By the time he retired in 1855, at the age of 81, Francis Beaufort could deem himself successful. He was an admiral and a Knight of the Bath, and he had transformed the Hydrographic Office of the British Navy from little more than a depot for the storing of charts of mediocre quality into the finest maritime surveying and cartographic institution in the world.
Moreover, partly ex officio, Beaufort had become a landmark in virtually every corner of the globe. The Beaufort Dyke, for example, is a trough beneath the North Channel that separates Antrim from the coast of Scotland. The Beaufort Gyre is a current in the Arctic, the Beaufort Sea lies north of Canada, and there are Beaufort Straights, Beaufort Islands, and half a dozen towns called Beaufort in America. There is even a Beaufort under the Macgillycuddy Reeks in Co Kerry, although one doubts if this had any direct connection with the admiral.
Most people, however, associate the name of Francis Beaufort with the well-known scale for estimating the strength of winds at sea. In his early sea-faring days, Beaufort had been struck by the difficulties caused by the lack of a standard method for assessing wind-speed. Terms such as "light airs", "stiff breezes" and "half gales" were in common use among the maritime community, but they had no universally accepted meanings, and misunderstandings and ambiguities were rife.
Beaufort approached the problem scientifically. He decided that wind needed to be assessed against a well-known standard, in much the same way as a standard unit might be used to determine the length of a familiar object. He selected as his "standard" the typical full-rigged man-o'-war of the British navy, and he defined what we now know as the Beaufort Scale by effect of the wind on such a vessel - and in particular by the amount of sail it could carry in high winds without getting into trouble.
A light air, for example, which he called Force 1, was a wind just sufficient "to give steering way". A moderate breeze, Force 2, was a wind such that a "well-conditioned man-o'-war, under all sail . . . would go in smooth water at from 5 to 6 knots". With Force 8, a whole gale, the same ship could only bear "close-reefed main topsails and a reefed foresail". And the highest number on the scale, hurricane Force 12 , was when a man-o'war could show no canvas whatsoever.
Beaufort devised his scale in 1806. It began to be used officially by the navy in the early 1830s, and its form has changed only superficially in the intervening years.