CHAPTER IL
THE MAGIC LANTERN WITH AN ALTERNATING
CURRENT ARC LAMP AND ITS USE
§ 100. Apparatus and Material for Chapter H:
Suitable room with screen (Ch. XII) ; Magic lantern with lan¬
tern table (§ 102) ; Arc lamp for alternating current with suitable
carbons (§ 108); Alternating current supply; Rheostat, choke-coil
or other balancing device (§ 105-106); Ammeter for alternating
current (§ 111) ; Incandescent lamp, flash-light, gloves with asbes¬
tos patches, testing lamp, fuses, extra condenser lenses, screw
driver, pliers, opera-glasses, lantern slides as in Ch. I (§ 1).
§ 101. For the historical development of the alternating cur¬
rent arc lamp see the Appendix; and for the character and advan¬
tages and disadvantages of alternating current see § 652-653, and
modem works on the subject.
The same books of reference given in § 2, Ch. I, are available for
this chapter.
Comparison of Alternating and Direct Electric
Currents and Lanterns
§ 102. A magic lantern for alternating current may be pre¬
cisely like one for direct current, the only essential difference being
that the arc lamp must be of the hand-feed type and the mechanism
for feeding the carbons gives equal movement to the upper and to
the lower one, both carbons being of the same size.
One would never use an alternating current with the magic
lantern if direct current were available. It frequently happens,
however, that the lighting system of a place is of the alternating
current type, and no direct current is available. In such a case
one must make the best of it, or use a motor-generator set or a
rectifier (see § 682-683).
The objections to an alternating current for the arc lamp in
projection are: (1) The lamp is noisy; (2) It requires about two
and one-half times as much current for the same effective light.
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