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from Vulcan, the name which the Romans gave to their imaginary god of fire, and is applied to those mountains which send forth, from their summits or sides, flame, smoke, ashes, and streams of melted matter called lava. Upon ascending to the top of a mountain of this kind, there is found to be an immense and deep hollow, which is denominated the crater or cup.
From most of the volcanos which are not extinct, there is a smoke more or less frequently arising; but the eruptions, which are discharges of stones, ashes, lava, &c. accompanied with lofty columns of fire, violent explosions, and concussions of the earth, happen at irregular and sometimes very long intervals. It seems to be a very general rule that the greater the mass and the elevation of the mountain, the less frequent and more tremendous are the eruptions. Stromboli, the small volcano on one of the Lipari islands, is almost always burning ; Vesuvius has more frequent eruptions than Etna; while the immense summits of the Andes, Cotopaxi and Tungurahua, have an eruption hardly once in a century. The volcanos of America, besides the common lava and rocks, &c. cast out scorified clay, carbon, sulphur, and water, accompanied, in some instances, by fishes. The mountain of Maccaluba in Sicily, some hills near the town of Zaman in the Crimea, and a volcano which is situated towards the middle of the island of Java, in a plain abounding with salt springs, send forth eruptions of mud.
It is remarkable that, in the Old Continent, the principal chains of mountains contain no volcanos, and that islands and the extremities of peninsulas are alone the seats of these convulsions; while in the New World, the immense range which runs along the shore of the Pacific Ocean, possesses more volcanos than are to be met with in the whole of the Old Continent and its adjacent islands. No volcano has yet been discovered on the continent of Africa, but most of its groups of islands are distinguished by them. A line drawn round the great Pacific Ocean, so as to include the long range of mountains on the west of America, the Asiatic peninsula of Kamtschatka, and the islands
of Sumatra and Java, will have within it by far the greatest and most extensive volcanic system on the globe. From Terra del Fuego (the land of fire) to the peninsula of Alaska, a complete series of volcanos may be traced. The Aleutian islands, which stretch from that peninsula to the opposite peninsula of Kamtschatka, possess several. On Kamtschatka, there are some of great violence. The islands of Japan and Formosa have several ; and, beginning with Sumatra and Java, they are scattered over all that immense archipelago, which forms so remarkable a feature of the Pacific Ocean. In the Indian Ocean, the islands of St. Paul, Amsterdam, and Bourbon, have volcanos in action. The most formidable volcanos of the Mediterranean, are Etna in Sicily, and Vesuvius near the coast of Naples. Between these two mountains are the Lipari islands, all of volcanic character. The Atlantic Ocean contains several groups of this kind ; Iceland has suffered frequently from the terrific eruptions of its volcanos; the Azores and the Canaries, and some of the West India islands, also experience the effects of subterranean fire. In some places, parts of the land which are covered by the waters of the ocean, are the seats of volcanos; and it has sometimes happened that new islands have been formed during submarine eruptions. Several mountains bear evident marks of having, at some very distant period, been the outlets of fires, and, on this account, they are called extinct volcanos. Altogether about 205 volcanos are known, including only those which have been active within a period to which history or tradition reaches.
The vast body of water which surrounds the continents, and is the common réceptacle of their running waters, is indispensably necessary to the support of animal and vegetable existence upon the earth. Its perpetual agitations purify the air; and the vapours
which the atmosphere draws from its surface, being condensed and dispersed through the upper regions form clouds, which are the source of a constant supply of rain and moisture to the land. The ocean, also, by the facilities for communication which it offers, is the means of uniting the most distant nations, while it enables them to interchange, with mutual advantage, the productions of their several climates.
The bottom of the sea appears to have inequalities similar to those on the surface of the continents; the depth of the water is therefore extremely various. There are vast spaces where no bottom has been found; but this does not prove that the sea is bottomless, because the line is able to reach to but a comparatively small depth. If we were to found our opinion upon analogy, we might conclude that the greatest depth of the ocean is, at least, equal to the height of the loftiest mountains, that is, between 20,000 and 30,000 feet. Along the coast, its depth has always been found proportioned to the height of the shore. When the coast is high and mountainous, the sea that washes it is deep; but when the coast is low, the water is shallow. If we reckon its average depth at two miles, the ocean will contain 296 millions of cubical miles of water. We shall have a more specific idea of this enormous mass of water, if we consider that it is sufficient to cover the whole' globe to the height of more than eight thousand feet; and if this water were reduced to one spherical mass, it would form a globe of more than 800 miles in diameter.
