A porous paper wick atmometer. The instrument consists of a graduated tube, closed at one end, that is filled with distilled water and then covered with a larger circular piece of filter paper held in place by a disc and collar arrangement. In operation the instrument is inverted so that the distilled water is in contact with the filter paper. The amount of evaporation that occurs during an interval of time is determined by noting the change in level of the meniscus of the water. See Dines anemometer, Pitot-tube anemometer; Compare Venturi tube.