[MCLENNAN- young-ireton] ULTRA-VIOLET SPECTRA 71 



m= 2 3 4 5 6 7 



A= 4571-27 2090-08 1843-08 1757-1 1711-6 1621-00 

 Although the existence of a Hne at A = 2091 A.U. was verified in 

 the present work in both arc and spark spectra in air, no indication 

 was obtained of the existence of members of the series with higher 

 frequencies. 



Summary 



1. The spectra of magnesium for spark in air and arc in air has 

 been investigated in the region between A = 2026 A.U. and A = 1850 

 A.U. and some seven new Hues recorded. 



2. The spectrum of the magnesium arc in vacuo has been in- 

 vestigated in the region between A = 2300 A.U. and A = 1400 A.U. and 

 seven new arc Hues measured. Several of these agree with lines 

 found by Saunders with the spark in hydrogen and with lines found 

 by Handke with the spark in air. 



3. The series i^= (1 -5,S) — (m,P) has now been verified for 

 values of m from two to six, but the experiments have failed to detect 

 any further lines of the series i^ = (l-5,S) — (m,p2) beyond, possibly, 

 the second member. 



Selenium 



These experiments were also a continuation of previous work.^ 

 To secure an arc in vacuo emitting selenium radiation, solid com- 

 mercial carbons were bored to a depth of one and a half inches and 

 filled with compressed selenium metal powder. These were placed 

 in the vacuum arc lamp previously mentioned, and a steady bright 

 arc was obtained with a current of 4 to 6 amperes at 100 volts. 



In the illustration, Fig. II, the upper spectrum is that of the carbon 

 arc in vacuo, and the lower that of selenium in the carbon arc. The 

 following table contains the wavelengths of all the lines measured 

 with relative intensities. As before, several of the best of a large 

 number of plates were measured. 



1 McLennan and Young, Phil, Mag., VoL XXXVI, p. 450, Dec. 1918. 



