to observe that there are many, and those very large caverns or hollows in the bottom of the sea, especially where it is rocky; and that the like caverns are sometimes found in the perpendicular rocks which form the steep sides of those fisheries. These caverns are often of great depth, as well as extent, and have sometimes wide mouths, and sometimes only narrow entrances into large and spacious hollows. The bottom of the sea is covered with a variety of matters, such as could not be imagined by any but those who have examined into it, especially in deep water, where the surface only is disturbed by tides and storms, the lower part, and consequently its bed at the bottom, remaining for ages, perhaps, undisturbed. The soundings, when the plummet first touches the ground, on approaching the shores, give some idea of this. The bottom of the plummet is hollowed, and in that hollow there is placed a lump of tallow; which, being the part that first touches the ground, the soft nature of the fat receives into it some part of those substances which it meets with at the bottom: this matter, thus brought up, is sometimes pure sand, sometimes a kind of sand made of the fragment of shells, beaten to a sort of powder, sometimes it is made of a like powder of the several sorts of corals, and sometimes it is composed of fragments of rocks; but beside these appearances, which are natural enough, and are what might well be expected, it brings up substances which are of the most beautiful colours. Dr. Donati, in an Italian work, contain ing an essay towards a natural history of the Adriatic Sea, has related many curious observations on this subject; having carefully examined the soil and productions of the various countries that surround the Adriatic Sea, and compared them with those which he took up from the bottom of the sea, he found that there is very little difference between the former and the latter. At the bottom of the water there are mountains, plains, vallies and caverns, similar to those upon land. The soil consists of diferent strata, placed one upon another, and mostly parallel and correspondent to those of the rocks, islands, and neighbouring continents. They contain stones of different sorts, minerals, metals, various putrified bodies, pumice stones, and lavas formed by volcanos. One of the objects which most excited his attention, was a crust, which he discovered under the water, composed of crusta ceous and testaceous bodies, and beds of polypes of different kinds, confusedly blended with earth, sand, and gravel; the differ ent marine bodies which form this crust, are found at the depth of a foot or more, entirely petrified and reduced into marble; these, he supposes, are naturally placed under the sea when it covers them, and not by means of volcanos and earthquakes, as some have conjectured. On this account he imagines, that the bottom of the sea is constantly rising higher and higher, with which other obvious causes of increase concur; and from this rising of the bottom of the sea, that of its level or surface naturally results; in proof of which, this writer re cites a great number of facts. M. Dassie has been at great pains to prove, that the sea has a general motion, independently of winds and tides, and of more consequence in navigation than is generally supposed. He affirms, that this motion is from east to west, inclining towards the north, when the sun has passed the equinoctial northward, and that during the time the sun is in the northern signs; but the contrary way after the sun has passed the said equinoctial southward: adding, that when this general motion is changed, the diurnal flux is changed also; whence it happens, that in several places the tides come in, during one part of the year, and go out during the other, as on the coasts of Norway, in the Indies at Goa, Cochinchina, &c, where, while the sun is in the summer signs, the sea runs to the shore; and when in the winter signs runs from it. On the most southern coasts of Tonquin and China, for the six summer months, the diurnal course runs from the north with the ocean; but the sun having re-passed the line toward the south, the course declines also southward. There are two principal reasons why the sea does not increase by means of rivers, &c. falling every where into it. The first is, because waters return from the sea by subterranean cavities and aqueducts, through various parts of the earth. Secondly, because the quantity of vapours raised from the sea, and falling on the land, only cause a circulation, but no increase of water. It has been found, by calculation, that in a summer's day there may be raised in vapours, from the Mediterranean Sea, 5,280,000,000 tuns of water; and yet this sea receiveth not, from all its nine great rivers, above 1,827,000,000 tuns per day, which is but a third part of what is exhausted in vapours. The ascent of the sea-water, for the formation of springs, by a subterranean circulation of its water to their sources, has been a great objection with many, against the system of their being formed of the sea; but Dr. Plat has observed, that there are many ways by which the water may ascend above its own level: 1. By the means of subterranean heats. 2. By filtration. 