The 27-day recurrences of magnetic activities were treated by many authorities, but J. Bartels said that no trace was found of the existence of any disturbance-interval which is an exact submultiple of 27 days.
In this short report, I have examined whether the 14-day recurrences exist or not. After K. Takahasi and K. Husimi's method, which is applicable to the determination of the period and the damping factor of a vibrating system exposed to irregular forces, the character figures for calcium flocculi, the sun-spot numbers, the international character numbers and the numerical character numbers at Kakioka Magnetic Observatory, were treated. The materials used were taken from April 1 to Oct. 24, 1930, for all the four elements.
In the recurrence-diagram we find that not only 27-day recurrences but also 13-14 days recurrences are apparent, and moreover, the maxima of these four curves occur almost simultaneously. These facts show that the new appearance of eruptive phenomena on the solar disk, are the main causes of the terrestrial magnetic activities, and moreover, that the phenomena occur simultaneously on nearly opposite sides of the Sun. But it cannot be concluded with confidence that such two regions are antipodal or symmetrical.
According to the result of calculation of the variability made by Dr. H. Hatakeyama, using the observated values at Toyohara Magnetic Observatory during the period between VIII 1932-VIII 1935, it seems that the 27-day recurrence lasts about 4 or 5 months, and it constitutes one system. And it is also interesting that the phase difference between the two consecutive systems are often nearly 13 or 14 days.