AND SEMI-ANNUAL SEISMIC PERIODS. 
1165 
Summary of Results. 
82. Annual Period. —The number of seismic records examined is 62, 45 belonging 
to the northern hemisphere, 14 to the southern, and 3 to equatorial countries. Only 
five fail to indicate a fairly well-marked annual period, namely. South-east Europe 
(Perrey), East Indies (Bergsma), New Zealand, Districts V. and VI. (Hector), and 
Chili (Fuchs) ; and in all these cases the failure may, I think, be attributed to incom¬ 
pleteness in the seismic record. Different lists for the same district do not always 
give the same date for the maximum epoch, though in most cases they agree closely 
enough. The principal exceptions are Italy, Zante, Japan, West Indies, and the 
Southern Hemisphere ; and in the three first of these districts the discrepancy may, 
perhaps, be explained. Excluding these somewhat doubtful cases, the distribution in 
time of the maximum epochs is given in the following table : — 
Northern 
hemisphere. 
Equatorial 
countries. 
Southern 
hemisjjhere. 
January .... 
6 
0 
0 
Februaiy .... 
1 
I 
0 
March. 
0 
0 
0 
April. 
I 
0 
2 
May. 
I 
I 
2 
J line . 
I 
0 
0 
July. 
0 
0 
3 
August. 
1 
0 
2 
September 
0 
0 
0 
October .... 
3 
0 
0 
November. 
4 
0 
0 
December .... 
16 
0 
0 
These figures strongly support the view that the maximum of the annual period 
ocmrs during the local ivinter in each hemisphere. The evidence for equatorial 
countries is somewhat scanty, but it shows that in them, also, there is a well-marked 
annual period. If we were to include the two districts of India and Peru, Bolivia and 
Quito as equatorial, this conclusion will be further strengthened, the date of the 
maximum epoch being variable. 
83. In amplitude, the results given by different lists for the same districts are 
more variable; and this is due in a great measure, I believe, to different definitions 
of the unit earthquake. This is esj^ecially shown in three cases in which the 
periodicity has been investigated both with my own definition and with that adopted 
by the cataloguer (§§ 45, 46, 59, 60, 76, 77). 
The amplitude of the annual period ranges from '05 (New Zealand) to ’67 (Sicily 
and Algeria). The average amplitude obtained from 57 records is ‘33 ; the corre¬ 
sponding ratio of the number of shocks in the maximum and mininum halves of the 
year is 1‘53, or, roughly, 3 : 2. 
