290 EAETHQUAKES. 



magnitude. As the facts stand, it appears that the 

 maximum pulls exerted by the moon and sun are only 

 sufficient to cause a slight preponderance in the number 

 of earthquakes felt at particular seasons, and therefore 

 that these pulls only result in earthquakes when the 

 distorting effort has been exerted on an area which, by 

 volcanic evisceration, the pressure of included gases, and 

 other causes, is on the verge of yielding. 



Earthquakes and the tides, — If we assume that 

 earthquakes are in many cases due to the overloading of 

 an area and its consequent fracture, such loading may 

 occur by the rising of the tide. A belief that the earth- 

 quakes of Japan were attributable to the tides may be 

 found in the diary of Eichard Cocks under the date 

 November 7, 1618, who remarks: — 



'And, as we retorned, about ten aclock, hapned a 

 greate earthquake, which caused many people to run 

 out of their howses. And about the lyke hower the 

 night following hapned an other, this countrey being 

 much subject to them. And that which is comunely 

 markd, they allwais hapen at a hie water (or full sea) ; 

 so it is thought it chauseth per reason is much wind 

 blowen into hollow caves under ground at a loe water, 

 and the sea flowing in after, and stoping the passage 

 out, causeth these earthquakes, to fynd passage or vent 

 for the wind shut up.' ^ 



Although we may not acquiesce in Cock's views re- 

 specting the imprisoned wind, it would seem that a 

 comparison of the occurrence of earthquakes and the 

 state of the tide would be a legitimate research. Inas- 

 much as the stresses which are brought to bear upon an 

 area by the rising of the tide are so very much greater 

 than those due to barometrical changes, it is not unlikely 

 > iVa^wre, April 26, 1883. 



