A ball moving on a vertical rod or pole, placed in some prominent elevated position, for the purpose of indicating mean time, which it does by dropping at a certain moment each day from the top to the bottom of the rod, usually by the closing of an electric circuit.

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  The time thus indicated is usually 1 P.M., in U.S. noon.

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1858.  Simmonds, Dict. Trade, Time-ball, a ball, moved by electricity, which is dropped from the summit of a pole to indicate the true meridional or mid-day time.

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1878.  Lockyer, Stargazing, 279. This [wire] is used for dropping the time-ball at Deal.

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1884.  Britten, Watch & Clockw., 263. The time ball at Greenwich Observatory is of very thin copper.

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