2 9 (S F. OMORI. 



Tlie curves of 5-diiily and lO-dnily earthquake frequencies seem 

 t.) indicate periods whose average lengths are about oo davs and 

 .'i montlis respectively. 



The curve of monthly earthquake frequency (Fig. 1) indicates 

 distinct fluctuations, of which there are seven between August, 1889, 

 and December, 189o. The dates of maximum and mininunn fre- 

 quencies as given by the curve are as follows : — 



Maximviui. Miniuinin. 



September, 1889, (?) 

 February, 1890, 

 November, ,, 

 August, 1891, 

 February, 1892, 

 August, 

 between March and August, 1898. 



The successive intervals between the earlier well-defined maxima 

 or minima are from 7 to 9 months. 



§ 21. Tlie Miiio-Ou-ari Eartliqunlr. 



The curve of hourly earthquake frequency for Gifu (Fig. 10) 

 indicates a period of 8 or 9 hours, and also a shorter one of about 4 

 hours. The former is clearly shewn in the curve of 2-hourly earth- 

 cjuake frequency (Fig. 11), which gives an average length of 9 hours. 



The curve of hourly earthquake frec[uency for Xagoya (Fig. 12) 

 indicates regular fluctuations, whose average length is about 4^ hours, 

 and amongst which prominent maxima, marked a, h, c, d, e,f, occur 

 at successive intervals of nearly twenty-four hours, shewing an 

 evident diurnal variation. The curve of 2-hourly earthquake fre- 

 cpiency indic-ites a period of mean length of about 9 hours. 



The curves of daily, 2-daily, and 5-daily earthquake frequencies 



