154 F. OMORi : 



falling of a heavy weiglit on the ground or by tlie discharge 

 of a cannon at a distance. 



The results of the seismographical observations at Midori, 

 carried ont between the 11th and the 28th November, 1891, 

 may be summarised as follows : — Of the 18 earthquakes, whose 

 motion was large enough to be distinctly measured, the strongest 

 was that on the 28th November, 1891, at about 9.39 a.m., (No. 

 2, Table, § 2), of which the whole duration was 35 seconds 

 and that of the preliminary tremor 4.2 seconds, the origin of 

 this shock being much nearer to Gifu than to Midori. Four 

 other earthquakes also originated at some distances from the 

 observing station, and their movements consisted of compara- 

 tively slow undulations ; the total duration varied between 7 and 

 43 seconds, and the maximum duration of the preliminary tre- 

 mors was 2.7 seconds. The remaining 13 earthquakes were all 

 small local shocks and consisted of very minute vibrations, of 

 periods which varied between 0.023 and 0.17 seconds. All 

 these shocks, whose duration varied between 0.9 and 4.3 seconds, 

 had no preliminary tremor, but began at once with well- 

 pronounced movements, except in one case in which the motion 

 began with a well marked preliminary tremor of 0.1 second 

 in duration. 



It may be noted that the subterranean sound was perceived 

 simultaneously with, or very shortly, say 1 or 2 tenths of a 

 second, before the tremblings of the ground. 



10. Let us put, for the sake of abbreviation, y = the dura- 

 tion, in seconds, of the preliminai}^ tremor of an earthquake 

 at a given station, whose distance from the origin of disturbance 

 is X kilometres. Then, fig. 1, PL XIII, graphically illustrates the 

 relation between x and y for the large distant earthquakes noticed 



