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

The Source of the Light. It is imperative that the motion picture operator should thoroughly understand the electric current and the rules which govern its action under any given circumstance likely to be met with in the line of his work. It is not enough that he know that a few certain things will produce certain results. He should know WHY these results are obtained; in other words, he should understand the force he is handling, and understand it thoroughly if he expects to obtain the best possible results. Moreover, while the one who has not an elementary knowledge of electricity may learn to handle the current with very good results under one certain set of conditions, he is likely to be practically helpless under other and different conditions, particularly should he be called to "go on the road," thus being obliged to "hitch up" on different systems of wiring, different lighting systems, and meet with a wide range of voltage. Also the man who, while able to get fair, or even good, results under conditions with which he is familiar, does not thoroughly understand the force with which he is working is not in position to improve re- sults already obtained through the medium of intelligent experiment. He must perforce depend almost wholly on what someone else tells him without being able to form an opinion as to whether what he has heard is likely to be cor- rect or incorrect. Good light is of prime importance in picture projection, and the one who is able to produce and maintain a clear, silvery-white spot has mastered three-fourths of the diffi- culties between him and the goal of good operating. THE CURRENT—DIRECT AND ALTERNATING. The difference between direct and alternating current is simple, once it is understood. Direct current flows constantly in one direction, so that one carbon of the lamp is always positive and the other