Specific Gravity. 10030 Wind at E. 1.0047 Wind at W. Specific Gravity. 10118 Storm at W. 10098 Wind at N. W. It appears from this table, that the proportion of salt in the waters of the Baltic is least when the wind is east, greater when it is west, and greatest during the prevalence of a westerly storm. This is readily explained. An east wind co-operates with the natural current of the Baltic to keep out the waters of the open sea, while a west wind checks the current, changes its direction, and causes an influx from the ocean. Sometimes, during a strong easterly gale, the Baltic water is sufficiently fresh to be fit for domestic use. It is owing to its inferior saltness and scanty depth, that its shores are ice-bound, and large portions of its surface are frozen over, during a severe season. In the year 1333, the sea presented a surface of solid ice from the Danish islands to the coast of Prussia, over which for some time communication was uninterruptedly maintained, and public-houses were erected along the road. The Swedish monarch Charles X. marched his army in 1559 over both Belts to the conquest of Zealand, and in 1809 the Russian soldiers travelled across the ice from Finland to Sweden. The water of the Mediterranean exhibits a striking difference to that of the Baltic, containing a somewhat larger proportion of salt than the ocean. The specific gravity of the Atlantic west of the Straits of Gibraltar has been found to be 1.0294, while that of the Mediterranean to the east of the Straits is 1.0338. This is perhaps the combined effect of a variety of causes, and may be due to the mineral character of its bed, to the strong current which sets into it from the Atlantic, and to the extensive evaporation to which the water of this close sea is subject, produced by a temperature which is five or six degrees higher than that of the ocean under the same latitude. From a series of experiments made some years ago by Dr. Marcet, the following general conclusions were deduced: 1. That the Southern Ocean contains more salt than the Northern Ocean, in the ratio of 1.02919 to 102757. 2. That the mean specific gravity of sea water near the equator is 1.0277. 3. That there is no notable difference between sea water under different meridians. 4. That there is no satisfactory evidence that the sea at great depths is more salt than at the surface. 5. That the sea in general contains more salt where it is deepest, and that its saltness is always diminished in the vicinity of large masses of ice. 6. That small inland seas, though communicating with the ocean, are much less salt than the ocean. 7. That the Mediterranean contains rather larger proportions of salt than the ocean. Sea water taken from the surface has a bitter as well as a saline taste, which does not belong to it when taken from a considerable depth. This is supposed to arise from animal and vegetable matter, in a state of decomposition, impregnating the surface fluid. To the same cause, the extraordinary presence of sulphuretted hydrogen in various parts of the ocean is attributed. The evolution of this gas has been observed in water brought by Captain Hall from the Yellow Sea in the Chinese Ocean; in a specimen brought by Mr. Schmidtmeyer from N. L. 10° 50' and W. L. 24° 26', which had an hepatic smell, and blackened the bottle in which it was contained; and it exists in large quantities in the waters along the north-west coast of Africa. Vessels going to the latter region were observed to have their copper sheathing speedily injured; a fact which attracted attention to the composition of the water, of which eight bottles, taken up in different places, were submitted to Professor Daniell for analysis. He found the saline contents in the proportions usually appertaining to sea-water, but analysis disclosed a strong impregnation with sulphuretted hydrogen, which in the case of a portion taken from Lopez Bay amounted to almost as much per gallon as in the Harrowgate waters. It was shown by subsequent investigations that this gas impregnated the seas and rivers along shore, in enormous quantities, through an extent of more than 16° of latitude. Speculating upon its cause, the distinguished chemist remarks:- "It appears to me, that there are only two sources to which it can with any probability be referred, namely, submarine volcanic action, in which case its evolution might be considered direct or primary; and the reaction of vegetable upon the saline contents of the water, in which case it would be secondary. The probability of a volcanic origin is, I think, small, from the absence, I believe, of any other indications of volcanic action, and from the great extent of the coast along which it has been traced. What is known of the action of vegetable matter upon the sulphates, and the immense quantities of vegetable matter which must be brought by the rivers within the influence of the saline matter of the sea, renders, on the