is frequently used for that vast tract of water encompassing the whole earth; but is more properly a part or division of these waters, and is better defined a lesser assemblage of water, which lieth before and within the coasts of some particular countries from whence it is generally denominated, as the Irish sea, the Mediterranean sea, the Arabian sea &c.

What proportion the superficies of the sea bears to that of the land is not precisely known, though it is said to be somewhat more than two thirds. As the waters of the earth must necessarily rise to the surface thereof, as being specifically lighter than the earth, it was necessary there should be large cavities therein for receptacles to contain them; otherwise they would have overspread all the superficies of the earth, and so have rendered it utterly uninhabitable for terrestrial animals. For the centre of the earth being the common centre of gravity, and the nature of fluids being such that they equally yield to equal powers, and the power of attraction being everywhere equal at equal distances from the centre, it follows, that the superficial parts of the water will everywhere conform themselves to an equidistant situation from the centre, and consequently will form the surface of a sphere so far as they extend. Hence, that the sea seems higher than the earth or land, results from the fallacy of vision, whereby all objects, and the parts of land as well as sea, the farther they are off from us, the higher they appear; the reason of all which is plain from optics: for it is well known, that the denser any medium is through which we behold objects, the greater is the refraction, or the more their images appear above the horizontal level; also the greater quantity of the medium the rays pass through, the more will they be bent from their first direction; so both these accounts the appearances of things remote, and on the sea, will be somewhat above the horizon, and the more so as they are the more remote.

With regard to the depth or profundity of the sea, Varrenius affirms, that it is in some places unfathomable, and in other places very various, being in certain places English miles, in other places deeper, and much less in bays than in oceans. In general, the depths of the sea bear a great analogy to the height of mountains on the land, so far as is hitherto discovered.

There are two principal reasons why the sea doth 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 hath been found by calculation, that in a summer's day there may be raised in vapours, from the Mediterranean sea, 528000000 tons of water; and yet this sea receiveth not, from all its nine great rivers, above 182700000 tons per day, which is but a third part of what is exhausted in vapours.

With regard to the saltness of the sea-water, 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. 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 fort 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 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.

With regard to the use of this salt property of sea-water, it is observed, that the saltness of the sea preserves its waters pure and sweet, which otherwise would corrupt and stink like a filthy lake, and consequently that none of myriads of creature that now live therein could then have a being. From thence also the sea-water becomes much heavier, and therefore ships of greater size and quantity may be used thereon. Salt water also doth not freeze so soon as fresh water, whence the seas are more free for navigation. We have lately had published a dissertation, by Dr Russell, concerning the medical uses of sea-water in diseases of the glands, &c., wherein the author premises some observations upon the nature of sea-water, considered as impregnated with particles of all the bodies it passes over, such as submarine plants, fish salts, minerals, &c., and saturated with their several effluvia, to enrich it, and keep it from putrefaction; hence this fluid is supposed to contract a soapiness, and the whole collection, being pervaded by the sulphureous steams passing through it, to constitute what we call sea water, the confessed distinguishing characteristics of which are saltness, bitterness, nitrolity, and unctuosity; whence the author concludes, that it may be justly expected to contribute signally to the improvement of physic. The cases in which our author informs us we are to expect advantage from sea-water, are, 1. In all recent obstructions of the glands of the intestines and mesenteries. 2. All recent obstructions of the pulmonary glands, and those of the visceras, which frequently produce consumptions. 3. All recent glandular swellings of the neck, or other parts. 4. Recent tumours of the joints, if they are not suppurred, or become scirrhouss, or cancerous, and have not carious bones for their cause. 5. Recent defluxions upon the glands of the eye-lids. 6. All defluxions of the skin, from an erysipelas, to a lepra. 7. Diseases of the glands of the nose, with their usual companion a thickening of the lip. 8. Obstructions of the kidneys, where there is no inflammation, and the stone not large. 9. In recent obstructions of the liver this method will be proper, where it prevents constrictions of the belly, and assists other medicines directed in icteric cases. The same remedy is said to be of signal service in the bronchocle; and is likewise recommended for the prevention of those bilious colics that so frequently affect our mariners.

To make sea-water fresh is a thing long and much wanted, for the advantage of navigation and commerce; a method for doing which has been long ago invented by Mr Hauton, and the secret published in the Philos. Transact. It is performed by precipitating the water with oil of tartar, and then distilling it. But Mr Appleby's process, which was referred by the lords of the admiralty to the college of physicians, and communicated to the royal society, with some experiments therewith, on Feb. 8, 1753, appears to be more successful, and is performed thus: Into twenty gallons of sea-water put six ounces of a fixed alkali prepared with quick lime as strong as lapis infernalis, and six ounces of bones calcined to a whiteness, and finely powdered; with a slow fire, draw off, in a common still, fifteen gallons. Mr Appleby conceives that the alkali here employed is the best adapted to prevent the bituminous matter in sea water from rising by heat in distillation.

In the year 1755, a method of procuring any quantity of fresh water at sea was published by Dr Butler; together with a method also of preserving fresh-water entirely pure, sweet, and wholesome, during the longest voyage, and in the warmest climates. The method more expressly recommended by the doctor for making sea-water fresh is to put a measured wine-quart of the strongest soap leys to fifteen gallons of sea-water; which being distilled, he assures us, will generally yield twelve gallons of fresh water. The above quantity of soap leys, we are told, will bear a repetition of the same quantity of water four or five times.

This method of Dr Butler was tried, by order of the lords of the admiralty, at the same time with Mr Appleby's; but the latter, being found to be performed with a less quantity of fuel, was preferred.

In order to keep fresh water sweet, Dr Butler directs to take of fine, clear, white pearl-ashes, a quarter of a pound avoirdupoise, and put into one hundred gallons of fresh water; observing this proportion to a greater or less quantity. quantity, and stop up your cask as usual, till you have occasion to broach it.

For the ebbing and flowing of the sea, see Astronomy, p. 473.

Seamen, such as are referred to serve the king, or other persons, at sea, who may not depart without license, &c. Seamen fighting, quarrelling, 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 damage 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.