70 
DR. W. M. HICKS; A CRITICAL STUDY OF SPECTRAL SERIES. 
the series was first arranged by Saunders (‘ Astro. Phys. Jour., 28, p. 223), who com¬ 
pleted the list by the addition of the three lines 823 ( 8 ), Si(5). The highest triplet 
was observed as in Sr by Lehmann, but the numbers given in the list are those of 
Hermann (‘ Ann. d. Phys.’ (4), 16, p. 698). 
In ZnS the first three triplets were allocated by Rydberg (Zoc. cit.). The list was 
completed by K. and R., and their measures for the whole are inserted. We owe the 
discovery of ZnP to Paschen (‘ Ann. d. Phys.’ (4), 29, p. 644). 
In CdS, again, Rydberg gave the first two triplets, and the first two lines of the 
next, whilst K. and R. gave the remainder. They also gave 252174 for 83 ( 5 ), but it 
must be wrong, for it gives a separation from 83 ( 5 ) of 49477 instead of 541'90. It 
is, therefore, 3 A.U. too small. Sj ( 6 ) = 2582’86 makes la = 1156‘38 instead of 
117 POO. CdP is due to Paschen (Zoc. cit.), but the values inserted after the first 
are the later ones of Paschen and Wiedmann (‘ Ann. d. Phys.’ (4), 35). For Eu 
see Appendix I. 
In Hg 8 Rydberg arranged the first three triplets, Kayser and Runge added the 
fourth and the first line of the fifth. The remaining lines, m = 6 to 13, of Hg 8 were 
observed and arranged by Milner (‘ Phil. Mag.’ (6), 20, p. 636). The lines 83(5, 6 ) 
observed by 8tiles (‘Astro. Phys. Jour.,’ 30, p. 48), 83(5), 82(9, lO) observed by 
Huff (‘ Astro. Phys. Jour.,’ 12, p. 103), 8^(7) Exner and Haschek, 83(7) Eder and 
Yalenta have lieen inserted by the writer. They give for the fifth triplet 
vj = 4630'80, i '2 = 1762'59. 82 ( 6 ) gives I'j = 46307. The seventh triplet gives 
404P4 and 1747’0 ; a slight error in X — 23147 would put both these right. 83(9, lO) 
make respectively = 4659‘1, 4653’3, but the former is identical with 83(5). There 
may be some doubt aliout 83(7) and 83(7), as they are both spark lines, and 83(7) is 
rather too strong, but there can be little doubt about the others. For 81 (5) the 
measurement of 8tiles is inserted in place of that of K. and R., as it was observed 
under better conditions. For the HgP Paschen made an unsuccessful attempt to 
locate the first triplet in the same paper as that in which he published the results for 
the other P series, referred to in the text. The series was first determined as to its 
lower orders m = 4 to 15 by Milner {loc. cit.), then Paschen and Wiedmann 
observed the same set up to m =16, and attempted to settle the position of the top 
lines. In the list above, the arrangement is given as modified in the text (p. 54 ). 
In the tliird group of elements the P lines have been oliserved and allocated by 
Paschen ( Ann. d. Phys.’ ( 4 ), 29). 5105, as observed by liini, was the edge of a 
band, and, as poiiited out by him, was too strong to be AlP (4), although it should be 
close to it. 8ince then Manning, working in my laboratory, has found a very faint 
line at 51()7'5, which is doubtless the line in cpiestion. Rydberg in his original 
memoir gave the five doublets of the A18 series, and at the same time suggested four 
others. I he 8 and 13 lines here, however, come so close together that with the 
inexact values at his disposal his arrangement of these last is now seen to be incorrect. 
As m otlier cases, we owe to Kayser and Runge (‘ Ann. d. Phys.’ (3), 48, p. 143) 
