Baltic Sea, the great gulf or inland sea bordered by Denmark, Germany, Russia, and Sweden, and communicating with the Kattegat and North Sea by the Sound and the Great and Little Belts. Its length is from 850 to 900 miles; breadth, from 100 to 200; and area, including the Gulfs of Bothnia and Finland, 184,496 sq. m., of which 12,753 are occupied by islands. Its mean depth is 44 fathoms, and the greatest ascertained depth, between Gottland and Courland, 140. The group of the Aland Islands divides the south part of the sea from the north part or Gulf of Bothnia (q.v.). The Gulf of Finland (q.v.), branching off eastwards into Russia, separates Finland from Esthonia. A third gulf is that of Riga or Livonia. The Kurisch and other Haffs are not gulfs, but fresh-water lakes at the mouths of rivers. The water of the Baltic is colder and clearer than that of the ocean, and contains in most places only a fourth of the proportion of salt found in the Atlantic; though the salinity varies in different parts and at different seasons. Ice hinders the navigation from three to five months yearly. Rarely, as in 1G58 and 1809, the whole surface is frozen over. Tides, as in all inland seas, are little perceptible - at Copenhagen, about a foot. Upwards of 250 rivers flow into this sea, which, through them and its lakes, drains not much less than one-fifth of all Europe, its drainage area being estimated as 717,000 sq. m. The chief of these rivers are the Oder, Vistula, Niemen, Dwina, Narva, Neva, and Motala. The principal islands are Zealand, Funen, Bornholm, Samsoe, and Laaland (Danish); Gottland, Oland, and, Hveen (Swedish); the Aland Islands (Russian)-; and Rugen (Prussian). The Eider Canal, connecting the Baltic near Kiel with the North Sea at Tonningen, facilitates the grain trade; and the two seas are also connected by the Gotha Canal, which joins the lakes of South Sweden. These are navigable for boats of light draught only; but in 1887-95 a great canal was constructed from Brunsbuttel, at the mouth of the Elbe, to Holtenau and Kiel, to allow the passage of the largest vessels, being 61 miles long, 28 feet deep, 200 wide at the surface, and 85 at the bottom; and as the voyage round from the Elbe to Kiel represents nearly 600 miles of dangerous sailing or steaming, the canal must prove of great value to commerce and to the German navy. The cost was estimated at £8,000,000, and the yearly maintenance at £50,000. The most important harbours in the Baltic are: in Denmark, Copenhagen; in Germany, Kiel, Lubeck, Stralsund, Stettin, Danzig, Konigsberg, and Memel; in Russia, Riga, Narva, Cronstadt, and Sveaborg; and in Sweden, Stockholm and Karlskrona.