The absorption bands of titanium oxide, TiO₂, are the characteristic flutings[300][301] of the stars of Class , and the strength of these bands has been proposed[302] as a criterion of class for the stars in which they are found. It is perhaps noteworthy that titanium, zirconium, and carbon, the only elements which give oxides in stellar spectra (hydrogen excepted) belong to the fourth group of the periodic system. VANADIUM (23) The vanadium lines are best identified by intensity from Rowland’s table. The following multiplets[303] are present in the solar spectrum: , , , , , , . The multiplet is well seen in stellar spectra from onwards, and increases in strength as cooler stars are approached.[304] Slipher[305] called attention to the strength in Ceti of the vanadium group near 4400, presumably the two multiplets , , with excitation potential 0.28 volts. [Pg 76] IONIZED VANADIUM Three multiplets, all far in the ultra-violet, are tabulated for ionized vanadium by Meggers, Kiess, and Walters,[306] and two of them are within the range of Rowland’s table. All the lines of these, the and multiplets, have been satisfactorily identified with solar lines. The strength of the ultimate lines of ionized vanadium, which occur in the multiplet last named, is a little greater, in the solar spectrum, than that of the strongest lines of the neutral atom, at 4379, which are also ultimate lines. The following tabulation contains, in the same form as Table XI, the data respecting the two multiplets which are identified in the solar spectrum. TABLE XII Series Wave-Lenght Int. Cl. Attribution Int. Wave-Lenght 3727.348 20 - 1 3727.488 3760.230 5 - 1 3760.364 3718.163 3 - 3718.291 3750.873 15 - 2 3751.015 3778.359 3 - (Fe 3 3778.463) 3743.63 3 - (Cr 1 37243.726) 3770.976 10 2 3771.116 * 3093.10 40 III Er 3093.229 3121.144 20 IV E V 4 3121.270 * 3102.301 40 III Er V 3 3102.404 3145.35 - - 3 3145.484 3126.221 25 IV E V, Fe 5 3126.319 * 3110.710 30 III Er Ti, V ? 3110.810 3145.979 5 V Er Zr 1 3146.091 3130.270 25 III E V 3 3130.380 * 3118.382 30 III Er V 3 3118.498 3145.344 10 IV E 3 3145.484 3133.336 20 III E V 2 3133.449 * 3125.286 40 III Er 5 3125.399 [Pg 77] CHROMIUM (24) The lines of chromium were classified by Catalan,[307] and those which occur in the sun are comprised in the following multiplets:[308] , , , , , , , , , , , . The ultimate lines , at 4254, 4274, 4289 increase with advancing type.[309] The maximum for subordinate lines[310] is at . IONIZED CHROMIUM Of the six multiplets of ionized chromium tabulated by Meggers, Kiess, and Walters,[311] only two are within the measured range of the solar spectrum, but every line in these two multiplets accords satisfactorily in wave-length and intensity with a line in Rowland’s table. The ultimate lines are in the neighborhood of 2800, and are therefore unattainable. The lines, and the solar intensities, are contained in the appended table. TABLE XIII