Xll CONTENTS. 



PAGB 



Waves as recorded in countries distant from the origin — Records 

 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 , . . . . 163 



CHAPTER X. 



DETERMINATION OF EARTHQUAKE ORIGINS. 



Approximate determination of an origin — Earthquake -hunting in 

 Japan — Determinations by direction of motion — Direction in- 

 dicated by destruction of buildings — Direction determined by 

 rotation — Cause of rotation — The use of time observations — 

 Errors in such observations -Origin determined by the method 

 of straight lines — The method of circles, the method of hyper- 

 bolas, the method of co-ordinates — Haughtons method — Differ- 

 ence in time between sound, earth, and water waves — Method 

 of Seebach , .187 



CHAPTEK XI. 



THE DEPTH OF AN EARTHQUAKE CENTRUM. 



The depth of an earthquake centrum — Greatest possible depth of 

 an earthquake — Form of the focal cavity 213 



CHAPTER XII. 



DISTRIBUTION OF EARTHQUAKES IN SPACE AND TIME. 



General distribution of earthquakes— Occurrence along lines — Ex- 

 amples of distribution — Italian earthquake of 1873 — In Tokio — 

 Extension of earthquake boundaries — Seismic energy in relation 

 to geological time ; to historical time — Relative frequency of 

 earthquakes — Synchronism of earthquakes —Secondary earth- 

 quakes . • • 226 



