In the fifteenth century Korea was a drought-plagued realm, and King Sejong (1397-1450) wished to levy land taxes based on an assessment of each farmer's potential harvest. To this end a nationwide network of rain gauges was established and the local magistrates of every village were commanded to report the rainfall to the central government.
In 1441 each village was provided with a standard cylindrical container, 17 inches (43 cm) high and 7 inches (17 cm) wide, that was mounted on a stone stand; a special ruler was used to measure the depth of rainwater that entered the gauge over a specific time. Its inventor was a civil-servant scientist, Jang Yeong-Sil. Needless to say, the method of rain measurement was rather labor-intensive. The Chinese, meanwhile, had used a similar technique to measure snowfall in 1247C.E.
In 1662 Sir Christopher Wren (1632-1723) invented the "pluviometer," a mechanical, self-emptying, tipping-bucket rain gauge. It consisted of two small, well-balanced buckets that collected rain sequentially. When a specific amount of water had fallen into one of the buckets—usually about 0.03 inches (0.1 cm)—it tipped over, emptied itself, and produced a mechanical signal. Also, a hole was punched into a slowly moving paper tape as the bucket tipped. The second bucket then started to collect rain, only to tip over when full. The more signals recorded, the greater the rainfall.
Care had to be taken in positioning Wren's gauge. It had to be sufficiently high off the ground to avoid splashes and animals, and be well away from trees, fences, and buildings to prevent shadowing and an unrepresentatively low reading. Heated gauges are now used when hail and snow are expected.
