CHAPTER IX. 



DISTURBANCES IN THE OCEAN. 



Sea vibrations — Cause of vibratory blows— Sea waves : Preceding 

 earthquakes ; Succeeding earthquakes — Magnitude of waves — 

 Waves as recorded in countries distant from the origin — Kecords 

 on tide gauges — Waves without earthquakes — Cause of waves — 

 Phenomena difficult of explanation — Velocity of propagation — 

 Depth of the ocean — Examples of calculations — Comparison of 

 velocities of earthquake waves with velocities which ought to exist 

 from the known depth of the ocean. 



Sea vibrations. — Whilst residing in Japan I have had 

 many opportunities of conversing with persons who had 

 experienced earthquakes when on board ships, and it has 

 often happened that these same earthquakes have been 

 recorded on the shore. For example, at the time of every 

 moderately severe earthquake which has shaken Yoko- 

 hama, the same disturbance has been felt on board the 

 ships lying in the adjoining harbour. In some cases the 

 effect had been as if the ship was grounding ; in others, as 

 if a number of sharp jerks were being given to the cable. 

 The effect produced upon a man-of-war lying in the 

 Yokohama harbour on the evening of March 11, 1881, 

 was described to me as a 'violent irresistible shaking.' 

 Vessels eighty miles at sea have recorded and timed shocks 

 which were felt like sudden blows. These were accom- 

 panied by a noise described as a * dull rattle like 

 thunder.' 



