DR. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 



453 



Still more striking, and as will be seen later, important, are parallel series with the 

 separations discovered by WATSON. In addition are found also others at 1932 behind 

 F (2). They are 



(5)15149'24 1932-22 F (2) 1429-38 (6) 18510'84 422'33 (l) 18933'34 



22108 1941-7 5 F (3) see Note* 



25087 1922-96 F (4) 1429-43 (6)28438'85 417-44 (4) 28856'29 



(3)26628-53 1924 F (5) 14268 29976'5 424 30203^ 



* F (3) has a link 423 to 24467 5 and then 1432 to 25899 5 suggesting a mesh in which the required 

 line is wanting. Here the 1932 separation goes better with the strong displaced F(3) 24039-45, giving 

 1936 5. The mesh should be 



423 6 $4467 1432 



F (3), 24044 25899 



1429-42 [25474-30] 425 + 6 



t Note that 1426 + 424 = 1429-4 + 420-0 9. 



Any lines of the P type up to in = 4 will unfortunately lie in the ultra-violet 

 beyond the observed region. P (4) should be 36690, and the largest frequency 

 observed by WATSON is (l) 36536. The others should be weak and in a region where 

 glass apparatus would only allow strong lines to be registered. F (5) should be at 

 35148"01+2f but is not seen. The line 35259'2 is about a v link ahead, in fact 

 v.35259'2 = 35152'4. It may, however, be noticed that 36536 above is just 154 

 behind the expected P (4), so that it is the P line corresponding to the parallel F set 

 above with the separation 1.56 (say F'). In the same series is also found 

 P' (6) = (2)34087'l corresponding to the F' (6) = 29196/w. These are of value in 

 that it gives the means of determining the limit with great exactness. Denote the 

 parallel series by F'. For m = 2 using B.M.M.'s measure for F'(2) the separation is 

 17081'460-16925'43-05 = 156'03'05. For m = 5 both lines have been 

 measured interfereiitially and the separation is 28553'342 28397'167 = 156'175, 

 correct to the second decimal place. The two separations differ by more than the 

 allowable observation error, and is possibly due to the common change in sequent for 

 series with different limits. In these cases in the separation with the larger <m, this 

 effect is very small. Consequently we are justified in taking the separation as 156 '17 0. 

 For m = 4 we have F (4) and P' (4) but only a L.D. line for F' (4). The separation, 

 however, gives its exact value as 27009'47-156'17 = 26853'30. F' (4) is 36536'62 

 '66(d\ = '05). The mean gives the limit for the F' series as 31694'96'33 and 

 consequently for F as 3185ri3'33, i.e., = '94 '33. 



But further in the neighbourhood of calculated P (6) = [34242] are found also 

 (1)34336'06, (3) 33918'08 respectively 94 ahead and 323'9 behind it. In analogy 

 also are found (5) 17176'34, (3) 16757'91 respectively about the same amounts ahead of 

 and behind <F (2), but no other corresponding F (m) lines appear. We are justified in 



