382 Scientific Intelligence. 



the rays were affected by a magnet, aod regarded them as the 

 prolongations of the kathode rays. This discovery was at the 

 «nd of last year followed by that of Rontgen, who found that 

 the region round the discharge tube is traversed by rays which 

 affect a photographic plate after passing through substances such 

 as aluminium or cardboard, which are opaque to ordinary light ; 

 which pass from one substance to another, without any refrac- 

 tion, and with but little regular reflection ; and which are not 

 affected by a magnet. We may, I think, for the purposes of dis- 

 cussion, 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 physical character. We have (1) the kathode 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 

 kathode rays ; one view is, that they are particles of gas carrying 

 charges of negative electricity, and moving with great velocities 

 which they have acquired as they traveled through the intense 

 electric field which exists in the neighborhood of the negative 

 electrode. The phosphorescence of the glass is on this view pro- 

 duced by the impact of these rapidly moving charged particles, 

 though whether it is produced by the mechanical violence ot the 

 impact, or whether it is due to an electro-magnetic impulse 

 produced by the sudden reversal of the velocity of the negatively 

 charged particle — whether, in fact, it is due to mechanical or 

 electrical causes, is an open question. This view of the con- 

 stitution of the kathode 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 Perrin. 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 

 kathode rays could, by means of a magnet, be guided so as either 

 to pass into the cylinder through the aperture, or turned quite 

 away from it. Perrin found that when the kathode-rays passed 

 into the cylinder the gold leaf of the electroscope diverged, and 

 had a negative charge, showing that the bundle of kathode rays 

 enclosed by the cylinder had a charge of negative electricity. 

 Crookes had many years ago exposed a disc connected with a 

 gold-leaf electroscope to the bombardment of the kathode rays, 

 and found that the disc received a slight joost^^'ye charge ; with 

 this arrangement, however, the charged particles had to give up 

 the,ir charges to the disc if the gold leaves of the electroscope 

 were to be affected, and we know that it is extremely difficult, if 

 not impossible, to get electricity out of a charged gas merely by 

 bringing the gas in contact with a metal. Lord Kelvin's electric 

 strainers are an example of this. It is a feature of Perrin's 

 experiment that since it acts by induction, the indications of the 



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