On Eapid Periodic Variations of Terrtstrial Magnetism, 



29 



The results are also plotted in Fig. <S. As will be clearly 

 seen, tlie waves with periods less than 70' show decided maximum 

 frequency in the da}^ time, more or less near noon, while those 



X 



6 li ;i z^ 6 



Fig. 8, X. 



70-90 90-130 



(30-200 



30-200 



::^5^iz 



7tt\ ^ 



^%' 



IS 1+ 6 li IÎ 



longer than 90^ are more frequent during the night. For 30'-50^ 

 waves, a tendency is suggested in the X-component that the hour 

 of the maximum frequency is earlier in winter than in summer. 

 Besides, for X- as well as for Y-components a secondary minimum 

 near noon is èuspected in spring and autumn. For 50^-70^ 

 waves, the hours of the day time maxima seem to fall somewhat 

 earlier in the morning than for the shorter waves, and a secondary 

 maximum in the early evening is suggested in some of the 

 Y-diagrams. 70'-90' weaves form apparently a transition stage to 

 the still longer waves. For 90^-130^ and 130^-20^ waves, the 



