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



383 



same time will give some reliable data which have a bearing on the present problem 

 of the actual D and F series. The line 20312 and those in its neighbourhood show 

 the following sets of separations, viz. : 



1. (1) 17615-06 832-13 (10)18447-19 1865-51 (6)20312-70 



f 827-92 (2) 18466-47 1866 -75' 



2. (6) 17638-55^ 



(.1864-74 (5)19503-29 829-93 



3. (3) 17628-29 831-70 (1)18459-99 1860-26 



4. (1) 17772-38 835'41 (8)18607-79 



5. (3) 19503-29 829'93 (1)20333-22 



(1)20333-22 



(4)20320-25 (1)22180-04 



1859-79 



1862-96 (6)20470-75 

 830-62 (2)21163-84 



1864-93 (2)22198-15 (1)24062-12 (<1) 25925-07 

 1863-97 1862-95 



In the general survey at the commencement of the investigation a large number 

 of separations of an amount near 1864 was noticed. Suspecting that it indicated 

 the existence of a second type of sharp series, a second smaller separation (for 

 triplets) was looked for, analogous to the i/ 2 =815 of the 1778 set. A further 

 separation was found for a value about 830.* The whole spectrum was searched within 

 the limits 1864 + 2. The result is shown in the occurrency curve of Plate 2, fig. 3. 

 This curve is unique amongst those hitherto observed in its great height above the pure 

 chance line and also in the steepness of its rise and culmination to a single definite 

 peak. The search brought to light also a very considerable number of long successive 

 chains and of meshes (see e.g., Nos. 2 and 5 above) of the same amount, proving that 

 1864 enters not only on its original source, as due to a displacement on some 

 fundamental sequence, but also as a link. Now the c link of the normal v l 1778 

 is 1872'63 and c (3$) = 1865'16, thus suggesting a possible origin, also a 

 corresponding c link for v a , i.e., a separation produced by a second A 3 displacement 

 is 833'84, or with a modified c' (3<5) = 83070. These suggest triplets formed by the 

 same A 1; A 2 on p ( A^ instead of on p, in other words, series whose limits are 

 51025 + 1778 = 52803, 54675'6, 55509 - 4. But the way in which the separations 

 enter with the suggested D line 20312 indicates that they stand in fundamental 

 relation to it and neither in a linkage relation, nor with the limits named. For in 

 the latter cases it would throw out of gear the whole relation of 20312 with the D set,- 

 which some provisional work had seemed to establish. In this work they were 

 considered as part of the D system through 20312 regarded as a Dj (l) line with 

 18447, 17615 as satellites. In this case the d t sequence is of the order 51025 

 20312 = 30713. As against this idea is, of course, the greater intensity of 18447, 

 the supposed satellite over that of the D n , and also the fact that no normal v^ 



* As a fact, however, there are several others depending on oun multiples also present, but which at 

 present we need not deal with. 



VOL. CCXX. A. 3 G 



