For historical allocation purpose,
the first transmission of the spoken words on wires was held
by Alexander Graham Bell and his assistant Thomaz Watson on
June 2nd, 1875 when conducting experiments on the transmissions
of a number of telegraph messages to be sent simultaneously
over a single wire by means of
|Fig. 344 - The first Bell’s telephone
interrupted tones of different frequencies as known as harmonic
telegraph. Fig 344
The harmonic telegraph consisted of an electromagnet comprising
tuned vibrating reeds at the transmitting end and similar
ones at the receiving end.
From the theory only the reed tuned in the corresponding frequency
should receive a signal sent by mean of a vibrating reed.
Thus, by using different frequencies it should be possible
to send several telegraphic messages simultaneously over a
While starting one of the instruments as the transmitter,
Watson pressed too hard the fixing screw contact point against
the reed and so it stopped in vibrating accordingly. Thus,
in order to readjsut it he tapped the reeds gently with the
fingers and suddenly the generated vibrating sound could be
heard in the receiving device held by Bell located in a nearby
Through this historical experiment Bell was aware that the
vibrating sound could be transmitted on wires, which certainly
was the foundation for building of the first telephone device.
Originally it consisted of a wooden frame on which was assembled
the electromagnet provided with a steel latch. In one of the
latch’s free ends was mounted a tightly stretched membrane.
When speaking over the assembling mouthpiece, the sound waves
force the membrane to follow the vibration of the voice and
so generate voice-shaped electric undulation.
Soon the first telephone was tested using a harmonic telegraph
as receiver for listening. Even considering that on the course
of the experiment it was possible to hear only feeble noisy
produced by the spoken words, certainly it arose the feeling
that the inventor was on the right track.
In March 7, 1876, U.S. patent n° 174,465, was issued to
Alexander Graham Bell for his telephone system. Therefore,
it was three days later, in March 10, 1876, that finally the
inventor succeeded to transmit the first complete intelligible
message by by mean of electricity.