Smithsonian Miscellaneous Collections Volume 52, PT. 3 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1909 Excerpt: ...of spot spectra were soon obtained with this instrument. After some minor technical difficulties had been overcome, it appeared that the photographs could be counted upon to show nearly all that can be seen visually, while at the same time they would permit the positions of the lines to be accurately measured and their relative intensities to be determined. From negatives taken with the Snow telescope, Ellerman prepared a preliminary map of the Sun-spot spectrum, extending from the violet to the extreme red. Casual inspection of this map, which comprises twenty-six sections of one hundred Angstroms each, is sufficient to show that the number of lines whose intensities are affected in Sun-spots is several thousands. In the hands of observers cooperating in the work of the International Solar Union, this map has greatly facilitated visual observations, and has considerably strengthened the view, now almost universally held, that the Sun-spot spectrum undergoes few striking variations from spot to spot or at different periods in the eleven-year cycle of solar activity. The negatives having been secured and a preliminary map of the spectrum prepared, it became necessary to draw up a catalogue of all the lines affected, showing their intensities in the spot and in the ordinary solar spectrum. The first section of this catalogue, extending from A 4000 (the extremity of the visible spectrum) to A 4500 in the violet, has been published by Adams.1 In this limited region of the spectrum, where the Sun-spot and solar spectrum were previously regarded as identical, about eight hundred lines of altered intensity are recorded. The publication of the second section of the catalogue has been somewhat delayed by the fact that negatives of the spot spectrum made with the 30-f..