Current, 
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 
Rontgeu 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. 
Fig. 5. 
Phil. Mag. Feb. 1901. 
