A frost-tolerant porous-pot evaporimeter

[Fist paragraphs...]
A severe limitation to the usefulness of porous-pot evaporimeters in the field has been their restriction to frost-free periods, since ice formation causes air locks and often breaks the pot.
In lowland areas with relatively long frost-free periods, measurements may be obtained for most of a year. In mountainous country, however, at least above about 4000 ft., severe frosts usually occur during all months. Thus, using improved, conventional-type evaporimeters (Baylis 1957), only occasional measurements of evaporation from December until March have been possible in the high altitude snow-tussock and alpine zones of the Old Man Range, Central Otago, during the past three years. One short period of sub-freezing temperature is usually sufficient to upset or to destroy the instrument.