346 



PHENOMENA, ATOMS, AND MOLECULES 



30 r 

 40 



30 



O I 2 3 4 5 6 

 V {VOLT^ 



Fig. II. Electron emission (ve) vs. voltage for Cs on W. Example of curves used 



to determine Ve at zero field. 



4- 



y 



e 

 I 



O 2 3-456 



V (vows) 



Fig. 12. Change of effect of external field on Ve with 0, Dotted line indicates slope of 



curve for pure tungsten, ^ = 0. 



experiments on atom evaporation as described in Section VII, the corre- 

 sponding values of the contact potentials against a pure tungsten surface 

 are plotted in Fig. 14 as functions of 6. The heavy line curve is calculated 

 from data on Vg by the methods described in Section VII, by using a 

 temperature of 800° K. The values obtained with T = 600° or T = 1000° 

 are practically identical with those at 800° (within about 0.02 volt for Vc)- 

 The points indicated by circles, etc., are the contact potentials calculated 

 by Eq. (19), from the ratio of the observed electron emission to that from 

 pure tungsten. The agreement is excellent up to 6 of about 0.50. At this 

 point the values obtained from v^ deviate and show no maximum as do the 

 points calculated from the observed electron emission. The deviation in this 

 region is probably to be explained by a change in the law of force between 

 adatoms as the atoms become crowded. The force varying as r"'^, as used in 

 the theory, is evidently no longer adequate. 



