in 1931. The first practical iconoscope was constructed in 1931 by Sanford Essig, when he accidentally left one silvered mica sheet in the oven too long. Upon examination with a microscope, he noticed that the silver layer had broken up into a myriad of tiny isolated silver globules. He also noticed that: the tiny dimension of the silver droplets would enhance the image resolution of the iconoscope by a quantum leap. As head of television development at Radio Corporation of America (RCA), Zworykin submitted a patent application in November 1931, and it was issued in 1935. Nevertheless, Zworykin's team was not the only engineering group working on devices that use a charge stage plate. In 1932, Tedham and McGee under the supervision of Isaac Shoenberg applied for a patent for a new device they dubbed "the emitron", a 405-line broadcasting service employing the super-emitron began at studios in Alexandra Palace in 1936, and a patent was issued in the US in 1937. Meanwhile, in 1933, Philo Farnsworth had also applied for a patent for a device that used a charge storage plate and a low-velocity electron scanning beam. A corresponding patent was issued in 1937, but Farnsworth did not know that the low-velocity scanning beam must land perpendicular to the target and he never actually built such a tube. The iconoscope was presented to the general public in a press conference in June 1933, and two detailed technical papers were published in September and October of the same year. Unlike the Farnsworth image dissector, the Zworykin iconoscope was much more sensitive, useful with an illumination on the target between 4ft-c (43lx) and 20ft-c (215lx). It was also easier to manufacture and produced a very clear image. The iconoscope was the primary camera tube used in American broadcasting from 1936 until 1946, when it was replaced by the image orthicon tube. In Britain, a team formed by engineers Lubszynski, Rodda, and MacGee developed the super-emitron (also superikonoscop in Germany and image iconoscope in the Netherlands) in 1934, this new device was between ten and fifteen times more sensitive than the original emitron and iconoscope, and it was used for a public broadcasting by the BBC, for the first time, on Armistice Day 1937. The image iconoscope was the representative of the European tradition in electronic tubes competing against the American tradition represented by the image orthicon. See also Image dissector Video