The spectra of the rare earths are so rich in lines that spurious identifications with lines in stellar spectra are often likely to occur. Numerous attributions to lanthanum (57), cerium (58), and [Pg 86] neodymium (60) are given in Rowland’s table. The occurrence of some of these elements has also been definitely established in the spectra of certain stars. Kiess[347] has demonstrated the presence of europium (63) and of terbium (65) in Canum Venaticorum. Numerous lines, identified with those of rare earth elements, are reported by Mitchell[348]in the chromospheric spectrum. If the lines in the chromosphere and the star are indeed derived from the rare earths, the atoms concerned must be at least singly ionized. No series relations have as yet been published for any rare earth element, excepting a short list of relative term values for lanthanum.[349] From analogy with the previous long period it would seem unlikely that the first ionization potential of these atoms can be as great as 13 volts, the value which would be required if the lines have a maximum intensity at . LEAD (82) A single line is attributed to lead in Rowland’s table. RADIUM (88) Giebeler and Küstner[350] suggested the occurrence of radium lines in the chromosphere. The identification was discussed by Dyson[351] and by Mitchell.[352] In the light of later knowledge it appears improbable that an element so heavy, and terrestrially so rare,[353] would be present in the sun at sufficient heights and in great enough quantity to appear in the flash spectrum. The identification is probably to be regarded as spurious. ELEMENTS NOT DETECTED IN STELLAR SPECTRA The table which follows contains a list of elements which are absent, or of doubtful occurrence. The rare earths are omitted from the list. [Pg 87] The elements marked “doubtful” in the list are those for which coincidences with very faint solar lines occur.[354] Twelve out of the twenty-nine elements enumerated are halogens, inert gases, or metalloids, and it is significant that all the elements of these groups are absent, with the sole exception of helium. At. No. Element Remark At. No. Element Remark 4 Beryllium Doubtful 53 Iodine Absent 5 Boron Absent 54 Xenon Absent 9 Fluorine Absent 73 Tantalum Doubtful 10 Neon Absent 74 Tungsten Doubtful 15 Phosphorus Absent 76 Osmium Doubtful 17 Chlorine Absent 77 Iridium Doubtful 18 Argon Absent 78 Platinum Doubtful 32 Germanium Doubtful 79 Gold Absent 33 Arsenic Absent 80 Mercury Doubtful 34 Selenium Absent 81 Thallium Doubtful 35 Bromine Absent 83 Bismuth Doubtful 36 Krypton Absent 86 Radon Absent 49 Indium Doubtful 90 Thorium Doubtful 51 Antimony Absent 92 Uranium Doubtful 52 Tellurium Absent FOOTNOTES: [125] M. N. R. A. S., 83, 166, 1923; ibid., 84, 368, 1924. [126] Ap. J., 61, 38, 1925. [127] Wright, Lick Pub., 13, 242, 1918. [128] A. Fowler, M. N. R. A. S., 80, 692, 1920. [129] H. A., 91, 7, 1918. [130] Fairfield, H. C. 264, 1924.