On the Probable Existence of a Magnetic Field in Sun-Spots

The lines in the spectra of Sun-spots differ from those of the ordinary solar spectrum mainly through changes of intensity and width. Most of the spot lines are more or less widened, some of them are double, and a few are triple. These characteristics of the lines, and the fact that the revolution of electrically charged particles in a solar vortex might be expected to produce a magnetic field, led to a search for evidences of the Zee man effect in Sun-spot spectra. Light from a spot was passed through a Fresnel rhomb and Nicol prism, mounted before the slit of a spectrograph of 30 feet focal length, used in conjunction with the tower telescope of the Mount Wilson Solar Observatory. Photographs of the spectra were made in the third order of a Rowland grating, having 14438 lines to the inch. It was found that the relative intensities of the components of the double lines in the spot are reversed by rotating the Nicol through an angle of 90°. The widened lines are also shifted when the Nicol is rotated. Just such changes are observed if the same doublets are examined under the same conditions along the lines of force of a powerful magnetic field.