BOOK nearly the nature of lakes, which have generally a higher level than the ocean. XIV. Chemical nature of Sea water contains, besides pure water, several extraneous substances, in proportions which vary in different places. Muriatic, or marine acid, vitriolic, or sulphuric acid, fixsea water. ed mineral alkali, magnesian, and sulphated lime, form in general the component parts. By boiling or by evaporation in the air, common salt is obtained, (muriate of soda,) which is preferred for salting meat, to the salt of springs. The saltness and bitterness of sea water, renders it disagreeable to the taste, and unfit for the use of man. Saltness of the sea. generally in all gulfs The saltness of the sea seems in general to be less towards Near Iceland, the sea contains of salt, In the Baltic Sea, to of its wt 7 5 miles to the north of Malta, 17 Sea water is in several places less salt at the surface than at the bottom. In the straits of Constantinople, the proportion is as 72 to 62. In the Mediterranean, as 32 to 29. It has been found, says Bergmann, that in the Eresund, the water taken at the surface, and from the * Physical Geog. i. 431. Comp. Ingenhousz, Experiments upon Vegetables, D. 284. + Hierne, Tentam. Chem. ii. 178. Swedenbourg, Miscel. Observat, 103. XIV. depth of 5 to 20 fathoms, was in proportion to melted BOOK snow water, as 10,047, 10,060, and 10,189 to 10,000. Water ought to be denser and heavier at a certain depth, and from the result of experiments, in which a pressure has been applied to it, equal to what it sustains 1,800 fathoms from the surface, it has been computed that at that depth it should be compressed by its own weight. Sea water, by acquiring additional saltness seems, at a certain depth, to lose its bitterness; so, at least, it appears from the observations of Sparrmann, who took up a bottle of sea water from the depth of 60 fathoms, and found it had the taste of fresh water, in which common salt had been dissolved. According to chemical analysis, it had very little magnesia.* 1 3 1000 of the salt ness of sea Sea water experiences great changes from the agitation Variations of the waves, from the variations of seasons, and from the action of the currents. Near Walloë, in Norway, where water. there is a salt-pit, it has been remarked, that the sea water taken at the surface contains of its weight of salt at the moment the ice is detached, which extends SO feet down; whilst the salt in every other season is in the proportion only of Upon the coasts of Cumberland, in England, a still stronger evaporation is experienced, as there is generally of salt in the sea water, which is sometimes reduced by excessive rains to Upon the coast of Malabar, the sea water sometimes becomes drinkable. In the Sound, the waters change their weight and saltness with the winds and currents: when they come from the east, the water weighs only 1 more than melted snow; on the contrary, when they come from the west, it weighs T. It is supposed that in Iceland the sea is more salt during the flow than the ebb of the tide, whilst in the Gulf of Bothnia, it is quite the contrary; for the inhabitants know by the progressive increase of the saltness during the ebb, 47 * Bergmann, dans la Magasin de Physique de Gotha, ii. cah. i. p. 99-101. (2d edit. German.) + Duhamel, Philos. Burg. cité par Bergmaun, i. 434. XIV. BOOK the moment when the flow approaches. In this gulf, the saltness of the sea is in general greater towards the winter, and less towards the summer solstice, which unquestionably arises not only from the flowing of the rivers, but also from the melting of the ice.* Origin of the salt ness of sea water. It is easier to perceive the great advantages resulting from the saltness of sea water, than to discover its origin. Without this saltness, and without the agitation in which they are continually kept, the waters of the sea would become tainted, and would be infinitely less adapted for the motion of vessels, and probably it is to this that the inhabitants of the ocean owe their existence. But whence comes this saltness? Is it from beds of salt lying at the bottom of the sea? These beds themselves appear rather to consist of deposits which the sea has formed by precipitation. Does the saltness originate from the corruption of river water? It seems, in fact, that the fresh water which is discharged into close and stagnant lakes becomes corrupted, decomposed, and forms deposits of salt. Now the ocean may be considered as a great lake, the common reservoir of all terrestrial waters. But in this case, it is said, that the saltness should increase from day to day. Halley, who broached this opinion,t wishes that experiments were made which, in future ages, might conduce to throw light on the subject. Several modern philosophers consider the sea as the