ON SEISMOLOGICAL INVESTIGATIONS, 61 
these places or at any other station in the world. The distance 
between these places is 80 degrees, and the times taken for com- 
pressional, distortional, and surface waves, or P,, P, and P,, to travel 
this distance would be 15, 24, and 50 minutes. A disturbance 
originating in Java might after one of these intervals be recorded 
in Cairo or it might in the vicinity of Cairo bring into existence 
a secondary disturbance. There would be practically the same time 
intervals between the observations at these two places if the primary 
disturbance had its origin somewhat to the East of Java. Had the 
origin of the primary been between Batavia and Cairo the time 
intervals might be anything less than the given three intervals. If 
the time intervals exceed 50 minutes it is extremely likely that these 
two records refer to independent earthquakes. 
The following are illustrations of records peculiar to Batavia and 
Cairo made in 1911 :— 
Feb. 4at 7.8 in Batavia and 64 m. later in Cairo. 
2 Feb. Sat 4.0 ae xt $5 
Feb. 9 at 18.40 . 42 m. 4 
| Feb. 10 at 17.25 i 42 m. a 
Feb. llat 0.54 sk 2. 2m: * - Felt in Sumatra. 
March 6at 9.57 5 11 m. earlier in Cairo. 
March 19 at 0.59 G 41 m. later in Cairo. 
April 26 at 10.0 a 16 m. ra 
Aug. 2at 10.7 55 22 m. <i 
Aug. 19 at 0.49 12m . Felt in Sumbawa. 
Sept. 14 at 23.16 in Samoa and 19 m. later in Cairo. 
The fact that with but one exception all these disturbances were 
recorded at Batavia before they were recorded at Cairo suggests that 
their origins were nearer to the former place than the latter. 
Well-equipped stations nearer to Batavia than Cairo, and at which 
we should have expected to find records of these earthquakes, are 
the following: Mauritius, Tokio, Irkutsk, Zikawei, Tsing-tau, Calcutta, 
Bombay, Kodaikanal, Manila, Perth, Sydney, Wellington, Christ- 
_ church, Tiflis, Beirut, Harpoot, and Tashkend. 
X. Recurrence of Megaseismic Groups. 
Between 1899 and 1909 I find 88 groups of megaseisms. The 
number of disturbances in a group varies from 2 to 14, while the 
number of days over which a group extends varies between 1 and 
25. The former numbers divided by the latter give what I call the 
seismicity of a group period. If three earthquakes have taken place on 
one day I call the seismicity 3, but if four have happened in 5 days 
T call it 8. These seismicities, or earthquake-activity numbers, vary 
between 4 and 3. In the following lines I give in the form of 
numerators and denominators the relationship between seismicities 
and the average number of days of rest which have followed each 
group. 
‘ed 5 6 “7 ao} 9 1: 12 “9 . . 
ES ae a: ea: er: oa FA: Peis (7) 
No definite conclusion can be drawn from these figures, but in 
connection with them I must call attention to a.somewhat similar 
investigation referred to in the Report for 1910, p. 54, where it is 
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