288 



OCEAN. 



1 1 has been calculated that the land of the northern 

 hemisphere is to the sea of the same as 419 to 1000 ; 

 in thr soul lirrn hemisphere, the proportion is as 129 

 to 1000. To account for this great disproportion, it 

 has been conjectured that there is a great southern 

 continent surrounding the south pole ; but the voy- 

 ages of navigators have not revealed the existence of 

 such an extent of land. The bed of the ocean presents 

 the same irregularities of aspect as the surface of the 

 land. It is diversified by rocks, mountains, plains, 

 and deep valleys. In some places it has been found 

 impossible to reach the bottom : but the notion that 

 it is any where without a bottom is incompatible 

 with the spherical figure of the earth. The mean 

 depth of the ocean has been shown, by Laplace, to 

 be about the same as the mean height of the conti- 

 nents and islands above its surface, which does not 

 much exceed 3000 feet. This distance is but a small 

 fraction of the excess of the equatorial over the polar 

 radius, which is about 60,000 feet. The greatest 

 depth that has ever been sounded is 7200 feet (by 

 Scoresby, in 1819). But it is probable that there 

 are deep cavities or valleys in the bed of the ocean 

 corresponding to the elevation of the mountains on 

 the surface of the earth. 



Sea-water is well known to contain foreign sub- 

 stances mixed with it ; its saltness and bitterness 

 give it an extremely disagreeable taste. Its specific 

 gravity varies from 1-0269 to 1-0285. The degree 

 of saltness differs according to different localities; 

 but the difference is not very great. In 100 parts 

 of sea- water the greatest proportion of salt is 3 - 77, 

 and the smallest 3-48. The experiments of Spar- 

 maim go to show that the water of the surface, while 

 it is less salt than that at a considerable depth, is 

 much more bitter. Gulfs or inland seas, such as the 

 Baltic, are less salt than the main ocean, on account 

 of the quantity of fresh water poured in by rivers. 

 The polar seas are less salt than the equatorial, ow- 

 ing to the low temperature of the former, which dis- 

 poses them to deposit the saline substances. Natu- 

 ralists have endeavoured to account for the saltness 

 of the sea ; some have supposed it to be caused by 

 primitive banks of salt at the bottom ; but if such 

 banks exist, they have probably been formed by de- 

 posits from the water, rather than been the cause of 

 its saltness ; others have ascribed it to the corruption 

 of vegetable and animal matter conveyed to the sea 

 by rivers ; but if this is true, the saltness would be 

 increasing. Some have conceived the ocean to be 

 the residue of a primitive fluid, which held in solu- 

 tion all the substances of which the earth is com- 

 posed, and on depositing the others, retained the sa- 

 line principles which it still contains. The only 

 method of freeing sea-water from its salt is by distil- 

 lation ; and the process is so slow, that it can rarely 

 be applied to any practical purpose. Even after dis- 

 tillation it retains its bitter taste. This bitterness, 

 which renders sea-water so nauseous, probably pro- 

 ceeds from animal and vegetable matter in a state of 

 decomposition. The most common ingredients found 

 in it are muriatic acid, sulphuric acid, soda, lime, and 

 magnesia. These substances in combination may 

 form six salts ; but it is not probable that all of these 

 latter actually exist at the same time. They are 

 muriate of soda, or common salt, muriate of magne- 

 sia, or Epsom salt, sulphate of soda (Glauber's salt), 

 &c. The saltness of the sea-water does not preserve 

 it from corruption, as is shown by the water in a 

 ship's hold, arid sometimes even in the equatorial seas 

 after a long calm. Many substances are corrupted 

 more rapidly by being plunged into it ; and its odour, 

 when 'corrupted, is extremely offensive. It is pre- 

 served pure by its constant motion. 

 The general colour of the sea, in the open ocean, 



is a deep greenish-blue ; the blue tint, which is pre- 

 dominant, seems to proceed from the same cause as 

 the colour of the sky ; the blue rays being reflected 

 in the greatest quantity on account of their superior 

 refrangibility. The other shades, which have some- 

 times been observed in different seas, seem to be 

 owing to local causes, and often, perhaps, to optical 

 illusions. In approaching soundings, the water as- 

 sumes a lighter shade. The luminous appearance of 

 the sea by night is an imposing and magnificent phe- 

 nomenon. It has been ascribed by some to animals 

 of the zoophyte and mollusca classes, which are said 

 to possess phosphorescent qualities ; some attribute 

 it to the phosphorescence of decaying animal and 

 vegetable substances ; others to the spawn of fish. 

 Some have explained it to be the effect of friction. 

 But the appearances are extremely different at differ- 

 ent times, and all these causes probably operate to 

 produce them. 



Observations made, on the temperature of the sea, 

 show that the sun's rays rarely penetrate below the 

 depth of forty-five, or, according to some, of 113 

 fathoms, below which the sea receives no light, and 

 consequently little or no direct heat from the sun ; 

 and that the temperature increases with the depth to 

 a certain degree, but never to freezing. The con- 

 stant motion of the sea contributes, in some measure, 

 to render its temperature equable. (See Ice.) " We 

 must distinguish," says Humboldt, " four different 

 phenomena with respect to the ocean ; the temper- 

 ature of the water at the surface in different latitudes ; 

 the decrease of temperature in the lower strata ; the 

 effect of waves on the temperature of the surface ; 

 and the temperature of currents. The region of 

 warmest water is between 5 45' N., and 6 15' S. 

 lat. ; and different observations give from 82 to 84 

 as the maximum. In the parallel of warmest wa- 

 ters the temperature of the surface of the sea is 

 from 3 to 5 higher than that of the superincumbent 

 air." The observations of Humboldt also show that 

 both in the Atlantic and Pacific, in changing the lati- 

 tude and longitude, the waters often retain nearly the 

 same temperature over a great extent, and that be- 

 tween 27 N. and 27" S. lat., the temperature of the 

 sea is entirely independent of the changes in the at- 

 mosphere. From the equator to 25 or 28 N. there 

 is a remarkable constancy of temperature, but in 

 higher latitudes there is more change. See Tem- 

 perature. 



The great periodical oscillations of the sea, caused 

 by the attraction of the sun and moon, are treated of 

 in the article Tides; the particular movements, which 

 prevail in different parts of the ocean, and set in 

 different directions, are described in Hie article Cur- 

 rents. See also Winds. 



In some places springs of fresh water are observed 

 to issue from the sea, entirely unaffected by the salt 

 water. The most remarkable of these phenomena 

 are in the gulf of Spezia, in the Persian gulf, and in 

 the bay of Xagua, on the south coast of Cuba. It is 

 probable that these are subterraneous streams, which 

 find their way under the bed of the ocean, until they 

 encounter a fissure, into which they are impelled in 

 the same manner as spouting springs on land. 



A variety of plants are nourished by the ocean, to 

 which are given the general denomination of fuci, 

 and which are vulgarly known by the names of sea- 

 weed and rock-weed. Some species adhere to tho 

 bottom, while others rise to the surface even from u 

 depth of sixty fathoms. In the North Atlantic there 

 is a space extending between lat. 20 and 40 N., 

 and Ion. 20 and 45 W. f which is at all seasons 

 covered with a species of weed (fucus natans) of a 

 beautiful green colour, whence the Dutch navigators 

 called this tract Kroos Zee, Duck- weed sea. (See 



