PROF. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 71 



that which agrees most closely with that calculated from the formula, and I have 

 treated RITZ in the same way, calculating his S (2.6.7.8). The observations for 

 S (2) are by B. They are in no way comparable with the corresponding values by P. 

 in the case of Na and K. In fact, B.'s readings give v = 245 '07, or an error of about 

 16 A.U. in the wave-length differences of Si (2) and S 2 (2). Probably RITZ is closer to 

 S (2) than the formula in a./m ; on the other hand, he has errors from nine to ten 

 times the allowable in two cases. 



RbD. In the D series it has been thought that Rb .has a satellite to 7753 (L.), 

 viz., 7759 (S.). If we take p, = f and use K.R.'s values for D (4.5.6), it can be shown 

 that it is impossible to get within wide limits of either S. or L.'s D (3), or of 

 BERGMANN'S D (2) ; but it is possible to satisfy conditions for D (3) if what has been 

 supposed to be the satellite is actually the line D n (3), i.e., 7759'5 S. instead of 

 77 53 '5 8 L., but still DI (2) comes far wide of B.'s value on the side of longer W.L. 

 With /j, = 1 + f the calculated place of D n (3) is close to the supposed satellite, and it 

 can only be modified to bring it to the supposed D u , i.e., 7753, by giving large 

 possible errors, alternately positive and negative, to K.R.'s observations of D (4.5.6). 

 Also the D n (2) line, as calculated, falls half-way between B.'s Dj (2) and D 2 (2). It 

 can be made to fall on his D 2 (2), but not on his Dj (2). I arn inclined to think, first, 

 that B. has a large error here, and, second, that Rb has no satellite series. There are 

 two additional considerations pointing to the same conclusion. One is that, if a 

 satellite series exist, the doublet separation for D (2) will be considerably less than 

 the normal (237). Now B.'s two lines n = 15410, 14830 (those now taken to be T> 1 

 and D 2 ) give 253'73, aboiit 40 A.U. above the normal ; whereas, if there were satellites, 

 it should be expected to be somewhere about 40 A.U. less. Although B.'s actual 

 wave-lengths in this region might possibly err to this amount, it is not probable that 

 the difference of two lines so close should be wrong to the extent of 80 A.U. as 

 they would be if satellites existed. The other reason against Rb having satellites 

 is considered later in p. 86. The agreement of the formula with observation for the 

 whole spectrum when no satellite is supposed is remarkable. The values are given 

 for this case in the Column Rb II., and for the case of satellites in Column Rb I. 



CsP. K.R. have only three lines, of which one alone is good. R. has given from 

 P(2) to P(9)-; L. has given P(l) with v = 553. R. practically agrees with K.R. for 

 P(2), but deviates in P(3) from them by four times their estimated possible error ( - l). 

 The observations of R. were made with the oxyhydrogen flame, and the spectra were 

 probably better developed than in K.R.'s case. To compare the two, I have calculated 

 out the doublets, taking v = 553 for the first. For this purpose any approximate 

 formula will serve. The result is 553, 184, 84'2, 45'5. K.R.'s give 181 '07, 80'2, 

 41-1, and R.'s 180-8, 82'5, 45'3, which favours R.'s values for P(3) and P(4). I have 

 therefore calculated constants from R.'s P! (2.3) and L.'s P t (1), and those for P 2 from 

 P 2 (oo) = P!(QO), L.'s P 2 (l) and R.'s P, (2). In the table I have entered the 

 deviations from K.R.'s values for (2.3.4). Really, therefore, for our formula the 



