BeskrivelseSpinning disk television projector 1931.jpg
English: A mechanical-scan television projector from 1931, for displaying a television image on a screen. It was a prototype made by De Forest Radio Co. in collaboration with Jenkins Television Corp. of Passaic, New Jersey. During the 1930s before modern technology was developed, many stations broadcast low-resolution experimental television programs using mechanical scanning devices. This device consists of a spinning disk pierced with a spiral pattern of holes called a Nipkow disk in front of a bright neon bulb called a "crater lamp". Each hole moving in front of the bulb created a spot of light sweeping across the screen to make a scan line, and the scan lines collectively created the picture. The video signal from the television receiver electronics was applied to the crater bulb, so the brightness of the spot at any point was proportional to the brightness of the image at that point. A problem with earlier "spinning disk" mechanical televisions was that so little light got through the holes that the image could only be about 2 inches square. The water-cooled crater bulb in this device was bright enough to project an image 2 feet square. The image on the screen in this picture is of course artificial.
This 1931 issue of Television News magazine would have the copyright renewed in 1959. Online page scans of the Catalog of Copyright Entries, published by the US Copyright Office can be found here. [1] Search of the Renewals for Periodicals for 1958, 1959, and 1960 show no renewal entries for Television News. Therefore the magazine's copyright was not renewed and it is in the public domain.
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This work is in the public domain because it was published in the United States between 1929 and 1963, and although there may or may not have been a copyright notice, the copyright was not renewed. For further explanation, see Commons:Hirtle chart and the copyright renewal logs. Note that it may still be copyrighted in jurisdictions that do not apply the rule of the shorter term for US works (depending on the date of the author's death), such as Canada (70 years p.m.a.), Mainland China (50 years p.m.a., not Hong Kong or Macao), Germany (70 years p.m.a.), Mexico (100 years p.m.a.), Switzerland (70 years p.m.a.), and other countries with individual treaties.