278 



BELL SYSTEM TECHNICAL JOURNAL 



Now all the line-series observed in the spectra of excited atoms 

 and all which there is any reason to imagine as existent but undis- 

 covered, lie entirely at wave-lengths greater than 136A; indeed most 

 of them lie in the already-accessible region beyond 1200A, but a 

 few of the most important are in the newly-opened range. Hydrogen 

 is entitled to first mention, being the leader of the procession of 

 elements as well as the most completely understood of them. The 

 visible spectrum of (atomic) hydrogen consists of the archetype of 

 all line-series, the Balmcr series, extending from B.'iGH.-X to SOoOA, 

 the freciuencies of its lines being efiiial to tlie niiml)(.'rs of tlu' series 



(A) 



''^■r.-\)-^ih:-\)'<^-W 



and so forth, in wliiih R is a certain constant (/? = 3.2!1 • 10'''). Ac- 

 cording to Bohr's theory, this means that the energy-values" of the 

 consecutive orbits of the valence-electron (in this case the only elec- 

 tron) are gi\'eii In' tlie numbers of the succession 



(B) 



■Rh\ 



Q. -.^y- -^'(p)' -»(■=)• 



and so forth, and the consecutive rays of the series are emitted when 

 the electron drops into the first of these orbits from the second, third, 

 fourth and consecuti\e orbits. Most pcojik', on looking at the suc- 

 cession of numbers (B), would instincli\'el\' cnni|)]ete it by adding a 

 term —Rh at the beginning; and if there is truly an orbit of which 

 the energy-\'alue is — Rh there must be an additional line-series, '- 

 the frequencies of its lines being ecuia! i(i the ntinilnTs of tiie series 



(C) 



R\ 



('-!)■ ^^(l-i.).^(l-|..)' -Hi ..forth. 





The first three lines of this series should lie at iL'lli.V, ll)2ti.\ and 'J~2.\. 

 They were discovered by Lyman in 1913, and the series bears his name. 



" The cncrgy-v.'iliic of an orl)it is the energy of the atom when the valence-elcrtron 

 is in this orbit; the energy of the atom being set equal to zero, when the \alence- 

 electron is removed to infinity. It ff)llows from this hist convention that the energy- 

 vahie of an orl)it, with sign reversed, is equal to the energy which must lie imparted 

 to the atom to remove the valence-electron completely from the atom when it is 

 initially in the orbit in (pieslion. Thus the energy-value of the orbit which the 

 valence-electron normally inhabits is equal to the ionizing-potential of the atom, 

 when it is expressed in appropriate units and its sign reversed. The practical ad- 

 vantages of this convention are so great that we endure its annoying and confusing 

 consequence of making all the energy-values of non-ionized atoms negative. 



" The existence of this scries was anticipated long before Bohr's interfirelation of 

 the Balmcr scries, being suggested by the form of the scries itself. 



