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considering Bain’s system had several disadvantages, as slower messages transmission rate, commercial wise it was superseded by the much simpler Morse telegraphs invented one year later.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.
Fig. 320 - The “photophone” invented by Bell.
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.
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”. Fig 320
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 and receiver.
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 as “Telephotograph”.
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 potassium-iodide solution.
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.