John Logie Baird (1888-1946)

Television: a popular talk


A Popular Talk delivered by Mr. J. L. BAIRD.


The title of this talk is “Seeing by Wireless.”
This is the popular name given to Television. It is not, how-
ever, a fully accurate description, for Television means
seeing by telegraphy, whether with or without wires. With
the telephone, speech can be conveyed over enormous
distances either by means of wires or by wireless broad-
casting, and already both of these remarkable achievements
have become commonplace. While, however, we are
accustomed to hearing at a distance, and think nothing of
listening to a speaker who may be several hundred miles
away, the idea of actually seeing the speaker at the same
time is still strange. The one is in reality just as strange as
the other, but custom has reduced the telephone to a
commonplace, whereas the very idea of Television is still
novel except to those particularly interested in the subject.
When you speak into a telephone your voice sets in vibra-
tion a small diaphragm or thin plate; the vibrations of this
plate alter the resistance of some granules of carbon. This
again sets up a fluctuating current which fluctuates exactly
in unison with the vibrations of the voice. The fluctuating
current is sent along wires or by wireless to the receiver.
Here it passes round the coils of a magnet placed behind a
metal diaphragm, and causes the diaphragm to vibrate in
unison with the diaphragm at the sending station. These
vibrations set up again sound waves corresponding with the
original sounds made at the sending station, and so repro-
duce the speech.

Thus sound is turned into electricity sent through space
or over wires as electric vibrations, and at the receiving
station these electric vibrations are turned back into sound.

With Television very much the same process is gone
through. You stand in front of the transmitting televisor,
the light from your face affects a light sensitive cell, and
causes it to send out a fluctuating electric current. This
current is transmitted to the receiving station by wires or
by wireless, and at the receiving station is turned back into
light again and creates an image of the face of the person
seen. In telephony no actual sound passes through the
wires or the ether, only a fluctuating current of electricity,
and so also in Television all that passes through the ether
is a fluctuating electrical impulse: what the wireless man
would call a modulated carrier wave.