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United States Naval Observatory

(Encyclopedia)United States Naval Observatory, a federal astronomical observatory, located in Washington, D. C. It evolved from the Navy's oldest scientific institution, the Depot of Charts and Instruments, founded...

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...

sea level

(Encyclopedia)sea level, the level of the sea, which serves as the datum used for measurement of land elevations and ocean depths. Theoretically, one would expect sea level to be a fixed and permanent horizontal su...

pendulum

(Encyclopedia)pendulum, a mass, called a bob, suspended from a fixed point so that it can swing in an arc determined by its momentum and the force of gravity. The length of a pendulum is the distance from the point...

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...

megatherium

(Encyclopedia)megatherium mĕgəthērˈēəm [key] [Gr.,=large beast], extinct ground sloth, of the genus Megatherium, that was widely distributed in North and South America in the Pleistocene epoch. Fossil evidenc...

iron lung

(Encyclopedia)iron lung, device used to maintain artificial respiration over an extended period of time. Before the successful vaccination program against poliomyelitis, it was used mostly in treatment of that dise...

Djokovic, Novak

(Encyclopedia)Djokovic, Novak, 1987–, Serbian tennis player, b. Belgrade. He began winning European championships at age 14, and played in his first Grand Slam tournament, the Australian Open, in 2005. He won the...

Chamberlin, Guy

(Encyclopedia)Chamberlin, Guy (Berlin Guy “Champ” Chamberlin), 1894–1967, American football coach and player, b. Blue Springs, Neb., grad. Univ. of Nebraska, 1916. Chamberlin was one of the greatest ends of h...

Robinson, Sugar Ray

(Encyclopedia)Robinson, Sugar Ray, 1920–89, American boxer, b. Detroit as Walker Smith, Jr. He began boxing after three years of high school in New York City. Having won all his amateur fights (about 90), includi...