474 Prof. F. Horton on the Application of Thermionic 



The values of a/P are plotted as ordinates against the 

 corresponding values of X/P as abscissae in ng. 4. The 

 curve shown in that figure is drawn from Townsend's 

 values *. It will be seen that all the points (marked 



Fig-. 4. 



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J* 



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50 



100 



ISO 



200 



250 



X /P 



by circles) representing the results of the present expe- 

 riments fall very near to the curve, showing that the 

 results of the two methods of experimenting are in good 



agreement. 



In the experiments, the results of which have so far been 

 given, the ratio of the successive currents, when the distance 

 between the plates was increased by equal increments, 

 remained constant over the range of distances used, showing 

 that the ionizing action of the positive ions was negligible. 

 Two sets of observations were made with larger values 

 of X/p than those already recorded, and under conditions 

 in which the effect of the positive ions could no longer 

 be neglected. In these cases the values of a and j3 were 



* J. S. Townsend, Phil. Mag. (6) iii. p. 557 (1902). 