residuum of primitive fluid, which must have held in solution all the substances of which the globe is composed; that these sea waters having deposited all the earthy principles, both acid and metallic, with which they were impregnated, there remains in their residuum, (which) is the present sea.) some of these elementary principles too intimately combined with water to escape from it; and with respect to the bitterness of sea waters, as it diminishes in proportion to the depth, it can arise solely from the great quantity of decomposed and putrifying animals and vege *Palmstruck, Officier Suédois, cité par Bergmann, 1. c. table substances which float in the ocean, and which the run- BOOK ning waters never cease to bring into it. XIV. Attempts drinkable. Various methods have been employed to render sea water drinkable. The only one which has succeeded is distilla- to render tion; but it requires too much care, and too much fuel to be sea water made use of frequently, or on a large scale. Even distillation does not divest sea water of all its bitterness, when it contains sal ammoniac. Thus mariners, though sailing in the midst of water, often see themselves exposed to all the horrors of dying of thirst when their stock of fresh water has been exhausted. But should they be fortunate enough to fall in with floating or fixed ice, pieces of it, when melted, afford them water which is fresh, although a little insipid.* The colour of the sea varies very much in appearance, but Colour of it is generally of a deep bluish green, which becomes clearer sea water. towards the coasts. This apparent colour of the sea seems to arise entirely from the same causes which impart a blue shade to distant mountains, and which give the atmosphere its azure hue. The rays of blue light, being the most refrangible, pass in the greatest quantity through the aquatic fluid, which, from its density and depth, makes them undergo a strong refraction. The other shades in the colour of sea waters, depend on causes which are local, and sometimes illusory. It is said that the Mediterranean Sea, in its upper part, has sometimes a purple tint. In the gulf of Guinea, the Sea is white, and around the Maldive Islands black. The Vermeille, or Vermillion sea, near California, has received its name from the red colour which it often assumes. The same phenomenon was observed at the mouth of the river Plata, by Magellan, and also in other places. It is not impossible that a great number of certain insects may, for some time, give a reddish or whitish tint to See, amongst others, Forster's Observations made during his Voyages, p. 50-52, (in German.) Brehmar, Nouvelle Méthode de Distiller l'Eau de mer, dans Voigt, Magasin des Sciences Naturelles, vii. 417, 8qq. BOOK an expanse of sea. The infusion of certain earthy or mineral substances, the nature of the soil, and other causes, may produce these appearances. The green and yellow shades of the sea arise from marine vegetables. In some places, these vegetables have been observed to rise to the surface of the water, and cover it entirely, as between the Canary and Cape de Verd Islands, in the road or rade which the Dutch call Kroos-zee, and the Marine ve- Portuguese Mare di Sargasso. This marine vegetation pregetation. sents, upon a large scale, phenomena similar to the efflores Light of the sea. Phospho reseence of sea cence upon lakes. In the lakes, there are very thin masses covered with hair, which rise during the day to the surface of the water, and sink beneath it during the night. The light, or sparkling of the sea, is a magnificent and imposing spectacle. Sometimes the vessel, while ploughing her way through the billows, appears to mark out a furrow of fire; each stroke of the oar emits a light sometimes brilliant and dazzling, at other times tranquil and pearly. These moveable lights are grouped in endless varieties. Here thousands of luminous points, like little stars, appear floating on the surface; and then, multiplying together, form one vast sheet of light. There the scene becomes more tumultuous, the refulgent waves heave up, roll, and break in shining foam. At other times, we see large sparkling bodies resembling the forms of fishes, pursuing each other, disappearing, and bursting forth anew. The explanation of this phenomenon has very much occupied the attention of philosophers. Valisneri, Rigaud, animals. Dicquemare,* have shewn, that, on a number of occasions, this light was produced by a little animal called the glowworm of the sea. This animal has a body extremely thin and transparent, is possessed of astonishing activity, and emits a dazzling and vivid light. The observations of Rigaud, Journal des Savans, 1770, Cahier, de Mai, Dicquemare, Journal de Physique, Octobre, 1775. Vianelli, Nuove Scoperti alle Luce Nocturne. Venise, 1746. |