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Nov., 1934] SXROBOSCOPIC-LIGHT PICTURES 291 Fig. 2 is the wiring diagram of the stroboscope. A polyphase rectifier unit supplies about 10 kw. of power at 1000 volts to charge the condensers. In series with each condenser is a resistor large enough to limit the current from the source of power at the instant of discharge, but still small enough to allow the condenser to charge for the succeeding flash. The power required to operate a camera of the stroboscopic type depends upon the subject being photographed The size and color of the subject are the primary factors that determine the amount of light necessary for each exposure. The power is, of course, propor- tional to the number of exposures per second. The number of ex- posures required depends upon the degree to which it is desired to slow down the motion. To illuminate an area of a few square feet FIG. 2. Wiring diagram of stroboscopic lighting source for taking high- speed pictures. with subjects of fairly light color requires a bank of at least four 12- inch tubes with condensers of 2 microfarads' capacity connected to each, charged to 1000 volts. At 1200 flashes per second nearly 10 kilowatts of power are required to operate this bank of lamps. The circuit diagram of the pulse amplifier is shown in the lower part of Fig. 2. The operation is as follows: The commutator on the camera has narrow segments that close the circuit so marked at the right of the diagram. The grid of the thyratron, an FG-67 tube, is thus made positive for a few microseconds. Energy stored in the condenser C then discharges through the primary of the step-up transformer T. The high potential induced in the secondary of T is led to external starting bands or grids on the mercury-lamp tubes