12 THE PHYSICAL GEOGRAPHY OF THE SEA. 



and limited in depth only by the thickness of the soil which con- 

 tains them, have been set aside and sealed np for their use, be- 

 yond the reach of those thirsty winds or burning rays which are 

 suffered to carry off only the water which is superfluous, and 

 would be pernicious. They remove it to other lands, where its 

 agency is required, or treasure it up, as Ihe material of clouds 

 and dew, in the crystal vault of the firmament, the source, when 

 the fitting season comes round again, of those deluges of rain 

 which provide for the wants of the year. Such are some of the 

 examples which may be supplied of general laws operating over 

 nearly the whole surface of the terraqueous globe. Among the 

 local provisions ancillary to these are the monsoons of India, and 

 the land and sea breezes prevalent throughout the tropical coasts. 

 36. ""We have not noticed the tides, which, obedient to the sun 

 The tides. and moou, daily convey two vast masses of water 

 round the globe, and which twice a month, rising to an unusual 

 height, visit elevations which otherwise are dry. During one 

 half of the year the highest tides visit us by day, the other half 

 by night ; and at Bombay, at spring tide, the depths of the two 

 differ by two or three feet from each other. The tides simply 

 rise and fall, in the open ocean, to an elevation of two or three 

 feet in all ; along our shores, and up gulfs and estuaries, they 

 sweep with the violence of a torrent, having a general range of 

 ten or twelve feet — sometimes, as at Fundy, in America, at Brest 

 and Milford Haven, in Europe, to a height of from forty to sixty 

 feet. The tides sweep our shores from filth, and purify our riv- 

 ers and inlets, affording to the residents of our islands and con- 

 tinents the benefits of a bi-diurnal ablution, and giving a health, 

 and freshness, and purity wherever they appear. Obedient to the 

 influence of bodies many millions of miles removed from them, 

 their subjection is not the less complete ; the vast volume of wa- 

 ter, capable of crushing by its weight the most stupendous bar- 

 riers that can be opposed to it, and bearing on its bosom the na- 

 vies of the world, impetuously rushing against our shores, gently 

 stops at a given line, and flows back again to its place when the 

 word goes forth, 'Thus far shalt thou go, and no farther;' and 

 that which no human power or contrivance could have repelled, 

 returns at its appointed time so regularly and surely that the hour 

 of its approach, and measure of its mass, may be predicted with, 

 unerring certainty centuries beforehand. 



