in producing Electric Conductivity in Gases. 



303 



case of discharge in vacuum tubes, show that the negative ion is 

 very small compared with the molecule, while the positive carrier 

 is of molecular magnitude. 



In Prof. Townsend's 1 work on the ionisation produced by 

 Rontgen rays at low pressures the negative ion is active in 

 producing ionisation by its collisions with molecules, while the 

 positive ion is apparently inactive. In the case of the ionisation 

 produced by the incandescent wire the positive ion is also ap- 

 parently active in producing ionisation at pressures of 1 mm. and 

 less. The experiments described above are at a pressure of § mm. ; 

 we give another curve obtained at the same pressure with the 

 wire again charged positively. The secondary ionisation is more 

 marked in this case, due to the fact that the wire is at a lower 

 temperature and consequently the velocity of the carrier greater 

 for the same E.M.F. 



Volts 



Currents 



20 



17 



80 



24 



160 



32 



240 



39 



320 



55 



360 



71 



400 



100 



This curve is plotted in Fig. 5. 











































































































































































6 

























































































































































































































































20 40 60 80 "100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400 



Volts. 

 Fig. 5. 



1 Phil. Mag. Feb. 1901. 



