262 PROCEEDINGS OF THE AMERICAN ACADEMY 



XIV. 



EARLY EXPERIMENTS IN TELEGRAPHING SOUND. 

 By Edward C. Pickering. 



Communicatecl May 2G, 1885. 



In 1870, when Professor of Physics at the Massachusetts Institute of 

 Technology, I wished to show to an audience the experiment of trans- 

 mitting sound by electricity. The only means of doing this, of which 

 I was then aware, was by the sound jjroduced when a jjiece of soft 

 iron is suddenly magnetized or demagnetized. The sound thus pro- 

 duced is extremely feeble, and I proposed to replace it by the follow- 

 ing device. Loud sounds may be produced by the vibrations of a 

 plate, and a strong vibratory force may be applied to such a plate by 

 means of an electro-magnet. The first receiver consisted of a power- 

 ful electro-magnet attached to the bottom of a wooden box, whose 

 cover was replaced by a tin plate, to the centre of which a soft iron 

 armature was attached. The dimensions were such that the armature 

 was near the magnet, but not in contact with it. The plate appears 

 also to have been used without the armature. It is not certain but 

 that this form of apparatus may have been tried first, and the arma- 

 ture added to increase the energy of the vibration, and consequently 

 the loudness of the sound. A tin box was also employed, the bot- 

 tom of which replaced the plate and armature, and the box served 

 to reinforce the sound. The transmitter was composed of a sonome- 

 ter, around the wire of which a short wire was wound, dipping into 

 mercury. An electric current was passed througli both wires, the 

 mercury cup, and the magnet. When the principal wire of the so- 

 nometer was set in vibration by a violin bow, or otherwise, the current 

 was broken at each vibration at the surface of the mercury. When 

 the circuit was made, the magnet drew the plate down, and when it 

 was broken, the elasticity of the plate drew it back. A loud sound 

 was thus produced, whose jaitch could be varied by changing the length 

 or tension of the wire of the sonometer. On December 13, 1869, 

 I gave the first of eighteen lectures on Sound, forming one of the 



