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Brown, John, American abolitionist

(Encyclopedia)Brown, John, 1800–1859, American abolitionist, b. Torrington, Conn. He spent his boyhood in Ohio. Before he became prominent in the 1850s, his life ha...

guided missile

(Encyclopedia)guided missile, self-propelled, unmanned space or air vehicle carrying an explosive warhead. Its path can be adjusted during flight, either by automatic self-contained controls or remote human control...

lubrication

(Encyclopedia)lubrication, introduction of a substance between the contact surfaces of moving parts to reduce friction and to dissipate heat. A lubricant may be oil, grease, graphite, or any substance—gas, liquid...

rapid transit

(Encyclopedia)rapid transit, transportation system designed to allow passenger travel within or throughout an urban area, usually employing surface, elevated, or underground railway systems or some combination of t...

lock and key

(Encyclopedia)lock and key, fastening fitted to an entryway, such as a gate or door, or a container, such as a cabinet, drawer or safe, to keep it closed and/or prevent unauthorized access or use. Locks typically c...

tide

(Encyclopedia)tide, alternate and regular rise and fall of sea level in oceans and other large bodies of water. These changes are caused by the gravitational attraction of the moon and, to a lesser extent, of the s...

commerce, in economics

(Encyclopedia)commerce, traffic in goods, usually thought of as trade between states or nations. Engaged in by all peoples from the earliest times, it has been carried on in some areas and by some peoples more than...

aerodynamics

(Encyclopedia)aerodynamics, study of gases in motion. As the principal application of aerodynamics is the design of aircraft, air is the gas with which the science is most concerned. Although aerodynamics is primar...

trade

(Encyclopedia)trade, traffic in goods. Conducted by gift, barter, or sale, trade is one of the most widespread of all social institutions. The theory of commerce as imposed by the national state has varied from...

aviation

(Encyclopedia)aviation, operation of heavier-than-air aircraft and related activities. Aviation can be conveniently divided into military aviation, air transport, and general aviation. Military aviation includes al...

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