Enhanced Spectrum ot Magnesium in Low Voltage Arc. 1013 



being analogous to the line \468*>, which was at that time 

 called the principal line of hydrogen. The line A, 4686 had 

 been produced only by passing powerful discharges through 

 helium tubes containing hydrogen, and it was supposed that 

 in a similar manner the spark-lines of a metal were also 

 excited in the presence of the hydrogen liberated from the 

 electrodes. It is now known that the line X 4686 originates 

 in doubly ionized helium and has no relation to hydrogen. 

 Fowler's observations on magnesium are readily explained. 

 The spark-lines appeared in his arc for two reasons : 1st, the 

 high potential drop (at least 40 volts) across the discharge 

 was sufficient to doubly ionize magnesium. If any of the 

 electrons between collisions fell through a field of but 

 15 volts the enhanced spectrum would have resulted ; 2nd, 

 the high-current density employed would have excited 

 fundamental spark-lines by successive impact, as described 

 above. 



A summary of the fundamental energy quanta of lower 

 value, which the magnesium atom, in its normal or simply 

 ionized states, is capable of absorbing, is given in the 

 following Table. With high current density electrons may 

 be driven to the 2p and 2 ^} rings, in which positions other 

 quanta, not here tabulated, may be absorbed- -as, for example, 

 those represented by 2p — 2*55, 2p — ?jd, 2<JJ — 3 2\ etc.: — 



Table II. 



Energy 



absorbed. 



Volts. 



V. 



Energy 

 radiated. 



Notation. 



Spectrum. 



469 



380000 



L 



L-radiation X-rays. 



22-8 

 1497 



121270+61663 

 121270 



1-5 ©4-1-5 S 



1-5® 



Enhanced spectrum (No experimental 



evidence, but probably true). 

 (Also simple enhanced spectrum.) 



4-4 



7-61 



35772-680 

 61663 



1-5S-2SP 



1-5 S 



\2796 and X 2803 (atom must be first 



simply ionized). 

 (Also complete arc spectrum.) 



4-33 



35050 



1-5 S -2 P 



\2852 (also \ 4571). 



270 



21869 



1-5S— 2jp a 



X4571. 



At 46*9 volts* the L-radiation of magnesium is excited. 



* This value is computed from the relation L a =K a — K , and has been 

 confirmed experimentally by Mohler and Foote, of. J. Opt. Soc. Am.. 

 July 1921. In this work the limits of the L series were given down to 

 Neon. 



