Physics. — ''On the Excitation and ionization Potentials of Neon 

 and Argon'. (Appendix), \^y Dr. G. Hertz. (Communicated 

 by Prof. P. Ehrenfest). 



(Communicated at the meeting of November 25, 1922). 



Ill the measurements of the excitation and ionization potentials 

 of neon and argon discussed recently *), the value of 20,45 Volts 

 measured by Franck and Knipping was used as the first excitation 

 potential of helium, in order to determine the absolute value of 

 these potentials. Since then Lyman ^) succeeded in measuring the 

 spectrum of Helium in the extreme ultra-violet directly. It can be 

 shown from his results, that the values found by Franck and Knipping 

 for the critical potentials of helium, like Horton and Davies' values, 

 which are in close agreemeni with them, are too high. As Franck*) 

 shows by a comparison of the values measured optically and electri- 

 cally, 19.75 Volts must now be taken to be the first excitation 

 potential, which value is accurate within 0.1 Volt. In connection 

 herewith tlie excitation and ionization potentials of neon and argon, 

 having been nieasured relatively to helium must also be diminished 

 by 0.7 Volt so that the following values are oi)lained : 

 Neon: Excitation potentials: 16.65 and 18.45 Volts. 

 Ionization potential : 21.5 Volts. 



Argon: Excitation potentials: 1J.55; 13.0 and 14.0 Volts. 

 Ionization potential : 15.3 Volts. 



The conclusions relating to the optical spectrum are not affected 

 by this correction, as only the potential differences are used for 

 them. Only the term 0.5 s., which corresponds to the normal state 

 of the atom, must be diminished, and becomes J 74000 ± 1000 for 

 neon, and 124000 ± J 000 for argon. 



Eindhoven. Physical Laboratory of the 



N. V. Philips' Gloeilani'penfabrieken. 



1) These Proc. Vol, XXV N». 5 and 6, p. 179. 



2) Th. Lyman, Nature, 110, 278, 1922. 



3) J. Franck, Zeilschrift f. Phys. 11. 155, 1922. 



