266 Mr D. Milne on Earthquake- Shocks in Great Britain^ 



high water, the sea suddenly retired. In less than 8' it flowed 

 back with the utmost rapidity. The sea continued thus to 

 sink and swell alternately for half an hour. 



(3 ) Kinsale (Ireland). Between 2 and 3 p. m., when the 

 weather was **very calm," a large body of water burst sud- 

 denly into the harbour, which broke the cables of two sloops, 

 though each moored with two anchors. The sea then retired, 

 whirling the vessels and boats with inconceivable rapidity. 

 It continued to swell and fall in this way for about 10'. 



(4.) Swansea. At 6^ 21' p. m., " a great head of water 

 rushed with a great noise" up the Bristol channel. Two large 

 vessels, (one above 200 tons), had their moorings broken by it. 



(5 ) Barbadoes. At 5^ 20', " the sea ebbed and flowed in a 

 most surprising manner."* 



(6.) Antigua. The occurrence of waves is mentioned as 

 having been first observed here at &^ 58' p. m. 



From the foregoing data, it would appear that the wave of 

 the Lisbon earthquake travelled to 



Plymouth^ at the average rate of 2.1 miles per minute, 



It is obvious that the difi^erences in the rates of progression 

 may be explained by the differences in the depths of the ocean 

 traversed by the wave. It has been ascertained by expe- 

 riment, that the velocity of a wave is nearly proportional 

 to the square root of the depth.t 



* History of Earthquakes, p, 328. 



t Reports of British Association, vol. vi. p. i3©. 



