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MANAGERS AND PROJECTIONISTS 579
hand projector and approaching the end of the reel. He closes the carbons on the right-hand side, which permits enough current to flow through the resistor as the contactor is still open) to warm up this side while the other side is yet running. The resistors may need some adjustment to give proper warming up current. To bring the right-hand side into full operation he now throws the lever switch to same side. This closes the contactor, shorts out the resistances, and at the same time allows the contactor on left side to open, throwing a resistance in series with this arc. The arc probably will die out, but if not, the carbons can be separated slightly. To bring in the machine on left side, the operator brings the carbons together, and when ready throws switch to left, repeating the operations as for the right side.
We would most emphatically recommend to exhibitors the purchase of the large rectifier. Modern practice is to use high amperage and project a brilliant picture. The first cost will be greater, but it is well worth the money. This holds good even for the small towns, provided sufficient current is available to supply the large rectifier.
PRACTICAL OPERATION.— You need not be afraid to perform any of the various operations we shall describe in case of necessity. Just follow the directions and use a little common sense, remembering where each part goes, or better still, attaching a labeled tag to it as you remove it. There is no mystery about these things. All too often the projectionist hesitates to attempt the making of repairs through fear of being unable to get the thing back into shape. The rectifier is strongly made; its parts are very simple. We repeat: Follow the instructions here given, supplementing them by ordinary common sense, and you will not be likely to have any trouble.
Current-limiting resistance 3, Fig. 188, consists of a strip of resistance metal, wound in spiral form, covered with insulating material and supplied with contacts at either end. Resistances 1 and 9, Fig. 188, are of wire wound on asbestos, the whole dipped in an insulating material.
The purpose of current-limiting resistance 3, Fig. 188, is