In 1842 in Scotland, Alexander Bain did the
first atemp to transmit messages comprising text and pictures through
telegraph lines. Therefore, considering Bain’s system had
several disadvantages, as slower messages transmission rate, commercial
wise it was superseded by the much simpler Morse telegraphs invented
one year later.
Originally the Bain’s system used the principle of a pendulum
to scan a message. Thus, in the transmitter, the pendulum was comprised
as a sharp metal point that swung to and fro over a raised metal
plate where the message was set up, like that used in printing.
Whenever the pendulum’s point touched the surface of the metal
plate, an electrical current was generated and transmitted throught
a telegraphic line.
At the receiver, a similar pendulum swept over a piece of paper
impregnated with potassium iodide, which changes colour when an
electrical current pass through it.
In 1848, the British inventor, Frederick Bakewell, developed a copying
machine that had many of the features of modern facsimile system
basically comprising a rotating cylinder and a scanning device.
It was an advanced system for the time being as the machine was caplable
of transmitting either text messages as well simple line drawing through
the telegraphs lines even considering difficulites in the synchronization.
|Fig. 320 - The “photophone” invented
The “Pantelegraph” an acronym meaning Pan (Greek word
= All) + telegraph was invented by Giovanni Caselli in Italy in
1850. Caselli’s system began devising an improved version
of the earlier Alexander Bain’s invention.
As aforementioned the History of Science and Technology is plenty
of peculiar aspects, which are interconnected in a near epoch and
so interfering indirectly in new discoveries. Thus, in 1873, Willoughby
Smith, a senior electrician working in the maintenance of telegraphic
lines for a Bristish company looked for a material with very high
resistance to electrical current, but in the mean time not being
a complete isolator. After experiments with several types of material,
in 1873 he used bars of crystalline selenium, noting such substance
seemed to have peculiar inconstant resistance behaviour.
During his observations he noted that the resistance of the selenium
seemed to depend on the amount of ligh falling on it. As aforeseen
Smith had discovered casually the photosensitivity of the selenium,
several years before the cause of this curious property was reveled.
Later, Alexander Graham Bell, inventor of the telephone, used the
photoelectric phenomenon in the development of a machine for wireless
transmissions of sound, as known as the “Photophone”.
In reality, the “Photophone” was an erlier type of wireless
telephone, basically comprising in the transmitter a tube connected
to to a small mirror, on which a strong beam of light was reflected.
As the vibration of the voice struck the mirror, the direction of
reflected light changed slightly. At the receiver, a large parabolic
mirror collected the light from the beam and focused it on a phtosensitive
selenium cell. As the received light changed in strenght because
of the vibrations of the transmitting mirror, the lectrical resistance
of the selenium changed, so varying the current that could flow
through it. In the circuit, the selenium cell was connected to a
battery and a set of ordinay Bell telephones, which converted the
changing currents back into sound.
In spite of its good performance, the “Photophone” could
be used for over limited distance only as the apparatus’s
operation was related to a direct line of sigh between the transmitter
Based in the Bell’s “Photophone”, in 1870, the
Bristish scientist Shelford Bidwell invented a new kind of instrument
that really had the potential to transmit photographs as knowns
Therefore, even considering so many discoveries and improvements
there were still problems in the way of making a reliable commercial
system for transmitting images.
Around 1890, the Australian inventor Henry Sutton, proposed a relatively
simple mean to transmit photographic printing plates, similar to
the aforementioned Bain and Caselli’s systems. When compared
with those later systems, the Sutton’s machine sole difference
consisted in producing another printing plate at the receiving end,
rather than just use a piece of paper chemically treated with a
In fact, at the end of XIX century either the evolution of the television
as well as the facsimilie run together as both were based in the
discovery of the selenium’s photosensitivy.
Therefore at this point of the history of technology, it is interesting
to note that television begins to diverge from that of facsimilie.
Thus, in the former, it requires the transmission of the moving
images, generally at quite low-resolution level; hence the movement
carries on an enormous information data, pressing for a high capacity
communciation links. By other hand, facsimilie needs to transmit
images at high-resolution rates generally using ordinary telegraph
or telephone lines.