John Logie Baird, though little recognized in the US, was perhaps the most remarkable inventor in the early history of television. In a period of scarcely three years from 1924 to 1927, he invented the first successful mechanical-electric television system, infrared television (dubbed "Noctovision"), stereoscopic television, and the earliest means of recording a television signal, Phonovision. He also staged the first public demonstrations of television, and made the earliest transatlantic broadcast of a television signal. For several years in the early 1930's, 30-line television broadcasts via BBC facilities were produced by Baird's company, and the quality and variety of these programs was quite high, given the limited bandwidth the BBC and the GPO allowed for them. Baird's mechano-electrical systems were eventually replaced by completely electronic television, but nevertheless constituted the first television broadcasts, and the first regularly scheduled programs, in the history of the medium.
To us here in the Twenty-first century, the idea of "mechanical" television sounds almost absurd -- how could television ever have been anything but electronic? Nevertheless, the principle is amazingly simple, so much so that it would be fairly easy to tinker up a television in your garage today. The basic element of such systems is the Nipkow Disk, invented in the 1880's by Paul Nipkow. When we think of the classic television screen of the pre-HDTV era, we of course think of lines, each line containing some information about color and shade, each refreshed and compiled to create the illusion of a moving picture. Nipkow's disc did the same thing, only mechanically: on a disc of metal, tiny pinholes were drilled in a gradual spiral, such that each was just a bit further in from the edge, and a bit further (the size of one frame of the image) along the perimeter. As the disc spins, each pinhole passes by (or "scans") one vertical line; when assembled, the lines form a picture, which is refreshed each time the disc completes a rotation. For the effect of motion, the frame rate must be high -- at least 12 and preferably 20 or more frames per second; some discs used two sets of slightly offset pinholes to produce a better image with fewer rotations.
The Nipkow disc had been around for decades when Baird began his work on television in the early 1920's. Though the principle was sound, the problem lay in converting and amplifying the disc's scan signal, which required a light-sensitive material. Selenium, an ideal choice, posed problems because it was slow to respond to changes, and its signal output was very low. The invention of electronic amplification using valves (or "tubes" as they were commonly known in the US) solved half of the problem, and so Baird worked on the second. The use of very bright lights, and replacing the disc's pinholes with lenses, helped, but only enough to produce so-called "shadowgrams" of brightly back-illuminated cutouts. To get a signal from
reflected light -- the kind of light that a human face emits -- took considerable work. The exact nature of Baird's solution is still something of a mystery, but apparently involved the application of a carefully-calibrated boosting signal at the same frequency as that of the signal from the photocell. In March of 1925, he made a series of public demonstrations at Selfridge's department store on Oxford Street; By the fall of that year, he was close enough that he considered making a more formal demonstration in front of recognized experts.
To us here in the Twenty-first century, the idea of "mechanical" television sounds almost absurd -- how could television ever have been anything but electronic? Nevertheless, the principle is amazingly simple, so much so that it would be fairly easy to tinker up a television in your garage today. The basic element of such systems is the Nipkow Disk, invented in the 1880's by Paul Nipkow. When we think of the classic television screen of the pre-HDTV era, we of course think of lines, each line containing some information about color and shade, each refreshed and compiled to create the illusion of a moving picture. Nipkow's disc did the same thing, only mechanically: on a disc of metal, tiny pinholes were drilled in a gradual spiral, such that each was just a bit further in from the edge, and a bit further (the size of one frame of the image) along the perimeter. As the disc spins, each pinhole passes by (or "scans") one vertical line; when assembled, the lines form a picture, which is refreshed each time the disc completes a rotation. For the effect of motion, the frame rate must be high -- at least 12 and preferably 20 or more frames per second; some discs used two sets of slightly offset pinholes to produce a better image with fewer rotations.
The Nipkow disc had been around for decades when Baird began his work on television in the early 1920's. Though the principle was sound, the problem lay in converting and amplifying the disc's scan signal, which required a light-sensitive material. Selenium, an ideal choice, posed problems because it was slow to respond to changes, and its signal output was very low. The invention of electronic amplification using valves (or "tubes" as they were commonly known in the US) solved half of the problem, and so Baird worked on the second. The use of very bright lights, and replacing the disc's pinholes with lenses, helped, but only enough to produce so-called "shadowgrams" of brightly back-illuminated cutouts. To get a signal from reflected light -- the kind of light that a human face emits -- took considerable work. The exact nature of Baird's solution is still something of a mystery, but apparently involved the application of a carefully-calibrated boosting signal at the same frequency as that of the signal from the photocell. In March of 1925, he made a series of public demonstrations at Selfridge's department store on Oxford Street; By the fall of that year, he was close enough that he considered making a more formal demonstration in front of recognized experts. 
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