Vol. 62.] OP THE INTEKIOE OF THE EAKTH. 461 



The first of these disturbances is the group of earthquakes which 

 originated in September, 1899, off the coast of Alaska. The times 

 of origin can be determined from the records of the Italian 

 Observatories, which lay at distances of from 73° to 81°, and the 

 only records worth considering here are those from Cape Town, 

 at a distance of about 150° from the origin. In all of them the 

 commencement is almost imperceptible, and the recorded times, as 

 compared with the times of origin, show that it was too late to 

 represent the first phase of the original impulse, except possibly in 

 the case of the third of these shocks, which gives an interval of 

 21*5 minutes. The second phase is well marked on all the records, 

 and the times, as determined by me, on photographic copies of the 

 original records, give intervals of 44-6, 45*7, and 45*5 minutes 

 respectively l ; the true interval, therefore, may be taken as about 

 45 minutes or a little more. 



The second is the Ceram earthquake of September 29th, 1899. 

 The place of origin of this earthquake can be fixed with a great degree 

 of accuracy from Dr. Verbeek's description, 2 as close to 3°-5 S. lat., 

 128 0, 5 E. long. The time is not accurately known from local 

 observatories : but the earthquake was well recorded by distant 

 seismographs, and the records have been collected by Dr. E. Rudolph. 3 

 At Batavia, 22°-4 from the origin, the commencement was at 17 h 

 7*3 m , and at Calcutta, 46°'4 distant, the time was 17 h ll*4 m . Making 

 the allowances indicated by Table I (p. 472), these give the time of 

 origin as 17 h 3'l m and 17 h 3*2 m respectively, which might be taken as 

 near the true time of origin; but it will be noticed that the average- 

 curve drawn on fig. 1 (p. 462) makes the averages just used to be 

 about a minute and a half too early. The difference is due to one or 

 other of the causes noticed above ; and it will be better to adopt the 

 intervals indicated by the time-curve, and accept 17 h l'5 m G.M.T. as 

 the probable time of origin. 



Accepting this as the time of origin, we get a group-average of 

 observations from stations at distances of 103 o, 4 to 112°*2, the 

 mean value being 110 o, 3 ; the mean interval for the first phase, 

 from six records, is 17*1 minutes, and for the second phase, for ten 

 records, is 27*3 minutes. At Cordoba (Argentina), 143° from the 

 origin, the record as published in the British Association Seismo- 

 logical Circulars, gives the commencement at I7 h 21*8 m and the 

 maximum at 17 h 44*3 m Greenwich time. A tracing of the record 

 shows that this belongs to the second phase, which is well marked, 

 and commenced about *5 min. earlier. This gives intervals from 

 the origin of 20*3 minutes for the first, and 42-3 minutes for the 

 second phase. 



Such are the materials available. As may be noticed, there are 

 discrepancies, and the time-intervals do not increase regularly with 



1 In the first case, the time is a little uncertain, owing to failure of the 

 occulting watch. See Brit. Assoc. Seistnological Circular, No. 1, 1900. 



2 ' Kort Verslag over de Aard- en Zeebeving op Ceram den 30 Sept. 1899 ' 

 Natuurkundig Tijdschrift voor Nederlandsch-Indie, vol. lx (1900) pp. 219-28 



3 Beitrage zur Geophysik, vol. vi (1904) pp. 238-66. 

 Q.J.G.S. No. 247. 2i 



