X-Rays, Apparatus and Methods Page 3

To excite the Tesla coil, we may use either an interrupted direct current or an ordinary alternating circuit joined directly to the primary of the first coil. But the final result is, in either case, an alternating, high-potential, high-frequency current. In the tube, therefore, we also have an alternating discharge.

The Induction Coil. — We illustrate, in Fig. 2, the scheme of connections, etc., of the simple induction coil. The primary must be excited by an interrupted direct current, which may be secured from primary batteries, storage batteries, or a commercial circuit as may be determined by convenience or inclination. The secondary is joined directly to the tube terminals. The usual means employed for securing the interruptions is some form of vibrating spring device, automatically operated by the core of the coil itself, the magnetic pull of the core attracting a mass of iron which, by its motion, separates two contact points, thus allowing a properly placed spring to draw it back, closing the circuit again, when the cycle is repeated. Such a device is employed in most forms of virbating electric bells and is indicated in the diagram. Around the break is placed a condenser. At break, this condenser charges (thus preventing the extra induced current due to the large self-induction of