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594 HANDBOOK OF PROJECTION FOR
be noted in this connection that the voltage for which the link is set should be tested when the rectifier is in actual operation, since the voltage of the line may decrease with the added load. It is unlikely that once this connection is properly made it ever will be necessary to change it. The outfit, without any further adjustment, is now ready for operation.
Plate 5 shows the wiring diagram for the three types of the Westinghouse rectifier. These diagrams are, we believe, of questionable value to the average projectionist. However, there are a goodly number who will be able to make use of them. The upper one is for the 30 ampere, 110-220 volt, the center one for the 40 ampere, 110-220 volt, and the lowei one for the 50 ampere, 110 volt rectifier.
OPERATION. — With fuses of proper capacity in place, close both the A. C. line switch and the projector table switch and bring the carbons together, whereupon the tube will rock, a spark appearing between the two mercury pools at each tilt until the arc starts, when the whole tube will light up and come to rest in a vertical position. The carbons should be instantly separated until the greatest amount of light is obtained on the screen.
Where the size of the theatre and equipment only justifies the purchase of a single rectifier, the problem of blending one reel into the next has been solved as described below: The only extra equipment necessary is a compensator or economy coil such is is usually found in a theatre using alternating current, and a four-pole, double throw switch.
The wiring is shown in Fig. 195a and requires no elaborate explanation. By means of this plan the change-over may be made without any very seriously objectionable indication of the fact on the screen. The projectionist, we will say, is showing the first reel of a feature film on machine No. 1, which is fed from the rectifier, the switch being thrown to the left. About one minute before the end of the reel is reached he throws the switch to the right, starting the arc on machine No. 2 through the rectifier, while projector 1 is transferred to the alternating current supply of the compensator, and the reel is completed in this manner. This gives the carbons on No. 2 time to burn to their proper brilliancy on D. C, ready to begin the second reel. The process is repeated toward the end of the second reel on projector 2. The procedure may, if desired, be reversed; that is to say, starting machine No. 2 on alternating current and later changing it to direct current. However, the first