1911 Encyclopædia Britannica/Beaufort Scale

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Beaufort Scale, a series of numbers from 0 to 12 arranged by Admiral Sir Francis Beaufort (1774–1857) in 1805, to indicate the strength of the wind from a calm, force 0, to a hurricane, force 12, with sailing directions such as “5, smacks shorten sails” for coast purposes, and “royals, &c., ‘full and by’” for the open sea. An exhaustive report was made in 1906 by the Meteorological Office on the relation between the estimates of wind-force according to Beaufort's scale and the velocities recorded by anemometers belonging to the office, from which the following table is taken: — 

Beaufort scale. Corresponding wind. Limits of hourly velocity.
Numbers. Miles per hour.
0 Calm Under 2
1–3 Light breeze 2–12
4–5 Moderate wind 13–23
6–7 Strong wind 24–37
8–9 Gale 38–55
10–11 Storm 56–75
12 Hurricane Above 75