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March, 1930] TELEVISION AND RADIOMOVIES 347
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ported, preferably, in a vertical position, each lamp being an element of the picture.
The lamps are divided, electrically, into four banks. Bach lamp is individually wired to its particular contact of the switching gear. All the lamps in each bank have a common return connection, and the lamp face is, for certain uses, covered with ground glass or the like, for soft diffusion in the finished picture.
The switching gear is a four-part device, each of the parts being connected to its particular bank of lights. Such a division permits the construction of a commutator but one-fourth as large as if it were a single commutator structure. A 3600 rpm., 1/z hp. synchronous motor is quite suitable for driving the commutator brush in city service.
In operation, the motor being started, the incoming amplified radio signals are distributed to the several lamps in succession, fully lighting some of them, lighting others to partial brilliancy, and leaving others unlighted. The result is a picture built up in lights and halftones and shadow on the face of the plate, or the glass diffusion cover.
The picture on the plate is made up of glowing lamp elements, which persist in light value for an appreciable time, say, a tenth of a second. But as the exciting impulse is applied every fifteenth of a second, the lamp is aglow for the whole time the corresponding elementary area of the scene at the transmitting station is alight.
That is, in this scheme, persistence of light is substituted for persistence of vision, and the whole of the received picture is on the plate all the time instead of only a fractional part (l/2304th) — an elementary area time of the picture.
The amount of light available is the average light of a single lamp multiplied by the number of lamps. The average light of a single lamp can be approximately the normal lumens of the lamp because it can be flashed with a very much higher voltage than if the voltage were applied continuously.
Assuming a l/2 inch diameter lamp, the multiple lamp plate would be 2 X 2 feet square, as we built it. In front of this light source a lens is mounted for projecting it onto a theater screen. As the light source is the picture itself, the only loss of light in the projection is the reduction in foot-candles which results from the magnification. And fortunately the light is the usual color, that is, white light, not the pink light characteristic of neon.