268 Mr D. Milne on Earthquake- Shocks in Great Britain, 



This table has been constructed in the same way as the one 

 applicable to the earthquake of 1755 ; and it establishes the 

 same general result, that the shock reached different parts of 

 the earth's surface, at periods corresponding with their dis- 

 tances from a central point. 



The discrepancy in the rate at which the shock appears to 

 have travelled to different places, may in both tables be to a 

 great degree accounted for by some error in the reported 

 time of its arrival. But it may be expected, that some dif- 

 ference in the actual rate of transmission should occur, if there 

 be, as is probable, a variation in the density and structure of 

 the earth's crust in the parts traversed. 



On comparing the two tables, it will be observed, that, in 

 the last, the interval between the times of arrival of the shock 

 at the earth's surface, was much less in the earthquake of 

 1761 than in that of 1755. It may be inferred from this, that 

 the point where the shock originated, was in this last earthquake 

 much deeper below the surface than in the former one.* 



To the phenomena noted in the last-mentioned table, some 

 additional facts may be given, as to the propagation of the wave. 



(1.) Carrick, on the river Sure, about thirty miles from the 

 sea, on the south coast of Ireland. At 3^^ 52' p. m., the water 

 in 5' rose to the height of 4 feet ; at Dungarvon the fluctua- 

 tions are said to have commenced about 3^^ 53' p. m. At 

 Kinsale, the sea ebbed and flowed several times, taking 4' to 

 ebb and 4' to flow. The first fluctuation was the greatest. 



(2.) Scilly Isles. The sea rose here at 4^ 40' p. m., and con- 

 tinued for two hours in a state of fluctuation. 



(3.) Mounts Bay (Cornwall). At 4*' 45' p. m., the sea sud- 

 denly flowed upon the land, then it retreated ; and this flux 



* On the 2d February 1816, at Oh 40' a. m., a severe earthquake was felt at 

 Lisbon, which lasted almost an entire minute. The oscillations seemed to 

 pass from NE. to SW. Abundance of rain fell immediately after. This 

 earthquake was felt not only throughout the whole of Portugal, but also at 

 Madeira and in Holland. It is not known whether the concussion was per- 

 ceived in Great Britain. A ship at sea, about 120 leagues W.SW. from 

 Lisbon, felt the shock about two minutes after it was perceived there ; and 

 another ship, about 270 leagues from Lisbon also W.SW. from it, felt it 

 about six minutes after it was perceived there {Annalcs do Chiraie et de 

 Physique, tome xi. p. 324). 



