THE PHONOGRAPH. 



" The action of the apparatus will now be readily understood from 

 what follows. The cylinder is first very smoothly covered with tin-foil, and 

 the diaphragm securely fastened in place by clamping its support to the base 

 of the instrument. When this has been properly done, the stylus should 

 lightly press against that part of the foil over the groove. The crank is now 

 turned, while, at the same time, someone speaks into the mouthpiece of the 

 instrument, which will cause the diaphragm to vibrate, and as the vibrations 

 of the latter correspond with the movements of the air producing them, the 

 soft and yielding foil will become marked along the line of the groove by a 

 series of indentations of different depths, varying with the amplitude of the 

 vibrations of the diaphragm ; or in other words, with the inflections or 

 modulations of the speaker's voice. These inflections may therefore be 

 looked upon as a sort of visible speech, which, in fact, they really are. If 

 now the diaphragm is removed, by loosening the clamp, and the cylinder 



Fig. 195. BELL'S LONG-DISTANCE TELEPHONE 

 A. Compound magnet, d. Diaphragm, e. Speaking tube. < Telegraph wire. g. Line to earth, b, c. Small spaces. 



then turned back to the starting point, we have only to replace the diaphragm 

 and turn in the same direction as at first, to hear repeated all that has been 

 spoken into the mouthpiece of the apparatus ; the stylus, by this means, being 

 caused to traverse its former path, and consequently, rising and falling with 

 the depressions in the foil, its motion is communicated to the diaphragm, 

 and thence through the intervening air to the ear, where the sensation of 

 sound is produced. 



" As the faithful reproduction of a sound is in reality nothing more 

 than a reproduction of similar acoustic vibrations in a given time, it at once 

 becomes evident that the cylinder should be made to revolve with absolute 

 uniformity at all times, otherwise a difference more or less marked between 

 the original sound and the reproduction will become manifest. To secure 

 this uniformity of motion, and produce a practically working machine for 

 automatically recording speeches, vocal and instrumental music, and per- 



