Sunspot Groups of Irregular Magnetic Polarity.

Of 7890 spot-groups observed at Mount Wilson from January 1, 1917, to December 31, 1946, 6387 were classified magnetically. Of those classified, 5814, or 91.0 per cent, showed bipolar characteristics. Of the remaining groups, 24, or 0.4 per cent, were complex, with mixed polarities; 549, or 8.6 per cent, were unipolar. Among the 5814 bipolar groups were 180, or 3.1 per cent, which did not conform to the laws of sunspot polarity. Such spot-groups are said to be of irregular magnetic polarity. The purpose of the Investigation was to determine whether the groups of irregular polarity were irregular in other ways. Although irregular spot-groups may be of any size up to those visible to tFie unaided eye and may endure for several rotations, on the average they are slightly smaller and less stable than regular bipolar groups. The axes of irregular groups seem to be inclined at larger angles to the solar equator than are the axes of regular groups. Such large inclinations might be expected on the hypothesis of the origin of sun- spots proposed by V. Bjerknes. The frequency and mean latitude of regular and irregular groups were examined for the cycles 1922- 1935 and 1933-1945. No differences were revealed exceeding those between regular groups in different cycles and in opposite hemispheres. At the beginning of a cycle the mean latitude of the irregular groups was from 20 to 40 higher than that of the regular groups but decreased more rapidly, so that, when the cycle was about three-quarters over, the latitudes of the regular and the irregular groups were essentially the same. The ratio of irregular to regular groups in different cycles does not appear to be constant, the per- centage of irregular groups in the cycle 1922-1935 being about 30 per cent higher than in the cycles 1913- 1924 and 1933-1945. Mount Wilson Group No. 7732, first seen on March 24, 1945, in latitude 31° S., was a large stable spot of irregular polarity, exceptionally well suited for individual study. Investigation for magnetic field, Wilson effect, and Evershed effect failed to reveal abnormal characteristics. The vortex-structure of the surrounding hydrogen fiocculi showed a counterclockwise distribution, opposite to that in 75 per cent of the regular spot-groups studied. Thirteen recurrent spot-groups which were irregular in polarity during part of their lifetime were ex- amined during the transition period. In five groups the behavior during transition was closely similar