Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . nd be interposed between such a screen andthe tube, the shadow of the bones can be plainly seen on thescreen, the bones intercepting some of the Roentgen rays, andthus causing the shadow. Wood readily allows the rays topass through it, so that if an inch board be held between thehand and the screen, the shadow is still visible. In thefluoroscope such a fluorescing screen forms the bottom of abox, the opaque sides of which slant inward toward the topwhere an opening is left for observ
Lessons in practical electricity; principles, experiments, and arithmetical problems, an elementary text-book . nd be interposed between such a screen andthe tube, the shadow of the bones can be plainly seen on thescreen, the bones intercepting some of the Roentgen rays, andthus causing the shadow. Wood readily allows the rays topass through it, so that if an inch board be held between thehand and the screen, the shadow is still visible. In thefluoroscope such a fluorescing screen forms the bottom of abox, the opaque sides of which slant inward toward the topwhere an opening is left for observation, Fig. 294. The day-light is thus ex-cluded and theshadows of objectsinterposed betweenthe fluoroscope andthe tube are plainlyvisible upon theenclosed fluoresc-ing screen. illustrates themanner of viewingthe bones of thehand. The tube isnot generally en-closed, however, asshown in the cut. 310. The Tele-phone.—An in-strument designed for the transmission of articulate speechby an electric current is called a telephone. A section andperspective view of a Bell telephone is shown in Fig. 295. A. Fig. 295.—Transmission of Speech by the Bell transmitter and receiver are exactly alike. THE INDUCTION COIL. 327 small spool of fine wire encircles one end of a bar magnetmounted in a rubber tube, the ends of this coil being carriedto the far end of the tube and connected to the binding posts,PP. A thin circular iron diaphragm is located very close tothe pole of the magnet, at the coil end, and is supported by aconical-shaped piece of rubber, attached to the tube, whichserves either as a mouthpiece or ear trumpet. When twosuch instruments are connected by wires, as in Fig. 295,either one may be used as a transmitter and the other as areceiver. No battery is required. When a person talks to the disc of the transmitter, A, thesound waves striking it cause it to vibrate. The disc is mag-netised by induction from the magnets pole, and as it vibratesthe number of
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