HISTORY OF THE WIRE COMMUNICATIONS: BEGINNINGS OF THE TELEGRAPH AND THE TELEPHONE.

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The first transmission of images by cable
On May 19 , 1924, forty and four minutes exactly after to be developed a photography in Cleveland, Ohío, it was exhibited, completely printed, to a group of experts gathered in a room in New York, who had been observing how the photography was formed, sparkle by sparkle, on an sensible film arranged in a complicated machine. The distance between Cleveland and New York is of 932 kilometers.

The photography had been transmitted with all perfection of details (considering the state of the technology in years 1920 to 1930) and from such a long distance by a telephone line, introducing a new system, whose applications created great expectations as they multiplied in an amazing way.

Only five minutes in the transmission itself were used; the rest was spent in the development . The system had been devised by the engineers of the American Company of Telephones and Telegraphs and of the Western Electric Society, being the result of several years of work and tests. The apparatus used was constituted by the combination of many inventions produced in previous dates and the adaptation of that new application to the telegraphs and telephones with the greater advances of the time.

President Coolidge and his wife in the funerals of his predecessor. Photography transmitted from Marion, Ohio, until New York by the lines of the company American Telephone & Telegraph.

Partial sight of the photo where the impression vertical sweeping can be appreciated.

These photographs of Cleveland, Ohio, were transmitted to New York the May 19 , 1924, from a distance of 932 kilometers, by wires of telephone, in five minutes, as a demonstration of a system that initiated a new bright horizon to the informed press.

The method used was so simple, that a positive film of any photographer could be used for being transmitted, and the apparatus was set up to admit films of 125 by 175 millimeters, whose images could be transmitted in about five minutes, of such a way, that after being developed the photography in the usual process it was ready to be sent to newspapers or could be reproduced by any procedure. In the same way the drawings, pictures and the writing by hand could also be transmitted. As the films for the transmission could be used although they were humid, this system avoided, therefore, the delay that would cause drying them.

The procedure was as it follows: In the transmitter there was a cylinder where a photographic film was coiled in which an image had been developed .It was focused on it a light beam that illuminated an area of 6.25 square millimeters. This beam crossed the film and excited a photoelectric cell mounted within the cylinder. This apparatus had the sole mission of regulating and making the amount of current that was to be transmitted proportional to the amount of light that was received at the bulb from the light source. We can say that these inventions were the initial steps of the present fax machine, that with the present technologies does a similar work .

The electrical current that crossed the photoelectric cell was amplified by means of vacuum tubes (triodes), and passed regulated and amplified to the telephone line, by where it was transmitted in the same way that if it was an ordinary telephone conversation.
In the receiving station this current was amplified even more and it operated a piece of the device that was known with the name of "light valve". The passage of this current that was received by the telephone line varied the amplitude of an opening through which it passed a beam of light, regulating therefore the amount of this beam, that focused on a cylinder similar to the one used in the transmitter. On this cylinder was coiled a photographic film not exposed, ready to receive the copy of the image sent from the other station.

By means of a special synchronization system , the cylinders of each end of line turned exactly at the same speed, and by means of a screw mechanism the film advanced parallelly to the axis of the cylinder. The movement of the light with relation to the cylinder was the same one of that of the needle of the phonograph with respect to the disc. This synchronization system used a regulating current that was transmitted by the same pair of wires that transmitted the "current of the image". By means of devices known with the name of "filters", both currents were separated in the receiver. The regulation current was amplified separately making it move a small motor that rotated exactly at the same speed that another one comprised in the transmitter station. Thus when in the transmitter station the light beam crossed a determined point of the transparent film, in the other end of the line the light also focused in a point whose situation was exactly identical in the film not exposed.

The different emulsion densities of the film in the transmitting end of the line regulated the amount of light that passed it trough and was received on the photoelectric cell and it as well made vary the amount of electric current sent to the line. In the receiving end this electric current acted the valve of light, and this way the receiving film was exposed with a variable intensity.

As the cylinders turned advancing, the light beam in the receiving end drew up a line in form of helix around them. The intensity of the tone of this line in each point was determined by the transparency of the film in the corresponding point of the original image in the transmitting end. Thus were obtained the effects of light and shade and the image was reproduced exactly.

Besides obtaining that the turn takes place automatically, with full precision and at the same speed, in both stations, they were provided with devices that assured means to exactly initiate the movement at the same moment and in similar points.

This apparatus, invented to be used in the lines of the Bell system, could transmit any image that allowed to be photographed and considered interesting to be published in newspapers, obtaining in a few minutes illustrations of the most important events happened in distant places. The transmission of the images could take place exactly , simply and fast by the ordinary telephone lines, without interrupting in any case the regular and current telephone service. As it had been demonstrated in the diverse previous tests whenever the atmospheric conditions allowed it or be such that they provide calm communications and free of interferences, the system was also applicable to the radio transmission of images .

In the first days of February of 1926 it began to be disclosed the news of a transcendental invention on this matter, due to the illustrious Italian science man Guglielmo Marconi. According to these news, he was on the verge of transmitting "instantaneously" from New York to London or Paris a photography, a picture, or the whole page of a newspaper. It had been improved a new discovery in diverse laboratories, specially in those of the Telefunken Gesellschaft, Berlin. It was the result of five years of constant development of the Carolus battery, the most sensible photoelectric battery at the time, than replaced the selenium ones, which until that moment had been used for the images transmission .

The transmission imagined by Marconi was based on the Kerr method, from the famous English physicist. It consisted of influencing a polarized light ray in such a way that the high voltage created an energetic ray, while the low voltage only created a weak ray. Thus, all the variations of voltage went instantaneously accompanied of equal variations in the light ray that exposed the photographic film. The Carolus photoelectric battery transforms into electricity all variation of light, without delay, allowing therefore an enormous increase of speed in the transmission. The new battery produced only small electrical currents, that had to be amplified by radiotelegraphy. The task of the receiver consisted of transforming the electrical oscillations into light, acting on the photographic negative. The Dr Carolus managed to direct the strongest luminance energies with the weakest currents by a special development of the photoelectric battery.

The security of the transmission depended on the perfection of the subdivisions of the photography (term equivalent to the graph definition) that it had to be transmitted. A subdivision of a third of millimeter was sufficient for the reproduction of a page or newspaper article, whereas the photographies could be divided in squares that measured one tenth of a millimeter. For cinematographic purposes a subdivision of a millimeter had been considered sufficient. While the transmission with selenium could be done by the wires or without them, the transmission perfected by the Carolus system had a frequency of alterations of current so fast, that the transmission by wires had to be prescinded, and even in the wireless transmission , the shortest waves could only be used.