c with his right hand Gray noticed
that a sound proceeded from it, which had the pitch and quality of the
note emitted by the vibrating contact or electrotome of the coil. 'I
immediately took the electrode in my hand,' he writes, 'and, repeating
the operation, found to my astonishment that by rubbing hard and rapidly
I could make a much louder sound than the electrotome. I then changed
the pitch of the vibration, and found that the pitch of the sound under
my hand was also changed, agreeing with that of the vibration.'
Gray lost no time in applying this chance discovery by designing the
physiological receiver, which consists of a sounding-box having a zinc
face and mounted on an axle, so that it can be revolved by a handle. One
wire of the circuit is connected to the revolving zinc, and the other
wire is connected to the finger which rubs on the zinc. The sounds are
quite distinct, and would seem to be produced by a microphonic action
between the skin and the metal.

All these apparatus follow in the track of Reis and Bourseul--that is
to say, the interruption of the current by a vibrating contact. It
was fortunate for Bell that in working with his musical telephone an
accident drove him into a new path, which ultimately brought him to the
invention of a speaking telephone. He began his researches in 1874 with
a musical telephone, in which he employed the interrupted current to
vibrate the receiver, which consisted of an electro-magnet causing an
iron reed or tongue to vibrate; but, while trying it one day with his
assistant, Mr. Thomas A. Watson, it was found that a reed failed to
respond to the intermittent current. Mr. Bell desired his assistant,
who was at the other end of the line, to pluck the reed, thinking it
had stuck to the pole of the magnet. Mr. Watson complied, and to his
astonishment Bell observed that the corresponding reed at his end of the
line thereupon began to vibrate and emit the same note, although there
was no interrupted current to make it. A few experiments soon showed
that his reed had been set in vibration by the magneto-electric currents
induced in the line by the mere motion of the distant reed in the
neighbourhood of its magnet. This discovery led him to discard the
battery current altogether and rely upon the magneto-induction currents
of the reeds themselves. Moreover, it occurred to him that, since the
circuit was never broken, all the complex vibrations of speech might be
converted into