440 
DR. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERIES. 
not a D line, but is either a F line, or is attached to a D line (as in the 1864 set in X 
attached to the D group near 20312). The D-qualification test with D (co) = S( CO ) 
can he applied to these suspected D lines, taking the 20438 as a definite line. 
That is the mantissa difference of the lines from that of 20438 must be an oim 
multiple. A Teiy large number are found to satisfy this test. It must be remem¬ 
bered tliat as the oun is so large as 447 there can be no doubt as to the satisfaction of 
this test or not, even for the largest allowable observation errors, nor to the actual 
oun multiple when it is satisfied; on the contrary the possible observation errors are 
so great, that the observations do not enable us to increase the accuracy of the oun 
itself as already found. By combining a large number of cases it would no doubt be 
possible to diminish the probable error of its value, but the heavy work would not be 
justified at present, especially as there shoidd be hope of better measures in the 
immediate future. At the same time the existence of the D lines may be illustrated 
by the following two sets for m — 1. 
(2) 18641-4 (W.) 
5387-12 
18357 (C.R.) 
5671 ±4 
(1) 24028-52 (\V.) 2640-71 
(1) 21036-25 
5633-0 
(1) 26669-23 
2018 ^ 
(1) 19842-4 (W.) 5371-3 
19583 (Ram.) 
5630 
(2) 25213-7 (W.) 
348 
(2) 16062 (W.) 
5650 
-(6) 21712-09 (R.) 
5377-68 
(1) 21456-56 (R.) 
5633-21 
(2) 27089-77 (R.) 
(3) 16725-1 (W.) 5372-9 
(0)16445-61 
5652-4 
(4) 22098 (C.R.) 
(0) 19086-1 (W.) 
5662 
2650-6 (2) 24748-6 (W.) 
r(l) 17493-05 (R.) 
5375-2 
1818 J 
1(0) 18609-94 (R.) 
5383-9 
r(0) 14813 (W.) 
31ig 1 5625-8 
L(4) 20438-8 (W.) 
(1) 22868-07 (W.) 
(1) 18357 (C.R.) 
5636 
(10) 23993-82 (R.) 
In these it should be noted :— 
(1) The satellite separations are in the usual ratio 5 : 3, for in the lAst 20^x5 
= 101‘25, 34 X 3 = 102 or for D 23 20^x5 = 102'5, 33f x3 = 101'25. In the second 
18^x 5 = 9r25, 3l|-x 3 = 93'75. Both sets have the same undisplaced limit = 50403, 
and the fwo corresponding lines are displaced 23|-(1 in their sequences. 
( 2 ) The 21712 which acts as a line shows the modified i/j separation to a second 
line but of much smaller intensity, in close analogy with what has been seen in X. 
(3) The mantissa of 16725T±-5 is 804601-26-8^+13-4p = 25 (32166-16-r07^ 
-l-'53^j)-[-(^i = 25A_,-i-(li. The second line of the triplet 22098 is one of the copper 
