Rays of Positive Electricity. 573 



tube, or whatever the nature o£ the electrode, the deflected 

 phosphorescence splits up into two patches. For one of these 

 patches the maximum value o£ e/m is about 10 4 , the value for 

 the hydrogen atom : while the value for the other patch is 



Fig. 10. Fig. 11. Fig. 12. 



oo 

 Hydrogen. Helium. Air. 



about 5 X 10 3 , the value for a particles or the hydrogen 

 molecule. Examples of the appearance of this phosphor- 

 escence are given in figs. 10, 11, 12 : in fig. 12 the magnetic 

 force was reversed. 



The differences in the appearance are due to differences in 

 the pressure rather than to differences in the gas : for at 

 slightly higher pressures than that corresponding to fig. 12, 

 the appearance shown in figs. 10 and 11 can be obtained in 

 air. In all these cases the more deflected patch corresponds 

 to a value of about 10 4 for e/m, while ejm for the less deflected 

 patch is about 5 x 10 3 . 



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

 helium tube of rays for which e/m=2*5xl0 3 , which were 

 found in helium tubes at higher pressures ; at intermediate 

 pressures there are three distinct patches in helium, for 

 the first of which e/m — 10 4 , for the second elm = 5 x 10 3 , 

 and for the third <?/m = 2'5xl0 3 approximately. Helium 

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

 for which e/m=10 4 /M, 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 probable 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 

 investigating with this object the positive rays produced when 

 the perforated cathode is, as in Wehnelt's method, coated with 

 lime, when a potential difference of 100 volts or less is able to 

 produce positive rays. The interest of the experiments at very 

 low pressures lies in the fact that in this case the rays are the 

 same whatever gas may be used to fill the tube ; the charac- 

 teristic rays of the gas disappear, and we get the same kind 

 of carriers for all substances. 



I would especially call attention to the simplicity of the 

 effects produced at these low pressures : only two patches of 



