EAKTH TKEMORS. 



321 



and the other perpendicular to such a direction. These 

 movements, according to Bertelli, have no connection 

 with the wind, rain, change of temperature, and atmo- 

 spheric electricity. 



The disturbances, as recorded at different towns, are 

 not always strictly synchronous, but succeed each other at 

 short intervals. If, however, we take monthly curves of 

 the disturbances as recorded at different towns in Italy, 



P J F M A M J 



SON 



Bologna I874-J875 



Pome 1874 - 1875 

 Florence 1874-1875 



Mallets Curve 

 5879 Earthquakes 



Mean Micros!esmi& Curve 



for Florence 



1872-1876 



Fig. 38. 



we see that these are similar in character. The maximum 

 of disturbance occurs about the winter solstice, and the 

 minimum about the summer solstice, and in this respect 

 they exhibit a perfect accordance with the curves drawn 

 by Mallet to show the periodicity of earthquakes. The 

 accompanying curves taken from one of Bertelli's original 

 memoirs not only show this general result but also show 



