328 



PHYSICAL GEOGRAPHY. 



immense amount of the equatorial rains, and the neighbourhood of the polar snows, which 

 diminish its intensity. In the water of the Firth of Forth, an analysis of Dr. Thomson 

 gives ^th of saline contents, and in the neighbourhood of Great Britain -g^th of the 

 whole weight is salt. The origin and object of this peculiar constitution of sea-water 

 is one of the mysteries of physics. Why so great a difference between the waters 

 of the ocean and of the land ? Why are the former hateful alike to man and beast, 

 covering such a mighty expanse as they do, and feeding by evaporation, and in some 

 cases by filtration, the pure springs and streams which keep both man and beast alive ? 

 The saline quality of the ocean water alone does not preserve it from corruption. 

 The water of the Nile never becomes putrid, although kept for any length of time in 

 small vessels in a house, or in large cisterns out of doors. But that of the ocean soon 

 becomes offensive in the hold of a ship, and the state of the equatorial seas, after a long 

 calm, answers, to some extent, to the strong phrase of Coleridge, " the very deep doth 

 rot!" With reference to the cause of its saline quality, we only know the fact, that dif- 

 ferent salts are constituents of the, terraqueous system ; that beds of rock-salt of enormous 

 thickness, as in Cheshire and Poland, form part of the crust of the globe ; and analogy 

 leads to the conclusion, that immense banks of the mineral exist in the bed of the deep. 



Local causes operate in various parts of the ocean to lessen its saltness ; as at the 

 mouths of rivers, where large volumes of fresh water are constantly mingling with its 

 waves. The singular circumstance also has previously been referred to of freshwater 

 springs rising up in the midst of the sea. Humbolclt was informed by Don Francisco le 

 Maur, that in the Bay of Xagua, to the south-east of the island of Cuba, springs of this 

 kind gush up from the bottom with such force as to prove dangerous to small canoes ; and 

 that vessels sometimes take in supplies from them, while the lamartin, or freshwater 

 cetacea, abound in the vicinity. There are similar fountains in the Persian Gulf, which 

 furnish the inhabitants of Aradus with their ordinary drink ; and in several places in the 

 volcanic regions of the Mediterranean, the sea is fresher at great depths than at the sur- 

 face, owing to the presence of these springs ; a phenomenon which is not uncommon near 

 the islands of the Pacific. ^ 



The waters of inland seas are commonly less saline than those of the main ocean, 

 especially where they communicate with it by very narrow channels, and receive numerous 

 and extensive rivers. This is strikingly the case with the Baltic. Analysis shows that 

 three pounds of its water will yield about 390 grains of salt, while the same quantity 

 taken from the German Ocean, with which it is connected, contains 747 grains. This 

 small degree f saltness is to be attributed to the narrowness of its outlet, and to the 

 numerous rivers that flow into it, which drain more than one fifth of the surface of Europe, 

 and are fed by a larger amount of snow than falls in any other inhabited country of the 

 world. The average weight of the Baltic water, taken from the centre, is to that of fresh 

 water as 1-038 or 1-041 to 1-000, while that of the Atlantic is as 1-288. There are some 

 variations in the quality of the waters of this inland sea, which seem to depend upon their 

 locale, with reference to the ocean and the rivers. Thus, those of the Gulf of Bothnia con- 

 tain less salt than other portions of the Baltic, and here the in-flowing streams are the most 

 numerous, and the out-lying ocean at the greatest distance. The quality of the water 

 also changes according to the seasons ; for while at midwinter 50 tons of water taken from 

 the Gulf of Bothnia will yield a ton of salt, it will require 300 tons at midsummer to 

 produce the same quantity. It is the larger amount of fresh water poured into the 

 gulf, through the melting of the snows at the commencement of the summer, that con- 

 tributes to this result. The direction of the wind likewise largely influences the character 

 of the Baltic water. Its specific gravity, as ascertained by the experiments of Wilcke, 

 under the circumstances stated, is as follows : - 



