A D V E N T U R E S   in   C Y B E R S O U N D

The discovery leading to the possibility of mechanical television was an accident. While measuring the conductive capabilities of various metals for the first trans-Atlantic telgraph cables, it was discovered selenium conducted more electricity while lit than in darkness. Selford Bidwell used a photoelectric cell to transmit an image electronically in 1881: over the course of several minutes, a two-inch square image could be sent via telegraph lines. Three years later, Paul Nipkow was granted a German patent for the Nipkow disk -- a complete and functional television system in 1884. The development of the neon tube in 1910 furthered mechanical television.

Film achieves the illusion of motion by taking advantage of the persistence of vision: still images in a fixed location which are refreshed at a rate of sixteen times per second (or more) are interpreted by the human mind as moving images. Television achieves the illusion of motion in a similar but unique fashion. Rather than refresh the entire image at once, as film does with each cell that passes in front of the projector's light, television refreshes an image one line at a time in a scanning process. Within the cathode ray tube, an electron gun scans a single line of an image from one side to the other, then scans the line underneath it, until it has scanned an entire image.

The Nipkow disk is an earlier, mechanical means of achieving the same side-to-side, top-to-bottom scan process. It consists of a disk that rotates on its axis. A series of evenly spaced, uniformly sized holes are cut into the disk, spiraling in toward the center. The disk is housed in a box with a small viewing window: the outermost hole of the disk will form the outermost scan line visible in the viewing window, and each additional hole will form additional scan lines. The rotation of the disk as seen through the viewing window provides scanning from side to side, and the spiral placement of the holes provides scanning from outermost to innermost scan line. A light source which can be varied in intensity is placed on the opposite side of the disk behind the viewing window. As the light flickers and the disk rotates, television is achieved.

Mechanical television cameras and receivers alike use the Nipkow disk, but where the receiver uses a flickering light to produce an image, the camera uses a photosensitive cell to generate an image. The rotation of the disks are synchronized by part of the transmission signal (which has included radio, short wave and telephone) or direct wiring. The disks rotate at around 900 rpm and initially produced television two inches square. The earliest mechanical televisions offered between 16 and 24 scan lines.

By the late 1920s, they offered between 48 and 60 lines. Double and triple spirals of scanning holes were used, as well as scanning drums and belts. Lenses were fixed in the scan holes to project the image onto a larger screen (up to 8 inches in some cases). Mechanical television cameras were synchronized with film projectors, allowing the transmission of film. Studio B of the BBC used a hybrid of this system: the subject was filmed, the film was instantly processed and then scanned for transmission. There was a delay of around one minute between event and transmission as the film developed.

The light required for mechanical television is intense, so much so it was nearly impossible to perform while being televised. The flying spot camera was one solution to this problem: the light source, rather than the camera, was scanned across the subject. Fluorescent lights were syncronized with the flying spot to provide high-flicker but constant light source. The rest of the studio, including the control room, was kept in complete darkness. Another solution to this problem was the use of multiple arrays of concave lenses to focus light into the camera more efficiently.

Scotsman John Logie Baird had long been an entrepreneur and inventor. When he was twelve he built his own telephone. He had invested in chutney in the West Indies, artificial diamonds in Glasgow and soap in London. In 1918 he held the patent for the Baird Undersock, a sock worn beneath regular socks. In 1920, at the age of 31, he began his life's work -- the undercredited discovery and development of television.

Beginning with a personal ad in the London Times ("SEEING BY WIRELESS: Inventor of apparatus wishes to hear from someone who will assist [not financially] in making working model"), Baird set out to build a working television system using borrowed money and the material he had at hand, which included darning needles, hat boxes, a Rich Mix biscuit tin, sealing wax and a bicycle lantern. His Nipkow disk was cut from an old tea chest. In February 1923 he entered the shop of Hasting radio dealer Victor Mill and asked for assistance, saying "I've fitted up an apparatus for transmitting pictures and I can't get it to go." Mills accompanied Baird back to his laboratory/apartment and waved his hand in front of the neon: when Baird shouted "it's here, it's here!", the first real-time electronic moving picture in world history occurred. Not long after Baird demonstrated his system to the local press, but was evicted from his apartment.

Baird relocated to London and set up a second and lab in Soho. Using ventriloquist dummies (better able to withstand the intense heat and light of his equipment), he succeeded in transmitting a televised image one yard across his room. In March 1925 he gave the first public demonstration of television, sponsored by Selfridge's Department store. A demonstration of television in January 1926 in Baird's small, drafty attic apartment failed to impress the Royal Institute, particularly when the long white beard of one of the men became entangled in the mechanism. In Autumn of the next year he transmitted eight miles, and formed a company: Television Ltd.

The first recorded television images were made on 10" wax disks called Phonovisors no later than September 1927 in Baird's labs: he had been awarded a patent for this technology the year before. Phonovisor disks captured 12.5 frames of 30-line resolution television per second. Baird also patented Noctovision, the use of infared light in television, and demonstrated color television (using a rotating filter system) in 1927.

