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 f, 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 
