JOURXAL OF THE COLLEGE OF SCIENCE, IMPERIAL UNIVERSITY, 

 TOKYO, JAPAN. 



VOL. XXXII., ARTICLE 7. 



The Systematic Motions of Sun-spots. 



BY 



S. Hirayama, Bigahuhalcusln 

 Professor of Astronomy, Scieuce College, Imperial University, Tokyo. 



With 3 plates. 



The Systematic Motions of Sun-spots. 



1. The object of this paper is to call attention to the possible 

 existence of certain systematic motions of the sun-spots, which 

 has not, so far as I know, been hitherto noticed. It was 

 suggested to me by ]\Ir. and Mrs. Maunder' s paper ''The Solar 

 Rotation Period from Greenwich Sun-spot Measures," (Monthly 

 Notices, vol. LXV, pp. 813-825) in which they summarized various 

 important results relating to the solar rotation period. Among 

 others, the following statement is made: "The rotation periods 

 given by different spots in the same zone of latitude differ more 

 widely than do the mean rotation periods for different zones of 

 latitude." This is based on their Table II, which shows the 

 number of the spot-groups, arranged in zones of latitude 5° wide, 

 giving different synodic rotation periods. Graphical study of that 

 Table led me to think that there is a tendency in the spot-groups 

 to concentrate upon two particular periods. I was also able to find 

 a similar tendency in Carrington's and Spörer's observations of 

 the sun-spots. 



2. To begin with the Greenwich sun-spots observations 

 (1879-1901), I simply took the said Table II prepared by Mr. and 

 Mrs. Maunder, and combined the zones of the same latitudes north 



