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



is a line by LEHMANN at 13096'55, but its collateral displacement cannot be 2<? within 

 any likely limits of even LEHM ANN'S measurements. As to the second supposition, 

 there is a line at n = 12992'53 by LEHMANN which gives denominator 2'892050. 

 This gives a difference with F 12 (3) of 82 (11943 > 5-1'90^), which with = -10 

 would again make A 2 = 11962'5. It would thus appear that the normal F n (2) 

 line is 12992, and the system receives a double displacement, first to 13089, and 

 again to 13471. The mantissa is 912483-112'6 The addition of 2A 2 makes it 

 936403 112'6 which with = 10 is 937529, well within error limits of the same 

 quantity in the case of Ca and Sr. Again we are met with the apparent 

 simultaneous existence of two explanations which cannot be compatible. Is the true 

 explanation that the typical first line is 937300 2A 2 , but that the corresponding 

 configuration is not very stable and transforms to one depending on the nearest 

 complete multiple of A 2 . Certainly such instability is indicated in Ba. 



Radium. -The discussion for radium is rendered even more uncertain than that 

 for barium, in that the ultra-red region has not been observed, the process of 

 disintegration and re-aggregation has proceeded further, and, in addition, there is 

 some uncertainty about A 2 = S7S 2 adopted. 



RUNGE and PRECHT'S plates were only sensitive up to 6500 A.U., and EXNER and 

 HASHEK give only two lines above this, 664273 and 6641 '38, both of which belong 

 to the F cycle. The number of lines, however, coming within this cycle is very large, 

 but a complete discussion would involve the consideration of the new kinds of 

 relationships referred to under barium, and cannot therefore be undertaken here. It 

 will be sufficient to deal only with some generalities, specially bearing on the series 

 proper, which will also give some further light on the general D series. 



There are a large number of triplets with 'separations in the neighbourhood of 692 

 and 432, which are roughly in the proper ratio 5 : 3, allowing for the fact that the 

 actual separations must be larger. Those in the table of F lines above are roughly 

 parallel to the BaF, and give a limit somewhere about 24520. VD n (2) would 

 therefore be about this, and VD 13 (2) more than 692 + 432 = 1124 larger. The 

 denominator of VD 13 (2) should be a multiple of A 2 . Using the most probable value 

 of A 2 = 374, it is found that the denominator comes out very close to a multiple of 

 31A 2 . If this be made exact it is found that VD 13 (2) = F 3 (oo) = 2575275. The 

 value of F 3 (oo) is then taken 25752 7 5 + The values of S are so large that there 

 can be no ambiguity about the multiples to be chosen to give the separations, viz., 

 16(5, 1QS. These multiples march well with those for Ca, Sr, Ba. The separations 

 resulting are 705'93, 456'69, with F^oo) = 24590'! 3 and F 2 (oo) = 25296'06. If we 

 apply the rule shown in the preceding elements for F 13 (2), the denominator is 

 2'937300-2A 2 = 2'868676. Satellites depending on 38, 28 would give separations 

 51 '44 and 34 '20, and the fact that these separations occur in connection with 

 n = 17300 renders the identification of that for F(3) rather doubtful, a doubt which 

 is increased when we test the allocation by the law indicated above that the 



