156 F. OMORT : 



11. According to equation (1), which is to be regarded 

 as applicable to great earthquakes at distances, say above 100 

 kilometres, from the observing station, the duration of the pre- 

 liminary tremor is increased at the rate of 15 seconds per 100 

 kilometres of the distance y. This, if found to be always 

 true, would enable us to estimate, from the diagram at any 

 station by a sufficiently sensitive seismograph, the approximate 

 distance of the origin of a shock. Or, if the seismographic 

 records be simultaneously taken at two or more stations, we 

 can, from the comparison of the durations of the preliminary 

 tremors, easily fix the approximate position of the origin. I 

 give next a few illustrations of the application of equation (1). 



12. The durations of the preliminary tremors of the two 

 large earthquakes of the 5th August, 1897, and of the 23rd 

 April, 1898, recorded instrumen tally at the Meteorological 

 Observatory of Miyako (lat. 39°38^ long. 14r590 were re- 

 spectively 22 and 13 seconds, the corresponding durations in 

 Tokyo being, as given in § 6, 45 and 54 seconds. According 

 to equation (1), the distances of the origins of these two earth- 

 quakes from Miyako would respectively bo about 190 and 120 

 kilometres, while the corresponding distances from Tokyo would 

 be 360 and 430 kilometres. The positions of the origins as 

 determined by the intersections of the circles drawn with radii 

 equal to these distances about Miyako and Tokyo as centres 

 are, as indicated in fig. 2, not very different from those to be 

 inferred from the isoseismal lines. 



13. The earthquake of the 8th June, 1898 ; 9.10 a. m. 

 The earthquake was recorded by my Horizontal Pendulum at 

 Miyako, the machine having been set up there just the day 

 before. It was also signalised by the seismograph at the Miyako 



