EARTHQUAKE MEASUREMENTS OF RECENT YEARS. 59 



impossible to measure the absolute duration of earthquakes as 

 they usually begin with exceedingly feeble tremors and end 

 with very slow undulations. 



7. — The distance and direction of the origin of each earthquake 

 from Tokyo, and its area. These w^ere kindly supplied by 

 the Imperial Meteorological Observatory. Existence of vertical 

 motion, the range and the direction of horizontal motion, etc., 

 may be examined in reference to the position of the origin of 

 shocks and their area. 



By Tremors are meant feeble shocks whose range of motion is 

 less than one-tenth of a millimeter. 



Local shocks marked hocal are small earthquakes shaking only 

 limited regions of the country usually from five to fifteen miles around. 



Prof. J. A. Ewing's Horizontal Pendulum and Vertical-motion 

 Seismographs were mainly used in making these measurements. 

 They are automatically started by the earthquake motion when it 

 attains one-fifteenth part of a millimeter. By increasing the sensi- 

 tiveness of the instruments the number of records may be propor- 

 tionally increased. 



The records, unless otherwise stated, are those obtained at 

 Hitotsubashi. 



