On the Telephone. 79 



telephone ; b is a box or small resonant cavity into which the 

 operator sings through the mouthpiece a; a diaphragm of 

 bladder or paper c covers the upper part of the box. This is 

 thrown into vibration by the voice, and comes into contact with 

 the platinum point d. The centre of the diaphragm is furnished 

 with a fragment of platinum foil whereby contact is made and 

 broken with the battery e. The intermittent currents thus 

 transmitted through the line arrive at the receiver/, which is 

 simply a straight iron wire, surrounded by the coil through which 

 the current passes. The rapid magnetizations and demagnetiza- 

 tions of the iron wire by the current give rise to a musical note 

 emitted by the iron, the pitch of the note corresponding to that 

 sung into the receiver. 



The discovery that a sound was produced in iron by magnetiza- 

 tion is due to an American page in 1837. It was explained by 

 De la Rive, of Geneva, in 1843, who showed that it was caused by 

 the slight elongation of the iron which accompanies the act of 

 magnetization, a fact discovered by Joule in 1842. The author 

 of this paper has found that the magnetic metals nickel and 

 cobalt also yield a corresponding sound on magnetization : 

 with cobalt the note is clearer and more metallic. The author 

 has also corroborated the fact noticed by De la Rive, that stretch- 

 ing the iron wire diminishes the sound, because it diminishes the 

 elongation by magnetization, and further at a certain tension the 

 sound ceases, the elongation here ceasing. At a still greater 

 tension iron shortens by magnetization, and the author has found 

 that here too, as we might expect, the sound again is produced, 

 and shortly before the breaking strain of the wire is reached the 

 loudness of the "magnetic tick" is almost as great as with the 

 unstretched wire. By attaching the iron wire, surrounded by its 

 coil, to a monochord, and using a rapidly interrupted current, the 

 rise and fall and extinction of the sounds by varying the tension 

 of the wire can be easily heard throughout a very large theatre. 



After his first success Reis improved both his transmitting 

 and receiving instruments. In a report on Reis's telephone by 

 Legat, Inspector of Telegraphs in Cassel, &c, published in 1862 in 

 the journal of the East-German Telegraph Company and reprinted 



