272 CATHODE RAYS AND RONTGEN RAYS. 



l)ut of the public itself. Presented to the members of the British 

 Association at their meeting- at Sheffield in 1S79, repeated in 1880 at 

 one of the soirees of the French Association, held in the Observator}^ 

 of Paris, these new and brilliant phenomena aroused immense enthu- 

 siasm. Crookes attributed them to a special condition of matter which 

 he called "radiant matter." Cathode rays are simply radiant matter 

 electrihed. The English scientist laid great stress on this fourth state 

 of matter; he believed, and others believed with him, that he had 

 opened a new path to science. 



This hope was vain, or at least deferred for a long time; it was neces- 

 sary to wait fifteen years until the discovery of X-rays (connected with 

 cathode rays, as will appear presently) attracted the attention of scien- 

 tific men. However, investigators had not abandoned this new track; 

 they had followed it with perseverance in the silence of their labora- 

 tories. Among these zealous workers must be named in the tirst rank 

 the German physicist, Hittorf , to whom must be given the honor of 

 having discovered cathode ra3^s. He had pointed out their existence 

 ten years before W. Crookes. In justice to him cathode rays might be 

 called Hittorf rays, for the same reason and on the same ground that 

 the X-rays are called Rontgen rays, and the radio-active rays Bec- 

 querel rays. 



Besides Hittorf should be named Hertz, Wiedemann, and Ebert, 

 Schmidt, Lenard, and J. J. Thomson, whose researches were grad- 

 ually developed until 1895. At this period suddenly appeared the 

 discovery by Rontgen, and investigations received a new impulse. 

 Soon after appeared in different countries the publications of Birke- 

 land, of Majorana, of W. Wien, and in France those of J. Perrin, of 

 Villard, of Deslandres. and of H. Poincare. 



These numerous researches had a double oliject. It was proposed 

 on one hand to complete the experimental study of the phenomena, 

 and on the other hand to furnish an explanation of them. The task 

 in both cases is very attractive, but the interest of the theoretical 

 question is incomparably greater. On this new field of cathode phe- 

 nomena was renewed the discussion which for more than a century 

 had agitated the physicists concerning the interpretation of luminous 

 phenomena. Cathode rays are not luminous rays, but their explana- 

 tion was equally opposed to the theory of emission and to the theory 

 of undulation, to ponderable matter and to ether. The discussion of 

 the commencement of the century with reference to light was renewed 

 in its last decade with reference to electricity. Sensational and theat- 

 rical effects succeeded each other. With Crookes in 1880 the emission 

 theory triumphed; the cathode ray certainly appeared to be a material 

 projection, a ballistic trajectory. With Lenard in 1894 (who had 

 caused the cathode rays to penetrate a vacuum without diminishing 

 the latter) the theory of an immaterial foundation, rays of ether, was 



