This idea was clear in Bell’s mind by the summer of 1871, but he did not
then know how to reduce it to practice. On June 2, 1875, he succeeded in
doing so. In adjoining attic rooms at 109 Court Street, Boston, he and
Watson were trying out several pairs of harmonic telegraph instruments
each consisting of an electromagnet with a steel organ reed vibrating
over it. One reed stuck. Watson plucked it with his finger to start it
again, but it did not come free, so Bell heard an unusual sound. Instead
of hearing a series of electric pulsations, he recognized the twang of a
vibrating reed! He knew then that, as Watson has put it, “he was
hearing, for the first time in human history, the tones and overtones of
a sound transmitted by electricity.” That afternoon Bell directed Watson
to make the instrument that was to be the first Bell telephone. This
instrument transmitted voice tones, but not until March 10, 1876, did
Bell succeed in transmitting an intelligible sentence of speech.