Some Experiments with Cathode Rays. 



95 



lasted for some seconds, becoming gradually fainter as the vacuum 

 fell. By re-exhausting the tube with, the pump, however, the 

 original appearance shown in fig. 23, as also the appearance 

 shown in fig, 2i could be produced as often as desired. 

 Apparently the particles of carbon become heated to incandescence 

 either by the action of the cathode rays upon them while they are 

 flying through space, or by their friction in passing through the 

 residual gas, and possibly by their mutual collisions, for in the 

 stage shown in fig. 24, when the cathodes themselves show no 

 luminescence, the flying particles appear to be most intensely 

 luminescent wdien in the centre of the tube. It may be mentioned 

 that after this experiment had been repeated several times, the glass 

 of the tube became perceptibly blackened, which, taken with the fact 

 that a similar tube with cathodes of aluminium showed no stream of 

 bright particles, goes to show that the particles consist of carbon 

 torn off the surfaces of the cathodes. 



The Production of X-Bays. 



The tnbe, fig. 22, with carbon cathodes was found to produce 

 feeble X-rays, which, when observed with a fluorescent screen, 

 appeared to come either from the fluorescent glass of the bulb or 

 from the travelling; particles of carbon. 



In order to ascertain whether it is necessary that the cathode rays 

 should fall on solid matter in order to produce X-rays, another tube 

 was constructed, similar in all respects to that shown in fig. 22, with 

 the exception that the two cathodes were made of aluminium. 



It was thought that with this tube the opposing streams of cathode 

 rays might possibly produce X-rays at the point where they met. 

 This does not, however, appear to be the case, as though this tube, 

 when exhausted to so high an extent that the alternative spark in 

 air leapt fully 8 inches, gave X-rays in considerable quantity, these 

 rays appeared to come entirely from portions of the glass of the tube 

 that were covered with green fluorescence, and not at any rate 

 appreciably from the central point between the two cathodes, where 

 the opposing streams of cathode rays would meet one another. 



It seems, therefore, that X-rays can only be produced by cathode 

 rays when these strike solid matter. 



In conclusion I wish to mention how much I owe in carrying out 

 these experiments to the assistance of Mr. J. C. M. Stanton and Mr. 

 H. Tyson Wolff, who have made and exhausted all the tubes, and to 

 whom I am also indebted for many valuable suggestions. 



VOL LXT. 



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