124 



F. OMORI. 



(II) Eecorüed by THE Gray-Milne Seismograph. 



As fur u.s the total iiumljer of recorded earth(|iiake.s is concerned, 

 the frequency appears to be greater in the later epoch, (II), tlian in 

 the earlier, (I). l>ut, as the record of the number of tremors or very 

 small shocks may have been modified l)y the change in sensibity with 

 the change of instrument we can .safely take only those shocks whose 

 motion was distinctly registered, and then we see that their average 

 yearly number is neiu'ly identical in the two groups (I) and (H)/ 



The Yedo (Tokyo) earthquake of the 2nd year of Ansei (LSoo) 

 to(jk place 21 years before 1(S7(), and 38 years before 1893. The 

 above table shews that the resichiai effect of this earth(piake had 

 ceased to be sensil)le l)efore 1876, and tliat the )nmn seismic frequency 

 in Tokyo has remained ever since practically constant. It may here 

 be remarked that the intensity of motion in Tokyo on the occasion 

 of the eartluj^uake of the 2nd year of Ansei was far less than that in 

 the Neo-A^alley and neighbouring tracts on the occasion of the recent 

 Mino-Owari earthquake, the former earthquake being also smaller in 

 extent than the latter. 



§ 17. On ilic Estimaium of the Frohahlc Total Number of Jflcr- 



1 "Tremors" here mexn those shocks whose motion was too small to be distinctly 

 measured by the Gi'ay-Milne seismograph. 



2 See Note to Tabic XVII. 



3 See § 29. 



