.. .. -2 -7 -1 -4 -0 -1 + 4352 CrMg ? .. .. 0 +2 0 +1 +0 -3 .. 4360 Cr n .. .. 0 .. +1 .. .. .. .. 4370 Fe n .. .. +1 .. 0 .. +0 .. .. 4376 Y+ * .. -1 +2 0 .. +1 +2 .. 4383 Fe n .. .. 0 +3 +1 -2 -4 -2 .. 4405 Fe n .. .. -1 .. .. 0 -1 -2 .. 4415 Fe+ * .. +1 0 +3 0 0 -1 .. 4435 Ca n .. .. -1 .. +1 .. 0 -2 - 4444 Ti+ * .. 0 0 +1 s -3 .. .. 4455 Ca n .. .. -2 .. -1 w -1 -3 - 4476 Fe n .. .. -1 .. +1 -1 .. .. .. 4481 Mg+ * .. .. -1 0 0 0 +0 +1 .. 4490 Fe n .. .. 0 .. .. +1 -0 +2 .. It is seen from the table that the general agreement with the anticipations of theory is satisfactory, and that the deviations, when they occur, rarely exceed one unit. The agreement is not less good than would be expected of the material, since the measures are here used differentially. The majority of the discrepancies are apparently accidental; for example, the deviations shown by the first six entries in the first column are almost certainly the result of better definition in the giant spectrum. There remains, however, the same [Pg 151] discrepancy for the lines of Sr+ that was noted in the earlier part of the chapter. There can be no doubt that these lines are stronger in giants than in dwarfs. The strengthening of the ionized lines of the alkaline earths is explained, when the spectra are examined, by the fact that the neutral lines are still fairly strong long after the ionized lines have passed their maximum—neutral strontium[426] is found at and neutral calcium[427] at . The lowered pressure, then, must increase the concentration of singly ionized atoms at the expense of the residual neutral atoms. There is, however, apparently no satisfactory theoretical explanation of the survival of large quantities of neutral calcium long after the ionized atoms have passed their maximum. The effects predicted above would appear to be the only ones that can be anticipated if the theory holds rigidly. Clearly some factor such as effective level must be further considered. THE STRONTIUM LINES The strontium problem is perhaps one that will lead to more comprehensible results when it is treated as a whole. It is impossible to resist the feeling that there is some definite abnormality associated with strontium. The “strontium stars” in the still earlier classes, where the lines 4215, 4077 appear with great intensity, and the stars Circini and Equulei, as well as the apparently erroneous absolute magnitudes obtained by the spectroscopic method for several other stars of low intrinsic luminosity, all point in some such direction.