Page:Heroes of the telegraph (IA cu31924031222494).djvu/243

 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 purpose of paring off an old message, and preparing a fresh surface of the wax for the reception of a new one. This can be done in advance while the new record is being made, so that no time is lost in the operation. A small voltaic battery, placed under the machine, serves to work the electric motor, and has to