Stationary calcium lines have long been known to occur in the spectra of certain spectroscopic binaries, having first been noticed by Hartmann[282] for Orionis. Various “calcium cloud” hypotheses have been advanced to account for the phenomenon. It appears, from several considerations, notably the apparent small oscillation of the calcium lines with the same period as the star, that there is some physical connection between the two. Lee[283] discussed the idea that the system of 9 Camelopardalis was surrounded by a cloud of calcium vapor, which, as he showed, could be made to account for the behavior of the lines of ionized calcium. The same idea was discussed by J. S. Plaskett, who suggested that we might “assume that the absorbing material is near to or envelopes the stars, which is probable from its wide distribution, and in this form it combines the two original hypotheses of interstellar and surrounding clouds.”[284] The lines of sodium[285] [Pg 72] and possibly the hydrogen lines[286] have been added to the list of stationary lines, and Plaskett[287] has suggested that the ultimate lines of the ionized atoms of strontium and barium should also show the effect, which has not yet, however, been observed. SCANDIUM (21) The element scandium[288] is represented in the solar spectrum by faint lines corresponding to the multiplets , , . The multiplet may possibly be present, but the lines are very weak. The element is not recorded in the spectra of stars; most of the lines are unsuitably placed in the green. IONIZED SCANDIUM Six multiplets of ionized scandium, out of the eight tabulated by Meggers, Kiess, and Walters[289] appear in the solar spectrum, and all the corresponding lines have been traced in Rowland’s tables. The intensity of two of the lines is great enough for their behavior to be traced through the stellar sequence, and they are greatly enhanced in the spectra of the c-stars. The ultimate lines are near 3600, but in the solar spectrum they are less powerful than the lines near 3500. Table XI on page 73 contains, in successive columns, the series relations, the wave-length as determined in the laboratory, the intensity, the temperature class, and the attribution, solar intensity, and wave-length given by Rowland, for the six multiplets which lie within the observed range of the solar spectrum. Ultimate lines are designated by an asterisk. TITANIUM (22) [Pg 73] The spectrum of titanium is so rich in lines, and is so largely represented in stellar spectra, that a tabulation would occupy an undue amount of space. TABLE XI Series Wave-Lenght Int. Cl. Attribution Int. Wave-Lenght 3613.84 60 II -, Sc 4 3613.947 3645.31 30 III Sc?, - 3 3645.475 3630.76 50 II 4 3630.876 3666.54 3 III 1 3666.676 3651.81 25 III -, Sc 4 3651.940 3642.79 40 II Sc 2 3642.912 3572.53 50 II -, Sc 6 3572.71 3558.55 20 II (Fe 8 3558.672) 3590.48 20 II 2 3590.609 3576.35 35 II -, Sc? 3 3576.527 3567.70 20 II 4 3567.835