42 



SCIENCE. 



[N. S. Vol. XII. No. 289. 



the kathode rays. Since their discovery by 

 Pliicker in 1859, and the first systematic 

 study of their properties by Hittorf and 

 Crookes, the importance of a more com- 

 plete understanding of their nature has 

 been generally recognized, and many em- 

 inent physicists have made them the sub- 

 ject of extended experimental investiga- 

 tion. In consequence, our knowledge of 

 the kathode rays has progressed during the 

 last few years with startling rapidity. To 

 make clear how great the progress has been, 

 let us consider first the condition of the 

 subject of 1890, at which time the theory 

 of vacuum tube phenomena was just begin- 

 ning to take systematic and consistent 

 form. 



Almost from the time of the first dis- 

 covery of the kathode rays, widely diflferent 

 opinions had been held regarding their 

 nature. According to one view, the ka- 

 thode rays were to be regarded as distur- 

 bances in the ether, propagated in a manner 

 somewhat analogous to that in which light 

 is transmitted. The rays were not con- 

 sidered as essential to the passage of the 

 current, but as a secondary phenomenon, 

 produced by the discharge. Hertz, for ex- 

 ample, suggested that the production of the 

 kathode rays by the discharge in a vacuum 

 tube is analogous to the production of light 

 by the ordinary arc discharge in air. This 

 view furnished a ready explanation of most 

 of the observed phenomena, such, for ex- 

 ample, as the rectilinear propagation and 

 diffuse reflection of the kathode rays, and 

 the thermal, mechanical, and luminous ef- 

 fects produced by them. The explanation 

 of the well-known deflection of the rays in 

 passing through a magnetic fleld was^ 

 however, a matter of greater difficulty. I 

 am not aware that a thoroughly satisfactory 

 explanation of this phenomenon, based 

 upon what may be called the ether theory 

 of the kathode rays, has ever been pro- 

 posed. 



The theory proposed by Crookes in 1879, 

 and which usually bears his name, differed 

 radically from that just mentioned. By 

 Crookes and his followers the kathode rays 

 were thought to consist of a stream of 

 negatively electrified particles projected at 

 high velocity from the negative electrode. 

 Such particles would naturally travel in 

 straight lines ; upon colliding with solid 

 obstacles their energj^ would be transformed 

 into that of heat, light, or visible motion ; 

 and when moving across the lines of force 

 of a magnetic field they would be deflected 

 from their straight path. The theory of 

 Crookes possessed the great advantage of 

 being concrete and definite, while, at the 

 time the theory was proposed, it was in 

 qualitative agreement with practically all 

 the observed phenomena. 



The work of later experimenters, how- 

 ever, had in many instances tended to dis- 

 credit the theorj' of Crookes. Thus, the 

 various mechanical effects produced by ka- 

 thode rays, such as the rotation of radio- 

 meter wheels and the like, were found to be 

 due largely, if not wholly, to secondary 

 causes, such as the heat developed by the 

 rays, and the varying static charges on the 

 walls of the tube. Again, if the rays con- 

 sist of negatively electrified particles, we 

 should expect a conductor placed in their 

 path to acquire a negative charge. Ex- 

 periments made to test this question were 

 contradictory, but in the majority of oases 

 it was found that the charge was positive 

 instead of negative.* Electrified particles 

 moving at right angles to an electrostatic 

 field should be deflected from their straight 

 course ; but experiments made by Hertz f 

 and others to detect such an electrostatic 

 deflection gave only negative results. Since 

 the kathode raj's are deflected in passing 

 through a magnetic field, we should expect 

 these rays, if they consist of material par- 



* Crookes, Phil. Trans., 1879. 



t Hertz, Wied. Ann., 19, p. 782, 1883. 