3. By the unequal height of several seas. 4. By the distance of the centre of magnitude from the centre of gravity, in the terraqueous globe: the superficies of the Pacific Sea is said to be further from the centre of gravity, than the top of the highest hill on the adverse part of the globe. And, 5. By the help of storms. The sea-water actually ascends above its own level, coming into wells whose bottoms lie higher than the surface of the sea at high-water mark. With regard to the saltness of the seawater, it is very rationally judged to arise from great multitudes both of mines and mountains of salt, dispersed here and there in the depths of the sea. The salt being continually diluted and dissolved by the water, the sea becomes impregnated with its particles throughout; and for this reason the saltness of the sea can never be diminished. Dr. Halley supposes, that it is probable the greatest part of the sea-salt, and of all salt lakes, as the Caspian Sea, the Dead Sea, the Lake of Mexico, and the Titicaca, in Peru, is derived from the water of the rivers which they receive; and since this sort of lakes has no exit or discharge, but by the exhalation of vapours; and also since these vapours are entirely fresh, or devoid of such particles, it is certain, that the saltness of the sea and such lakes must, from time to time, increase, and therefore, the saltness at this time is greater than at any time heretofore. He further adds, that if, by experiments made in different ages, we could find the different quantity of salt, which the same quantity of water (taken up in the same place, and in all other the same circumstances) would afford, it would be easy from thence, by rules of proportion, to find the age of the world very nearly, or the time wherein it has been acquiring its present saltness. The Bishop of Landaff has recommended a most simple and easy mode of ascertain ing the saltness of the sea in any latitude: we insert it in his own words. "As it is not every person who can make himself expert in the use of the common means of estimating the quantity of salt con. tained in sea-water, I will mention a method of doing it which is so easy and simple, that every common sailor may understand and practise it, and which, from the trials I have made of it, seems to be as exact a method as any that has yet been thought of. Take a clean towel, or any other piece of cloth, dry it well in the sun, or before the fire, then weigh it accurately, and note down its weight; dip it in the sea water, and when taken out, wring it a little till it will not drip, when hung up to dry; weigh it in this wet state, then dry it either in the sun, or at the fire, and, when it is perfectly dry, weigh it again. The excess of the weight of the wetted cloth above its original weight, is the weight of the sea-water imbibed by the cloth; and the excess of the weight of the cloth after being dried, above its original weight, is the weight of the salt retained by the cloth; and by comparing this weight with the weight of the sea-water imbibed by the cloth, we obtain the proportion of salt contained in that species of sea-water. "Whoever undertakes to ascertain the quantity of salt contained in sea-water, either by this or any other method, would do well to observe the state of the weather preceding the time when the sea water is taken out of the sea, for the quantity of salt contained in the water near the surface may be influenced both by the antecedent moisture and the antecedent heat of the atmosphere." Whether the sea is salter or not at different depths, has not yet been properly ascertained; but that its temperature varies considerably in proportion to the depth, we have decisive proof. "With respect to the temperature,” says Bishop Watson, "of the sea at different depths, it seems reasonable enough to suppose, that in summer time it will be hotter at the surface than at any considerable depth below it, and that in winter it will be colder. "Mr. Wales describes the instrument he made use of for trying the temperature of the sea at different depths, in the following terms: The apparatus for trying the seawater at different depths consisted of a square wooden tube of about eighteen inches long, and three inches square externally. It was fitted with a valve at the bottom, and another at the top, and had a contrivance for suspending the thermometer exactly in the middle of it. When it was used it was fastened to the deep sealine, just above the lead, so that all the way as it descended, the water had a free passage through it, by means of the valves which were then both open; but the instant it began to be drawn up, both the valves closed by the pressure of the water, and of course the thermometer was brought up in a body of water of the same temperature with that it was let down to. With this instrument, which is much the same with one formerly described by Mr. Boyle, in his observations about the saltness of the sea, water was fetched up from different depths, and its temperature accurately noticed, in different seasons and latitudes. "August 27, 1772, south latitude 24° 40. The heat of the air was 721, of the water at the surface 70, of water from the depth of 80 fathoms 68. "December 27, 1772, south latitude 58° 21. The heat of the air was 31, of the water at the surface 32, of water from the depth of 160 fathoms 334. "In the voyage to the high northern latitudes before mentioned, they made use of a bottle to bring up water from the bottom, which is thus described: The bottle had a coating of wool, three inches thick, which was wrapped up in an oiled skin, and let into a leather purse, and the whole inclosed in a well-pitched canvas bag, firmly tied to the mouth of the bottle, so that not a drop of water could penetrate to its surface. A bit of lead shaped like a cone, with its base downwards, and a cord fixed to its small end, was put into the bottle; and a piece of valve leather, with half a dozen slips of thin bladder, were strung on the cord, which, when pulled, effectually corked the bottle on the inside.' We have here put down two of the experiments which were made during that voyage. "August 4, 1773, north latitude 80° 30'. The heat of the air was 32, of the water at the surface 36, of water fetched up from the depth of 60 fathoms under the ice, 39. "September 4, 1773, north latitude 65°. The heat of the air