Terrestrial Magnetic Disturbances and Sun-spots

Abstract

REFERRING to Father Cortie's letter on this subject (NATURE, October 27, p. 272), the sequence of magnetic disturbances following at 27-day intervals the storms of May 12–21, 1921, was recorded also at Kodaikanal, but those storms recorded in England as “very great” on September 2 and 28–29 were classed here as “moderate” only. There were also recorded here “grea” storms on March 21–22 and April 18–19, which appear to belong to the same sequence, the whole interval from March 22 to September 29 giving a mean period of 27.29 days. Assuming this to be the synodical period of the sun, the equivalent sidereal period is 25.42 days, closely agreeing with Carrington's mean value of the rotation for spots.