420 New Series of Lines in the Spectrum of Magnesium. [Mar. 9, 



Another formula* which may be conveniently employed is 



C 



n = n x - -. or • 



(in + /x)- - m Q 



This formula gives for the two magnesium series the equations : 

 "Rydberg" series, n - 26,601-49 - (m+ ^^3282 , 



m • n „ co » , 100,033-6 



New series, n = 26,o87-4 ^ , 



% being the oscillation frequency in vacuo in each case. 



It will be seen that the convergence frequency of the new series is 

 as nearly equal to that of the Eydberg series as can be expected with 

 the comparatively rough wave-lengths employed, and it may be added 

 that in each case the constant m is of unusual magnitude. These 

 facts, in conjunction with the general characters and relative intensities 

 of the lines, render it highly probable that the new series is associated 

 with the Ryclberg series as second and first subordinate series 

 respectively. 



Applying the formula to the calculation of the members of the new 

 series for which m = 3 and m = 2, the corresponding wave-lengths in 

 air are 5065-0 and 6674'5. The first is probably represented by 

 a line having an approximate wave-length 5067, which is not so readily 

 observed in the photographs as the others, because the plates employed 

 are comparatively slow for this part of the spectrum, and if the expo- 

 sure be lengthened, the banded spectrum of magnesium becomes strong- 

 enough to almost mask the line. The line 6674*5 is perhaps too far 

 in the red to be conveniently observed, seeing that it is probably 

 feeble and not well defined. 



It may be reasonably concluded that the arc spectrum of magnesium 

 includes two subordinate series of single lines in addition to the 

 two well-known subordinate series of triplets. No such combination 

 of series appears to have been previously noted in the spectrum of a 

 metal, but two sets of series, each set consisting of a principal and two 

 subordinate series, are well-known in the spectra of helium and oxygen. 



The author desires to express his obligations to Mr. Herbert Shaw 

 for valuable assistance in making the computations involved in 

 investigating the various formulae which have been suggested for 

 series, as applied to the series which forms the subject of the present 

 paper. 



* After much labour, this formula was arrived at by Mr. Herbert Shaw and 

 the author as the one giving the most consistent results for series in general, but it 

 was afterwards found that a similar formula, expressed in wave-lengths, had 

 already been employed by Mr. Eummel (' Rov. Soc. Victoria Proc.,' vol. 10, Part I, 

 1897, p. 75). 



