Jrom Faraday to J. J . Thomson. 401 



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 radia- 

 tion 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 Kontgen's researches. It is, that the X-rays are 

 transverse vibrations of the aether, of exceedingly small wave- 

 length. A suggestion which was put forward later in the year 

 by E. Wiechertf and Sir George StokesJ 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 Eontgen pulses is that 

 the harmonic vibrations into which they can be resolved by 

 Fourier's analysis are of very short period. 



* Nature, January 23, 1896, p. 268. Fitz Gerald independently made the same 

 suggestion in a letter to O. J. Lodge, printed in the Electrician xxxvii, p. 372. 



t Ann. d. Phys. lix (1896), p. 321. 



I Xature, September 3, 1896, p. 427 : Proc. Canib. Phil. Soc. ix (1896), p. 215 ; 

 Mem. Manchester Lit. & Phil. Soc. xli (1896-7). 



$ Journ. de Phys. v (1886), p. 354. 



2 D 



