140 Prof. W. M. Hicks on High- frequency 



long series of 64 elements (jd = 4), Xe through Ra Em to ?, 

 the end containing unknown elements. The first half of 

 this, like the others, begins at a rare gas (Kr) and ends at 

 one (RaEm), and this contains 32 elements in place of the 

 accepted 36. On the other hand, there should be a series 

 corresponding to^> = l of 4 elements. These are H (1), two 

 unknowns, and He (4), and at the beginning stands the rare 

 gas. Electron. And he suggests Coronium and Nebuliumfor 

 the unknowns. If we apply Nicholson's theory of the spectral 

 lines of these, Coronium has one positive charge in excess of 

 Xebulium. The latter should therefore be associated with 

 X = 2 and the former with N = 3. For evidence, reference 

 must be made to the original paper, but as it is not every- 

 where accessible, the above general statement has been given 

 to render the present note intelligible. The accompanying 

 table, given by Rydberg, will also make the arrangement 

 clear. 



As the table shows, Rydberg eliminates the old spaces 

 between Ra and Os, Rh and Ir, the space after Cs, and that 

 between Xe and Ra Em. He allows as two spaces for un- 

 known elements (1) that of the next atomic number to Nd 

 (in the Mn group) as does Moseley, and that between Ce 

 and Th, the last of which Moseley 's numbers directly con- 

 tradict. The observed high-frequency lines for Yb make it 

 come two places behind Ta, placing it, as the chemists have 

 done, in the La group. There is, moreover, spectroscopic 

 evidence putting La and Yb in the same group. This makes 

 Lu provisionally occupy the space between Yb and Ta. 

 Rydberg again places Sa between Pd and Pt, Eu between 

 Ag and Au, Gd between Cd and Hg. Bat the spectrum of 

 Eu is of the triplet, whilst Ag and Au are of the doublet 

 type, and they cannot therefore belong to the same group. 

 I have also given evidence* from spectral considerations, 

 which though not perhaps conclusive points to the suppo- 

 sition that Eu comes between Cd and Hg. As Moseley has 

 determined the atomic numbers of Sa, Eu, Gd to be con- 

 secutive, this would place Sa between Ag and Au and Gd 

 between In and Tl. Although the spectrum of Gd has not 

 been thoroughly investigated, I find indications that it is of 

 a doublet type with separations intermediate between those 

 of In and Tl. So far 3 therefore, as any spectroscopic evidence 

 goes at present, it tends to placing Eu between Cd and Hg 

 and Gd between Ag and Au. A slight modification of 

 Rydberg's table would bring it into agreement with this 



* Trans. Roy. Soc. A. ccxii. p. 58 (1912;, also A. ccxiii. p. 328 (1913). 



