190-').] New Scries of Liars in the Spectrum of Magnesium. 419 



" On a New Series of Lines in the Spectrum of Magnesium." By 

 A. Fowler, A.RCJSc, F.K.A.S., Assistant Professor of 

 Physics, Eoyal College of Science, South Kensington. Com- 

 municated by H. L. Callendae, F.E.S. Eeceived March 9, — 

 Eead March 26, 1903. 



Although the spectrum of magnesium has been the subject of many 

 investigations, certain lines which occur in the arc spectrum appear to 

 have hitherto escaped notice. The lines in question are comparatively 

 feeble, but on account of their theoretical interest it seems desirable 

 to draw attention to them. 



The new lines make their appearance in the spectrum when the arc 

 is made to pass between poles consisting of magnesium rods, but 

 they do not always appear with equal intensity. They are somewhat 

 nebulous, especially on their less refrangible sides, so that their 

 positions cannot be determined with great accuracy ; but as nearly as 

 they can be ascertained with the instruments at my disposal, the 

 wave-lengths are (in air), 4511-4, 4251*0, 4106*8, and 4018*3. 



A mere inspection of the photographs suggests that these lines 

 constitute a regular series, associated with the much stronger series 

 described by Eydberg*, having wave-lengths 5528*75, 4703*33, 

 4352*18, 4167*81, 4058*45, and 3987*08, according to the measures 

 of Kayser and Eunge. This view seems to be sufficiently confirmed 

 by calculation. 



Eydberg found that neither his own general formula nor that of 

 Kayser and Eunge could be applied with sufficient accuracy to the 

 stronger series, and employed a combination of the two formulae, 

 namely, 



b c 

 n = a + — + 



(m + /x) 2 (w + /a) 4 ' 



where n is the oscillation frequency, m has the values 3, 4, 5, &c, 

 and a, b, c, and /x are constants to be determined from four lines 

 belonging to the series. For the magnesium series, the equation 

 calculated by Eydberg is 



- 9C fiqi aa 111,856*92 147,764*05 

 n - -6,b.>l*14 (m + . 406)2 + (^7<^067 ' 



n being the oscillation frequency in air, and m having the values 

 3, 4, 5, 6, 7, 8 for the six lines named above. 



Using the same formula for the new series, and calculating the con- 

 stants from the four lines, the equation for frequencies in vacuo is 



102,496*6 168,840*5 

 n = 26,595*4-.- ' g1Q ., + 



(m + 0-618) 2 (m + O-QISy 

 Ofyersigt af Kond. Yet. Akad. Forhandl.,' 1893, Stockholm. 



