292 EAETHQUAKES. 



tensile stresses are induced, resulting in fracture. The 

 fluid interior of the earth, being no longer restrained, 

 would move polewards, and, leaving equatorial portions 

 unsupported, this would gradually collapse. The primary 

 fractures would be north and south, while the secondary 

 fractures would be east and west.^ 



That the rise of the tide is accompanied by a greater 

 percolation of .water to volcanic foci, which, in conse- 

 quence, assume a greater state of activity, is a theory 

 which was advanced many years ago. To determine 

 how far tides may directly be connected with earthquakes, 

 the necessary records have yet to be examined. 



Variations in atmospheric pressure, — When we 

 consider the immense load which, by a sudden rise of 

 the barometer, is placed upon the area over which this 

 rise takes place, it is not difficult to imagine that this 

 rise may occasionally be the final cause which makes the 

 crust of the earth to give way. A barometric rise of 

 an inch is equivalent to a load of about seventy-two 

 pounds being put upon every square foot of area over 

 which this rise takes place. On the other hand, a fall 

 in the barometric column indicates that a load has been 

 removed, and whatever elastic effort may be exerted by 

 subterranean forces in endeavouring to escape, being 

 met by less resistance, they may burst these bonds, and 

 an earthquake will result. For reasons such as these 

 the final cause of earthquakes has often been attributed 

 to Variations in atmospheric pressure. In Japan there 

 are practically as many earthquakes with a high barometer 

 as with a low one. 



The extent to which barometric fluctuations have 

 acted as final causes in the production of earthquakes 

 may be judged of by a comparison of the times of baro- 



» Phil. Sue.,, Wellington, New Zealand, 1875. 



