Excerpt from An Investigation of the Rotation Period of the Sun, by Spectroscopic Methods

All of the preceding determinations of the rotation period of the sun, with the exception of that Of Jewell, have been based on visual observations. While it is probable that the photographic method does not possess for such an investigation the overwhelming advantages which it has in the case of faint and difficult spectra, it has certain points of superiority which render an independent determination by its aid of the greatest value. Two Of these are especially important. The Visual determinations have been based upon a very limited number of lines in the less refrangible part of the spectrum. With the photo graphic method it is possible to employ a much larger number of lines and to utilize the more refrangible part of the Spectrum where the lines are more numerous and the variety of elements which can be employed correspondingly greater. These facts were fully realized at the time Of the establishment of the Mount Wilson Solar Observatory, and plans were made for taking up a photographic investigation of the rotation period of the sun as soon as suitable instrumental equipment was ready. With the completion of the Snow telescope, and the powerful I8-foot Spectrograph used in conjunction with it, a combination of apparatus admirably adapted for the work was available, and accordingly in the spring of 1906 the first observations were begun. These were continued until June, 1907, after which all Observational work on the rotation of the sun was transferred to the tower telescope.

Since the investigation was commenced five series of observations have been made and are discussed in the pages which follow. Two of these deal with lines selected from the spectrum of the general reversing layer, two with the a. Line of hydrogen, and the fifth with A 4227 of calcium. The lines of hydrogen and calcium give results differing widely from those Obtained for the reversing layer, and so, of course, should be treated individually. Moreover, Since the two series of determinations for the reversing layer are separated by a considerable interval of time, and the apparatus employed in the second series was entirely different from that in the first, it seems desirable to treat them separately in the present discussion. Brief accounts of the main results of these two series of observations have already been published, the first in 1907 (to) and the second in 1909 (u). A detailed account of the observations and reductions follows in Sections 1 - 10. The discussion and comparison Of the results will be considered in Sections 1 1 - 20.

About the Publisher

Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com

This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.