98 PROF. W. M. HICKS: A CRITICAL STUDY OF SPECTKAL SERIES. 



taking the atomic weight term as about that of Na, i.e., 



p. = l-074520-m~ 1 x -016080, 



giving 



VP(1) = 25885 = S(oo). 



The /A of the S would be about '005 more than jn '5 of P, and the a about '8 that of 

 P, judging from analogy with the other series, i.e., 



p = -5795--^ -0130, 



whence 



VS (1) = 44693 = P( oo ), VS (2) =16566. 



The values for I) are more difficult to estimate, owing to uncertainty as to the a/m. 

 The//. = 1-'074560-(40) = '92540, and the denominator = m+ '92540 + a/m. Whence 

 VD (1) = 29584-30726a. These give 



P(l) = 44693-25885 = 18808, 



S (2) = 25885-16566 = 9319, 



D(l) = 25885-29584 + 30726a = -3699 + 30726a. 



The P(l) or the first of the typical principal series would give A. = 5316. S(2) 

 would be about \ = 10731. Neither have been observed. The S and D should be 

 doublets with about v = l - 9. The D line,?;- = 3699, is clearly the same as PASCHEN'S 

 3719. If we make it so, must be given by 



3072G = -20 + error in D ( oo ), 

 or 



The error in U ( oo ) is probably considerable, which would make a small positive 

 quantity. Not only is the deduced line close to the observed one, but the observed 

 is a doublet of the proper amount. The doublet D (2) would be at X = 7651, and has 

 not been seen. 



The foregoing is professedly speculative. If the. relations found for the other 

 elements really hold for Li, it shows that while in the others all the energy goes into 

 vibrations of the positive type, in Li it goes into those of the negative type. It 

 might be objected in the above, that there has been no evidence that the S and D 

 forms, when used in a positive group of spectra, are different from the corresponding 

 forms in a negative group. A similar difference will, however, be shown to exist 

 when the spectrum of helium is considered. As we look down through the different 

 elements we find traces of the negative type (VD-VF), (VD-VP). In Na the D 

 series is not the ordinary but the F type, but we have seen indication of three lines 



