Dowsing (also called radiesthesia) is the practice of searching for hidden things, water, minerals, buried objects, even lost persons, using a simple hand-held tool held to respond to subtle signals. The dowser walks a site holding a forked stick, a pair of angled L-rods, or a pendulum, and interprets its movements, the dip of the rod, the swing of the pendulum, as indicating the presence of the sought-for target. "Water witching" for well sites is the most familiar form, with a long folk history in Europe and the Americas, and dowsing has also been applied to mineral prospecting, archaeology, and, in the pendulum form, to answering questions and diagnosing health.
The practice is old (a version is described in Agricola's sixteenth-century mining treatise) and remains widely used at the folk level. Its explanation is well established scientifically: controlled tests have consistently failed to show that dowsers can locate hidden targets at rates better than chance, and the movements of the rod or pendulum are understood as the product of the ideomotor effect, small, involuntary muscular movements produced by the dowser's own expectations, below the level of conscious awareness. Presented fairly, then, dowsing is a genuine and sincerely practised tradition whose results are attributable to the operator's unconscious responses and knowledge of the terrain rather than to any detected external force, a point on which the folk practice and the scientific assessment diverge.