402 Conduction in Solutions and Gases, 



The rapidity of the vibrations explains the failure of all 

 attempts to refract the X-rays. For in the formula 



= !- "** 



of the Maxwell-Sellmeier theory,* n denotes the frequency, and 

 so is in this case extremely large ; whence we have 



/*' = !, 



i.e., the refractive index of all substances for the X-rays is unity. 

 In fact, the vibrations alternate too rapidly to have an effect 

 on the sluggish systems which are concerned in refraction. 

 Some years afterwards H. Haga and C. H. Wind,f having 

 measured the diffraction-patterns produced by X-rays, concluded 

 that the wave-length of the vibrations concerned was of the 



o 



order of one Angstrom unit, that is about 1/6000 of the wave- 

 length of the yellow light of sodium. 



One of the most important properties of X-rays was 

 discovered, shortly after the rays themselves had become known, 

 by J. J. Thomson,]: who announced that when they pass through 

 any substance, whether solid, liquid, or gaseous, they render it 

 conducting. This he attributed, in accordance with the ionic 

 theory of conduction, to " a kind of electrolysis, the molecule of 

 the non-conductor being split up, or nearly split up, by the 

 Kb'ntgen rays." 



The conductivity produced in gases by this means was at 

 once investigated! more closely. It was found that a gas which 

 had acquired conducting power by exposure to X-rays lost this 

 quality when forced through a plug of glass-wool; whence 

 it was inferred that the structure in virtue of which the 

 gas conducts is of so coarse a character that it is unable to 

 survive the passage through the fine pores of the plug. The 



* Cf. p. 293. 



t Proceedings of the Amsterdam Acad., March 25th, 1899 (English edition, i, 

 p. 420), and September 27th, 1902 (English edition, v, p. 247). 

 % Nature, February 27, 1896, p. 391. 

 J. J. Thomson and E. Rutherford, Phil. Mag. xlii (1896), p. 392. 



