Sunspot Activity during 1931.—In the annual report of the Council to the Royal Astronomical Society, a summary is included of the sunspot activity for 1931. The average daily area of sunspots measured at Greenwich was approximately 260 millionths of the sun's hemisphere. This value for 1931 is half that for 1930, and the average daily number of spots showed a decrease in about the same ratio. On about forty days during 1931 no spots were seen on the sun's disc. Large groups of spots were, however, by no means entirely absent, and the following dates are the times of central meridian passage of groups of spots of 500 millionths or larger, that is, of the order of size at which a spot is visible near the centre of the disc without telescopic aid: Jan. 12.5, Feb. 20.6, Feb. 20.7, March 15.4, May 20.5,Nov. 26.9. The largest of these groups, with central meridian passage on Feb. 20.7 and in latitude 6° north, had a maximum area of nearly 1900 millionths. A note on this group was given in NATURE, 127, 321; 1931.