The general colour of the sea is a deep bluish green, which becomes clearer towards the coasts. This colour is thought to arise entirely from the same cause as the azure of the sky; the rays of blue light, being the most refrangible, pass in the greatest quantity through the water, which, on account of its density and depth, makes them undergo a strong refraction. The other colours exhibited in parts of the sea, depend on causes which are local, and sometimes deceptive. The Mediterranean in its upper part is said to have at times a purple tint.. In the gulf of Guinea, the sea is white;
around the Maldive islands it is black; and in some places it has been observed to be red.
These appear. are probably occasioned by vast numbers of minute marine insects, by the nature of the soil, or by the infusion of certain earthy substances in the water. The green and yellow shades of the sea proceed frequently from the existence of marine vegetables at or near the surface.
The water of the sea contains several extraneous substances, in proportions varying in different places. The component parts, in addition to pure water, are commonly muriatic acid, sulphuric acid (vitriol,) fixed mineral alkali, magnesia and sulphated lime. By boiling or evaporation in the air, common salt (muriate of soda) is obtained, which for salting meat is preferred to the salt of springs. The saltness of the sea appears, with some local exceptions, to be less towards the poles than near the tropics; and, in particular places, it varies from temporary causes. The violent tropical rains have an effect in diminishing it, especially near coasts, where an increased volume of fresh water is brought down by the rivers. The Baltic is at all times less salt than the ocean, and when a strong east wind keeps out the North Sea, its waters are said to become almost fit for domestic
The most.curious phenomenon of all, is that of springs of fresh water rising up in the midst of the sea. In the bay of Xagua, on the southern coast of Cuba, springs of this kind gush up with great force at the distance of two or three miles from the land; and other occur near Goa, on the western coast of Hindostan, and in the Mediterranean Sea, not far from Marseilles. Various theories have been advanced to account for the saltness of the ocean. Some assert the existence of vast beds of salt at its bottom. Others have supposed that the sea nay have originally received all its saline para ticles from those existing on the surface of the earth, which were dissolved and carried down to the ocean by the action of the rivers. The most probable solution of the matter is, that it is an essential and absolute quality impressed upon it from the creation of the world by the Great Author of nature. Its presence,
united to the action of the tides and waves, preserves the vast mass of waters from corruption, and at the same time gives it a specific gravity sufficient to float the large bodies which move in it, or upon its surface. The bitterness which exists in sea-water, but apparently not beyond a certain depth, is with much probability considered to be owing to the vegetable and animal matter held there in a state of decomposition. From the same cause some account for the luminous appearance which the sea often presents at night, particularly in summer and autumn, while others ascribe it to electricity, or to innumerable minute animals moving rapidly through the water in all directions.
Water being a bad conductor of heat, the temperature of the sea changes much less suddenly than that of the atmosphere, and is by no means subject to such extremes as the latter. It is also modified by currents, which mingle together the waters of different depths and regions, and by the neighbourhood of shallows and banks. Thus bays, inland seas, and the spaces among clusters of islands, where the action of the waves is more confined, and the water usually of less depth than at a distance from land, are the most favourable places for the production and accumulation of marine ice. It is on this account that the navigation of the Baltic is annually stopped by the ice in a latitude not more northerly than that of tracts which, in the main ocean are always open to the passage of ships. In like manner, ice extends from five to eight degrees farther from the south than from the north pole, owing, it is probable, to the almost entire absence of land near the Antarctic Circle; while the north pole is so nearly surrounded by land, that the ice of the Arctic Ocean is shut up, and cannot be carried forward to such a distance by the current, which sets towards the equator.
The ocean has three kinds of motion. The first is that undulation which is produced by the wind, and which is entirely confined to its surface. The second motion is that continual tendency which the whole water in the sea has towards the west, which is greater near the equator than towards the poles. It begins on