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metric system

(Encyclopedia)CE5 metric system, system of weights and measures planned in France and adopted there in 1799; it has since been adopted by most of the technologically developed countries of the world. It is based...

rock music

(Encyclopedia)rock music, type of music originating in the United States in the mid-1950s and increasingly popular throughout much of the world. A turning point in rock music occurred in the mid-1970s in the ...

fan

(Encyclopedia)fan, device for agitating air or gases or moving them from one location to another. Mechanical fans with revolving blades are used for ventilation, in manufacturing, in winnowing grain, to remove dust...

hygrometer

(Encyclopedia)hygrometer hīgrŏmˈətər [key], instrument used to measure the moisture content of a gas, as in determining the relative humidity of air. The temperature at which dew or frost forms is a measure of...

gluon

(Encyclopedia)gluon, an elementary particle that mediates, or carries, the strong, or nuclear, force. In quantum chromodynamics (QCD), the quantum field theory of strong interactions, the interaction of quarks (to ...

Gell-Mann, Murray

(Encyclopedia)Gell-Mann, Murray gĕlˈ-män [key], 1929–2019, American theoretical physicist, b. New York City, grad. Yale 1948, Ph.D. Massachusetts Institute of Technology, 1951. He was associated with the Univ....

neutron

(Encyclopedia)neutron, uncharged elementary particle of slightly greater mass than the proton. It was discovered by James Chadwick in 1932. The stable isotopes of all elements except hydrogen and helium contain a n...

Xi'an

(Encyclopedia)Xi'an shēˈänˈ, sēˈ– [key], city (1994 est. pop. 2,114,900), capital of Shaanxi prov., China, in the Wei River valley. Situated on the Longhai RR, China's principal east-west line, it is an imp...

pump

(Encyclopedia)pump, device to lift, transfer, or increase the pressure of a fluid (gas or liquid) or to create a vacuum in an enclosed space by the removal of a gas (see vacuum pumps under vacuum). The centrifugal ...

propeller

(Encyclopedia)propeller, device consisting of a hub with one or more blades that propels a craft to which it is attached by rotating its blades in a fluid such as air or water. In the latter part of the 1830s the S...