DR. W. M. HICKS: A CRITICAL STUDY OF SPECTRAL SERll.s. 



What is the nature of the modification ? Perhaps the simplest explanation to test 



is that a fraction of J, is transferred. The third column gives the fraction of ^ which 



is equal to the transfer. It is noticed at once that the two groups fall into two 



separate sets. With the exception of Sr, the fraction in the first is about '17. Mg 



and Ca can both fit in with this, for the values are so small that they depend on 



decimals in the value of A 1} A 3 , and therefore beyond our significant figures. In Ca, 



indeed, evidence is given later that A 2 is somewhat higher and would bring the ratio 



close to '18. But Sr is quite out of step with the others. Zn has no transfer, Cd 



and Eu are equal, but Hg is 5030. If the ratio in Hg be taken to be 82 : 243 



however, the fraction agrees with those of Cd and Eu. The Hg oun is then 361'43w* 



in place of 362'54 and closer to the mean value, and as will be shown later there is 



evidence for the new value of A 3 (see p. 397). If this explanation is valid it must be 



possible to bring Sr into the scheme with a transfer of 11 '7, but it is difficult to see 



how this can be done. '639 is about four times too great, in other words, where the 



others are modified by a fraction of S lt Sr is modified by the same fraction of S. The 



above arrangement brings Mg into the Ca group and upsets the law whereby its first 



A, should be a multiple of 5^. As this law seems to have a considerable weight of 



evidence in its favour, and moreover, as will be seen shortly, Mg tends to go 



spectroscopically with the Zn group, it may be well to see the result of keeping 



A, = 405 and the ratio A 3 : A, = 19 : 40. This will require a transfer of about 6*3 



with a considerable uncertainty owing to the small values of A 3 and A,, and 



A 3 = 4087. With this the fraction of S l is T1727. To bring to the same fraction as 



in Cd the transfer should be about 4, which the uncertainty in 6 '3 is not great 



enough to permit. As the fraction 77 is of the order 1 "215 it suggests that the 



modification is produced by adding S l to the atomic volume term in the sequence 



of the P series, viz. (atomic weight term 



l- 





The question must be left 



open at present. It has been noted that the arrangement which gives A, = 159^ for 

 Mg throws it out of the rule that the first members of the different groups are 

 successive multiples of ^. When the calculations were first made, the values of the 





