sang-e âhak (#)
Fr.: castine, calcaire
A → sedimentary rock composed principally of calcium carbonate. Limestone is usually formed from shells of once-living organisms or other organic processes, but may also form by inorganic precipitation.
Variously colored → sedimentary rock composed mainly of sand-like quartz grains cemented by calcite, clay, or iron oxide. The sand accumulated originally underwater in shallow seas or lakes, or on the ground along shorelines or in desert regions.
The hard nonmetallic mineral or group of consolidated minerals either in mass or in a fragment of pebble or larger size. See also → rock.
O.E. stan; cf. O.N. steinn, Dan. steen, O.H.G., Ger. Stein; from PIE *stai- "stone," also "to thicken, stiffen" (cf. Skt. styayate "curdles, becomes hard;" Av. stay- "heap;" Gk. stear "fat, tallow," stia, stion "pebble").
Sang "stone, rock;" Mid.Pers. sang; O.Pers. aθanga-; Av. asenga- "stone;" PIE *aken-.
asr-e sang (#)
Fr.: âge du fer
A prehistoric period during which the main material used to make tools and weapons was stone. The Stone Age is usually divided into three separate periods (Paleolithic Period, Mesolithic Period, and Neolithic Period) based on the degree of sophistication in the fashioning and use of tools. The Paleolithic time period is by far the longest, beginning some two million years ago and ending around 10,000 BC to coincide with the end of the last ice age (Pleistocene epoch).
Fr.: pont de Wheatstone
An device consisting of four → resistances in series, used to determine the value of an unknown electrical resistance when the other three resistances are known.
Named after Charles Wheatstone (1802-1875), British physicist, who extensively used the circuit (1843) but was not its inventor. Such an arrangement of four resistances was first used by Samuel Hunter Christie (1784-1865) in 1833; → bridge.