DISTEIBUTION OF EARTHQUAKES IN TIME. 243 



regular curve. At this point, however, the decrease be- 

 comes slightly more rapid, and is represented by a second 

 curve. If, instead of calculating ordinates for my curve, 

 in which intensity has been considered, simply the number 

 of earthquakes are counted, a similar result is obtained. 

 From this it appears that the rate at which seismic 

 energy decreased during the last 500 years was about 

 the same as that at which it decreased during the 500 

 years previous to this period. 



If the lists for the Italian and Turco-Hellenic districts 

 could be similarly analysed, and the earthquakes of any 

 particular district picked out from the others, it is very 

 probable that a similar decrease or alteration in seismic 

 energy might be observed. 



Provided that we have at our disposal records of the 

 various earthquakes which have occurred in any given 

 district during a sufficiently long period of time, one 

 conclusion that we may expect to arrive at is that we 

 shall be able to trace some variation in the seismic 

 activity of that district. For the Kioto area, it has been 

 shown that there is a diminution in seismic activity, 

 In other districts, however, there may possibly be an 

 increase.^ 



Relative frequency of earthquakes. — A question which 

 is of great interest to those who dwell in shaken districts 

 is as to how often disturbances may be expected to occur. 



From a general examination of this question, consider- 

 ing the earthquakes of the whole world. Mallet arrived at 

 the following conclusions : — 



* A notable example of a rapid diminutioa in the number of earth- 

 quakes felt at a place is that of Comrie in Scotland. In 1839-40, no 

 less than sixty shocks were felt in eleven months. In 1842-43, about 

 thirty shocks were felt, and in the following year thirty-seven. Since 

 this time the number of shocks has decreased until they are almost of 

 as rare occurrence at Comrie as in other portions of the British Isles. 



