The Beaufort scale was made a standard for ship's log entries on Royal Navy vessels in the late 1830s and was adapted to non-naval use from the 1850s, with scale numbers corresponding to cup anemometer rotations. In 1916, to accommodate the growth of steam power, the descriptions were changed to how the sea, not the sails, behaved and extended to land observations. Rotations to scale numbers were standardized only in 1923. George Simpson, Director of the UK Meteorological Office, was responsible for this and for the addition of the land-based descriptors.
The measure was slightly altered some decades later to improve its utility for meteorologists. Today, many countries have abandoned the scale and use the metric-based units m/s or KM/h instead, but the severe weather warnings given to public are still approximately the same as when using the Beaufort scale (source: wikipedia.org)
1 Miles/h : 1-3 KM/h : 1-5 Knots : 1-3 Description : Light air Direction of wind shown by smoke drift, but not by wind vanes
2 Miles/h : 4-7 KM/h : 6-11 Knots : 4-6 Description : Light Breeze Wind felt on face; leaves rustle, ordinary vanes moved by wind
3 Miles/h : 8-12 KM/h : 12-19 Knots : 7-10 Description : Gentle Breeze Leaves and small twigs in constant motion; wind extends light flag
4 Miles/h : 13-18 KM/h : 20-28 Knots : 11-16 Description : Moderate Breeze Raises dust and loose paper, small branches are moved
5 Miles/h : 19-24 KM/h : 29-38 Knots : 17-21 Description : Fresh Breeze Small trees in leaf begin to sway; crested wavelets form on inland waters
6 Miles/h : 25-31 KM/h : 39-49 Knots : 22-27 Description : Strong Breeze Large branches in motion, whistling heard in telegraph wires; umbrellas used with difficulty.
7 Miles/h : 32-38 KM/h : 50-61 Knots : 28-33 Description : Near Gale Whole trees in motion, inconvenience felt when walking against the wind.
8 Miles/h : 39-46 KM/h : 62-74 Knots : 34-40 Description : Gale Breaks twigs off trees, generally impedes progress
9 Miles/h : 47-54 KM/h : 75-88 Knots : 41-47 Description : Severe Gale Slight structural damage occurs (chimney-pots and slates removed)