was 66, of the water at the surface 55, of water from the depth of 683 fathoms, 40. "It appears from all these experiments that, when the atmosphere was hotter than the surface of the sea, the superficial water was hotter than that at a great depth; and when the atmosphere was colder than the surface of the sea, it is evident that the superficial water was somewhat colder than at a considerable distance below it." Sea-water may be rendered fresh by freezing, which excludes or precipitates the saline particles; or by distillation, which leaves the salt in a mass at the bottom of the vessel. Upon these principles, a mode of obtaining a supply of fresh water at sea was recommended some years ago to the Admiralty, by Dr. Irving. It consisted in only adapting a tin tube of suitable dimensions to the lid of the common ship's kettle, and condensing the steam in a hogshead which served as a receiver. By this mode a supply of twenty-five gallons of fresh water per hour might be obtained from the kettle of one of our ships of war. The saline taste of sea-water, is chiefly derived from common salt which it holds in solution. Sea-water is also distinguished by a nauseous bitter taste, which is ascribed to the animal and vegetable matters which are floating in it. This taste has been considered as in some measure foreign to it, for it is only found in the water on the surface of the ocean, or near the shores. Sea-water, taken up at considerable depths, contains ouly saline matters. The specific gravity of sea-water varies from 1.027 to 1.028. Its greater density is owing to the salts which are dissolved in it; and to this impregnation also it is owing, that it is not frozen till the temperature is reduced nearly to 28°. The salts which are chiefly found in sea-water, are muriate of soda, or common salt, muriate of magnesia, sulphate of magnesia, sulphate of lime and soda. The quantity of saline ingredients in the waters of the ocean varies from to part. Mr. Kirwan makes the average quantity about of its whole weight. The quantity of saline contents of water, taken up by Lord Mulgrave at the back of Yarmouth Sands, in latitude 53°, amounted nearly to while Bergman found the water taken up in the latitude of the Canaries, to contain about of its weight of saline matter. These quantities, however, vary even in the same latitude, during rainy and dry seasons, near the land, or the mouths of great rivers. The difference of latitude does not seem to make any considerable difference in the proportion of saline matter. In latitude 80° north, sixty fathoms under ice, sea-water taken up by Lord Mulgrave, yielded about; in latitude 74°, nearly the same; and in latitude 60°,. Pages obtained four per cent. from water taken up in latitude 81°, and the same quantity of saline matter from water taken up in latitudes 45° and 39° north. In southern lati tudes the proportion was still greater; he found it to contain the following proportions: In the Mediterranean the proportion is said to be still greater; but the Euxine and Caspian seas are found to be less salt than the ocean. This is also the case with the Baltic. If the saline matters of the waters of the ocean did not consist of different kinds, the proportion of salts which it contains might be ascertained by the specific gravity. The experiments of Mr. Wilcke show that the proportion of saline matter in the Baltic is less than that of the ocean and that it is salter during the prevalence of a westerly wind, by which the water is driven from the ocean, than during an easterly wind. The proportions of the different salts in an analysis, by Bergman, are the following: : The luminousness of the sea is a phenomenon that has been noticed by many nau. tical and philosophical writers. Mr. Boyle ascribes it to some cosmical law or custom of the terrestrial globe, or at least of the planetary vortex. The Abbé Nollet was long of opinion, that the light of the sea proceeded from electricity; and others have had recourse to the same principle, and shown that the luminous points in the surface of the sea are produced merely by friction. There are, however, two other hypothe ses, which have more generally divided between them the solution of this phenomenon; the one of these ascribes it to the shining of luminous insects or animalcuJes, and the other to the light proceeding from the putrefaction of animal substances. The Abbé Nollet, who at first considered this luminousness as an electrical phenomenon, having had an opportunity of ob serving the circumstances of it, when he was at Venice in 1749, relinquished his former opinion, and concluded that it was occasioned either by the luminous aspect, or by some liquor or effluvia of an insect which he particularly describes, though he does not altogether exclude other causes, and especially the spawn or fry of fish. A similar conjecture is proposed by a correspondent of Dr. Franklin, in a letter read at the Royal Society in 1756; the writer of which apprehends, that this appearance may be caused by a great number of little animals, floating on the surface of the sea. And Mr. Forster, in his account of a voy. age round the world with Captain Cook, describes this phenomenon as a kind of blaze of the sea; and having attentively examined some of the shining water, expresses his conviction that the appearance was occasioned by innumerable minute animals of a round shape, moving through the water in all directions, which show separately as so many luminous sparks when taken up on the hand he imagines that these small gelatinous luminous specks may be the young fry of certain species of some medusæ or blubber. And M. Dagelat and M. Rigaud observed several times, and in different parts of the ocean, such luminous appearances by vast masses of different animalcules; and a few