Francis Beaufort. an English Naval commander, devised a scale in 1805, which is still in use - with modifications - today.

The beauty of his system is that its 12 divisions are based on significant changes in the effect the wind has on a ship and what the sailors have to do in response.

It doesn't rely on having instruments to measure wind speeds. Later were added descriptions of phenomena happening on land.

Beaufort Number: 0 Calm Description on land: Calm, smoke rises vertically Description at sea: Sea like a mirror

Beaufort Number: 1 Light Air Description on land: Direction of wind shown by smoke Description at sea: Ripples with appearance of scales

Beaufort Number: 2 Light Breeze Description on land: Wind felt on face. Vane moved by wind. Description at sea: Small wavelets.Crests have glassy appearance but do not break. Wind fills sails of smacks

Beaufort number: 3 Gentle Breeze Description on land: Leaves in constant motion. Wind extends light flag. Description at sea: Large wavelets. Crests begin to break. Scattered white horses. Smacks begin to careen.

Beaufort Number: 4 Moderate Breeze Description on land: Raises dust and loose paper. Description at sea: Small waves becoming longer. Fairly frequent white horses. Smacks carry all canvas, with good list

Beaufort Number: 5 Fresh Breeze Description on land: Wavelets form on inland waters. Smalltrees in teaf begin to sway Description at sea: Moderate waves taking longer form. Many white horses. Smacks shorten sail.

Beaufort Number: 6 Strong Breeze Description on land: Whistling heard in telegraph wires. Large branches in motion Description at sea:Large waves forming extensive white foam crests.

Beaufort number: 7 Near Gale Description on land: Whole trees in motion. Inconvenience felt when walking against wind. Description at sea: Sea heaps up. White foam from breaking waves begins to blow in streaks. Smacks remain in harbour.

Beaufort Number: 8 Gale Description on land: Breaks twigs off trees. Generally impedes progress. Description at sea: Moderately high waves of greater length. Edges of crests break into spindrift.

Beaufort Number: 9 Strong Gale Description on land: Slight structural damage. Chimney pots and slates removed. Description at sea: High waves. Dense streaks of foam. Sea begins to roll.

Beaufort Number: 10 Storm Description on land: Seldom experienced inland. Trees uprooted. Considerable structural white damage. Description at sea: High waves with overhanging crests. Sea rolling heavily.Sea surface

Beaufort Number: 11 Violent Storm Description on land: Very rarely experienced. Accompanied by widespread damage. Description at sea: Exceptionally high waves. Long white patches of foam. Ships may be lost to view.

Beaufort Number: 12 Hurricane Description at sea: Air filled with foam and spray.Sea completely white with driving spray. Visibility greatly reduced.