A simple device for measuring the vertical distance between two points; it consists of a clear container (e.g. a plastic can), a piece of clear plastic tubing about 10 m long, wire to attach the tubing to the container, and a clip. The container is filled with water and one end of the tubing inserted almost to the bottom and fixed to the mouth. Water is siphoned into the tubing to within about 50 cm of its further end and that end is sealed with the clip. The tubing is extended downslope over the surface, its end raised until the water level in the tubing is higher than that in the container, and the clip is removed, allowing the water level in the tubing to fall to that in the container. The difference in the height above the surface of the water levels in the tubing and the container represents the vertical distance between the two sites. The method was devised by the biologist C. Wood-Robinson and first described in 1981.
Subjects: Ecology and Conservation.