the highest, and the neap-tides the lowest of all others; for the nearer the moon approaches the poles, the less is the agitation of the ocean, which is greatest of all when the moon is in the equinoctial, or farthest distant from the the poles; whence the sun and moon being either conjoined or opposite in the equinoctial, produce the greatest spring-tides, and the subsequent neap-tides are always the least, being produced by the tropical moon in the quarters.

But besides these general tides, which would happen regularly every where, if the earth were all covered with deep sea, there are many others in which we find a vast diversity, and not to be accounted for, without an exact knowledge of local circumstances, as the position of the land, the shallowness of the water, the narrowness of the channels, &c., for the tide is always found to set strongest where the sea is narrowest, the same quantity of water being in that case to run through a smaller passage. This is evident between Portland and Cape la Hogue in Normandy, where the tide runs like a sluice, and would be yet stronger between Dover and Calais, if it were not checked by the tide coming round the island. In short, every thing relating to the tides is to be accounted for from the Newtonian doctrine; as why lakes, such as the Caspian sea, and midland seas, such as the Baltic, the Black Sea, and the Mediterranean, have scarcely any sensible tides; for lakes having no communication with the ocean, can neither increase nor diminish their water, so as to rise or fall; and seas that communicate with it by such narrow inlets, and are of such a vast extent, cannot in a few hours receive or empty water enough to raise or sink their surface in a sensible manner. Sir Isaac Newton accounts for the strong tides in the port of Tonquin in China, (where there is but one flood and ebb in 24 hours, and none at all when the moon is near the equinoctial,) from the concurrence of two tides, the one out of the great South Sea, the other out of the Indian Sea between the islands; and as the appearance of those tides is naturally deducible from his principles, it is a strong argument in favour of his whole theory.

We shall conclude this subject with observing, that though the Mediterranean has no sensible tides, except some small ones in the Gulf of Venice and that of the

Euripus, &c., yet a strong current continually sets into it from the ocean through the straits of Gibraltar, and likewise through the Hellespont from the Euxine and the Propontis; whence one would imagine, that instead of not swelling like the ocean, it should rather overflow its Dounds, and inundate the adjacent countries. What becomes of the vast quantity of water thus poured into the Mediterranean, is a speculation that has long employed the philosophers. Dr. Smith accounts for it, by supposing an under current to carry off as much water as the upper one brings in, and such currents it is probable there are in several parts of the sea; but Dr. Halley, without having recourse to this hypothesis, solves the phenomenon from the great evaporation. The result of an experiment, made by this excellent author, to find the quantity of vapour raised from the sea by the action of the sun, was, that the thickness of water evaporated from the surface of the sea in summer, is one fifty-third part of an inch in the space of two hours, which, for the ease of calculation, being supposed only a sixtieth part, the quantity exhaled in twelve hours will be one-tenth of an inch. On this principle, every square mile will be found to evaporate in twelve hours 6,914 tons of water; and every square degree, supposed of 69 English miles, will evaporate 33 millions of tons. Now the area of the Mediterranean being estimated at 160 square degrees, it will lose in vapour, in a summer's day, 5,280 millions of tons; and yet this quantity of vapour, great as it is, is only the remains of what is raised by the winds, which sometimes sweep off the water faster than it is exhaled by the heat of the sun.

With respect to the quantity of water received by the Mediterranean, the Doctor supposes the Ebro, Rhone, Tyber, Po, Danube, Neister, Boristhenes, Tanais, and Nile, to furnish each of them ten times as much water as the Thames; not that any of them are in reality so great, but so to allow for the lesser rivers that fall into it; and as the Thames is computed to evacuate daily 20,300,000 tons of water, the nine rivers above-mentioned will only evacuate 1,827 millions of tons in a day, which is little more than a third of what is raised in that time in vapour. To this vast store of vapours raised by the sun, winds, or

subterraneous fires, from the sea, lakes, rivers, &c., the Doctor refers the origin of springs.

This account may serve to explain why the Caspian sea, into which many vast rivers discharge themselves, and which has no visible outlet, does not overflow its banks; and it may also show why the Almighty has placed spacious lakes in many other countries, at a distance from the sea. Were it not for these bodies of water that supply the clouds with rain, such countries would have no refreshing showers; the reservoirs in the hills and mountains, which gush out in springs, and give rise to many rivers, would soon fail: water would be in a manner unknown, vegetation would gradually cease, and many regions, now remarkable for their fertility, would become barren and desolate.-SMITH's Wonders.

LIGHT-HOUSES.

THE PHAROS OF PTOLOMY.

THE wonderful light-house, named Pharos, from the island of Pharos, on which it stood, was surrounded on all sides by water. It was a most magnificent tower, consisting of several stories, and galleries, with a lantern at top. It was of a prodigious height, and its lantern continually burning, could be seen for many leagues at sea, and along the coast. It was built for the benefit and direction of sea-faring men, by one of the Ptolomies, in the year of the world 3670, under the direction of the architect Guidius, who dedicated it to its founder. But in after-times, that being decayed, another inscription ap peared finely cut in marble, viz., "Sostrates Gnidius, son of Dixiphanes, consecrated this work to the gods, our preservers, for the benefit of sea-faring men." How long this structure stood, is not very certain, but it was of such universal esteem, that we find antiquity called all the light-houses after it, by the common name of Pharos.Old Universal Magazine.

THE COLOSSUS OF RHODES.

THIS enormous building has justly been classed among the wonders of ancient architecture. It was a vast struc ture of brass, or statuary metal, erected in honour of Apollo, or the sun, the tutelar god of the island, whose stride was 50 feet asunder, each foot being placed on a rock at this distance from each other, and which bounded the entrance into the haven. Its height, according to Pliny, was not less than 105 feet, or 70 cubits; and hence ships of considerable burden were capable of sailing between its legs. It is said to have been erected by the Rhodians, with the money produced by the sale of the engines of war which Demetrius Poliorcetes employed in fruitlessly besieging the city for a twelvemonth, and which he gave to them upon his reconciliation. Pliny affirms that it was commenced by Chares of Lindus, a disciple of Lysippus, and finished upon his death by Laches of the same town. It was thrown down by an earthquake 60 years after its completion.-Gallery of Nature and Art.

THE EDDYSTONE LIGHT-HOUSE.

THIS most celebrated light-house is built on the Eddystone rocks. These are situate nearly S. S. W. from the middle of Plymouth sound, according to the true meridian. The distance from the port of Plymouth is nearly 14 miles; and from the promontory called Ramhead, about 10 miles. They are almost in the line, but somewhat within it, which joins the Start and the Lizard points; and as they lie nearly in the direction of vessels coasting up and down the channel, they were necessarily, before the establishment of light-houses, very dangerous, and often fatal to ships under such circumstances. Their situation,

likewise, with regard to the Bay of Biscay, and the Atlantic Ocean, is such, that they lie open to the swells of the bay and ocean from all south-western points of the compass, which swells are generally allowed by mariners to be very great and heavy in those seas, and particularly in the Bay of Biscay. It is to be observed, that the soundin