days after, the sea was covered, near the coasts, with whole banks of small fish in innumerable multitudes, which they supposed had proceeded from the shining animalcules. But M. le Roi, after giving much attentention to this phenomenon, concludes, that it is not occasioned by any shining insects, especially as, after carefully examining with a microscope some of the luminous points, he found them to have no appear ance of an animal; and he also found that the mixture of a little spirits of wine with water just drawn from the sea, would give the appearance of a great number of little sparks, which would continue visible longer than those in the ocean: the same effect was produced by all the acids, and various other liqours. M. le Roi is far from asserting that there are no luminous insects in the sea; for he allows that several gentlemen have found them; but he is satisfied that the sea is luminous chiefly on some other account, though he does not so much as offer a conjecture with respect to the true cause. Other authors, equally dissatisfied with the hypothesis of luminous insects, for explaining the phenomenon which is the sub ject of this article, have ascribed it to some substance of the phosphoric kind, arising from putrefaction. SEA, in law: The sea shall be open to all merchants. The main sea beneath the low water mark, and round England, is part of England; and the admiralty has jurisdiction there. SEAMEN, such as are reserved to serve the King, or other persons, at sea, who may not depart without license, &c. Seamen fighting, quarreling, or making any disturbance, may be punished by the commissioners of the navy, with fine and imprisonment. Registered seamen are exempted from serving in any parish office, &c. and are allowed bounty money besides their pay. By the law of merchants, the seamen of a vessel are accountable to the master or commander, and the master to the owners, and the owners to the merchants, for da mage sustained either by negligence or otherwise. Where a seaman is hired for a voyage, and he deserts it before it is ended, he shall lose his wages; and in case a ship be lost by a tempest, or in a storm, the seamen lose their wages, as well as the owners their freight. SEAMEN, in law: by various statutes,sailors having served the King for a limited time, are free to use any trade or profession, in any town of the kingdom. By 2 George II. c. 36, made perpetually by 2 George III. c. 31, no master of any vessel shall carry to sea any seaman, his own apprentice except ed, without first entering into an agreement with such seaman for his wages; such agreement to be made in writing, and to declare what wages such seaman is to receive during the whole of the voyage, or for such time as shall be therein agreed upon; and such agreement shall also express the voyage for which such seaman was shipped to perform the same, under a penalty of 101. for each mariner carried to sea without such agreement, to be forfeited by the mas. ter to the use of Greenwich Hospital. This agreement is to be signed by each mariner within three days after entering on board such ship, and is, when executed, binding on all parties. SEAL, a puncheon, or piece of metal, or other matter, usually either round or oval, whereon are engraven the arms, device, &c. of some prince, state, community, magis trate, or private person, often with a legend or suscription, the impression of whereof in wax, serves to make acts, instruments, &c. anthentic. Before the time of William the Conqueror, the makers of all deeds only subscribed their names, adding the sign of the cross, and a great number of witnesses; but that monarch and the nobility used seals with their arms on them, which example was afterwards followed by others. The colour of the wax wherewith this King's grants were sealed was usually green, to signify that the act continued fresh for ever, and of force. A seal is absolutely necessary in respect of deeds, because the sealing of them makes persons parties thereto, and without being sealed, they are void in law. SEALER, an officer in chancery appointed by the Lord Chancellor, or Keeper of the great seal, to seal the writs and instruments there made in his presence. SEAMS of a ship, are places where her planks meet and join together. There is also a kind of peculiar seam in the sowing of sails, which they call monk seam; the other seam of a sail is the round-seam, so called from its being round like the com mon seams. SEARCHER. See ALNAGER. Searcher is also an officer of the customs, whose business is to search and examine all ships outward bound, to see whether they have any prohibited or unaccustomed goods on board. SEAR cloth, or CERE cloth, in surgery, a form of external remedy somewhat harder than an unguent, yet softer than an emplaster, though it is frequently used both for the one and the other. The sear-cloth is always supposed to have wax in its composition, which distinguishes and even denominates it. In effect, when a liniment or unguent has wax enough in it, it does not differ from a scar-cloth. SEBACIC acid, the acid of fat. The penetrating fumes which are exhaled from melted tallow, and which affect the eyes, the nostrils, and even the lungs, had been long ago observed. Little attention, however, was paid to their nature and properties. In 1754 appeared a dissertation by M. Seguer, on the acid of animal fat, which contained a number of well-conducted experiments. Crell endeavoured to improve the process for the separation and purification of this acid, and to ascertain the properties of its combinations. These were published in the Philosophical Transactions for the years 1780 and 1782. But it appears, that the acid obtained by those who first treated of the subject, was either the acetic acid, or some acid different from the |