RED SEA, an arm of the Indian Ocean, running N. N. W. from the Gulf of Aden, with which it communicates by the Strait of Bab-el-Mandeb, 131/2 miles across. Its length is about 1,200 miles, and its width in the central portion is between 100 and 200 miles, the greatest breadth being about 205 miles; it nar rows toward the S. entrance, while in the N. it is divided by the peninsula of Sinai into two gulfs, the Gulf of Suez, 170 miles long by 30 miles wide, and the Gulf of Akaba, 100 miles in length.
The Arabian coasts of the Red Sea are usually narrow, sandy plains backed by ranges of barren mountains; the African coasts toward the N. are flat and sandy, but farther S. high table-lands rise some distance inland, culminating still farther S. in the lofty mountains of Abyssinia. A marked feature in the configuration of the Red Sea is found in the large ex isting and upraised coral reefs running parallel to both the E. and W. shores, those to the E. being more extensive and farther from the coast than those to the W.; the most important are the Farsian Archipelago in the E. reef, and the large island of Dahlak, lying off Annesley Bay, in the W. reef. In addition to the islands of organic formation mention may be made of the volcanic group lying in lat. 14° N., the largest of which, Jebel Zugur, is 10 miles long, 7 miles wide, and 2,074 feet in height; farther N., on the islet of Jebel Teir, is a volcano which was active till quite recently. A dangerous reef, the Daedalus, lies directly in the path of steamers in lat. 24% ° N., and a lighthouse has been placed on it. The principal harbors on the Red Sea are Mocha, Hodeida, Lokeyyah, Jiddah, and Yenbo, on the Arabian coast, and Massowah, Khor Nowarat, and Suakim on the African coast.
In ancient times the Red Sea was used as a means of communication by the Phoenicians and other maritime peoples, till the discovery of the route round the Cape of Good Hope diverted the traffic into another channel, only to be revived, however, on a much more extensive scale with the construction of the Suez Canal.
The tides are very variable, depend ing largely on the direction and force of the winds, which also to a great extent determine the direction and velocity of the surface currents. The hot climate is due to the almost cloudless sky, and consequent want of rain, the altitude of the sun, and the absence of rivers. The mean temperature of the air generally ranges between 70° and 94° F. during the day, though readings of over 100° are often registered in the shade; but during the night the temperature may fall to the freezing point, owing to radi ation in the clear atmosphere. The pre
vailing wind on shore is N. N. W. almost universally, but from October to May S. S. E. winds prevail over the S. por tions of the sea, a belt of calms and variable winds occurring in the central regions, while in the N. portions the usual N. N. W. winds are met with. Evaporation is very great, and the air over the water is always very moist in the summer; hurricanes are unusual, but rain squalls frequently occur with the S. winds, and moderate gales and sandstorms, called "dragons" in the popular language of the Arabs, are not uncommon.
The temperature of the water below the surface decreases down to a depth of about 200 fathoms, from whence down to the bottom a mean temperature of about 71° is found all the year round; this agrees with the temperature condi tions prevailing in the inclosed seas of ale East Indies, for instance, according to the observations made on board the "Challenger," the depth at which the minimum temperature occurs (i. e., 200 fathoms in the Red Sea) indicating the depth of water over the barrier sepa rating the sea from the open ocean. In winter, in the N. part, the whole body of water from surface to bottom usually has a mean temperature of 71°.
The salinity of the water is almost constant at about 1.030 (ordinary ocean water is about 1.026), and this is due to the fact that no rivers flow into it, little rain falls, and the evaporation is excessive. It has been estimated that, were the Red Sea entirely inclosed, it would become a solid mass of salt in less than 2,000 years, but this is prevented by an inflow of water through the Strait of Bab-el-Mandeb, and it is also known that a current of very salt water flows out underneath the incoming surface current.
The greatest depth in the Red Sea is about 1,200 fathoms, and the mean depth of the whole area about 375 fathoms. From the point of greatest depth, which is near the center, the bottom rises toward each end. Owing to the absence of rivers the deposits approach in char acter those formed in the open ocean, being largely composed of Foraminifera, Pteropods, and other pelagic shells. The marine fauna and flora are extensive, and have been described by Haeckel and other naturalists; it has been shovm that a migration of the Red Sea and Mediter ranean faunm is taking place along the Suez Canal. The path by which the Israelites went out of Egypt was along the course of the valley called Wady Tumeilat, apparently an old arm of the Nile now silted up. The Lake of Ismailieh (Timsah) was then most prob ably the head of the Gulf of Suez, but the exact point of passage of this arm of the sea still remains obscure.