116 BELL SYSTEM TECHNICAL JOURNAL 



It Is a very important fact that the atom may pass from a State of 

 one family to a State of the other, — in terms of the model, that the 

 19th electron passes from its n^ orbit to its Wi orbit, and simultane- 

 ously the 20th electron makes some transition or other of its own. 

 The emitted radiation contains the energy resulting from both changes 

 simultaneously, fused together without any discrimination. 



R. Building-up of Atoms by "Binding" 

 OF Successive Electrons 



I next point out that the processes whereby the lines of an optical 

 spectrum are emitted may be regarded, if this theory of the atom is 

 valid, as stages in the gradual formation of an atom. Consider the 

 hydrogen spectrum to begin with; each line is emitted as the atom 

 passes from one Stationary State to another of lower energy-value, 

 the state of least energy being the Normal State of the perfected atom 

 and the state of greatest energy being the condition in which the 

 atom-residue and its electron are torn apart. The various lines of the 

 spectrum correspond to various partial steps along the path from the 

 latter of these states to the former, to various stages of the formation 

 of a hydrogen atom from two separated parts. The specific conception 

 of each Stationary State as a definite orbit of the electron about a 

 nucleus merely reinforces this way of envisaging the process. In the 

 spectra of ionized helium and of neutral helium, we read the testimony 

 of the gradual formation of a helium atom out of a nucleus and two 

 electrons initially quite dissevered. The various lines of the ionized- 

 helium spectrum correspond to different stages in the advance of an 

 electron from the state of freedom to the state of most stable asso- 

 ciation with a nucleus of charge 2e, or in Bohr's language, to different 

 stages in the "binding" of an electron by a nucleus of charge 2e. The 

 various lines of the neutral-helium spectrum correspond to stages in 

 the "binding" of a second electron by a system composed of a nucleus 

 of charge + 2e and an electron already bound to it. Thus the two 

 spectra of helium testify to two consecutive processes in the upbuilding 

 of a helium atom out of its constituent parts. 



The process of building up an atom, by successive adhesions of 

 electrons to an incomplete electron-system surrounding a nucleus — 

 that is to say, the process of building a system of Z electrons around a 

 nucleus bearing the charge Ze, out of a system of {Z-h) electrons 

 surrounding the nucleus, by consecutively adding b electrons one 

 after the other — evidently occurs very profusely in intense high- 

 current high-voltage discharges in vapours, such as the condensed 



