86 PROF. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 



number of 13711 is 7291'4. VD n (2) = 17040* roughly, VP 2 (2) = 31400-217647 

 = 9635-3, so that VD,, (2)-VP 2 (2) = 7405. There is just a possibility, therefore, 

 that 13711 may be the latter ; but, if so, it is curious that the P 2 should come in and 

 not P], which we should expect to give a stronger line. 



Rb. The lines to be accounted for are 13442 B., 10069 B., 8872 B., 8271 B., 

 8513-26 L., 6306-8 R, 5165'35 R., 4967 R, to which should possibly be added that 

 hitherto supposed to be D n (3), viz., 7753'58 L. 



The first four form a series. Using the first three for the constants, there results 



n = 14295-N/(m+l-04968-m~ 1 x-15177) 2 . 



This reproduces the fourth with an error 10 A.U., which is not excessive when the 

 inexactness of the whole measurements is considered, but they are sufficient to settle 

 that the limit is close to 14295. The value of VD (2) as calculated is 14270. 

 BERGMANN'S value for D, (2) lias a wave-number 6487, which with the reliable value 

 of Dj ( oo ) = 20876 gives VD (2) = 14389, but we have seen that BERGMANN'S value 

 is probably considerably wrong. The evidence, however, is sufficient to indicate that 

 Rb also lias a series in which the limit is VD (2). The corresponding series in Cs 

 \vas a doublet owing to the D series having satellites. The absence of duplicity here, 

 therefore, favours the view put forward on other grounds, that RbD is not a satellite 

 series. On the contrary, it is possible that, if there were a doublet series, the doublet 

 separation would be too small for BERCJMANN to have separated : for instance, he did 

 not separate NaD (2), which lie observed as one. The formula gives the next two 

 lines to be 7938 '6 and 7720 "6. The first, allowance being made for its uncertainty, 

 probably comes close to 7950, which is RbP a (l), and the latter may well be 7753, the 

 line which lias generally been taken to be D,, (3), but which we have had reason to 

 suppose not to belong to the D series. 



The lines 8513'26 L, 6306 -8 R, 4967 R. satisfy the equation 



n = 21703-N/(m+ 1-350891- - for m = 2.3 and 7. 



/ \ ml 



The N/D 2 is practically the same as for the P 2 series. The missing members should 

 be at 5602, 5270, 5084. The first has not been observed, the others are in the 

 neighbourhood of D,(7) (5260) and D 2 (8) (5089 R or 5088 S.). The limit 

 21703 = N/(2'2481) 2 , so that it is not apparent how it arises. The arrangement 

 does not give much confidence, although the connection with P 2 is curious. 



Of the other line, 5165 R., SATJNDERS has pointed out that it is near the edge of a 

 carbon bond, and is therefore a doubtful Rb line. 



* 17040 is extrapolated from a not very accurate formula. VD n (2) is probably somewhat greater than 

 the limit in the series just discussed, viz., 16810, making VD, 2 (2) about 16910, which would give 

 VD 12 (2) - VP 2 (2) = 7275 + 1 agreeing. 



