ON SEISMOLOGICAL INVESTIGATION. 



8^ 



Nos. 333, 337, and 338. In the 'Toronto World 'of September 25 we 

 read that on September 3, about 2.30 p.m., houses in Yakuta Bay were 

 rocked violently, doors were slammed, dishes rattled, and tables moved. 

 On September 10, about eight o'clock, a more violent movement occurred. 

 Trees swayed, and there were slight shakes every few minutes. Just as 

 the earthquake ceased tidal waves came rolling in. There were three of 

 these waves following each other at intervals of about five minutes. The 

 rise was 15 feet from low tide to a foot above the highest tide point. 

 On the island of Ivanak, opposite Yakuta, a graveyard sank so that on 

 the next day a boat was able to row over the place where it had been, 

 and the tops of the submerged trees could be seen. 



These shocks disturbed the declinometer, duplex, and vertical force 

 magnetographs in Toronto. 



Scanty as these notes are, they apparently indicate an origin somewhat 

 to the east of that shown in Plate III. 



The period of the earth waves for No. 333 as recorded at Shide was 

 15 seconds, whilst the maximum angle of tilting was 8". With a velocity 

 of 3 km. per second, and the assumption that the motion is simple harmonic, 



so that the height of the waves=-— • tan a, where ^=len2th of wave and 



* 27r *= 



a=maximum angle of tilting, we may conclude that these waves were 

 45 km. in length and 29 cm. in height. With periods of at first 40 and 

 afterwards 15 seconds for the disturbance recorded in the Isle of Wight 

 on September 10, No. 338, it would appear that at first there were waves 

 120 km. long and 39 cm. high, followed by others 45 km. long and 43 cm. 

 high. Whether we can accept vertical displacements of this order repre- 

 senting accelerations not unf requently ^^ of gravity is yet suh judice, and 

 an experiment to confirm or modify these conclusions is now in progress. 



250. The key to the origin of this group is given by earthquake No. 250. 

 From Sefior Jose Zandizas, director of the observatory in Mexico, we 

 learn that it took place on January 24, 1889, at approximately llh. 

 45.5m. P.M. It was severe, caused some damage, but it cannot be siad 



