THERMIONIC ELECTRON EMISSION 



453 



vs. iJ.e/kT for 9 subcheckers and for 25 subcheckers. For ne/kT = 5 

 the former curve is only 4 per cent higher than the latter ; for fxe/k T = \0 

 the difference is about 6 per cent; for (xe/kT less than 5 the difference is 

 negligible. This makes us feel that our average curves which are 



1.8 



1.6 



1.2 



o0.8 



0.6 



0.4 



0.2 



-0.2 



-0.4 



40 60 80 100 120 140 



Vf~ (V volts per cm ) 



160 



180 



200 



Fig. 16 — Variation of average emission current with applied field for hill and valley 

 checkerboard; h variable, T and p. fixed. 



based on 18" subcheckers are essentially the same as would be obtained 

 for a much larger number of subcheckers. Equation (73) is analogous 

 to equation (69). Note that it depends on ^ but not on h. 



Figure 16 might have shown log ijis instead of log i\iao. To convert 

 it to this coordinate it is merely necessary to reduce all values of the 

 ordinate by log is\iao or by 1.44. The advantages of this ordinate will 

 become apparent when we compare theoretical and experimental 



