Rear-Admiral, Sir Francis Beaufort, was born in Ireland in 1774. He entered the Royal Navy at the age of 13 and was a midshipman aboard the Aquilon. By 1800 he had risen to the rank of Commander. In the summer of 1805 Beaufort was appointed to the command of the Woolwich, a 44 gun man-of-war.

  In 1806 he wrote in his log book a wind force scale. The scale was simple and very simular to one that Alexander Dalrymple had written in a book in 1789. A year later he added some criteria to the 0-12 scale that indicated how much of a ship's sails would be employed by a British man-of-war under each condition. It was not relate to the speed of the wind.

  Over the following years he continued to use his scale in his logs. It was finally adopted in December 1838 by the British Admiralty for use in all Royal Navy logbooks. However, as ship design and the introduction of steam power became widespread even that scale had to be modified.

  In 1912 the International Commission for Weather Telegraphy sought some agreement on velocity equivalents for the Beaufort scale. A uniform set of equivalents was accepted in 1926 and revised slightly in 1946, extending the scale to 17 values (the added five values further refining the hurricane-force winds). By 1955, wind velocities in knots replaced Beaufort numbers on weather maps.

Calm; smoke rises vertical.

Sea like a mirror.
Waves height: 0 meters.

Direction of wind shown by smoke drift, but not by wind vanes.

Ripples with the appearance of scales are formed, but without foam crests.
Waves height: 0 - 0,1 meters.

Wind felt on face; leaves rustle; ordinary vanes moved by wind.

Small wavelets, still short, but more pronounced. Crests have a glassy appearance and do not break.
Waves height: 0,1 - 0,6 meters.

Leaves and small twigs in constant motion; wind extends light flag.

Large wavelets. Crests begin to break. Foam of glassy appearance. Perhaps scattered white horses.
Waves height: 0,6 - 1,25 meters.

Raises dust and loose paper; small branches are moved.

Small waves, becoming larger; fairly frequent white horses.
Waves height: 1 - 1,5 meters.

Small trees in leaf begin to sway; crested wavelets form on inland waters.

Moderate waves, taking a more pronounced long form; many white horses are formed. Chance of some spray.
Waves height: 1,5 - 2,5 meters.

Large branches in motion; whistling heard in telegraph wires; umbrellas used with difficulty.

Large waves begin to form; the white foam crests are more extensive everywhere. Probably some spray.
Waves height: 2,5 - 4 meters.

Whole trees in motion; inconvenience felt when walking against the wind.

Sea heaps up and white foam from breaking waves begins to be blown in streaks along the direction of the wind.
Waves height: 4 - 5,5 meters.

Breaks twigs off trees; generally impedes progress.

Moderately high waves of greater length; edges of crests begin to breakinto spindrift. The foam is blown in well-marked streaks along the direction of the wind.
Waves height: 5,5 - 7,5 meters.

Slight structural damage occurs (chimney-pots and slates removed).

High waves. Dense streaks of foam along the direction of the wind. Crests of waves begin to topple, tumble and roll over. Spray may affect visibility.
Waves height: 7 - 9 meters.

Seldom experienced inland; trees uprooted; considerable structural damage occurs.

Very high waves with long over-hanging crests. The resulting foam, in great patches, is blown in dense white streaks along the direction of the wind. On the whole the surface of the sea takes on a white appearance. The 'tumbling' of the sea becomes heavy and shock-like. Visibility affected.
Waves height: 9 - 12,5 meters.

Very rarely experienced; accompanied by wide-spread damage.

Exceptionally high waves (small and medium-size ships might be for a time lost to view behind the waves). The sea is completely covered with long white patches of foam lying along the direction of the wind. Everywhere the edges of the wave crests are blown into froth. Visibility affected.
Waves height: 10 - 14 meters.

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The air is filled with foam and spray. Sea completely white with driving spray; visibility very seriously affected
Waves height: over 14 meters.