ox THE AFTER-SHOCKS OF EARTHQUAKES. 



123 



almost the whole of Japan, might have had some share in making the 

 distribution of seismic energy in this country such as it is at the 

 present day. 



§ IG. Bujnsslon on the Seismic Fre^iucncij in Töhjö. 



In connection with this subject, it may be interesting to examine 

 whether there has been in recent years a secular variation in the 

 seismic frequency in Tokyo. 



Tlie systematic instrumental observation of earthquakes at Tokyo 

 dates from the 8th year of Meiji (1<S75) and has now been continued 

 for more tlian eighteen complete years. At first the record was 

 taken by means of Palmieri's seismograpli, but since 1887, it has been 

 taken by means of the Gray-Mihie seismograph. The numl)ers of 

 earthquakes during eighteen years (1876-1893) are given in the 

 followimi- table : — 



(I) Eecorded by Palmieri's Seismograph, 



1 " Tremors " mean those shocks whose direction of motion Avas not distinctly shewn hy 

 Paliiiieri's Seismograph. 



2 The Central Meteorological Observatory, where the record has been taken, was moved 

 in 1883 from its old position in the southern part of Tokyo to its present one in the Castle 

 grounds. The observation during that year might be imperfect and is rejected in taking the 

 average number of earthquakes. 



