EVAPORATION OF ATOMS 



347 



3 -a- 



^A/ (volts) 



Fig. 13. Theoretical Schottky slope (straight lines) compared to actual course of 

 current-voltage curves as zero field is approached. 



F"iG. 14. Contact potential V c. Variation with d as determined from measurements of 

 Ve given by circles, etc. V c from measurements of Vp given by triangles. Values 

 calculated from atom evaporation data given l)y heavier solid curve. 



Table III contains the data on Vg for a series of values of B and T at 

 four different Cs pressures, together with the contact potentials calculated 

 from Eq. (19). Over the entire range of Q, T changed about 500°. At con- 

 stant 6, \'a varied about 100-fold and T changed 20 to 30° in going from 

 the lowest to the highest Cs pressure. This small range of T prevents any 

 conclusions as to the effect of temperature on the contact potentials. How- 



