THE OCEAN. 327 



In the year 1843, while in the South Atlantic, the weather calm and the water smooth, 

 Sir James C. Ross sounded with a line of 4600 fathoms, or 27,600 feet, equal to nearly 

 5| miles, and found no bottom. The particular spot was in latitude 15 3' S., and 

 longitude 23 14' W., about midway between the coast of South America and the 

 island of St Helena. Subsequently, to the south of the great banks of Newfoundland, no 

 bottom has been found with a line of 34,200 feet ; but in latitude 36 49' S., longitude 

 37 6' W., in the South Atlantic, bottom has been found with a line of 46,236 feet. This is 

 the longest line that has ever been used, upwards of eight miles ; but Lieutenant Maury 

 believes that no depth has yet been ascertained beyond all possibility of doubt greater than 

 25,000 feet. It is, however, very certain that the ocean has depths corresponding to the 

 height of the loftiest terrestrial mountains. Between Valentia Bay in Ireland and St 

 John's in Newfoundland, the points selected for the establishment of telegraphic 

 communication between the two continents, the Atlantic has a soft and uniformly level 

 bed, the greatest depth of which is 12,480 feet. This is at a point somewhat nearer 

 Ireland than the opposite coast. As the pressure of the ocean increases with the depth, it 

 must be enormous in its profound abysses. A sensible proof of it came under the notice 

 of Captain Scoresby. A piece of wood that got entangled, and was drawn down by a 

 whale, was found when hauled up so saturated with water forced into its pores, that it 

 sank like a stone for a twelvemonth afterwards instead of floating. 



Some variations of level are observed between different sections of the universal ocean, 

 chiefly occurring in land-locked seas, as the effect of local currents. Thus the equatorial 

 current flowing westward across the Atlantic causes an accumulation of water in the Gulf 

 of Mexico, where its progress in that direction is arrested by the continent, and raises the 

 surface above the level on the opposite coast of Africa where the current commences. The 

 detached basin of the Black Sea is likewise considerably higher than the Mediterranean, 

 for it receives a much larger proportionate supply of river- water, and is subject to much 

 less evaporation. Hence there is a strong and powerful stream constantly flowing 

 from the former to the latter, through the Bosphorus, the Sea of Marmora, and the 

 Dardanelles. 



The saltness of the ocean is one of its prime characteristics ; but we are profoundly 

 ignorant of its cause, and are almost equally in the dark as to its design. In addition to 

 pure water, it has been ascertained by the analysis of different chemists, to hold in solution 

 chloride of sodium, or common salt, the chlorides of potassium and magnesium, the 

 sulphates of magnesia and lime, besides the animal and vegetable matter, in a state of 

 decomposition, mechanically suspended in the fluid. The curious fact has also been 

 recently ascertained that it contains a certain proportion of silver. The great specific 

 gravity of sea-water, resulting from these ingredients, explains its buoyancy. The 

 proportional gravity of different kinds of water may be stated to be as follows : 



Sea-water - 1 -028 I Pure spring-water - 1 '001 to 1 '005 



River-water - 1-010 ' Distilled water - TOGO 



The sea was formerly supposed by physical inquirers to be the saltest under the equator ; 

 but Humboldt has deduced from good experiments conclusions as follows : 



Proportion of salt between and 14 lat. =0*0374 



15 26 -- =0-0394 



30 44 =0-0386 



50 60 =0-0372 



Prom this table it appears that the saltness of the ocean is greater towards the tropics 

 than at the equator, and least towards the poles ; for which a reason may be found in the 



