THE CARBON BUTTON. n 



ing to the accomplishment of that end were begun nearly twenty- 

 years ago. 



The first successful experiments were made by Philip Reis, of 

 Fredericksdorf, Germany, in 1861. He argued that if it could be 

 found practicable to convert sound pulsations into electric pulsations, 

 and then convert these pulsations back again into sound pulsations, 

 the same effect would be produced as if the vibrations had been actu- 

 ally transmitted through the air. In his instruments a membrane 

 rigidly secured on the sides was caused to vibrate in the center by the 

 motion of the air produced by any sound. In the center of this mem- 

 brane was a delicate circuit-breaker so arranged as to break the circuit 

 of an electric telegraph line at every vibration, thus successively mag- 

 netizing and demagnetizing an electro-magnet at the receiving station, 

 and causing its armature to vibrate in accordance with the vibrations 

 of the membrane at the transmitting station. The vibrations of this 

 armature, properly mounted on a sounding-board, set into vibration 

 the surrounding air, which carried the sound to the ear. His first in- 

 strument is represented in Fig. 1. A is the transmitting and B the 

 receiving instrument, supposed to be placed at different stations and 

 connected with each other by a metallic conductor. A conical tube, 

 a b, six inches long, four inches in diameter at the larger, and one and 

 a half inch in diameter at the smaller end, is closed at b by a col- 

 lodion membrane o, against the center of which rests one end, c, of the 

 lever c d. This lever has electric connection with the wire of the line 

 joining the two stations at its point of support, e. The end d of the 

 lever rests against the flat springy, which can be properly adjusted by 

 means of the screw h, and which, through the metal standard/*, is con- 

 nected with the battery C. At station B the conducting wire passed 

 around the electro-magnet m, which is mounted on a sounding-box W ; 

 thence to the ground. Attached to the armature at the pole of the 

 magnet is a thin plate i, which is hung on an horizontal axis projecting 

 from the upright k ; the motion of the plate can be regulated by the 

 screw I and the spring s. The best dimensions and most suitable ad- 

 justments of the instrument were determined by experiment. Its 

 operation is as follows : When at rest the small spring n keeps the 

 lever c d in contact at g, the circuit is closed, and the magnet in attracts 

 the armature i. But, when by speaking into the tube a b, the air in 

 the tube and therefore the membrane o is set into vibration, the con- 

 tact at g is alternately broken and closed, and consequently the magnet 

 at B is demagnetized and magnetized, alternately releasing and attract- 

 ing the armature i. It is evident that the vibrations of i correspond 

 in number and interval to the vibrations of the membrane o ; so that 

 the sound which enters the tube a b is reproduced at B so far as its 

 pitch is concerned. But as the strength of the current is constant, 

 neither the intensity nor the quality of the sound is reproduced. 



In 1874 Elisha Gray, of Chicago, accomplished the reproduction of 



