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BELL SYSTEM TECHNICAL JOURNAL 



\oltage of the electron-streiim is raised just past the value V, at 

 which the incii\idual electron has just enough energy to raise the 

 valence-electron from its normal to one of its transient-sojourn orbits, 

 there is an outburst of radiation. This comprises rays of a single 

 frequency, emitted when the valence-electrons return in single leaps 

 from the orbits to which they were momentarily raised to the orbits of 

 their normal habitation. This frequency conforms to the relation: 



(2) hv = eVr. 



The law for excitation-potentials involving displacements of deep- 

 lying electrons bears a certain resemblance to the first of the fore- 

 going laws. When the accelerating-voltage of an electron-stream 

 playing against a multitude of atoms assembled in a solid or liquid 

 is raised just past the value Ve at which an indi\idual electron has 

 just enough energy to extract a certain deep-lying electron, say a 

 X'-electron, there is an outburst of radiation comprising many fre- 

 quencies, all conforming to a relation resembling (1), to wit: 



(3) hv<eV,. 



But it would he misleading to assuine that the processes resulting 

 in (Ij and in (3) are identical. In the first place, it is not certain that 

 the deep-lying electron need be completely extracted. Suppose it 

 possessed a set of transient-sojourn orbits in the outskirts of the 

 atom, their energy-values differing from one another and from that 

 of the "orbit at infinity" (the state in which the electron is quite 

 detached) by amounts less than the 25 volts which is the maximum 

 difference between the energy-values of any valence-electron. Then 

 there might be several excitation-potentials, differing from one another 

 by 25 volts at most; but this difference would be so inconsiderable a 

 fraction of the value of the extraction-potential Ve, which ranges 

 from more than 100, ()()() \olis for the A'-electrons of uranium to about 

 1100 volts for those of lu'oii. that tliey would be difficult to dis- 

 tinguish. Indications of nuilliplc excitation-potentials have, how- 



an immense number of orbits of a certain set, but not to transient-sojourn orbits 

 of certain other sets. Lately it has been affirmeci that impinging electrons of the 

 right energy ran lift the valence-electron to any one at all ol its transient-sojourn 

 orbits, even those to which ir cannot be lifted by ([uanta; but this rule, if it is the 

 true one, has not yet been illustrated by any extensive set of experimental (lata, 

 though llert? has latcl\- intimated in a brief note that he has assembled such a set 

 by experiments on helium. Franck and Knipping detected excitation-potentials 

 corresponding to the lifting of the valence-electron of helium from its normal orbit 

 to several distinct P-orbits; but I gather from a later paper by Franck that nobody 

 has been able to reproduce the result. Olmstead and Compton discerned excitation- 

 potentials corresponding to the lifting of the electron of hydrogen from its normal 

 orbit to each of the next six transient-sojourn orbits. 



