375 UNSUSPECTED RADIATIONS. 



Hungarian professor, Lenard. began to .study them, in the 3'ears 1893- 

 1895. It is evident that the g-]a.ss tu))e may be given any shape 

 that is found convenient for .some special purpose, and that the degree 

 of exhaustion of air (or of an^' other gas with which the Ae.ssel wa.s 

 tilled before exhau.stion). the forms and the disposition of th<> two 

 poles, as also all othei- details of construction, may be varied at will, 

 according to the experiments which are intended to ])o made. Now, 

 if such a tube ))e j)laced inside a l>lack cardl)()ard nnitf which iiiteice])(s 

 its light, and if it l)e l)rought into a dark room near to a .scivmmi painted 

 with some phosphore.scent sub.stance. this substance begins to glow, 

 although no visible light is falling 111)011 it. If a Avire l)e placed 

 between tlie tul>e and the screen, its shadow appears on the screen, and 

 if the hand be placed instead of the wire, darkshadowsof the bones, ]>ut 

 ahnost none of the flesh, art^ })rojected. A thick 1)()ok gives, however, 

 no sliadow at all; it is transpjirent for these rays. Some* radiations, 

 proceeding along straight lines, nuist consequently issue from th(> tul)e 

 and ])ass through the cardboard nmrt'. Like light, they make the 

 phosphorescent screen glow, move in straight lines (as they give 

 .shadows), and decompose the .salts of the photographic rilm: but they 

 are invisibh' and pass through such luxlies as are opa<[ue for ordinary 

 light. These are the X or Rontgen rays. 



Various secondary rays originate from them. ]i the Rontgen rays 

 meet a metallic mirror, the}' ar(^ not reflected ))y it, lait simjily 

 dift'used - that is, thrown irregularly in all directions; and. although 

 they do not pa.ss through metals as a i-ule. the}' may be made strong 

 and penetrating enough to pass through thin metallic plates. But in 

 both ca.ses they will acijuire some new properties which Avill depend 

 upon the metal which has ditfused them or through which the}- have 

 passed. Some new radiations wmII be added to them, and these radia- 

 tions were named secondary raA's, or S rays, by M. Sagnac. avIio discov- 

 ered them. On the other hand, if kathode rays have been passed 

 through a perforated metallic plate, they also get altered, and in this 

 case they will sometimes be named Goldstein rays. And, Anally, there 

 is a ver}" wide set of extremely interesting (also invisible) radiations 

 emitted by phosphorescent substances. The}' were discovered by H. 

 Becquerel, and are named now Becquerel rays or uranium rays. More 

 will be said of them presently. 



This is, then, the woi-ld of radiations the very existence of which 

 was mostly unsuspected five years ago, and which have to be ex- 

 plained — the difficulty being in that they link together the Hertzian 

 waves which are now used for wireless telegraphy, the visible light, 

 the invisible radiations in the ultra-red and the ultra-violet parts of 

 the spectrum, to so-called '" actinic " glow of various substances placed 

 in the violet portion of the spectrum, and many other phenomena. 

 Light, electricity, magnetism, and the molecular movements of gases, 

 liouids, and solids — all these formerl}- separated chapters of physics 



