Fig. 215.
Figs. 210, 211 show forms of short arc lamps, for use under low ceilings, so common in basements, etc.
Fig. 212 shows a hand-feed focussing type of arc lamp. In regular street lamps, the upper carbon only is fed by mechanism, as it burns away about twice as fast as the lower one, thus bringing the arc lower and lower. When it is desired to keep the arc at the focus of a reflector, both carbons must be fed.
Fig. 213 shows a theatre arc lamp, used to throw a strong beam of light from the balcony to the stage.
Fig. 214 shows the arc lamp used as a search-light. The reflector throws a powerful beam of light that can be seen for miles; in fact, the light is used for signalling at night. Fig. 215 shows how search-lights are used at night on war-vessels.
CHAPTER XXIII.
X-RAYS, AND HOW THE BONES OF THE HUMAN BODY ARE PHOTOGRAPHED.
