422 



BELL SYSTEM TECHNICAL JOIRSAL 



20 equi\alent volts of energy, if the blows fall closely enough together — 

 as if the energy spent in raising the atom to its first excited state 

 were paid into account, and could be used toward detaching the 

 electron when the deficiency is supplied. This fact is exceedingly 

 important for the theory, and I mention it here as a passing anticipa- 

 tion. In the second place it is desirable — for a j-eason which will 

 presently appear — to measure the energy-values of the normal and 

 of the excited states not from the energy of the normal state, as I 

 have done in Tabic I, but from the energy <>f the ionized atom as 

 zero-value. This is done in Table II. 



With this convention, all the energy-values for the non-ionized atom 

 liecome negative— a source of confusion, but not of nearly so much 

 confusion as the previous convention would eventually entail. It 

 is well to remember tenaciously that, in at least nine cases out of 

 ten in the literature, the energy-values of the normal state and the 

 excited states are referred to the energy of the ionized atom as zero, 

 and that the\' all should aKva\s bear the minus sign, though generalK' 

 it is left olT. 



For the excited states and for the normal state, I will employ the 

 common general name of Stationary States; occasionalh', for the .sake 

 of variety, the alternati\e name levels. Another conininn word is 

 term, the origin of which will appear in the next section. '- 



As the reader will be forced to make himself familiar with schematic 

 representations of the Stationary States, he may as well begin at 

 once with a simple one. Fig. 1 is a diagram showing the stationary 

 states listed for helium in the foregoing tables. The levels are repre- 

 sented by horizontal lines, separated by distances proportional to the 



"Anyone who reads the physical literature of today soon becomes familiar with 

 the phrase "the electron is in the . . . orhit" used instead of "the atom is in the 

 . . . state." This phrase expresses theory rather than facts of observation, and 

 docs not always express theory adequately; 1 have avoided it in this article. 



