Motion picture handbook; a guide for managers and operators of motion picture theatres (1910)

FOR MANAGERS AND OPERATORS' 37 to 220 instead of. 110 volts, you would have to insert more resist- ance wire or you would get more current and your resistance would heat unduly. The more resistance wire of a given size you insert in a circuit at a given pressure the less current you will get, and the less resistance the more current will go through. The higher the voltage the more resistance you must have to get a given number of amperes. The rheostat is nothing more nor less than a case carrying a certain number of feet of resist- ance wire wound into coils to save space and mounted on insula- tors. Some are so arranged that a part of the coils can be cut out or cut in by moving a lever or changing a connection. In the non-adjustable rheostats there are two binding posts, one being attached to the end of the first coil and the other to the end of the last coil, the current thus being obliged to pass through the entire length of all coils in the machine. Now, if a binding post be attached to the end of the fourth coil of a rheostat con- taining six coils and one of the wires be attached to that post instead of the one at the end of the sixth coil, two of the coils would be "cut out," thus decreasing the resistance by one-third and correspondingly increasing the resultant current. When you see a rheostat with more than two binding posts, it is that kind of an arrangement exactly. One post is always a "permanent" and one wire must always be attached to it, but you vary the amount of current according to which post you attach the other wire. The adjustable rheostats, which have a sliding lever, ■B ElkM amount to the same thing, each contact being in effect the same as a separate binding post as above described. The coils of rheostats are connected with each other, as shown in A, Fig. 16. Taking A, Fig. 16, as an example: 1 is the permanent binding