May 7 – Blow Hard

Today’s Factismal: Sir Francis Beaufort was born 240 years ago today.

One of the big problems in science is measurement. How do you create an easy method for measuring something? And how do you set it up so that it actually means something? For example, consider the wind. Though it is fairly easy to know which direction the wind is blowing (for example, by looking at the way smoke rises), it can be incredibly difficult to know how fast the wind is blowing without specialized equipment.

And in 1805, specialized equipment was pretty sparse. But what was plentiful was ships and their sails. Because most commerce traveled by sailing ship, there were plenty of people who were both interested in knowing how the winds were moving and motivated to share their knowledge. All that they lacked was a common language.

Francis gave them that language. By establishing a twelve-point scale for wind tied to how the water around a ship and the sails of the ship behaved, Beaufort made it easier for sailors and meteorologists to measure the wind and to communicate their discoveries. His scale was:

Beaufort number Description Wind speed Wave height Sea conditions
0 Calm < 1 mph 0 ft Flat sea
1 Light air 1–3 mph 0–1 ft Ripples on sea
2 Light breeze 4–7 mph 1–2 ft Small wavelets, non-breaking
3 Gentle breeze 8–12 mph 2–3.5 ft Large wavelets with some whitecaps
4 Moderate breeze 13–17 mph 3.5–6 ft Small waves, crests break. More whitecaps
5 Fresh breeze 18–24 mph 6–9 ft Medium waves with lots of whitecaps and a touch of spray.
6 Strong breeze 25–30 mph 9–13 ft Some long waves with frequent foamy crests and airborne spray.
7 High wind 31–38 mph 13–19 ft Sea piles up, spray and foam forms streaks.
8 Gale 39–46 mph 18–25 ft Lots of spray and moderately high waves with breaking crests.
9 Strong gale 47–54 mph 23–32 ft Crests of high waves may roll over. Spray reduces visibility.
10 Storm 55–63 mph 29–41 ft Very high waves, tumbling with lots of spray and large patches of foam.
11 Violent storm 64–73 mph 37–52 ft Like ten, only at “11”.
12 Hurricane ≥ 74 mph ≥ 46 ft Why are you on the water? Waves are huge, sea is covered with foam and spray, and you can’t see anything. Go home.

The Beaufort scale is still used today, even though we now have instruments capable of providing much more detailed measurements. If you’ve ever heard a weatherman speak of “gale force winds”, then you’ve heard the Beaufort scale. If you’d like to try it at home and maybe gather some other weather data while you’re at it, then consider joining the Citizen Weather Observer Program:

One thought on “May 7 – Blow Hard

  1. Pingback: August 11 – Terrible Lizards | Little facts about science

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s