in producing Electric Conductivity in Gases. 
The curve in Fig. 3 is plotted from these numbers. 
301 
Fig. 3. 
Care is taken in the above experiments that the highest e.m.f. 
used is not in itself sufficient to produce discharge or even to 
maintain it when started. 
We have above ascribed the secondary ionisation to the 
negative ions alone because the wire probably only produces 
ionisation close to itself, in which case only negative ions would 
have moved through the body of the gas. Of course when the 
secondary ionisation has started positive ions will be travelling 
through the gas towards the wire. But to account for the above 
results it would be sufficient to assume that the negative ions by 
collisions with molecules can produce ionisation, and we know 
that in a gas at such a pressure the velocity of the negative ion is 
great, its mass being small. 
5. It is found, however, that when the wire is charged positively 
we get a similar effect. The form of the curve giving the relation 
between current and e.m.f. in this case again shows a rapid 
increase of current with e.m.f. after the e.m.f. has reached a 
certain value. 
The following numbers give the result of such an experiment, 
the wire being charged positively. 
22—3 
