The atmometer or evaporimeter is a scientific instrument used for measuring the rate of evaporation from a wet surface to the atmosphere. It was invented by either the Dutch scientist Pieter van Musschenbroek (1692–1761)[1] or the Scottish mathematician and engineer Sir John Leslie (1766–1832).
A simple set up may be made by use of a porous flat plate-like object (a filter paper, for example) which can draw water from an easily measurable source (a graduated cylinder, for example) via a wick of some sort. As water evaporates from the surface, it tends to draw more water from the source through the wick by capillary action to replace the water lost by evaporation. By periodic measurements of the quantity of water remaining in the graduated cylinder, a rate of evaporation can be established. Also, using the surface area of the plate, we can establish a rate of evaporation per unit area.