Frederick H. Seares

The General Magnetic Field of the Sun. Apparent Variation of Field-Strength with Level in the Solar Atmosphere

The preliminary results of a study of the Zeeman effect due to the general magnetic field of the sun have been given in a previous paper. With the aid of suitable polarizing apparatus, used in conjunction with the 75-foot spectrograph of the 150-foot tower telescope, four lines in the third-order spectrum of an excellent Michelson grating were found to show displacements corresponding in sign and agreeing closely in magnitude with theoretical values calculated for a uniformly magnetized sphere. The extreme minuteness of the displacements, usually less than a thousandth of an angstrom, led us to defer final acceptance of the provisional conclusions until they could be rigorously tested by additional measures. The present paper contains results which amply confirm those previously published, and reveal a relation between the intensity of the sun’s general field and the character of the spectral lines used for its determination. The stronger fines give smaller values of the field-strength, and, since the intensity of a fine depends upon the level in the solar atmosphere at which it originates, it is natural to interpret these differences in field-strength as a consequence of differences in level. In the original paper only four fines were shown to have displacements attributable to the general field of the sun. A number of others, mainly stronger fines known from laboratory investigations to have large Zeeman separations, showed no corresponding solar displacements. Fortunately an explanation of this apparent contradiction was offered in the circumstance that the displaced fines probably originate at a low level in the solar atmosphere, while 1 Contributions from the Mount Wilson Solar Observatory, No. 148. 2 Hale, Mt. Wilson Contr., No. 71; Astrophysical Journal, 38, 27, 1913. See also Hale, Terrestrial Magnetism, 17, 173, 1912. 206

ADDRESS OF THE RETIRING PRESIDENT OF THE SOCIETY IN AWARDING THE BRUCE MEDAL TO PROFESSOR MAX WOLF

In thirty-three years the Bruce Medal has been awarded twenty-five times. It is my privilege to announce that the twenty-fifth award has been made to Geheimrat Max Wolf, director of the observatory at HeidelbergKonigstuhl and professor of astronomy at the University of Heidelberg. The whole scientific life of our medalist has been associated with that ancient city on the Neckar. As a boy he became familiar with telescopes in the small private observatory established by his father in 1877, and there in 1884, at the age of 21, he made his first scientific contribution in the discovery of the third comet of that year. A little later he was probably the first to see, as a star of the sixth magnitude, the remarkable nova which blazed up in the Andromeda nebula. Although haze and moonlight misled him as to the importance of what he saw, his observations fix the outburst between August 16 and 25, 1885. After that we find him observing comets and occultations of stars, writing on telescope objectives, and proposing ingenious methods of testing a driving clock and of focusing an objective for photography.. The energy and resourcefulness which have marked his career were already evident. The close of his university years coincided with the first widespread application of photography to astronomy. Gills photographs of the great Comet of 1882 had revealed the surprising efficiency of ordinary portrait lenses in recording faint stars and led to the Paris Conference of 1887 at which the great Astro graphic Chart of the sky was planned. The memorable work of E. C. Pickering at the Harvard Observatory was under

TRIGONOMETRIC SOLUTION OF THE QUADRATIC EQUATION

distance-velocity relationship is statistical only, the lines may nevertheless be interstellar. Weak and sharp D lines with shortward (i.e., toward shorter wave lengths) displacements corresponding to the velocity of the expanding shell of the B5 source were visible on three plates. Measurements of these and several other stellar lines are in Table II. The results for the D lines confirm previous observations by Greenstein and Page2 with lower dispersion.

THE MAGNITUDE SCALE TODAY

. m e n the international magnitudes of the North Polar Sequence (NPS) were adopted at the Rome conference of 1922l there was reason to believe that future data would scarcely change the photographic scale in the region above the sixteenth magnitude. There was also evidence that the photographic and photovisual scales were mutually consistent to at least the eighteenth magnitude. Beyond thii limit the results admittedly were less certain. In reviewing the situation today I shall be more interested in the present state of theae fundamental standards than in the numerous uses to which they have been put. It is convenient first, however, to say something about a recent extension of the standards. It is not always easy to transfer the system of the original standards to other parts of the sky. The bright stars especially are too few in number and their color system is badly defined. To remove this defect and at the same time to supply abundant data for determining the complicated plate corrections required by photographs made with large-field cameras, the International System has been extended to about 2000 neighboring stars brighter than the twelfth photographic magnitude? The results are based partly on existing catalogs but mainly on recent photographs obtained by Dr. F. E. Ross of the Yerkes Observatory. The precision is usually comparable with that of the NPS itself, the average mean error (exclusive of zero point) df a catalog magnitude being C 0.02, and, under favorable conditions, scarcely in excess of -i0.01 mag. The color system Beemingly agrees with the ill-defined system of the bright NPS stars within 0.01C (C = color index) , although, owing to spectral peculiarities, the relations for early A-type stars are less certain. Deviations in zero point over the polar region of loo radius rarely exceed 0.01 mag. This estimate depends on comparisons of independent determinations from overlapping plates, on closing errors for different zones of declination, and on comparisons with existing catalogs after reduction to the International System. For example,

A New Determination of the Distribution of Stars with respect to Magnitude and Galactic Latitude

THE significance of the numbers of stars visible in different parts of the sky has been recognised since the time of Sir, William Herschel, whose star gauges first indicated the flattened, watch-shaped form of the galactic system. The stars having parallaxes which can be measured, either by trigonometric or spectroscopic methods, are all so near that their distances tell nothing of the structural features of the system. These must be learned from counts, like those of Herschel, of stars of different magnitudes in different parts of the sky.