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304 MOTION PICTURE HANDBOOK
The Arc Controller operates as follows: In P. 1, A is a small motor which drives the mechanism of controller B, illustrated in P. 3. Controller B, P. 1, is connected to the arc lamp by means of rod 2, P. 1 and 2, this rod being driven by gear 44, P. 3. By tracing through the connection you will see that motor A is thus positively and directly connected to rod 1, P. 2, which is commonly known as the "feed handle" of the arc lamp— the handle by means of which the carbons are fed together. Motor A, P. 1, is connected to the line by means of wires contained in cable 9, P. 1, the other end of which is seen at 7, P. 1, where it joins the fuse box. The motor is not connected directly to the supply line, but to the projection machine table switch contacts, through cables 8, P. 1, which are controlled by switch 5, P. 1. It will thus be seen that motor A does not receive the full line voltage, but only the arc voltage, which varies with the length of the arc. Now, even the novice will understand that the speed of motor A will depend upon the voltage of the current with which it is supplied, hence, any rise in arc voltage, no matter how small, will increase the motor's speed.
Referring to P. 2, knurled knob 12 passes through fibre disc 9, through the end of brass lever 16, and impinges on the surface of fibre disc 8.
Brass lever 16 is hinged to a steel collar, which passes over and is attached to feed rod 1, P. 2. Now, when knurled knob 12 is backed off (unscrewed somewhat), it has the effect of unlocking fibre disc 8 and driving gear 4, from fibre disc 9 and feed rod 1. In other words, when knob 12 is loosened, or backed off, the lamp becomes a plain handfed lamp, of which fibre disc wheel 9 is the feeding knob or wheel, and the motor is allowed to drive gear 4 and fibre disc 8, without moving rod 1, P. 2. Conversely, when knurled knob 12 is screwed in the whole thing is locked together, and the motor then drives lamp feed rod 1, P. 2, direct, by means of gear 6 acting on gear 4, thus feeding the carbons of the lamp together. To make matters still more clear, gear 4 and fibre disc 8 merely use rod 1 as an axle. They are entirely independent of disc 9 and rod 1, except when locked to them by knurled knob 12. When not so locked, gear 4 and disc 8 can rotate without in any way affecting disc 9 and rod 1. The operation of the device is as follows: When the operator is ready to strike his arc, he closes switch 5, P. 1, which starts motor A running, but it is only driving fibre disc 8 and gear 4, P. 2. The operator now strikes his arc by means