September 18, 1896.] 



SCIENCE. 



395 



do wing a laboratory for research, the oppor- 

 tunities for pursuing original investigations 

 in this country have been greatly increased. 

 The discovery at the end of last year by 

 Prof. Eontgen of a new kind of radiation 

 from a highly exhausted tube through 

 which an electric discharge is passing, has 

 aroused an amount of interest unprece- 

 dented in the history of physical science. 

 The effects produced inside such a tube 

 by the cathode rays, the bright phos- 

 phorescence of the glass, the shadows 

 thrown by opaque objects, the deflection of 

 the rays by a magnet, have, thanks to the 

 researches of Crookes and Goldstein, long 

 been familiar to us, but it is only recently 

 that the remarkable effects which occur out- 

 side such a tube have been discovered. In 

 1893, Lenard, using a tube provided with a 

 window made of a very thin plate of alu- 

 minium, found that a screen impregnated 

 with a solution of a phosphorescent sub- 

 stance became luminous if placed outside 

 the tube in the prolongation of the line from 

 the cathode through the aluminium window. 

 He also found that photographic plates 

 placed outside the tube in this line were af- 

 fected, and electrified bodies were dis- 

 charged ; he also obtained by these rays 

 photographs through plates of aluminium 

 or quartz. He found that the rays were 

 affected by a magnet, and regarded them 

 as the prolongations of the cathode rays. 

 This discovery was at the end of last 

 year followed by that of Eontgen who 

 found that the region round the dis- 

 charge tube is traversed by rays which 

 can affect a photographic plate after 

 passing through substances such as alu- 

 minium or cardboard, which are opaque 

 to ordinary light ; which pass from one 

 substance to another, without any re- 

 fraction, and with but little regular re- 

 flection; and which are not affected by a 

 magnet. We may, I think, for the pur- 

 poses of discussion, conveniently divide the 



rays occurring in or near a vacuum tube 

 traversed by an electric current into three 

 classes, without thereby implying that they 

 are necessarily distinctly different in physi- 

 cal character. We have (1) the cathode 

 rays inside the tube, which are deflected by 

 a magnet ; (2) the Lenard rays outside the 

 tube, which are also deflected by a magnet ; 

 and (3) the Rontgen rays, which are not, 

 as far as is known, deflected by a magnet. 

 Two"views are held as to the nature of the 

 cathode rays ; one view is, that they are 

 particles of gas carrying charges of nega- 

 tive electricity, and moving with great ve- 

 locities which they have acquired as they 

 travelled through the intense electric field 

 which exists in the neighborhood of the 

 negative electrode. The phosphorescence 

 of the glass is on this view produced by 

 the impact of these rapidly moving charged 

 particles, though whether it is produced by 

 the mechanical violence of the impact, or 

 whether it is due to an electro-magnetic 

 impulse produced by the sudden reversal of 

 the velocity of the negatively charged parti- 

 cle — whether, in fact, it is due to mechani- 

 cal or electrical causes, is an open question. 

 This view of the constitution of the cathode 

 rays explains in a simple way the deflection 

 of those rays in a magnetic field, and it has 

 lately received strong confirmation from 

 the results of an experiment made by Per- 

 rin. Perrin placed inside the exhausted 

 tube a cylindrical metal vessel with a small 

 hole in it, and connected this cylinder with 

 the leaves of a gold leaf electroscope. The 

 cathode rays could, by means of a magnet, 

 be guided so as either to pass into the cyl- 

 inder through the aperture, or turned quite 

 away from it. Perrin found that when the 

 cathode rays passed into the cylinder the 

 gold leaf of the electroscope diverged, and 

 had a negative charge, showing that the 

 bundle of cathode rays enclosed by the cyl-- 

 inder had a charge of negative electricity. 

 Crookes had many years ago exposed a disc 



