1907.] 



on Rays of Positive Electricity. 



589 



The results obtained at these low pressures are very interesting. 

 Whatever kind of gas may be used to fill the tube, or whatever the 

 natui'e of the electrode, the deflected phosphorescence spHts up into 



two patches. 



For one of these patches the maximum value of — is 



m 



about 10*, the value for the hydrogen atom ; while the value for the 

 other patch is about 5 x 10^, the value for a particles or the hydrogen 



Hydrogen 



Helium 



Fig. 10. 



Fig. 11. 



Air 



oo 



Fig. 12. 



molecule. Examples of the appearance of this phosphorescence are 

 given in Figs. 10, 11 and 12. In Fig. 12 the magnetic force was 

 reversed. 



The differences in the appearance are due to differences in the 

 pressure rather than to dift'erences in the gas ; for at slightly higher 

 pressures than that coiTCsponding to Fig. 12, the appearance shown in 

 Figs. 10 and 11 can be obtained in air. In aU these cases the more 



deflected patch corresponds to a value of about 10-* for — while ~ 



m m 



for the less deflected patch is about 5 x 10^. 



It will be noticed that in Fig. 11 there is no trace in the helium 



tube of rays for which — =2*5 x 10^, which were found in helium 

 m 



tubes at higher pressures ; at intermediate pressures there are three 



distinct patches of helium, for the first of which — = 10'^, for the 



m 



•5 X 10^ approximately. 



e ~ p 



second — = 5 x 10^, and for the third — 



m m 



Hehum is a case where there are characteristic rays — i.e. rays for 

 which — = — -, where M is the atomic weight of the gas, when the 



discharge potential is comparatively small, and not when, as at very low 

 pressures, the discharge potential is very large. I think it very pro- 

 bable that, if we could produce the positive rays with much smaller 

 potential differences than those used in these experiments, we might 

 get the characteristic rays for other gases. I am at present investi- 

 gating with this object the positive rays produced when the perforated 

 cathode is, as in Wehnelt's method, coated with lime, when a potential 



