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



come between the D'" and D" series. The limit taken is 22926' 11 and the scheme is 



as follows : 



O - C. O. 



3'969545-8 .... '01 '03 



6A, 

 4-968512 + 7 .... '04 



6A! 

 5-967480 + 24. ... '5 



Moreover, the difference between the first denominator and the corresponding one for 

 D'" is 2924, and this is 17Aj. It is of course understood that the digits "11 in the 

 limit have been chosen so that the l7Aj, 6A 1; come very close.- The argument 

 depends on the possibility of doing this. In fact RYDBERG'S tables give the limit 

 22926, so that the modification by '11 is extremely slight. Thus the observed line is 

 the line corresponding to m = 5 of this series, and it probably hides the weaker line 

 of D" (8). This accounts for the deviation noted above between calculated and 

 observed in D" (8). I have no explanation to offer for the corresponding deviation 

 for m = 7. All the others come so close that it is difficult to imagine that this does 

 not fall in with the rule. It is equivalent to an error in X of about 1'2 A.U. The 

 doublet separation for D" is "62 very closely, and the corresponding doublet difference 

 is 15(5j = A say. A lateral displacement of 7 A on the limit would just make the 

 change, but that explanation seems out of place here. The separations 7' 8 3, 12 "4 3 

 of the new lines require denominator differences in the limit of 373 and 473, and 

 4A 2 = 380 and 5A 2 = 475. There is another line at 6267'06, showing a separation of 

 5 "81 ("3). If this has the same VD as 6261 it requires a denominator difference in 

 the limit of 277 and 3A 2 = 285.. The four lines aj-e therefore (-5A 2 ) (6261), 

 (-3A 2 ) (6261), 6261, and ( + 5A 2 ) (6261). 



S. 



If RUNGE and PASCHEN'S estimates of their errors are valid the value of the limit 

 of the S series is determinable very accurately. It is 20085 '46 (l'34), but to bring 

 m = 7 as calculated within limits it is necessary to take S ( oo ) more than 1 less. 

 Accordingly the D lines have been calculated on the supposition that D ( oo ) = 20084 '5, 

 and it cannot be far from this. To bring the differences within multiples it has been 

 necessary to diminish this limit by putting = -'3. The multiples then come in 

 partly as multiples of A 2 and partly of A,. The value of A 2 given in the first part 

 of the paper is 651, but this gives A 2 = 35 x 180'67w 2 , whereas it should be, if 

 the rule there established is correct, in the neighbourhood of 180 '9, or -^ larger, 

 say 6517. This value has been adopted in the table, although the old one can be 

 made to fit in though not so well. The agreement is good, especially when it is 

 remembered that K. and P.'s estimates are less than possible errors, 



