282 CATHODE RAYS AND KONTGEN RAYS. 



cathode ray either in a .simple or transformed condition. G. Le Bon 

 deserves the credit of having- lirst perceived the universality of this 

 order of phenomena. Although he, indeed, made use of the inappro- 

 priate term " black light," nevertheless he recognized the general 

 character and the principal properties of this creation. Above all, 

 he assigned to the phenomenon its true place, transferring it from the 

 workroom of the physicist to the grand laboratory of nature. P. de 

 Heen, the well-known professor of the University of Liege, adopted 

 a similar conception. He considers that nearly all the centers of dis- 

 turbance of the ether generate emanations similar to those which take 

 place in a Crookes tube. We shall have occasion to return to this in 

 connection with the radio-activity of matter. 



IV. 



The enthusiasm and admiration which the discovery by Rontgen 

 aroused at the close of the year 1895 is well remembered. The learned 

 phvsicist of Wiirzburg exhibited photographic silhouettes obtained 

 through opaque bodies, sheets of pasteboard, leaves of paper, thick 

 books, dictionaries, and wooden boards several inches in thickness. 

 He furnished the means of receiving on a screen the fluorescent 

 shadows of bodies concealed by wrappings, or inclosed in boxes, that 

 is to say, made it possible to see indirectlv through these obstacles. 



Very soon useful applications added to the interest of mere curiosity 

 which was manifested at the start. Radiography was applied to the 

 detection of the sophistication of certain products, to determining the 

 contents of a box without opening it, and to similar uses. But by far 

 the most important of these applications was that made to medicine 

 and surger3^ Everj'^one has seen these radiographs publicly exhibited. 

 They portray the malformations, the injuries of the skeleton, the 

 alterations of bones, the presence in the tissues of foreign bodies, 

 such as shot, needles, fragments of metal and the like, and in certain 

 cases they disclose the existence of lesions in the viscera of divers 

 kinds. When perfected, they will realize the dream and the aim of 

 normal and pathologic anatomy, w^hich is to show the body sound or 

 diseased as if it was transparent throughout. It is useless to dwell 

 further on these particulars; their history is developed right under 

 our eyes and the daily press details its progress from day to day. 



Rontgen ra^^s derive their origin from cathode rays. Crookes's tube, 

 the generator of cathode rays, was the means employed by the Ger- 

 man physicist, and b}'^ all investigators who have followed him. But 

 in this apparatus the only part useful for producing the effects which 

 we have seen is the fluorescent spot situated opposite to the cathode 

 from which it receives the emission. 



From that point the new ra3^s are projected in all directions and not 

 merel}' in the original line. All substances which arrest the cathode 



