and espeeiallt/ in Scotland. 269 



and reflux was repeated four other times, during an hour. 

 The first rise was the greatest. 



(4.) Dublin. At 5'' 49' p. m., the sea suddenly rose about 

 two feet, and then retired. This was repeated several times. 



(5.) Barbadoes. At 7^ 50' p. m., the sea suddenly retired 

 from the land, and in about 3' returned. In about 3i^ hours 

 the fluctuations abated ; but in two hours after, they were re- 

 newed. 



From these data, it may be inferred that the wave of this 

 earthquake travelled to 

 (1.) Scilly Isles and Mounts Bay, at the averag^e rate of 2 miles per min., 



(2.) Dublin, 2.1 



(3.)Carrick, 2.7 



(4.) Lisbon, •••.... 3.2 

 (6.) Barbadoes, 7.4 



These rates of transmission agree very closely with those 

 deduced from the earthquake of 1755. The wave, on this oc- 

 casion, took longer to travel to Lisbon and Mounts Bay, be- 

 cause it seems to have originated nearer the coast than in the 

 earthquake of 1755, and therefore traversed shallower parts 

 of the ocean to these places.* 



It will be observed, that, on both occasions, the sea is stated 

 to have retired from the land in many places, before it rose. 

 It is probable that the phenomenon occurred at all the places, 

 and was not observed, in consequence of its being less likely 

 to attract attention than the rise of the sea, and from having 

 occurred at the commencement. 



Indeed, when the nature and cause of the earthquake-wave 

 are considered, it is manifest that the sea had everywhere re- 

 tired first. That the elevation of the sea must, at the point 



* From the foregoing data, an approximative estimate may be made of 

 the depth of the Atlantic Ocean. Mr Scott Eussell in his Report on Waves 

 (British Association Reports, vol. vi. p. 446), states, that he had observed a 

 wave have a velocity of 20 miles per hour, where the depth was 53 fathoms. 

 Applying the rule before referred to, that the velocity of the wave is propor- 

 tional to the square root of the depth, — this would give a depth of 26 miles, 

 between Barbadoes and that part of the Atlantic Ocean, where the wave 

 originated. This is more than double what La Place estimated the average 

 depth of the entire ocean to be in all parts of it ; it may, therefore, be not 

 far from the truth in regard to the central parts of the Atlantic Ocean. 



VOL. XXXI. NO. LXII. OCTOBER 1841. S 



