31)8 I>i;. W. M. HICKS: A CEITICAL STUDY OF SPECTRAL SERIES. 



Magnesium. We are now in a better position to take up the consideration of the 

 place Mg is to occupy in the second group of elements, viz., whether it is allied with 

 the Ca or the Zn sub-groups. In the discussion of MgD (p. 356) there was evidence 

 in favour of either view. If it belongs to the former, then the line X = 14877 is 

 D^l); if to the latter we have PASCHEN'S allocations of 14877 to F(3) and 10812'9 

 to F (4). Take first the supposition that Mg is analogous to the earths. In this case 

 F() = 39751-08-6719-95 = 33031*15, 6719 being the wave number of 14877. If 

 the F series is formed on the type of the Ca set the denominator of the first line will 

 be 2*937300-2A 2 = 2'936474. This gives a line n = 20312. No line has been 

 observed sufficiently near to this to be identified with it. In the other case 

 F(oo) = D,(2) = 39751*08 - 2604'4*99 = 13706'09. PASCHEN'S allocations then 

 give denominators 3*962183-283*5 4*958710-5557 with a mantissa-difference 

 = 3473 + 272 With = '9 this is 3717 or 9A 2 . The value = '9 will upset the 

 difference in Table II. between D (2) and the supposed D (l) which in this case does 

 not exist. It still leaves the difference between the denominators of D (2) and 

 D (3) = 6A 2 . If Mg is completely analogous with the Zn set the combination lines 

 S(oo)-VF(3), S(oo)_VF(4) should exist. They should be at n = 32764'92 ('67), 

 + !/!, +v 2 , and 3529072 ("87), +i, +v. 2 . Now EDEB and VALENTA give two spark 

 lines of weak intensity at 3050*75, 3046'80, and SAUNDEBS a weak arc at 3051. 

 The wave numbers in vacuo are 32769*48 and 32811*95 separated by 42*47, which 

 is clearly Vl = 40"90. These are therefore the looked for 8 1 ( oo)-VF (3), and 

 S 2 ( ) - VF (3), the third S 3 ( oo ) - VF (3) not having been seen. As to the other set, 

 SAUNDERS has observed a line at 2833 giving n = 3528819 which is clearly 

 Sj ( co) VF(4). The existence of these combination lines seems to settle the question 

 in favour of Mg belonging spectroscopically to the Zn group of metals rather than 

 the alkaline earths. It is possible that as a transition element it belongs to both 

 types. Judging from PASCHEN'S various readings it might well be that X = 14877 is 

 double so that one might be D (l) and the other F(3). 



Group III. In Al and Tl alone have the ultra-red lines been observed, and 

 here the F lines are found in a similar position to those in the Zn groups, and with 

 them EITZ'S combinations S(oo) VF(3) and S(o)-VP(3). Using the values of 

 D(co) of [II] the values of F(oo) = VD (2) are 15837*92 for Al and 13064*21 

 with separation 81*98 (*24) for F 2 (oo) for Tl. For Aluminium PASCHEN gives 

 n = 8882*19 (*80) and 11392*8(3*90) for F(3) and F(4), from which result 

 VF (3) = 6955*73 (*80) and VF (4) = 4445*12 (3*90). The combination 



-- 41204*14 (3*39) = S, ( oo )-VF (3) gives VF (3) = 6957*32 (3*39). 



For Thalium PASCHEN gives n = 6118*19 (75), 6200*67(77) for F, (3), F 2 (3) and 

 8622*47 (*37), 8706*78 (l*5l) for F 1 (4), F 3 (4). These give separations 82*48 75 77, 

 and 84*31*371*51 instead of 8 1*9 8 '24, but the same within limits. He also 

 gives n = 34526*21 (179), 42321*40(2*69) for S(oo)-VF(8) and 37022*23(6*85) for 



