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



In the D series of Magnesium, as arranged by KAYSER and RUNGE and as generally 

 accepted, there are clearly certain abnormalities. D! (4) is more intense than we 

 should expect, and its separation from D.j(4) is 45'39 in place of 40'92, whilst that of 

 D a (4) and D 3 (4) is very close to the exact value. This cannot be due to observational 

 error, for this is very small ('03). Either, therefore, the true line is hidden by this 

 bright one, which can scarcely be the case, or it is a collateral. In the former case 

 the true line ought to be that found by deducting v l and v 1 + v a from the satellites. 

 In the second case it would require the addition of 19^ to the denominator of D ( o), 

 and the addition would explain the increased intensity. The two results agree, the 

 wave numbers resulting being respectively 35054'80 and '71. The former would give 

 a denominator '832041 in place of that in the table, but its observational error would 

 be that of D 3 , viz., 945, while that of the collateral depends on the observed D ls and 

 is 190. D(5) gives normal separations within limits. D (6) gives v = 46 '87 and 

 22*15, but normal within the observation errors (2'8) [see Note 1 at end]. 



But there is another question which arises in connection with Mg. In the Ca 

 sub-group the first lines have a denominator about 1'9, i.e., with m = 1. In the Zn 

 sub-group the lowest value of m is 2. In the MgD series, as generally accepted, the 

 first line is X = 3838, which requires m = 2. If there is a line corresponding to 

 m = 1 it should be in the neighbourhood of 14900. Now PASCHEN has observed a 

 strong line at X = 14877'!, but there is no triplet, which would be decisive against 

 the allocation if we could be certain all the lines must exist. But there are cases 

 where normal lines are observed weaker than we should expect, or are not seen at all. 

 The well-known case of KD(3) is one example, and it is curious that if 14877 be 

 taken as MgD(l) the denominator comes out as given in the table in a very natural 

 order with the other denominators. The question is considered later under the F 

 series, and the evidence there adduced is rather against the present suggestion 

 (p. 398). 



Ca. 



The value of S is calculated from A 2 as 58 '14, A^A;, would give 58' 18, practically 



the same. To bring the differences of the first three denominators to multiples of S 



it is necessary to diminish the limit given from the consideration of the S series by 



1'6 (variation limits given in [II.] = 5'8). The values can then be arranged as in the 



table. One result of this is to increase the value of A t (for the given Vl = 105'89) to 



from 2791, which gives S = 361'30^ in place of 361'17, and thus closer to the 



adopted value 361 '80. A noticeable peculiarity in this series is the very rapid falling 



the denominators after m =-- 4. It is so large and at the same time so 



that they cannot be brought into line with the others without diminishing 



the limit by a large amount and by different amounts. It clearly points to the existence 



