Christopher Buys Ballot was a Dutchman, and he was born 180 years ago today, on October 10th, 1817. His first major appointment was that of Professor of Physics at the University of Utrecht, but he indulged an abiding interest in meteorology by establishing a small weather observatory at Sonnenbergh in 1849. Five years later, in February 1854, this observatory, together with four other observing stations in the vicinity, formed the embryo of what was to become the Royal Netherlands Meteorological Institute. Buys Ballot was appointed its first director, and he occupied the post with great distinction for more than 30 years.
So, what? - I hear you ask.
Well, Buys Ballot was an energetic pioneer of the new science. He compiled daily weather maps for a large area of Europe and published them, together with tabulated weather observations for the Netherlands, in the annual Jaarboek published by the institute. Under his direction also, the institute became the first weather service in the world to issue storm warnings on a routine basis - beginning on June 1st, 1860, almost a year before Admiral FitzRoy did something similar in England. And Buys Ballot designed a new instrument for this purpose, which he quaintly called an aeroclinoscope - a kind of semaphore which stood near the shore and signalled information about the expected wind to nearby ships.
So what again? - say you. Well, in 1857 Christopher Buys Ballot wrote a famous paper which began: "Les grandes differences barometriques, dans les limites de notre pays, sont suivies par des vents plus forts . . . " Translated, this original version reads: "Great barometric differences, within the limits of our country, are followed by stronger winds; and the wind is in general perpendicular, or nearly so, to the direction of the greatest barometric slope, in such a way that a decrease of pressure from the north to south is followed by an east wind, and a decrease from south to north by a west wind". It was a principle that was to become one of the cornerstones of meteorology.
In more general terms, Buys Ballot's Law, as it is called, tells you that if you stand with your back to the wind in the northern hemisphere, the pressure is lower to your left than to your right. It is only a small step from this rule of thumb to the fundamental principle that underlies any meaningful interpretation of the weather map - the notion that the wind blows in an anti-clockwise direction around a depression and clockwise around a high. It is sometimes claimed to be the one infallible rule in the whole science of meteorology.