JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. VII OCTOBER 19, 1917 No. 17 



PHYSICS. — The resonance and ionization 'potentials for electrons 

 in sodium vapor. John T. Tate and Paul D. Foote, 

 Bureau of Standards. 

 When electrons are accelerated through mercury or cadmium 

 vapor two distinct types of inelastic impact have been observed 

 to take place. The first of these occurs at the experimentally 

 observed potentials of 4.90 volts for mercury 1 and 3.88 volts 

 for cadmium 2 and is accompanied by the radiation of light of a 

 single wave length, 2536.72 A for mercury 3 and 3260.17 A for 

 cadmium. 4 This radiation is not the result of a recombination 

 with the atom of an electron removed by the impact but is to be 

 regarded as due to an agitation of the electrons bound in the 

 atom. 5 The large transfer of energy from the moving electron 

 to the atom may be explained if we assume that at these critical 

 velocities the time of interaction between electron and atom 

 bears a simple relation to the natural period of vibration of one 

 of the electrons bound in the atom. Under these conditions the 

 electron may be said to have a resonance velocity characteristic 

 of the vapor through which it is moving. The resonance velocity 

 may be calculated theoretically 6 from the frequency, v, of the 

 radiation emitted, by making use of the relation 



hv =eV 

 where h is Planck's element of action (here assumed to be 



1 Franck and Hertz. Verh. d. D. Phys. Ges., 16: 457-467. 1914. 



2 Tate and Foote. Bull. Bur. Stds. (In press.) 



3 Franck and Hertz. Verh. d. D. Phys. Ges., 16: 512-517. 1914. 



4 McLennan and Henderson. Proc. Roy. Soc. Lond., 91: 485-491. 1915. 



6 Tate. Phys. Rev, 7: 686-687. 1916. Tate and Foote. Idem, 10: 81. 1917. 

 6 McLennan and Henderson. Loc. cit. 



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