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atomic clock
(Encyclopedia)atomic clock, electric or electronic timekeeping device that is controlled by atomic or molecular oscillations. A timekeeping device must contain or be connected to some apparatus that oscillates at a...glacial periods
(Encyclopedia)glacial periods, times during which large portions of the earth's surface were covered with thick glacial ice sheets. In the Pleistocene epoch, in the Carboniferous and Permian periods of the Paleozoi...Frederick III, Holy Roman emperor and German king
(Encyclopedia)Frederick III, 1415–93, Holy Roman emperor (1452–93) and German king (1440–93). With his brother Albert VI he inherited the duchies of Styria, Carinthia, and Carniola. He became head of the hous...Dylan, Bob
(Encyclopedia)Dylan, Bob dĭlˈən [key], 1941–, American singer and composer, b. Duluth, Minn., as Robert Zimmerman. Dylan learned guitar at the age of 10 and autoharp and harmonica at 15. After a rebellious you...seafloor spreading
(Encyclopedia)CE5 Schematic model of the oceanic crust, showing seafloor spreading seafloor spreading, theory of lithospheric evolution that holds that the ocean floors are spreading outward from vast underwate...poll
(Encyclopedia)poll, technique for ascertaining the attitudes or opinions of the total, or some segment of the total, population on given questions, usually on political, economic, and social conditions. Sampling ...transportation
(Encyclopedia)transportation, conveyance of goods and people over land, across water, and through the air. See also commerce. The first practical attempts at air transportation began with the invention of the h...clock
(Encyclopedia)CE5 A pendulum clock: Weight-driven clock mechanism clock, instrument for measuring and indicating time. Predecessors of the clock were the sundial, the hourglass, and the clepsydra. See also watc...influenza
(Encyclopedia)influenza or flu, acute, highly contagious disease caused by a RNA virus (family Orthomyxoviridae); formerly known as the grippe. There are three types of the virus, designated A, B, and C, but only t...continent
(Encyclopedia)continent, largest unit of landmasses on the earth. The continents include Eurasia (conventionally regarded as two continents, Europe and Asia), Africa, North America, South America, Australia, and An...Browse by Subject
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