1883.] Tie IlarthquaJce ofSlst Becemher, 1881. 65 



If we assume that tlie centre of impulse in this ease was at the point 

 mentioned, it will be found that it, and Port Blair and Kisseraing, are 

 almost in a straight line. The distance from Port Blair to Kisseraing is 

 400 miles ; and if we assume that the mark on the diagram at the former 

 place at 7h. 42m. was due to the earth-wave, it took 13 minutes to travel 

 400 miles, which gives a rate of 30 miles per minute— a velocity which I 

 find mentioned in books on the subject as probable under favourable cir- 

 cumstances. With this velocity the central shock should have taken place 

 at 7h. 35m., the distance to Madras, &c., being a little over 600 miles. 

 The distance from this assumed centre of impulse to Port Blair is 218 

 miles, which would take seven minutes in transit and cause the shock to 

 be felt there at 7h. 42m. 



This fixing of the locality of the centre is of course merely hypotheti- 

 cal : the whole of the region is volcanic. Narcondam and Barren island^ 

 to the east of the Andamans, are volcanoes, the latter having been in erup- 

 tion as late as 1792 j the only thing certain is that the centre must have 

 been not far from Port Blair and Car-Nicobar, and about equi-distant from 

 the whole of the east coast of the Bay of Bengal, and also it must have 

 been subaqueous in order to have caused such distinct tidal waves. 



All the times of the earth-wave reaching places on the west side of 

 the Bay agree very fairly ; but in all the cases except those mentioned, the 

 times are not likely to be sufficiently accurate to aid in the investigation. 



The force of the earthquake was great at Port Blair, where it did 

 damage to the barracks, &c., and at the Island of Car-Nicobar it was felt 

 severely, the huts of the natives and many of their palm-trees being 

 thrown down. 



Several slight shocks were felt at Port Blair on the same day and the 

 two succeeding days, and The Commonwealth, which, as mentioned, felt the 

 shock of the 31st December, felt three shocks again on the 1st January ofE 

 the Island of Car-Nicobar. All this points to there having been consi- 

 derable subterranean disturbances in those regions at that time. 



I can find no trustworthy indication of tlie direction of the motion as 

 felt at the various places. At Madras there are three estimations of it : 

 one north to south, and two others north-east to south-west ; whilst the 

 clerk of the tidal observatory says that there were two shocks-^the first 

 north to south and the second east to west. Mr. liendell, at False Point, 

 states that the direction appeared to him to be from north-west to south- 

 east, whilst a person at Calcutta says that it ap|3eared to go from west to- 

 east. At Kisseraing Island the motion was so slight that I could not 

 decide on any direction. My first impression was that it came from the- 

 west, but after careful consideration I could not decide sufficiently satisfao^ 

 torily to place it on record. 



