CATHODE RAYS AND RONTGEN RAYS. 285 



by M. Sagnac. In the same conditions the secondary rays originate 

 tertiary, and so on, in such a way that there exists at the surface of 

 metals struck by Rontgen rays a whole system of radiations, which 

 form a complicated envelope, conducting- electricity and photogenically 

 active. 



It is easy to see that the fact that Rontgen rays are not diffused 

 entails other differences between them and light, and these are impor- 

 tant. The rays are not diffused, because they do not submit to reflec- 

 tion or to refraction. Their reflection has been thought possible at 

 times, because they were mingled with other elements — for example, 

 ultraviolet nvys. M. Grouy has shown with wonderful accuracy that 

 in reality they do not suffer the slightest refraction. They do not 

 exhibit the phenomena of diffraction or of polarization. 



Reflection, refraction, diffraction, polarization, and interference are 

 universal characters of ethereal vibrations. They belong to all the 

 rays of the spectrum, from the slowest to the most rapid. They are 

 common to hertzian vibrations, to the infra-red or calorific, to the vis- 

 ible vibrations, and finally to the ultraviolet or chemical vibrations. 

 As to interference, the opinion of the scientific world is divided on 

 the point whether Rontgen rays allow this or not. It appears, how- 

 ever, that the phenomena observed by M. Jaumann, by means of two 

 parallel electrodes connected with the negative pole of the coil by wires 

 of equal length, should be regarded as illustrative of interference. 



Is it possible after this to compare Rontgen rays with luminous rays, 

 or even to attribute to them any form of ethereal undulations? This 

 is the general tendency. Wiedemann and Lenard regard them as 

 forming a new round in the spectrum ladder beyond the ultraviolet. 

 Rontgen and Jaumann consider them as the products of longitudinal 

 vibrations of ether. 



Rontgen rays discharge electrified bodies placed in their neighbor- 

 hood. The rudiments of this electrical property are exhibited in the 

 spectrum; ultraviolet rays destroy the negative charges of bodies with 

 which they are brought into contact. This shows a greater or less 

 analogy between the two kinds of radiations. It is only, however, 

 under certain conditions that the Rontgen rays may be referred to 

 small undulations, having the character of undulations of light, and 

 thus continuing the spectrum beyond the violet. It would be neces- 

 sary to conceive of these undulations as exceedingly short, or what is 

 the same thing, that the vibrations are very rapid, which is a means 

 of rendering the interference less appreciable, and still more so the 

 diffraction. Besides, the velocity of the propagation can not be dif- 

 ferent in the air and in the other bodies. A priori, this supposition 

 is not improbable — it explains the absence of refraction and renders 

 possible that of reflection. On the other hand, since there is no other 

 way of realizing polarization except through recourse to simple or 