contrary, the second origin extremely probable. Decaying vegetable matter abstracts the oxygen from the sulphate of soda, and a sulphuret of sodium is formed. This again, acting upon water, decomposes it, and sulphuretted hydrogen is one of the products of the decomposition." There can be no doubt but that extensive banks of vegetable detritus have been formed at the mouths of the rivers of the west coast of Africa. They flow from an interior country rich with the luxuriance of a tropical vegetation, and roll along in immense floods in the rainy season, bringing down masses of decaying foliage into the ocean; and what renders the preceding explanation the more certain, is, that those inlets along the coast of India, where the bottom contains carbonaceous matter, display the evolution of the same gas. With this circumstance, the unhealthiness of the West African stations, which has obtained for Sierra Leone the title of "the white man's grave," is intimately connected, for it has been experimentally found that so small a mixture as a fifteen hundredth part of sulphuretted hydrogen in the atmosphere acts as a direct poison upon small animals. The mangrove swamps in all parts of the world are notoriously unhealthy, arising from the tree requiring salt water for its growth, the sulphates of which are decomposed by the decaying vegetable matter which is annually furnished. The colour of the ocean is one of its sensible properties which has exercised the sagacity of a great number of inquirers to account for it, but the problem has not yet been entirely resolved. Sea-water is colourless when viewed in small quantities, but appears to be of a blue tint when seen in the mass. Scoresby compares the general hue of the polar seas to an "ultramarine blue;" M. Costaz assimilates that of the Mediterranean to a perfectly transparent solution of the "most beautiful indigo," or to "celestial blue;" and Captain Tuckey characterises the waves of the Atlantic in equinoctial regions as of “bright azure.” A blue, more or less deep, is undoubtedly the prevailing tint, for the blue rays of light are most apt to be reflected from masses of transparent fluid; and hence both the sea and the air appear of this colour. But the ocean remarkably varies its hue at the same place. It is observed by Humboldt, that towards evening, when the edges of the waves, as the sun shines upon them, are of an emerald green, the surface of the shaded side reflects a purple hue. Nothing, he states, is more striking than the rapid changes which the ocean undergoes beneath a serene sky, where no variations whatever are to be perceived in the atmosphere. In the midst of the tropical deep the water passes from an indigo blue to the deepest green, and from this to a slate grey, without any apparent influence from the azure of the sky or the colour of the clouds. In general the sea between the tropics is of a more intense and purer azure than in high latitudes. The ocean often remains blue when, in fine weather, the greater part of the sky is covered with light and floating fleecy clouds. Humboldt concludes his observations upon the tints of the ocean, and its changes from blue to green, with some general remarks, the substance of which is embodied in the succeeding paragraphs. Whatever relates to the colour of water is extremely problematic. The green tint of the snow waters that flow from the Alpine glaciers, which contain very little air in solution, might induce the belief that this colour is appropriate to water in its greatest purity. Chemistry is addressed in vain to explain this phenomenon, or that of the beautiful greenish blue colour of ice in a mass, or that of the blue of the Rhone near Geneva. There is hitherto no proof that waters exist which contain a greater or less degree of hydrogen; and the refrigeration of the seas in tempests is much too weak to permit us to attribute the reflection of different coloured rays to the mere change of density. It is improbable that the green colour of the water is owing to the mixture of yellow rays from the bottom, and blue rays reflected by the water; for the open sea is often green where it is more than four thousand feet deep. Perhaps, at certain hours of the day, the red or yellow light of the sun contributes to the colouring it green. The waves, like moveable and inclined mirrors, progressively reflect the shades and tints of the atmosphere from the zenith to the horizon. The motion of the surface of the water modifies the quantity of light that penetrates towards the inferior strata; and it may be conceived that these rapid changes of transmission, which act as it were like changes of opaqueness, may, when they are united to other causes unknown to us, change the tint of the ocean. The colour of the general body of the sea-a blue more or less intense-is far from being universal. In various parts of its basin other shades appear, the causes of which are local, and