THE TELEPHONE AND MICROPHONE. 473 



of the chronometer, telescope, microscope, balance, photo- 

 meter, thermometer, thermo-pile, electrometer, galvano- 

 meter, &c. ; and almost every kind of instrument for 

 measuring time, space, mass, motion, and their various 

 relations, all the forms of energy, and relations and 

 modes of action of the forces of nature. One of the 

 most extraordinary of recent inventions, extending the 

 sphere of use of our senses, is that of the telephone of Mr. 

 Graham Bell, by means of which our sphere of hearing is 

 vastly extended, and spoken words are instantly reproduced 

 at considerable distances by electric wires. The arrange- 

 ment consists substantially of two small bar electro- 

 magnets, distant from each other, each excited by an 

 uniform electric current, and each having a small and thin 

 armature of sheet-iron supported in front of its poles, 

 capable of freely vibrating. By speaking loudly through 

 a mouthpiece at one of the armatures, the latter is 

 caused to vibrate in accordance with the sounds, and pro- 

 duces, by induction upon the magnet, corresponding varia- 

 tions of the electric current in the wire which surrounds 

 the magnet. The variations of the current are transmitted 

 through the wire to the distant or second magnet, the 

 magnetism of which being thereby varied in a similar 

 manner to that of the first one, produces similar and 

 audible vibrations of the distant armature to those of 

 the near one. The vibrations of the distant armature are 

 not only synchronous with but similar in quality to those 

 excited in the sending one, and the voice of the individual 

 person speaking can be recognised. 1 The microphone is 

 another invention, the use of which enables us to detect 

 extremely feeble vibrations and sounds. There remains 

 yet great room for extending, by means of appropriate 



1 Telegraphic Journal, October 1, 1876, p. 257. 



