If you received a letter from Britain this morning, it may well give you an opportunity to change the weather. March 13th, two days ago, was the first day of issue by the Royal Mail of four stamps to commemorate the 150th anniversary of the first weather maps. They are printed in something called thermochromatic ink, which means that if you rub any area of grey sky portrayed on the stamps, it turns miraculously blue. You have a change to better weather at your fingertips.
The stamps are clever in another way. The four comprise a set: the 45p denomination shows a ship in stormy weather; a picture of raining cats and dogs decorates the 19p stamp; the 27p shows a nice big smiling sun; and the 65p stamp has a picture of butterflies and brightly coloured birds. But if you assemble the four together like a jig-saw puzzle, the collage reveals an ornate barometer, or weather glass.
The first stamps dealing specifically with meteorology were a matching set of nine issued by the UN in 1956 to celebrate the establishment of the World Meteorological Organisation some years previously. Several countries followed suit, often marking some anniversary of their national weather service. In 1973 - the centenary year of WMO's predecessor, the International Meteorological Organisation - weather as a thematic subject gained considerable popularity, and more than 60 countries issued stamps on meteorology, featuring aspects of it as diverse as satellites and Chinese weather gods. Ireland was among them: a matching pair issued in September of that year showed a weather-map with a deep depression over Cork.
It is unclear, to me at any rate, which first weather map this most recent set is intended to commemorate. The honour of having compiled the first weather chart is usually accorded to a German mathematician called Heinrich Brandes, who in 1820, in a book called Beitrage zur Witterungskunde, described a method for drawing lines on a chart which would show deviations of the atmospheric pressure from the norm - not quite the same thing as isobars, but a plausible notion nonetheless.
But in the middle of the 19th century, the invention of the electric telegraph made the construction of a daily weather map "in near real time", as we nowadays would say, a realistic possibility. At the Great Exhibition of 1851 in London, a current weather map was prepared daily from August 8th to October 11th, and lithographed copies were sold to the public at one penny each. It may well be this event 150 years ago that the Royal Mail intends to celebrate.