Abstract
MEASUREMENT OF CLOSE SOLAR LINES.—As a preliminary to the determination of the wave-lengths of solar lines in international units, and in connection with the search for mutual influence between neighbouring lines, Dr. C. E. St. John and Miss Ware have made a careful study of the difficulties attending the precise measurement of closely adjacent lines (Astrophysical Journal, xliv., p. 15). Micrometric measurements were made by at least two observers upon a series of spectrograms representing the first five orders of the 30-ft., and the first order of the 75-ft. spectrograph. and in the case of the closest pairs curves were also obtained with the registering photomicrometer; the separations derived by the latter process appeared to be least affected by accidental or systematic errors. The mean separations determined at Mount Wilson by three methods were systematically smaller than those indicated by Rowland's tables, the difference varying inversely as the separation. For six pairs, mean separation 0·274, the difference was + 0·003; for eight pairs, mean separation 0·145, it vvas + 0·008; and for eight other pairs, mean separation 0·075, it was +0·013. These differences are regarded as being probably due to errors in the Rowland values. The filar-micrometer values were found to vary with the width of the slit and the density of the spectrograms; whatever decreased the intensity of the space between the two components, as compared with the continuous spectrum outside, led to over-estimation of the interval. These results have evidently an important bearing upon recent attempts to detect effects due to anomalous dispersion.
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Our Astronomical Column . Nature 98, 40–41 (1916). https://doi.org/10.1038/098040a0
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DOI: https://doi.org/10.1038/098040a0