Enhanced Spectrum of Magnesium in Low Voltage Arc. 1009 



It is apparent from PL XXVII. that the spectrum is 

 developed in successive stages. Just above the iirst resonance 

 potential, 2*70 volts, as was first shown by Mohler, Foote, 

 and Meggers*, we have the single-line spectrum X— 4571 

 (\ = 4573 in vacuo). Just above the second resonance 

 potential, 4*33 volts, another line appears, \ 2852, forming 

 a two-line spectrum. No marked change then takes place 

 until the simple ionization potential, 7"61 volts, is reached. 

 At this voltage the entire arc spectrum is excited. When 

 the electron velocity exceeds 15 volts the enhanced lines are 

 prominent. The enhanced line \4481 is particularly well 

 defined in the 20-volt exposure illustrated. Other prominent 

 enhanced lines which show clearly in the reproduction are 

 marked in PL XXVII., but for a more careful consideration 

 reference must be made to Table I. 



Fig. 2 illustrates in a graphical manner the arc lines to be 

 expected on the basis of an atomic structure, in general 



Fio-. 2. 



TVinci|».l5er;ra Singlets 155-mP m=Z,3- 



Comb^QhonSen-sSinj/etS !.5S->Hft m=*.3.™ 



f Sub. Ser,e 5 S.rglfU Z?- ir.D 171= J, 4- 



Pnn. 5eries Triplets 154.- mf> u3 m= 3,4- 



I^Sufc Seri«sTKi{>Jets £Pi,i ? -Kid m = 3,4,— 



Z^Sub.SeriesTri'pkts Zp,',.-- *vi m-u;,2.S/ 



Ber^monn Sei-iss 3d- map }7i=4,5 l — 



4AJJ 



LI 



4d 



ikgneslum 



■7.61 Volts ionization- 

 ■ Complete arc spectrum - 



3 h 



3d 



2P 



e— 4.33 volts - 

 3 2853— 



AL. 



LLJJ L_J 



1.5 S 



S 2 — Z 10 Volts 



^457J 



-a 5173- 

 -2.3332- 



Schematic drawing representing lines of the arc spectrum. 



character similar to that postulated by Bohr. Most of the 

 orbits between 1"5 S and 3"5s are shown. As abscissa^ are 

 plotted the logarithms of the wave numbers. The series o\ 

 parallel lines broadly considered simply represent different 

 energy levels. Any spectral line is given by the difference 

 in wave numbers corresponding to a particular change in 



* Bureau of Standards Scientific Paper Xo. 403, 



