UNSUSPECTED RADIATIONS. 377 



electric eti'ects, and both have different degrees of penetration through 

 opaque bodies, which depend upon the source of electricit}^ and the 

 media through which they have passed. Moreover, the X-rays are cer- 

 tainly not homogeneous, and consist of a variety of radiations. 



And yet the many analogies which have been noticed between the 

 Rontgen rays and ordinary light stand in opposition to a full assimila- 

 tion of the X-rays to the kathode streams, and the opinion that, like 

 light, they are vibrations of the ether takes the upper hand.' These 

 may be vibrations of a very short wave length, perhaps a hundred 

 times shorter than the waves of green light; or they may be "longi- 

 tudinal vibrations," as Lord Kelvin had suggested at the outset;^ or, 

 as Prof. J. J. Thomson thinks, they may be a mixture of vibrations of 

 different sorts — "pulsations" of the ether, as he puts it — that is, some- 

 thing similar to what is called "a noise"' in the theory of sound. 



Already, in his second memoir, Rontgen had indicated that his rays 

 discharge an electrified body, l)oth directly when they fall upon it and 

 l)y their action upon the surrounding air, which they render a con- 

 ductor of electricit} . This was an important remark, because the 

 researches of the previous four years had firmly established that the 

 violet rays — i. e., the short waves of light — as well as the invisible 

 ultraviolet radiations, have the ver}' same effect. A link was thus 

 established between the problematic rays and common light, and some 

 of the best phvsicists (Lord Kelvin, Righi. Perrin, Guggenheimer, 

 Villari, Starke, and many others) engaged in a minute experimental 

 work in order to specify these analogies. The result was that the 

 resemblance between the X-rays and the short-waved radiations of 

 light was proved. 



A further confirmation of the same analogy was given by the dis- 

 coYGvy of the "secondary " and "tertiary " rays by the Paris professor, 

 G. Sagnac' He studied what becomes of the Rontgen rays when they 

 strike different metallic surfaces. Th(^y are not reflected by them, but 

 only diffused irregularly; however, this diffusion differs from reflec- 

 tion, not only by its irregularity, but still more by the fact that the 

 character of the "secondary" radiations (or "tertiary," if they have 

 been diffused twice) is altered. They become more like ordinary light. 



iSee Geitler's objections against such an assimilation, based upon their different 

 behavior toward electrified bodies (Annalen der Physik, Vol. LXVl, p. 65), to which 

 it may he added that the heating effect of the first radiations is very much smaller 

 than the same effect of the latter (E. Dorn), and compare these remarks with the 

 anode current, the existence of which was maintained by Crookes since 1891. Swm- 

 t(jn (Phil. Mag., 1898, XLVI, p. 387) confirmed its existence, and Riecke {Ann. der 

 Physik, XLYl, p. 954) has measured its ejiergy. 



^See Nineteenth Century, March, 1896, where the meaning of this suggestion was 

 explained. . 



«He gave an account of liis researches in Revue Generale .les Science, the .SOtU ot 

 April, 1898. 



SM 19U0 -Zl 



