An instrument for measuring the velocity of a ship. It is a flat piece of wood, some six inches in radius, and in the shape of a quadrant. A piece of lead is nailed to the rim to make the log float perpendicularly. To this log a line is fastened, called the log-line (q.v.). Other forms are also used.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894
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