DR. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 383 



In the case of Ca the observed lines, with differences somewhat less than 22'49 and 

 1375, seem to indicate the presence of close satellites. If 16203'40 is really Y^(2), 

 the separation of 'the first satellite is 1'32, with possible errors ('26'2G), which form 

 a very considerable proportion of the total amount. A displacement of 3<5 produces a 

 separation of T51 and it may be this. But 16203'40 has an excessive intensity for a 

 satellite line, viz., 6, as against 4 for F n , and, moreover, it may possibly be the 

 collateral Si (2) (- A 2 ) which gives O-C = '03 with = '10. If the latter allocation 

 is correct, it would hide F J2 , which should be 16225'15('26) 22'49 = 16202'6G ('26), 

 giving a separation of 2'06 ('52) due to 4<$ which gives 2'02. The same considerations 

 applied to the second set give a separation of 1'36 for the first satellite, in which 

 again 4<! gives 1"26, and '22 for the second, S giving '32. The separations are so small 

 that no certain conclusions can be drawn as to their origin. The actually observed 

 numbers may be due to 4(5 and S, but 3S and 2$ are just possible [but see Note 4]. 



For Sr the first doublet is useless, as the line is due to the early measurements of 

 LEHMANN, which are affected with considerable errors. The observed separation for 

 F n and F J2 gives 10173 instead of something less than 100'34. The second triplet 

 gives 2 '92 for the separation of the second satellite from the first and 2 '06 for the 

 separation of the satellite of the second line of the triplet, and from analogy with 

 other satellite series, this would be the separation of the first and second satellites of 

 the first line. Differences of 3(5 and 2<5 give separations of 3'OG and 2'04, so that it 

 may be concluded that the satellites depend on these differences, a conclusion 

 supported by the fact that a similar result is indicated as possible for Ca. 



Returning to the curious fact noticed above that the first triplets of the series 

 seem to be dislocated, the second fragment in Sr is found at a distance 143'68 below 

 its normal position. For the present we note this can be explained by one of two 

 possible collateral displacements, viz. (-18^) F (2) or F(2) (3A 2 ), where F stands for 

 the normal F 2 or F :) . The case of Ba below will give evidence in favour of the latter 

 explanation. 



In addition to the lines of the series itself, there are two sets of triplets and a 

 doublet which are clearly analogous in the two elements. They are given in the list 

 above, following the series lines. The first triplets in each are curious as having the 

 middle line the strongest.* They are also related to others in the way indicated in 

 the following scheme : 



(8) 17847*46 

 21-94 



Ca (8) 17842'52 13'98 (8) 17856'50 12'90 (10) 17869*40 



13-86 



(8) 17883-26 

 * A similar peculiarity has already been noted in the associated OD series. 



