CH. xxxvi. THE TELEPHONE. 389 



telephone to his ear. The currents pass into the coil <r, 

 affect the soft iron b, and make the iron plate a vibrate 

 exactly in the same way as the similar plate did at the speak- 

 ing end. So the same sounds are returned to the air at 

 exactly the same rate and of the same form as the sounds 

 caused by the voice at the other end, and we hear the very 

 tone of our friend's voice, not because the sound vibrations 

 have travelled, but because these have been changed into 

 electric currents at one end, and they are changed back 

 again into sound at the other. There are many difficulties 

 stiW about the working of the telephone ; other noises some- 

 times interfere with the wire and make confusion, and the 

 currents are so weak that a very little disturbance prevents 

 their acting properly, but numerous improvements have 

 been made ever since the above passage was written in 

 1879, and there are already many kinds constructed very 

 differently from the one I have described. Mr. Edison, 

 the well-known inventor in America, has now constructed 

 a carbon telephone which, when it is put in the circuit of 

 a battery, enables words uttered 115 miles distant to be 

 heard easily by a large audience, and the time may come 

 when speeches made in London may be listened to by 

 crowded meetings in all parts of England. . . ,, 



Chief Works consul fed. Lardner's Cyclopaedia' 'Electricity, 

 Magnetism, and Meteorology;' 'Annals of Philosophy,' New Series, 

 1822, vohs. ii. and iii. ; ' History of Magnetism ;' 'Encyclopaedia Me- 

 tropolitana,' art. 'Electro-Magnetism;' Faraday's 'Experimental Re- 

 searches in Electricity,' 1859; Tyndall's ' Faraday as a Discoverer ;' 

 Gladstone's ' Michael Faraday;' ' Nouvelle Biog. Universelle ' 'Am- 

 pere,' 'Oersted ;' Ampere, 'Observations Electro-dynamiques,' 1822 ; 

 Faraday, ' Various Forces of Nature ;' Proctor, ' The Sun ;' Herschel'a 

 'Familiar Lectures; Brande's 'Manual of Chemistry ;' Preece On 

 the Telephone, ' Nature,' vol. xvi. p. 403. 