By 1928, Baird Televisors sold for between 20 and 150 pounds (kits sold for 16 guinnies). Baird's assistant Benjamin Clapp travelled to New York City to receive the first transoceanic television signal. The box of equipment he used was labeled 'experimental radio equipment' to prevent customs from seizing it as a dangerous or profitable new technology. It took two months before a break in the weather allowed Clapp to see the image of Stukey Bill, the ventriloquist dummy head used in the Baird studio, but once the press was called in the event received one inch headlines across the nation. On the way home aboard the Berengeria, Clapp allowed the ship's wireless operator to see his fiance in England via television while 1,000 miles at sea.

Eighteen licensed transmitters were in operation in the United States by the late 1920s, transmitting faces and silhouettes. General Electric's House of Magic recorded synchronized sound and pictures in New York. In 1928 Bell Telephone transmitted a television image from New York to Washington D. C. The threat of losing television to the USA gave Baird leverage in convincing the BBC to begin television transmission.

In 1928 Baird convinced a London surgeon to lend him an eyeball removed from a young man's head. In his own words...

As soon as I was given the eye, I hurried in a taxicab to the laboratory. Within a few minutes I had the eye in the machine. Then I turned on the current and the waves carrying television were broadcast from the aerial. The essential image for television passed through the eye within half and hour after the operation. On the following day the sensitiveness of the eye's visual nerve was gone. The optic was dead. I had been dissatisfied with the old-fashioned selenium cell and lens. I felt that television demanded something more refined. The most sensitive optical substance known is the nerve of the human eye... I had to wait a long time to get the eye because unimpaired ones are not often removed by surgeons... Nothing was gained from the experiment. It was gruesome and a waste of time.

By this time, Baird's financial backers began to insist he look into the electronic television of Philo Farnsworth. When Farnsworth travelled to England while raising money in his legal battles with RCA/EMI, he met with Baird and demonstrated his system. Baird explained the superiority of his system to Farnsworth, but after watching several minutes of cathode ray tube television he left the room without a word. Baird's sponsors gave Farnsworth $50,000 to supply Baird with electronic television equipment. A fire that nearly destroyed the Alexandra Palace studios soon after closed down the BBC, and when they reopened they were fully committed to the electronic television of EMI.

After 1,500 successful mechanical transmissions, the BBC was ready to switch to the EMI system. Beginning September 1935, they held a final six-month trial, during which the two systems were transmitted on alternate weeks from Alexandra Palace, 12 miles north of London. Studio A used the EMI system, while Studio B used the Baird film pickup system.

Baird's system lost, and on 2 November, 1936 the BBC transmitted the first high-definition television signal using the EMI system. Many executives and technicians were invited to the studio on opening day, but when Baird showed up he was left wandering the halls, shut out from celebrating the technology he had developed. The final mechanical television transmission in England occurred in February 1937.

Baird continued to develop television technology. In 1940, he introduced the Telechrome, an electronic color television system in which two electron guns scanned 600 - 650 lines on a white mica sheet coated with orange phosphor on one side and blue-green phosphor on the other. War time restrictions prevented full scale production of the Telechrome. At the time of his death in 1946, John Logie Baird was working on stereoscopic television.

England and the United States were not the only countries that utilized mechanical television. The race to be the first country to develop television was truly international and included Canada, France, Germany, the Soviet Union and Japan. The base for mechanical television research in the Soviet Union was Leningrad. The first Russian television image was transmitted in 1928, and the first public broadcast occurred in 1934. The first broadcast began "Attention, attention, attention radio viewers: watch, listen to the first television concert." The station was soon flooded with letters from radio listeners asking where they were supposed to look to see the concert.

In March 1935, Germany offered the world's first low-definition (electronic) television service. It used 180 lines of resolution (compared to the 405 offered by the BBC over a year later) and was seen mainly in public viewing rooms. The Berlin Olympics were transmitted by television, and in March 1936 a video telephone system was established. No public official was recorded as using television: the medium was used entirely for entertainment during this period. While England, the USSR and the USA lowered or outright ceased transmissions during World War Two, Germany paused only during the invasion of Poland.

If the BBC had not adopted the EMI system, it is unlikely England would have had the facilities to manufacture cathode ray tubes on an industrial level. And had this not been possible, the manufacturing of radar screens -- and therefore the outcome of the war -- might also have been in question.

Mechanical imaging systems remain a vital technology. Computer mice use two slotted disks that are rotated by the track ball. These disks are positioned next to tiny lights: as the disks spin the lights are registered as on or off by photosensors, and software translates the blinking lights as x-y cursor position. Software or sound activated moving mirrors are the key component to laser light shows as well as some virtual reality headgear. While not commercially successful, video disks (as opposed to laser disks) were an entirely functional medium: a needle read changes in capacitance pressed in a large plastic disk. All of these technologies, as well as television, are directly indebted to John Logie Baird.

Copyright (C) 1998 Trevor Blake

Source:http://www.teleport.com/~box2321/127mtv.htm

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