sympathetic currents, which in turn would reproduce the
speech at a distance.

Reis had seen that an undulatory current was needed to transmit sounds
in perfection, especially vocal sounds; but his mode of producing the
undulations was defective from a mechanical and electrical point of
view. By forming 'waves' of magnetic disturbance near a coil of wire,
Professor Bell could generate corresponding waves of electricity in the
line so delicate and continuous that all the modulations of sound could
be reproduced at a distance.

As Professor of Vocal Physiology in the University of Boston, he was
engaged in training teachers in the art of instructing deaf mutes how to
speak, and experimented with the Leon Scott phonautograph in recording
the vibrations of speech. This apparatus consists essentially of a thin
membrane vibrated by the voice and carrying a light stylus, which traces
an undulatory line on a plate of smoked glass. The line is a graphic
representation of the vibrations of the membrane and the waves of sound
in the air.

On the suggestion of Dr. Clarence J. Blake, an eminent Boston aurist,
Professor Bell abandoned the phonautograph for the human ear, which it
resembled; and, having removed the stapes bone, moistened the drum with
glycerine and water, attached a stylus of hay to the nicus or anvil, and
obtained a beautiful series of curves in imitation of the vocal sounds.
The disproportion between the slight mass of the drum and the bones
it actuated, is said to have suggested to him the employment of
goldbeater's skin as membrane in his speaking telephone. Be this as it
may, he devised a receiver, consisting of a stretched diaphragm or drum
of this material having an armature of magnetised iron attached to its
middle, and free to vibrate in front of the pole of an electro-magnet in
circuit with the line.

This apparatus was completed on June 2, 1875, and the same day he
succeeded in transmitting SOUNDS and audible signals by magneto-electric
currents and without the aid of a battery. On July 1, 1875, he
instructed his assistant to make a second membrane-receiver which could
be used with the first, and a few days later they were tried together,
one at each end of the line, which ran from a room in the inventor's
house at Boston to the cellar underneath. Bell, in the room, held one
instrument in his hands, while Watson in the cellar listened at the
other. The inventor spoke into his instrument, 'Do you unders