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RICHARDSON'S BLUEBOOK OF PROJECTION
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Figure 73
tion is accomplished through transformers, which are very efficient.
(11) Fig. 73 shows the mercury arc vacuum tube. A and Al, at the end of the side extensions of the tube, are metal clips that connect through air-tight seals with a lug, of graphite or some other material, inside the tube, Extensions B and C are filled with mercury which forms an electrical connection through an airtight seal with the metal clips on the outer surface of the tube.
The action is as follows: (12) All current is supplied through a main reactance consisting of a specially designed transformer from the secondary coils of which the input connects directly with the positive carbon of the arc. (13) All good rectifiers designed for motion picture work have a regulating reactance by means of which amperage at the arc may be varied, within certain limits, but in no case in excess of the capacity of the rectifier vacuum tube.
(14) We will assume the rectifier to be idle, but connected to the current supply and ready to oper?te. On closing the main switch a "shaking magnet" tilts the tube sharply sidewise, which forces lugs BC (Fig. 73) to move upward to the left so that the mercury in them is thus brought into contact, whereupon the tube is rocked back to an upright position. This new action causes the mercury to separate again, and at the instant of breaking contact an electrical spark is formed.
(15) The spark vaporizes and ionizes enough of the mercury to fill the whole tube with mercury vapor — a state in which it is an excellent conductor of current.