X rays : an introduction to the study of Röntgen rays / by G.W.C. Kaye.

  • Kaye, G. W. C. (George William Clarkson), 1880-1941.
Date:
1914
Catalogue details

Licence: Public Domain Mark

Credit: X rays : an introduction to the study of Röntgen rays / by G.W.C. Kaye. Source: Wellcome Collection.

    39/280 (page 15)
    for the cathode ray ; for v = X/H, and e/m = X/(pH2). It was in this way that J. J. Thomson first arrived at the nature of the cathode rays (p. 8). (See Fig. 8.) Braun Tube. A practical application, due to Braun, of the bending of cathode rays under magnetic or electric force has come into use in electrical engineering for the purpose of studying the wave-form of rapidly changing alternating currents. In the Braun tube, a narrow pencil of cathode rays is received on a fluorescent screen, and is subjected en route to both a magnetic and an electric field. The two fields are at right angles, and are both actuated by the alternating current. The cathode rays, having practically no inertia, are able to follow the most rapid vagaries of the fields, and so trace out on the screen a pattern, from which the wave-form can be deduced. Magnetic Spectrum of Cathode Rays. Each interruption of the primary current in an induction coil produces a small train of strongly-damped oscillations in the discharge (p. 59). Thus the potential on the tube is intermittent, and the result is a stream of cathode rays with a variety of speeds, each peaklet on the oscillatory potential curve producing a group of uniformly fast cathode rays, of which the speed diminishes with successive oscilla¬ tions. Accordingly, if the cathode rays are subjected to a mag¬ netic field, the different groups are differently deviated—the greater the speed, the less the magnetic deviation. Thus a slit of cathode rays, when allowed to fall on a fluorescent plate, produces in a magnetic field a number of bright lines or bands which go to make up a “ magnetic spectrum ”— an appearance first noticed by Birkeland (C.R.) in 1896. The brightness of each band is a measure of the number of rays moving with the same speed : the displacement of the band from the undeflected position is inversely proportional to the velocity, and directly proportional to e/m and the strength of the field.