1883.] The Earthquake ofSlst Decemher, 1881. 63 



Memorandum hy Major M. W. Rogers, R. E., Deputy Superintendent, 

 4ith grade, on the earthquake of the ^Ist December, 1881, and the great 

 sea-waves resulting therefrom, as shown on the diagrams of the tidal 

 observatories in the Bay of Bengal. 



Port Blair mean time is used throughout. Latitude 11« 40' 30'' N., 

 longitude 92<> 45' E. 



The tide-wave can be traced clearly on the diagrams at seven tidal 

 stations, viz., Port Blair, Paumben, Madras, Negapatam, False Point, 

 Dublat, and may be suspected on an eighth, viz., Diamond Harbour, on the 

 Hooghly. 



At Port Blair, in the Andaman Islands, the first indication of the 

 shock is at 7h. 42m. A. M., and this, I am inclined to think, is due to the 

 earth-wave, or rather to the forced sea- wave, which is formed when the 

 earth-wave gets into shallow water ; for the tidal curve goes on undis- 

 turbed for some 30 minutes afterwards, and it is not until 8h. 10m. a. m. 

 that the first wave is recorded, followed by others in succession at about 

 15 minutes' interval, with a height of about 3 feet from crest to hollow. 

 The diagram is unfortunately incomplete, for the pencil of the gauge, in 

 its violent oscillations, caught in and tore the paper of the diagram, and 

 the clerk, being frightened, stopped the driving clock, which was not start- 

 ed again until 1 P. M. There is evidence that the waves continued to 

 follow one another with great regularity until about 3 p. m., when they 

 became of a much smaller size, but are traceable until 9 p. m. Small 

 shocks were felt on Ross Island all that day, and the violence of the great 

 shock, which damaged the barracks and did other injury, seems to indicate 

 that the centre of impulse could not have been far from the Andamans. 



At Madras, there is a trustworthy time for the advent of the earth- 

 wave ; it is obtained from the Telegraph Ofiice, where the shock affected 

 the recording instruments. It occurred at 7h."56m. a. m (7h. 5m. 45s. 

 Madras time), whilst the great sea-wave reached at lOh. 10m. a. m., and 

 continued until 7 p. M., with intervals of about an hour from crest to crest, 

 and the influence of the disturbance can be traced until 10 P. M. 



At Negapatam, the first and largest wave came in at lOh. 10m. A. M , 

 with a height of nearly four feet from crest to hollow, and it was succeed- 

 ed by a series at about half hour intervals, which continued until midnight. 

 Judging from the diagrams, the sea at this port seems to have been more 

 affected by the earthquake than at any other. 



At Paumben, the first wave was registered at llh. 35m. a. m., and was 

 followed until midnight by a succession of waves with about two hours' 

 interval between them. 



At Vizagapatam, the first wave was recorded at lOh. 48m. a. m., and 



