CONDUCTION THROUGH GASES 139 



are crossed as when the axes are parallel. Such 

 indications as these did not suggest an identity in 

 nature between Rontgen rays and ordinary light. 



On the other hand, the rays suffer no devia- 

 tion when acted on by a magnetic or by an electric 

 field of force, a result which indicates that they are 

 not projected particles carrying electric charges. 

 In this particular, they must be distinguished 

 carefully from their creative agency — from the 

 flight of negative particles or cathode rays which, 

 by impact on glass or metal, give rise to this new 

 type of radiation. 



In the year 1896, Sir George Stokes suggested 

 that an explanation should be sought in the hypo- 

 thesis that Rontgen rays were single pulses travel- 

 ling through the aether. Ordinary light is to be 

 represented as a series of regular waves, succeed- 

 ing each other at periodic intervals, many thousand 

 waves, almost exactly similar to each other, follow- 

 ing in order in a minute fraction of a second. 

 According to this view, Rontgen rays must be 

 regarded as single disturbances, propagated with 

 the same velocity as light, but not followed by 

 a train of waves. The thickness of the pulse, in 

 which the whole disturbance is concentrated, was 

 supposed to be considerably smaller than the 

 wave-length of any visible light. 



But this ingenious theory of single pulses had 

 to be discarded. Evidence accumulated that 

 X-rays were light, of very short wave-length, and 

 that interpretation was placed beyond doubt by 

 Laue in 191 2 and soon after by Sir William and 

 W. L. Bragg, who showed that X-rays could be 

 diffracted by crystals, as light is by a diffraction 

 grating. 



