362 



SCIENCE 



[N. S. Vol. XXXVII. No. 949 



tap the new gases present in the experiment 

 chamber could be detected. The processes 

 by which I have hitherto got the most plen- 

 tiful supply of X3 are : 



(1) By bombarding with kathode rays 

 metals and other bodies. 



(2) By the discharge from a Wehnelt 

 kathode through a gas at a low pressure. 



(3) By an arc discharge in a gas at a 

 comparatively high pressure. 



By far the larger number of the experi- 

 ments were made by bombarding metals, 

 but I will begin by describing an experi- 

 ment with the are, as it raises the question 

 of the origin of these lines in a very direct 

 way. An are between iron wires passed 

 through hydrogen at about 3 cm. pressure 

 (in this ease all the kathode rays would 

 be absorbed quite close to the electrode) 

 for an hour or so, and the gases liberated 

 in the experimenting chamber tested; X3, 

 helium, and neon were found. The experi- 

 ment, using the same wires for terminals, 

 was repeated the next day; the three gases 

 were again found. On the next day, still 

 using the same wires, the are was passed 

 through oxygen ; the X3 line was still there, 

 though much fainter than before; the 

 helium and neon could not be detected with 

 certainty. The next day, using the same 

 terminals, the arc was again passed through 

 oxygen; not one of the lines could be de- 

 tected. This looks as if these substances 

 were produced by the arc passing through 

 hydrogen. It was found, however, that, 

 still keeping to the same terminals, on 

 pumping the oxygen carefully out and 

 filling up again with hydrogen, the arc 

 through the hydrogen now did not give 

 even a trace of these lines. On replacing 

 the old iron wires by new ones, and send- 

 ing the arc through the hydrogen, the 

 lines reappeared. This experiment seems 

 to me to point very clearly to the 

 conclusion that these gases were in the 



terminals to begin with, were removed 

 from them by the long-continued sparking, 

 and were not produced de novo by the are. 



In the experiments when the discharge 

 was produced in a tube with a Wehnelt 

 kathode, the potential difference between 

 the terminals was only 220 volts, so that the 

 kathode rays in the tube had only a frac- 

 tion of the energy they had when the dis- 

 charge was produced by an induction coil ; 

 X3 and helium appeared when the dis- 

 charge passed through this tube. I did not 

 detect any neon. 



The method which gave X3 and also the 

 other gases, in the greatest abundance, was 

 to bombard metals, or indeed almost any 

 substance, with kathode rays. The tube 

 used for this purpose had a curved kathode, 

 which focused the rays on a table on which 

 the substance to be bombarded was placed. 

 The substance, round the spot struck by the 

 rays, was generally raised to a bright red 

 heat by the bombardment; the bombard- 

 ment was as a rule continued for five or 

 six hours at a time. I have got the X3 line, 

 as a rule, accompanied at first by the 

 helium line, and somewhat less frequently 

 by the neon line, when these following sub- 

 stances (which include nearly all I have 

 tried) were bombarded : iron, nickel, oxide 

 of nickel, zinc, copper, various samples of 

 lead, platinum, two meteorites, and a speci- 

 men of black mica given me by Sir James 

 Dewar, which was remarkable for the 

 amount of neon it gave off. 



The most abundant supply of X3 came 

 from platinum, and I will describe an ex- 

 periment with this metal. A piece of pla- 

 tinum foil was bombarded on four days, 

 and the gases produced each day examined. 

 At the end of the first day's bombardment 

 it was found that the line due to X3 was 

 very strong, those due to helium and neon 

 weaker, but still quite conspicuous. The 

 gases produced the first day were well 



