Foote, Moiileb, & Meggers. 



Phil. Mag. Ser. 6, Vol.43. PL XIII 



7-VOLT ARC SPECTRA OF POTASSIUM. 



70 ma. 



Z£ 



t- Tjl 



— ' -* -* 



2 '£. * 







■II^HIIIIHHL. i a HIHH 



1000 ma. 



Fig. 2. — The arc spectrum of potassium obtained with a hot-cathode 

 tube similar to that shown by fig. 1. The pair ls-3d appears 

 very prominently at 1000 milliamperes and 7 volts. This is an 

 exception to the principle of selection, since the change in 

 azimuthal quantum number is two units, which cannot be 

 attributed to a Stark effect. 





