The salts contained in sea water, and to which it owes its peculiar bitter and unpleasant taste, form about three and a half per cent. of its weight, and consist principally of common table salt (chloride of sodium), and the sulphates and carbonates of magnesia and lime. But, besides these chief ingredients, there is scarcely a single elementary body of which traces are not to be found in that universal solvent. Wilson has pointed out fluoric combinations in sea water, and Malaguti and Durocher (Annales de Chimie, 1851) detected lead, copper, and silver in its composition. Tons of this precious metal are dissolved in the vast volume of the ocean, and it contains arsenic sufficient to poison every living thing. Animal mucus, the product of numberless creatures, is mixed up with the sea water, and it constantly absorbs carbonic acid and atmospheric air, which are as indispensable to the marine animals and plants as to the denizens of the atmospheric ocean. In inclosed seas, communicating with the ocean only by narrow straits, the quantity of saline particles varies from that of the high seas. Thus the Mediterranean, when evaporation is favoured by heat, contains about one half per cent. more salt than the ocean; while the Baltic, which, on account of its northern position, is not liable to so great a loss, and receives vast volumes of fresh water from a number of considerable rivers, is scarcely half so salt as the neighbouring North Sea. In the open ocean, the perpetual circulation of the waters produces an admirable equality of composition: yet Dr. Lenz, who accompanied Kotzebue in his second voyage round the world, and devoted great attention to the subject, found that the Atlantic, particularly in its western part, contains a somewhat larger proportion of salts than the Pacific; and that the Indian Ocean, which connects those vast volumes of water, is more salt towards the former than towards the latter. * * * * * As water is a bad conductor of caloric, the temperature of the seas is in general more constant than that of the air. The equinoctial ocean seldom attains the maximum warmth of 83°, and has never been known to rise above 87°; while the surface of the land between the tropics is frequently heated to 129°. In the neighbourhood of the line, the temperature of the surface-water oscillates all the year round only between 82° and 85°, and scarce any difference is perceptible at different times of the day.