. Motion picture electricity. f cast-iron in series with the electriccircuit. Where the rheostat is not subjected to excessivevibration or jar, this form of construction is very desir-able and satisfactory. The grid type resistance is nowalso used for the control of projector arc lamps, and issometimes preferred to the wire rheostat because it willstand a heavier or greater overload, and is of very solidconstruction. The grid type rheostat should be examinedat frequent intervals in order to make sure that the boltsor clamps, which connect the resistance plates together,have not become loosened
. Motion picture electricity. f cast-iron in series with the electriccircuit. Where the rheostat is not subjected to excessivevibration or jar, this form of construction is very desir-able and satisfactory. The grid type resistance is nowalso used for the control of projector arc lamps, and issometimes preferred to the wire rheostat because it willstand a heavier or greater overload, and is of very solidconstruction. The grid type rheostat should be examinedat frequent intervals in order to make sure that the boltsor clamps, which connect the resistance plates together,have not become loosened—due to frequent expansionsand contraction. MOTION PICTURE ELECTRICITY 147 The rheostats so far mentioned, are of the non-adjust-able type. Under certain conditions it is necessary to usean adjustable rheostat, in which case, a switch arm, mak-ing contact with a number of buttons connected to differ-ent sections of the rheostat has to be used. Fig. 84 illus-trates an adjustable rheostat in diagrammatic form. RESISTANCE UNIT. Fig. 84 Adjustable Type.—Fig. 84 illustrates the principleon which an adjustable rheostat works. By referring tothe diagram, it will be seen that the entire resistance unit,which may be of any type desired, is stretched out ormounted in suitable manner. The beginning end may beattached to one line wire, the other end to a contact but-ton or contact plate, which forms the last step of an ad-justable or dial switch. Several additional buttons maybe provided, each one being connected with some inter-mediate point on the resistance unit. The distance be-tween these points determines the difference in voltagedrop between each contact button on the dial switchwhich, of course, increases the flow of amperes throughthe rheostat as the dial switch is swung to the left, cuttingout sections of the resistance unit in series with the lead from the arc lamp is connected to the lever ofthe dial switch, and the other arc lamp lead, not illustrated,is connected
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Keywords: ., bo, bookcentury1900, bookdecade1910, bookidmotionpictureele00hall
