In the early 19th century the postage fee for a letter was paid by the person who received it, the charge depending, rather erratically, on the distance travelled. A local letter might be delivered for a penny, but for greater distances the lowest charge was 4d, the average rate 7d, and the cost of taking delivery of a letter sent from London to Edinburgh, for example, was 1s 4d.
It was calculated that if an Irish labourer working in England sent a letter to his mother in Ireland and received a reply, it would cost more than a fifth of his wages for a week's work.
In 1840 the postal service was reorganised dramatically to reduce the cost, and a uniform rate of 1d, regardless of the distance, was inaugurated. In addition, prepayment of the postage fee was provided for by means of a little adhesive stamp.
The first of these, the famous Penny Black, was issued 149 years ago today, on May 1st, 1840. Philately has been a popular hobby ever since, and there are collectors who specialise in meteorology.
The first stamps dealing specifically with the topic were a matching set of nine issued by the United Nations in 1956 to celebrate the establishment of the World Meteorological Organisation some years previously.
The idea caught on, and individual countries followed suit, often marking some anniversary of their national weather service. It was in 1973, however - the centenary year of WMO's predecessor, the International Meteorological Organisation - that meteorology as a thematic subject gained potential.
In that year more than 60 countries issued stamps on meteorology, featuring aspects of it as diverse as Chinese weather gods and satellites. Ireland was among them: a matching pair issued in September of that year showed a weather-map with a deep depression over Cork.
Some collectors specialise in stamps portraying those who have made a contribution to the science. Benjamin Franklin and Galileo, for example, are easy to find because they have been honoured almost globally. But Torricelli, who invented the barometer, has featured only twice - in Italy and Russia - and Vilhelm Bjerknes, the father of the front, has appeared on only one occasion; as one might expect, it was in his native Norway, in 1962.
Other enthusiasts find a personal theme. The Irish meteorologist, the late Fred Dixon, for example, had a collection devoted entirely to the Beaufort Scale: specimens showing smoke rising vertically, ships with various amounts of sail, people having difficulty in walking against the wind, and many others were carefully arranged so that each step on the Beaufort Scale was fully represented.