266 Prof. J. J. Thomson on the Theory of Conduction of 



sented by fig. 3, where A is the positive and B the negative 

 plate, and the velocity of the negative ion is supposed to be 

 much greater than that of the positive. 



Ksr. 3. 



The investigation of the distribution of electric intensity 

 given on p. 262 shows that when the velocity of the negative 

 ion is much greater than that of the positive, the distribution 

 of the intensity has many features in common with that 

 associated with the passage of electricity through a vacuum- 

 tube, especially the great increase in electric intensity close 

 to the negative electrode. Thus this feature of the discharge 

 through vacuum-tubes can be explained by the greater 

 velocity of the negative ion than of the positive, a property 

 which seems to hold in all cases of discharge of electricity 

 through gases. And as the most important of the differences 

 between the phenomena at the two poles of a vacuum-tube 

 are direct consequences of the electric intensity at the cathode 

 far exceeding that at the anode, I think the most striking- 

 features of the discharge through vacuum-tubes are conse- 

 quences of the difference in velocity between the positive and 

 negative ions. In the case discussed on p. 261 we assumed 

 q constant, i. e. that the ionization along the path of the 

 discharge was constant ; in the case of the discharge through 

 vacuum-tubes, where the ionization is due primarily to the 

 electric field itself, it is unlikely that the ionization will be 

 constant when the field is so variable. We can derive 

 information as to the distribution of the ionization by a study 

 of the very valuable curves giving the distribution of electric 

 intensity in a vacuum-tube which we owe to the researches 

 of Graham (Wied. Ann. lxiv. p. 49, 1898). 



From the equations 



_= 4:7r(n l -n 2 )e, 



