244 



EARTHQUAKES. 



1. While the smallest or miDimum paroxysmal inter- 

 vals may be a year or two, the average interval is from 

 five to ten years of comparative repose. 



2. The shorter intervals are in connection with periods 

 of fewer earthquakes — not always with those of least in- 

 tensity, but usually so. 



3. The alternations of paroxysm and of repose appear 

 to follow no absolute law deducible from these curves. 



4. Two marked periods of extreme paroxysm are ob- 

 servable in each century, one greater than the other — 

 that of greatest number and intensity occurring about 

 the middle of each century, the other towards the end of 

 each. 



The form of the curves which Mallet has drawn seem 

 to indicate that seismic energy came in sudden bursts, 

 and then subsided, gradually gathering strength for another 

 exhibition. This is continually seen in the shocks ex- 

 perienced in various seismic areas — a large shock, or the 

 maximum of the activity dying out by repeated small 

 shocks on succeeding days. 



Mr. I. Hattori, writing on the large earthquakes of 

 Japan, remarks that on the average there has been one 

 large earthquake every ten years. They, however, occur 

 in groups, as shown in the following table. 



No. of shocks 



Period 



Interval 



6 



A.D. 827-836 



10 years 



6 



„ 880-890 



10 „ 



4 



„ 1040-1043 



4 „ 



5 



„ 1493-1407 



5 „ 



4 



„ 1510-1513 



4 „ 



5 



„ 1645-1650 



6 „ 



5 



„ 1662-1664 



3 „ 



4 



„ 1853-1856 



4 „ 



Dr. E. Naumann, who has also written on the earth- 



