A Table of Secular Variations of the Solar Cycle

The aim of the present paper is to provide workers on phenomena which are allied to solar activity with a new table on sunspot‐frequency in addition to the tables published by Brunner in the September 1939 issue of this JOURNAL. Brunner's Table 1, which contains the observed relative sunspot‐numbers for all months from January, 1749, to December, 1938, shows that the variations of the spot‐frequency through the eleven‐year cycle are disturbed by secondary short variations. On the assumption that these short variations are of an accidental character (this assumption is supported by the fact that investigations of the curve of observed spot‐numbers by periodogram‐analysis have revealed no persistent periods shorter than the eleven‐year cycle), they can be eliminated by smoothing the observed spot‐numbers. The method of smoothing used by the Zürich astronomers consists in forming the average of every 12 consecutive values of the observed monthly relative numbers and in taking the average of two consecutive averages; this latter is taken as smoothed relative sunspot‐number for the central of the 13 consecutive months whose observed sunspot‐numbers have been used for forming the average.