[Electric engineering.] . Fig. 57. the ordinary styles of arc lamp are not suitable, becausesuch lamps are not of the focusing type. For projectionwork, it is necessary to keep the arc in a fixed position; insome cases this is accomplished by hand feeding, while inothers the feeding is automatic. In Fig. 57, {a) showsan automatic focusing lamp and (I?) a hand-feed focusing /. III.—29 90 ELECTRIC LIGHTING. § 18 lamp. The lamp (a) is usually mounted on a stand andprovided with accessories to suit it to whatever kind ofwork it is used for. It is designed for 20 amperes andis operated on direct-cu
[Electric engineering.] . Fig. 57. the ordinary styles of arc lamp are not suitable, becausesuch lamps are not of the focusing type. For projectionwork, it is necessary to keep the arc in a fixed position; insome cases this is accomplished by hand feeding, while inothers the feeding is automatic. In Fig. 57, {a) showsan automatic focusing lamp and (I?) a hand-feed focusing /. III.—29 90 ELECTRIC LIGHTING. § 18 lamp. The lamp (a) is usually mounted on a stand andprovided with accessories to suit it to whatever kind ofwork it is used for. It is designed for 20 amperes andis operated on direct-current circuits of 75 to 125 hand-feed lamp shown at (b) also operates normally at20 amperes, but by using larger carbons, currents up to50 amperes may be employed. The hand-feed lamp mayalso be operated with alternating current, but the alter-nating current is not very satisfactory for use in projectionwork. The hum caused by the arc is often very annoying,and, moreover, the arc is continually shifting around
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