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617 HANDBOOK OF PROJECTION FOR
should last about 500 hours, or in a house running 10 hours a day for about two months.
About twice a year the oil well should be drained. After draining fill the oil well with kerosene and let the controller run for a short time, after which drain the kerosene out and re-fill the well with fresh oil.
CAUTION. — You are cautioned against using Three-in-One, and other very thin much advertised oils, as they are totally unfit for the lubrication of a device of this kind.
The manufacturers recommend any good grade of dynamo oil, which can be obtained from your supply dealer, or from any reliable oil dealer. The oil sold by projector manufacturers for use on their projectors will serve very well.
OPERATION. — The controller will maintain the length of arc for which it is adjusted, and the length of arc it will maintain may be altered by turning adjustment dial 20, Plate I, in the direction as indicated to maintain a longer or shorter arc.
The voltage of your supply lines may change during the day, and repeat these changes day after day. Arc controller adjusting dial has its face laid off in numbered divisions, and there is a pointer, so that by making a note, or by taking a record of its operation as the dial is set at different figures, the controller can be re-set at those times when the current changes take place, without the necessity of making the daily experiment of adjusting a thumb screw or nut so as to maintain the desired arc condition. If the projection room is equipped with a reliable voltmeter it only requires a little observation to know exactly where to shift the speed controller dial to obtain the desired results from any given voltage.
CARE. — Examine the oil cups of the motor once a week and keep them filled with oil; also examine the commutator of the motor occasionally. In this connection see general instruction No. 7, Page 502, on care of the commutator. Should everything go wrong with the interior gearing of the control (very unlikely, though all things are possible) it will be necessary to return the entire mechanism to the factory for adjustment. It is not advisable that the projectionist himself attempt to repair the control mechanism. The explanation of the mechanism is not given with the idea of enabling him to repair it, but because we believe any man can work more intelligently with a thing if he under