`Today I met Mr Wren," wrote a French visitor to London in 1661. "He is a great mathematician who, although small of stature, is one of the most civil and open persons that I found in England.
"Although he did not wish that his ideas be divulged, he did not neglect to speak most freely about his `weather clock', which moves a ruler on which there is a stylus that marks on concentric circles corresponding to the hours, all the changes in the wind indicated by a wind vane."
He was referring, of course, to Sir Christopher Wren, best known to posterity as the architect of St Paul's Cathedral in London, and who was born this day, October 20th, in 1632. Wren was a man of many talents, and before he took up building in his early 30s, he was already a scientist of some repute.
The diarist continued. "In the same way the rain, hail and snow are recorded by vases attached to this wheel, which pass at each hour under a funnel into which it can rain or snow or hail. The heat and cold are registered by a thermometer that raises or lowers a tablet against which a pencil on the above-mentioned ruler marks the hours cross-wise, while the tablet indicates the changes vertically."
To meteorologists nowadays, Wren's weather clock is just a curiosity. But another of his designs, the "tipping-bucket" rain recorder, is ideally suited to modern technology.
It consists of a triangular-shaped container divided into two compartments, and pivoted about its centre like a seesaw. At any particular time, one half of the bucket is directly underneath a pipe leading from the funnel in which the rain is captured.
When a certain amount of water - say half a millimetre - has been collected, the bucket over-balances. The water is tipped out, while at the same time the other half of the bucket is lined up with the water pipe. The device rocks back and forth indefinitely, "tipping" every time 0.5mm of rainfall has accumulated.
The difficulty in Wren's day - and for centuries afterwards - was that there was no convenient method of counting the number of times the bucket tipped, and thereby calculating the amount of rainfall in a given period.
Modern technology, however, has provided an almost trivial solution: it can be arranged that the bucket trips a micro-switch each time it tips, and the signal is then recorded electronically.
Voila - a continuous and vicarious record of the local rainfall at any place that one might wish to measure it.