THE CAUSE OF EARTHQUAKES. 291 



that a'marked connection would be found. But it must 

 be remembered that because researches, so far as they 

 have gone, tend to show that earth movements are more 

 frequent when an area is relieved of a load, it is not 

 unlikely that the greatest number of earthquakes may 

 be found to occur at low water. Prof. W. 8. Chaplin 

 attempted to make this investigation in Japan, but not 

 being able to obtain the necessary information respecting 

 the tides, was compelled to relinquish this interesting 

 work. 



Every foot of rise in a tide is equivalent to a load 

 being placed on the area over which the tide takes place 

 of sixty-two pounds to the square foot. This load is not 

 evenly distributed, but stops abruptly at a coast line. 

 Lastly, it may be observed that many coast lines are not 

 simultaneously subjected to stresses consequent upon this 

 load. Japan, for instance, may be regarded as an arch 

 placed horizontally. The area near the crown of this 

 arch is loaded by the tidal wave crossing the Pacific before 

 the areas near the abutment, and farther there is a 

 horizontal pressure at the crown which, if Japan were 

 like a raft, would tend, as the tide advanced, to straighten 

 its bow -like form, but as the wave passed its abutments 

 to increase its curvature. 



Prof. Gr. Darwin has calculated the amount of rise and 

 fall of a shore line due to tidal loads (see p. 336, ' Earth 

 Pulsations '). The result of these calculations apparently 

 indicates that these loads may have a considerable in- 

 fluence upon the stability of an area in a more or less 

 critical condition. 



Mr. J. Carruthers suggests that tidal action may hold 

 a general but indirect relationship to volcanic and seismic 

 action by the retardation it causes on the earth's rotation. 

 By this retardation the polar axis tends to lengthen, and 



