of the damp clay: the combined effect would be to keep the pond at a lower temperature than the surrounding earth and thus able to condense a disproportionate share of moisture. In turn these conclusions were disproved in the 1930s, when it was pointed out that the heat-retaining quality of water (its thermal capacity) was many times greater than that of earth, and therefore the air above a pond in summer would be the last place to attract condensation. The deciding factor, it was concluded, is the extent of the saucer-shaped basin extending beyond the pond itself: the large basin would collect more rainfall than a pond created without such a surrounding feature. Dew ponds are still common on the downlands of southern England, the North Derbyshire and Staffordshire moorlands and in Nottinghamshire. Measuring dew production The first scientific experiments to measure and correlate the rate of dew deposit with evaporation were made by Harry Pool Slade of Aston Upthorpe, Berkshire, between June 1876 and February 1877, at a dew pond on Aston Upthorpe Downs (). Slade measured overnight dew deposit (by weighing cotton wool when dry and after overnight exposure), evaporation from copper pans beside the pond, the depletion of the pond, and relative humidity. He found that on days with heavy overnight dewfall the level of water in the pond was not replenished but invariably diminished. In situ measurements of evaporation and condensation were taken at the Helmfleeth dew pond in Poppenbüll municipality (Eiderstedt Peninsula in Schleswig-Holstein, Germany) using meteorological measuring instruments and a floating evaporation pan after Brockamp & Werner (1970). These measurements proved the dew formation on the basis of temperature changes and the weather conditions. The Helmfleeth dew pond is part of the water supply for a marsh area and is still in use today. Reproductions of historical dew ponds In 2014, the traditional technique was verified by means of modern building material at reproductions of dew ponds in East Friesland. In this context, various techniques were tried in two terrestrial hollows. Commercially available PVC-film was used for the sealing and foam glass gravel for the insulation. The construction was carried out by craftsmen and the climatological analysis by Werner and Coldewey. See also Air well (condenser) Rainwater harvesting References Bibliography (Note: link is 1907 ed.) Journal articles Dewponds in specific locations Further reading External links Articles Building instructions from Popular Science Wiltshire Community History