AND SEMI-ANNUAL SEISMIC PERIODS. 
1139 
California, &c. 
59. *E. S. Holden, “ List of Recorded Earthquakes in California, Lower California, 
Oregon, and Washington Territory” (Sacramento, 1887). 
Duration of record, 1850-1886. Number of earthquakes, 949 (fig. 17). 
The six-monthly means for October, November, and December being very nearly 
equal, it is possible that the epoch of the maximum of the annual period may be 
placed too early. 
Fig. 17. 
Period. 
Maximum. 
Amplitude. 
Annual. 
October, h 
•30 
Semi-annual. 
r April, 1 1 
\ October, a J 
•16 
Annual barometric . 
December, b and January, b 
60. In Table A. of his memoir (p. 11) Professor Holden has given the number of 
earthquakes for each year groujDed in monthly intervals. Using these figures, we 
have the following results (the number of earthquakes being 768) :— 
Period. 
Maximum. 
Amplitude. 
Annual. 
October, b 
•19 
Semi-annual. 
f April, a 1 
\ October, a J 
•16 
Thus, while the maximum e230chs are practically the same, as also the amplitude of 
the semi-annual period, the amplitude of the annual period increases with the number 
of earthquakes, that is, by including a greater number of slight shocks. 
7 F 2 
