firth or frith, Scottish term applied to an arm of the sea, usually an estuary or strait. For Firth of Clyde, see Clyde; for Firth of Forth, see Forth.

Solway Firth, arm of the Irish Sea, c.40 mi (60 km) long, separating NW England from SW Scotland. The waterway receives the Esk, Annan, Urr, Eden, and Derwent rivers. It has important salmon fisheries. Near Annan the firth, which has a tidal bore, is crossed by a railway bridge. Hadrian's Wall terminated at Bowness, on the south shore.

Pentland Firth, channel, 6 to 8 mi (9.7-12.9 km) wide and c.14 mi (23 km) long, N Scotland. Connecting the North Sea with the Atlantic Ocean, it separates the Scottish mainland from the Orkney Islands. Its rough waters have proven dangerous to small vessels. Small islands dot the Pentland Firth.

Firth, Sir Raymond William, 1901-2002, British social anthropologist, b. Auckland, New Zealand. He was educated at Auckland Univ. and studied with Bronislaw Malinowski at the London School of Economics (Ph.D., 1927). He did much research in the Pacific, focusing chiefly on social organization and economic systems. From 1932 he taught anthropology at the London School of Economics, becoming a full professor in 1944. He retired from teaching in 1968 but continued research and writing. He was knighted in 1973. His works include Economics of the New Zealand Maori (1929, 2d ed. 1959), We, the Tikopia (1936, 2d ed. 1957), Human Types (1938, rev. ed. 1957), Social Change in Tikopia (1959), and Symbols: Public and Private (1973).

Cromarty Firth, deep narrow inlet of Moray Firth, c.15 mi (25 km) long, Highland, N Scotland. It provides excellent anchorage, its narrow entrance being protected by the headlands of the Sutor rocks, more than 400 ft (122 m) high. The surrounding area has been developed for North Sea oil production.