THE 



POPULAR SCIENCE 

 MONTHLY. 



DECEMBER, 1878. 



EDISON'S TELEPHONIC AND ACOUSTIC INVENTIONS. 



By GEOEGE B. PKESCOTT. 



SOME of tlie discoveries and inventions of Mr, Edison, that were 

 made during Iiis researches which culminated in the invention of 

 the carbon-telephone, have already been published. We now propose 

 to present a more complete description of the important forms of tele- 

 phone upon which he then experimented, and to describe his more 

 recent acoustic inventions. 



The carbon-telephone is only one of manj' contrivances for repro- 

 ducing articulate speech at a distance through the aid of electricity, 

 but, owing to its clear and truthful articulation, its simplicity of con- 

 struction, and the far greater volume of sound which it creates, is prob- 

 ably destined to be the most extensively used. Other instruments of 

 Mr. Edison's invention, however, are not far behind it, and may by 

 improvement be made equally effective. 



As a rule, Mr. Edison has succeeded better with those telephones 

 which produce a variation in the resistance of the circuit than with 

 those which depend for their action upon a variation of the electro- 

 motive force or static charge. An instrument very similar to the car- 

 bon-transmitting telephone is shown in Fig. 1, the essential difference 

 being that the carbon is replaced by bibulous paper moistened with 

 water. This semi-conductor, like the carbon, changes its resistance 

 under the influence of varying pressure. The paper is kept moist by 

 capillary action, a strip being used, one end of which dips into a res- 

 ervoir of water. 



In Fig. 2 is shown a form of the carbon-transmitting telephone, re- 

 quiring no adjustment whatever. It operates well, notwithstanding the 

 simplicity of its construction. A plate of metal rests on the bottom of 

 a hollow vessel. On this is placed a block of prepared carbon, upon 

 which a second and light plate is laid. 



TOL. XIV. — 9 



