Page:A history of the theories of aether and electricity. Whittacker E.T. (1910).pdf/421

 that radiation, capable of affecting sensitive plates and of causing fluorescence in certain substances, is emitted by tubes in which the electric discharge is passing; and that the radiation proceeds from the place where the cathode rays strike the glass walls of the tube. The X-rays, as they were called by their discoverer, are propagated in straight lines, and can neither be refracted by any of the substances which refract light, nor deviated from their course by a magnetic field; they are moreover able to pass with little absorption through many substances which are opaque to ordinary and ultra-violet light—a property of which considerable use has been made in surgery.

The nature of the new radiation was the subject of much speculation. Its discoverer suggested that it might prove to represent the long-sought-for longitudinal vibrations of the aether; while other writers advocated the rival claims of aethereal vortices, infra-red light, and "sifted" cathode rays. The hypothesis which subsequently obtained general acceptance was first propounded by Schuster in the month following the publication of Röntgen's researches. It is, that the X-rays are transverse vibrations of the aether, of exceedingly small wavelength. A suggestion which was put forward later in the year by E. Wiechert and Sir George Stokes, to the effect that the rays are pulses generated in the aether when the glass of the discharge tube is bombarded by the cathode particles, is not really distinct from Schuster's hypothesis; for ordinary white light likewise consists of pulses, as Gouy had shown, and the essential feature which distinguishes the Röntgen pulses is that the harmonic vibrations into which they can be resolved by Fourier's analysis are of very short period.