SEMI-ANNUAL SEISMIC PERIODS. 
1117 
cases, namely, the series felt at Tiflis in Georgia in 1804, at Pignerol and other places 
in Piedmont during 1808 and following years, at Lunroe in Norway, beginning in 
1819, and at Pesaro in Italy during the year 1826. The period investigated is that 
embraced by the third part of Mallet’s catalogue—the years 1785-1842 inclusive. 
Eig. 3. 
It seemed desirable to limit it thus closely in order to avoid any considerable 
variability in the estimation of a “ slight ” shock. The total number of such shocks" 
is 187. The curves of the annual and semi-annual periods are shown in fig. 3. 
Period. 
Maximum. 
Amplitude. 
Annual. 
Semi-annual. 
June, h 
f January, h 1 
1 July, h / 
•16 
•27 
Destructive Earthquahes .—Only those earthquakes have been counted in which it 
is expressly stated that some damage was done to buildings. The whole of the 
Christian era is included, but the first earthquake on which the month and day are 
Eig. 4. 
definitely stated occurred in the year 528, and in several succeeding centuries the 
year is frequently the only date given. The total number of destructive earthquakes 
recorded by Mallet is 641. The curves of the annual and semi-annual period are 
shown in fig. 4. 