are due to the existence of vast numbers of minute animalculæ; to a marine vegetation at or near the surface; to the nature of the soil at the bottom, or to the infusion of earthy substances in the water. The Mediterranean, towards its eastern extremity, has occasionally a purple hue. In the Gulf of Guinea the sea is white; about the Maldive Islands, black; and near the shores of California it has a reddish appearance. The reddish tinge marks the waters near the mouth of the La Plata, and prevails also in the Red Sea-whence its name. The colour in this latter locality has been definitely investigated by Ehrenberg, who refers it to the prevalence of a species of Oscillatoria, a family of microscopical animalculæ. In the spring of the year 1825, it was observed that the waters of the Lake of Morat, in Switzerland, had almost the hue of blood, which De Candolle demonstrated to proceed from an animal, figured and described by the botanist under the name of Oscillatoria rubescens, which confirms the conclusion of Ehrenberg respecting the peculiar tinge of the Red Sea waters. It will be recollected, that on the return of Captain Ross from his first expedition to the polar seas, much surprise was excited by his account of the red snow, as it was termed, observed upon some of the snow mountains near the shores of Baffin's Bay. But a similar phenomenon is of annual occurrence in the Alps, though not much noticed, because of its occurrence at a season when few travellers visit the country. Minute red grains appear scattered upon the snow in March, which usually are entirely gone by the close of May. Saussure has given an account of this appearance as occurring on the Great St. Bernard, but it is most abundant on Mount Breven, situated on the sunny side of the valley of Chamouni. The grains penetrate two or three inches into the snow, and are of a lively red colour, occurring chiefly where the snow lies in a cavity, deepest near the centre, and very faint upon the borders. Saussure came to the conclusion that it was the pollen of an Alpine plant, but no plant has ever been discovered in Switzerland to yield such a product. A similar opinion was entertained with reference to the red snow brought home by Ross, when the residue was examined, after the water had been evaporated. In all probability, the red tinge observed on the Arctic and Alpine snows, proceeds from precisely the same cause as that which coloured the waters of the Lake of Morat, and originates the tinge of the ocean at the mouth of the La Plata, in the Red Sea, and along the coast of California-the presence of minute forms of animal life. The waters of the ocean vary in their clearness, from a crystalline transparency to a dulness bordering on opacity. Those of the North Sea, along the west coast of the Scandivanian peninsula, have been remarked by all observers for being of an extraordinary transparency, which has, perhaps, no parallel in any other region. Here are those inlets of the sea, wild and romantic in their aspect, called the fiords of Norway, a name analogous to the Scottish firth, both having the same Norse derivation. "Nothing can be more surprising," says Sir A. de Capell Brooke, "and beautiful than the singular clearness of the Northern seas. As we passed slowly over the surface, the bottom, which here was in general a white sand, was clearly visible, with its minutest objects, where the depth was from twenty to twenty-five fathoms. During the whole Fiord of Norway. course of the tour I made, nothing appeared to me so extraordinary as the inmost recesses of the deep thus unveiled to the eye. The surface of the ocean was unruffled by the slightest breeze, and the gentle splashing of the oars scarcely disturbed it. Hanging over the gunwale of the boat, with wonder and delight I gazed on the slowly-moving scene below. Where the bottom was sandy the different kinds of asteriæ, echini, and even the smallest shells, appeared at that great depth conspicuous to the eye; and the water seemed, in some measure, to have the effect of a magnifier, by enlarging the objects like a telescope, and bringing them seemingly nearer. Now, creeping along, we saw, far beneath, the rugged sides of a mountain rising towards our boat, the base of which, perhaps, was hidden some miles in the great deep below. Though moving on a level surface, it seemed almost as if we were ascending the height under us; and when we passed over its summit, which rose in appearance to within a few feet of our boat, and came again to the descent, which on this side was suddenly perpendicular, and overlooking a watery gulf, as we pushed gently over the last point of it, it seemed almost as if we had thrown ourselves down this precipice, the illusion, from the crystal clearness of the deep, actually producing a sudden start. Now we came again to a plain, and passed slowly over the submarine forests and meadows, which appeared in the expanse