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MANAGERS AND PROJECTIONISTS
901
place arm D on contact 1. You will observe that the current will flow through wire E, through lamp 1, and thence back through the other wire, and that no other lamp will be affected. If we move the arm to contact 6, then only lamp 6 will be lighted. Such a board is simple, entirely practical, and, as we have said, is the best plan we have seen. It is also quite possible to substitute single pole, single throw knife switches for contacts 1, 2, 3, 4, etc., connecting wire B to one side of all these switches. The switches or the contacts should be located at the most convenient point, either on the stage, by the side of the musician or in the projection room. The transparency can be so made that only the figure or name actually illuminated will be visible. This may be done by covering the whole front of the board with grouncj glass, on which are the figures, or names blocked out in
Figure 374.
black, as shown in the illustration, each lamp, however, being contained in a light tight compartment of its own. Different colors may be obtained, if desired, by covering the various characters with light shades of gelatine or using colored globes.
In practice, we would by all means advise a double-pole single throw switch at AB, rather than the single-pole knife switch at C. In fact switch C would be a violation of Underwriters' rules.
In Fig. 374 a battery of 36 lamps is arranged in the form of a square, with 6 lamps either way. One wire (wire A, in the sketch) is connected directly to one side of each lamp. A board is now made, containing 36 sockets, arranged in a square, with 6 sockets each way, the same as are the lamps.