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 



