PHYSICAL GEDGRAPHY. 305 



Disturbances of equilibrium and consequent movements of 

 (he waters are partly irregular and transitory, dependent upon 

 winds, and producing waves which sometimes, at a distance 

 from the shore and during a storm, rise to a height of more 

 than 35 feet ; partly regular and periodic, occasioned by the 

 position and attraction of the sun and moon, as the ebb and 

 flow of the tides ; and partly permanent, although less in 

 tense, occurring as oceanic currents. The phenomena of 

 tides, which prevail in all seas (with the exception of the 

 smaller ones that are completely closed in, and where the ebb- 

 ing and flowing waves are scarcely or not at all perceptible), 

 have been perfectly explained by the Newtonian doctrine, 

 and thus brought " within the domain of necessary facts." 

 Each of these periodically-recurring oscillations of the waters 

 of the sea ha? a duration of somewhat more than half a day. 

 Although in the open sea they scarcely attain an elevation of 

 a few feet, they often rise considerably higher where the waves 

 are opposed by the configuration of the shores, as, for instance, 

 at St. Malo and in Nova Scotia, where they reach the re- 

 spective elevations of 50 feet, and of 65 to 70 feet. " It has 

 been shown by the analysis of the great geometrician La- 

 place, that, supposing the depth to be wholly inconsiderable 

 when compared with the radius of the earth, the stability of 

 the equilibrium of the sea requires that the density of its fluid 

 should be less than that of the earth ; and, as we have already 

 seen, the earth's density is in fact five times greater than 

 that of water. The elevated parts of the land can not there- 

 fore be overflowed, nor can the remains of marine animals 

 found on the summits of mountains have been conveyed to 

 those localities by any previous high tides."* It is no slight 



operations we have further confirmation of the equilibrium of the wa- 

 ters which coinmunicate round Cape Horn. (Arago, in the Annuaire 

 du Bureau des Longitudes pour 1831, p. 319.) I had inferred, from 

 barometrical observations instituted in 1799 and 1804, that if there were 

 any difference between the level of the Pacific and the Atlantic (Ca- 

 ribbean Sea), it could not exceed three meters (nine feet three inches). 

 See my Relat. Hist., t. iii., p. 555-557, and Annates de Chimie, t. i., 

 p. 55-64. The measurements, which appear to establish an excess of 

 height for the waters of the Gulf of Mexico, and for those of the noi-th- 

 ern part of the Adriatic Sea, obtained by combining the trigonometrical 

 operations of Delcrois and Choppin with those of the Swiss and Aus- 

 *rian engineers, are open to many doubts. Notwithstanding the form 

 of the Adriatic, it is improbable that the level of its waters iu its north- 

 ern portion should be 28 feet higher than that of tlie Mediterranean at 

 Marseilles, and 25 feet higher than the level of the Atlantic Ocean. 

 See my Asie Centrale, t. ii., p. 332. 

 * Bessel, Ueber Fluth niid Ebbe,in Schumacher's JaAriwc^, 1838, s. 225 



