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



th.it of m 5 in place of 50(50 above. But the observation error in this line is so 

 l.-ir^i- thai us it stands it may correspond really to a denominator equal to that of 

 /" - ^. If further the series of differences 75<?,, 31f,, 12<?,, be continued diminishing 

 further as l<x>ks probable, it would come more nearly in line. For instance, as each 

 term is about '4 the previous, suppose the next is 5<J, = 569. The value of D, (6) as 

 thus calculated differs from the observed by '19 while the possible error is '30. 

 This would make the constancy of the denominator begin at an order one higher than 

 in Xi i. The case of Hg will be seen to support this tendency. 



There are two sets of doublets, 364974, 3500'09, and 3005*53, 2903*24 with 

 separations 1171*13 and 1171*95 which are clearly associated with the D series. 

 If we write down the observed satellite separations in the D,(2) and the D, (3) 

 lines find of D, 3 with the above we get the following scheme: 18*23, 11*10, 

 267*13 and 7*98, 6*18, 262*40. At first sight it makes the new lines appear as 

 collaterals by the change of about A, on D(oo), but this cannot be the case, because 

 a change of this amount would very considerably diminish the doublet separations 

 below 1171. If the D 1:l D 13 separation be deducted from that of the lines in question 

 there results 267*1 3 11*10 = 256*03 and 262*40-6*18 = 256*22. Now the separations 

 ll'lO, 6*18 depend, as is seen above, on 11<J,, 15<J,, so that the new lines may be 

 written *P(oo)_VD I3 (2)(-llJ I )-A, D ( oo)_VD 13 (3)(-15<J,)-A, where A is a 

 constant which on more accurate calculation is found to be 255*80 '2. In other 

 words, the VD of the new lines is derived from VI) 1: , in the same way as that is from 

 VI), a . This formula is of a type of which there has been no example hitherto. If it 

 remained there the evidence, in spite of the curious connection with the other 

 satellites, would scarcely be weighty enough to cause the introduction of a new 

 departure. I hope however to show in a future communication that this expresses a 

 very common relation between sets of lines, the constant A being in reality a com- 

 posite one. The question naturally arises do the new terms give rise to an F series 

 in the same way as the ordinary D ? It should be at a distance about 2(57*13 in wave 

 number above that of F. The line 15713*3 (u = 6362*25) is 266*90 above that of the 

 line 16401*5 (n = 6095*35) which is allotted by PASCHKN to F 3 (3) and is clearly the 

 first of the lines in question. There is an F(4) line at 11630'8 (n = 8595*57) and 

 another at 1 1268*4 (n = 8872*01) is 266*44 above this. This may lie the corresponding 

 line sought for, but if so the line 11630 must be F 3 (4) and the lines F, (4), F a (4) 

 would then Ixi absent. These lines were at firstt assigned by PASCHEN to a new 

 doublet set of series, but later}! to combinations of his new singlet series with D, ( oo ), 

 D., ( w ). This question will be considered as a whole later, but the suggested 

 explanation given above points rather to the fact that we have to do with a triplet 

 series in which the third number is too faint to be observed. 



* DC 00 ) stands as usual for DI ( oo ) or Dj ( oo ). 



t ' Ann. d. Phys.,' 29, p. 650 (1909). 



| 'Ann. d. Phys.,' 30, p. 749 (1909). 



VOL. CCXIII. A. 3 A 