below; inhabited, doubtless, by thousands of animals, to which they afford both food and shelter-animals unknown to man ; and I could sometimes observe large fishes of singular shape gliding softly through the watery thickets, unconscious of what was moving above them. As we proceeded, the bottom became no longer visible; its fairy scenes gradually faded to the view, and were lost in the dark green depths of the ocean." Mr. Barrow, while remarking the extraordinary clearness of the northern waters, in language equally as strong as that of the preceding statement, speaks of the reflection of the mountains being often as well-defined upon their surface as the rocks themselves, so that when viewed at a short distance it is no easy matter to decide where the line is that separates the water from the shore. This uncertainty, when crossing one of the fiords in a boat, has a most singular effect. Every thing appears upside down; houses upset, trees growing the wrong way, men walking on their heads, cattle on their backs; the whole appearance having an air of reality which for the moment beguiles the senses. Great transparency, in various places, belongs also to the tropical deep. This is its feature around the Bahamas - that solitary and singular cluster of several hundred rocks in the Atlantic, aptly compared to one of the beautiful nebulæ in the heavens, which to ordinary sight seems an indivisible patch of cloud, but when viewed through a telescope is found to be a collection of stars. "The number," says Moore, "of beautiful islets, the singular clearness of the water, and the animated play of the graceful little boats, gliding for ever between the islands, and seeming to sail from one cedar grove to another, form altogether the sweetest miniature of nature that can be imagined. The water," he adds in another place, "is so beautifully clear around these islands, that the rocks are seen to a very great depth; and as we entered the harbour they appeared to us so near the surface, that it seemed impossible we should not strike on them." In verse, addressed to the Dowager Marchioness of Donegal, as well as in prose, the writer has celebrated the waters of the Bahama coves and coasts: "Believe me, lady, when the zephyrs bland It is in the tropical seas, towards the heart of the torrid zone, that several remarkable phenomena are witnessed in perfection: the phosphorescence of the ocean-the flying-fish chased by the dolphin-successive regions of steady breezes, and calms interrupted by sharp and sudden squalls—and enormous deluges of rain, which generally descend in equatorial districts in a perfectly still state of the atmosphere. No spectacle is more imposing and magnificent than the luminous appearance of the sea at night in these latitudes. The path of a vessel seems like a long line of fire, and the water thrown up in her progress, or dashed by the waves upon deck, flashes like vivid and lambent flame. Sometimes myriads of luminous stars and spots float and dance upon the surface, assuming the most varied and fantastic aspects. This phosphorescent or shining appearance of the ocean is by no means uncommon, but most frequent in the equatorial seas; and is usually ascribed to animalculæ, which exist there in inconceivable numbers, and to the semiputrescent matter of plants and fishes, developing electricity. As Humboldt entered the torrid zone, the phosphorescence of the ocean seemed to augment greatly the mass of light diffused through the air, so that he was able to read, for the first time, the minute divisions of a small snuff-box sextant, without the assistance of a taper. A most remarkable display of this phosphoric light is thus related by Mrs. Somerville:-"Captain Bonnycastle, coming up the Gulf of St. Lawrence, on the 7th September, 1826, was roused by the mate of the vessel, in great alarm, from an unusual appearance. It was a starlight night, when suddenly the sky became overcast, in the direction of the high land of Cornwallis county, and an instantaneous and intensely vivid light, resembling the Aurora, shot out of the hitherto gloomy and dark sea, on the lee bow; which was so brilliant, that it lighted every thing distinctly, even to the mast-head. The light spread over the whole sea between the two shores; and the waves, which before had been tranquil, now began to be agitated. Captain Bonnycastle describes the scene as that of a blazing sheet of awful and most brilliant light. A long and vivid line of light, superior in brightness to the parts of the sea not immediately near the vessel, showed the base of the high, frowning, and dark land, abreast. The sky became louring, and more intensely obscure. Long tortuous lines of light showed immense numbers of very large fish, darting about as if in consternation. The spritsail-yard and mizen-boom were lighted by the reflection, as if gas-lights had been burning directly below them; and until just before daybreak, at four o'clock, |