Our Astronomical Column

Abstract

BEHAVIOUR OF SPECTRUM LINES OF THE SAME SERIES.—The lines in a series are generally assumed to behave alike (omitting reversals), even under varying experimental conditions. In fact, their sharpness, diffuseness, or direction of unsymmetrical widening have been used as criteria in the detection of-series relationships. Thus if the strong lines of a series were unsymmetrically widened towards the red the remaining lines of the series would be expected to be widened in the same direction. This, however, is not the case, and an investigation bearing on these points is communicated by Dr. Royds to the forty-third Bulletin of the Kodaikanal Observatory (see also the Astrophysical Journal, March, vol. xli., No. 2, p. 155). In the case of the barium lines he finds that all the first members of the first subordinate series are displaced to the red, and the second members to the violet. In the case of -the calcium series he finds this not so extreme a case as that of barium, but still a noteworthy exception to the general run of series. The strontium series, on the other hand, is stated to be quite normal if the infra-red lines the character of which is unknown are excepted. Dr. Royds directs attention to the whole question of the relationship between pressure shifts and series, since the pressure shift may even be in opposite directions for lines of the same series. He points out, further, the importance of isolating the pressure effect from the density effect, the elimination of the latter in order to obtain true pressure shifts being “one of the most pressing problems for those interested in the displacements in the sun's spectrum.”