THE CAUSE OF EARTHQUAKES. 293 



metric variation and tlie times at which earthquakes have 

 occurred. 



Three important laws of barometric variation are the 

 following : — 



1. In the world generally the average barometric 

 pressure is highest in winter. (Exceptions occur near 

 Iceland and in the North Pacific.) 



2. The summer and winter monthly mean barometer 

 differs least near the equator and over the great oceans. 

 They differ most over the great continents and generally 

 with increasing latitude. 



3. The greatest number of barometrical fluctuations 

 usually take place in winter. 



Inasmuch as there are generally more earthquakes in 

 winter than in summer, the first of these laws would 

 indicate that this might be due to the greater load which 

 acts upon the crust of the earth at that season. The 

 second law would indicate that the distinction between 

 the winter and summer earthquakes ought to be most 

 marked in high latitudes, which, if we refer to the table 

 on p. 257, we observe to be borne out by the results of 

 observation. The countries where there are as many 

 earthquakes in winter as in summer are chiefly those in 

 low latitudes. The number of these countries from which 

 we have records are, however, few. 



Facts opposed to the idea that earthquakes may be 

 caused by an increase of barometric pressure are the 

 results of observations like those of Schmidt and Eossi, 

 which show that earthquakes chiefly occur with a low 

 barometer. 



Assuming that these latter observations will be found 

 by future investigators to be generally true, we must 

 conclude that the relief of atmospheric pressure has an 

 influence upon the occurrence of earthquakes. Such a 



