520 



TATE AND FOOTE : RESONANCE POTENTIALS 



ionization potentials is well within the limits of experimental 

 error. 



The object of the present investigation is the experimental 

 determination of the critical potentials for electrons in sodium 

 vapor. The experimental arrangement was identical with that 

 used by the writers in the work on cadmium vapor and the 

 method of measurement that already described for the deter- 

 mination of critical potentials in mercury vapor. 



Fig. 3. Variation with accelerating potential of total current from hot wire. 

 Upper abscissae values apply to curves 9, 10, 11; middle values to curve 10 a; and 

 lower values to curves 9 a and 11 a. 



The results of the present work are represented graphically 

 by figures 1, 2, and 3. Curves 1 to 8, figures 1 and 2, show the 

 variation with the accelerating potential between hot wire and 

 gauze of that portion of the current which reaches the outside 

 cylinder against a retarding field of about 0.8 or 0.9 volts. The 

 sudden falling off in the rate of increase of current which takes 

 place at the points a, b, c, d, etc., indicates that at the effective 

 potentials of these points inelastic impact has taken place. 



