This is the sonorous record which, on
being passed under the stylus of the reproducing tympanum, will cause
it to give out a faithful copy of the original speech. A flexible
india-rubber tube, branching into two ear-pieces, conveys the sound
emitted by the reproducing diaphragm to the ears. This trumpet is used
for privacy and loudness; but it may be replaced by a conical funnel
inserted by its small end over the diaphragm, which thereby utters its
message aloud. It is on this plan that Edison has now constructed a
phonograph which delivers its reproduction to a roomful of people.
Keys and pedals are provided with which to stop the apparatus either in
recording or receiving, and in the latter case to hark back and repeat a
word or sentence if required. This is a convenient arrangement in using
the phonograph for correspondence or dictation. Each instrument, as we
have seen, can be employed for receiving as well as recording; and as
all are made to one pattern, a phonogram coming from any one, in any art
of the world, can be reproduced in any other instrument. A little box
with double walls has been introduced for transmitting the phonograms by
post. A knife or cutter is attached to the instrument for the