354 MEDITERRANEAN SEA nelles leads into the sea of Marmora (the Pro- pontis of the ancients), which communicates through the Bosporus or strait of Constantino- ple with the Black sea or Euxine, the latter in its turn communicating through the strait of Yenikale or Kertch (the Cimmerian Bosporus of the ancients) with the sea of Azov. The eastern part of the Mediterranean bears among sailors the general name of the Levant ; it was formerly subdivided into the Pamphylian, Sy- rian, and Phoenician seas. Five large islands and a great number of smaller ones are scat- tered through the Mediterranean. The former are Corsica, Sardinia, Sicily, Candia or Crete, and Cyprus. They are all mountainous, the summits rising to considerable heights. The principal of the smaller islands are the Baleares with Iviza and Formentera, the Tuscan islands between Corsica and the Italian mainland, the Lipari or ^Eolian islands, Malta and its smaller neighbors, the Ionian islands, the Dalmatian islands in the Adriatic, and the islands of the Archipelago (the Cyclades and Sporades of the ancients), the largest of which are Negropont (Eubosa), Rhodes, and Samos. Volcanic phe- nomena are well developed in southern Ita- ly and Sicily, where Vesuvius and Etna are frequently active; and Stromboli in constant eruption. In the Archipelago the island of Santorin is a partly submerged volcano, occa- sionally active and forming new islets. (See GRAHAM ISLAND.) Only four rivers of impor- tance empty into the Mediterranean : the Ebro, Rh6ne, and Po on the N. shore, and the Nile in Egypt. Besides these may be mentioned the Guadalaviar, Tiber, Adige, Maritza, Mean- der, and Orontes. The Mediterranean is no- ted for its bright and deep blue color, when undisturbed, though probably it does not differ much from the ocean in that respect. Prof. Tyndall attributes this tint to minute particles in suspension, the existence of which he proved by optical experiment. Carpenter found by filtration that these particles were inorganic, and much more abundant than in the Atlantic. According to Admiral Smyth, a greenish tinge is prevalent in the Adriatic ; it borders on pur- ple in the Levant basin, while the Black sea often has the dark aspect from which it derives its name. The eastern basin is very deep ; S. E. of Candia 1,600 fathoms have been sounded, and in a line from Candia to Malta the greatest depth is about 2,000 fathoms. The alluvium of the Nile forms a submarine promontory in front of the delta. In the Archipelago the islands rise steeply out of deep water, as much aa 600 fathoms being found between them. The Adriatic is shallow in its northern part, but in the south has a depression of 500 fathoms. The bottom of the Sicilian sea forms a plateau of less than 500 fathoms, with several shoals. The depth of the Tyrrhenian sea is probably great, though not known in much detail. The Balearic sea reaches 2,000 fathoms in its deep- ->t parts, the l.ottnm rising toward the strait of Gibraltar, which measures a little more than 900 fathoms in its deepest part. Although the Mediterranean is usually said to be tide- less, this is not strictly true ; tidal motions are noticed in several localities, though small and irregular, and modified by the force and direction of the wind. The Atlantic tide wave can be directly followed but a short distance along the coast of Spain; on the coasts of France and Italy a small rise and fall occurs, though not regular enough to be formulated in the absence of accurate observations. In the strait of Messina the tidal current, accord- ing to Admiral Smyth, runs alternately six hours north and six hours south, though the vertical rise and fall is only a few inches. In the Adriatic the tide is felt sensibly at Venice, but is exceedingly weak in the southern part. On the coast of Africa, Admiral Smyth has observed tides fairly developed in the Lesser Syrtis. A connected study of the tides of the whole basin by means of good instruments, such as modern self -registering tide gauges, is still a desideratum. The local currents of the Mediterranean are partly tidal, and partly due to the winds. At the strait of Gibraltar, how- ever, a strong and constant current runs in from the Atlantic, which cannot be attributed to either of those causes, which merely modify it. This current occupies the middle of the channel, and has a mean velocity of 3 or 4 m. an hour. On either side of it a tidal current is observed, which runs alternately with and against the main current. The true cause of the latter has given rise to much speculation among physicists. That it is due to the evap- oration in the Mediterranean being in excess of the river supply has been generally admit- ted ; but this would imply a constant increase of salinity, unless this increase were kept in check. An undercurrent carrying out the den- ser water had to be almost necessarily admit- ted, but its actual existence was not proved un- til the experiments of Prof. Carpenter, in the cruise of the Porcupine, showed it conclusive- ly. This physicist has observed that the water of the Mediterranean contains more salt than that of the Atlantic, that this excess of salinity is greater in bottom water than at the surface, and that in the strait of Gibraltar this denser water flows out into the Atlantic, thus resto- ring the equilibrium of density between the two seas. Observations in the Hellespont and Bos- porus ha've shown that a surface current flows out of the Black sea, and an undercurrent in. The relation of densities is here reversed, the Black sea having the least ; but the evaporation being less in proportion to the river supply, the current is due less to a restoration of level than to the difference of densities. The pre- vailing winds are mostly from the north and west. Some of them are known by specific names, such as the mistral, a cold wind blow- ing^ from the Alps along the valley of the Rhone to the sea; its opposite, the sirocco, a scorching hot wind carrying the dry heat of the African deserts over Sicily and all Italy;
