A Barn, a Moving Pipe, and Ten Thousand Trials

The design deserves credit before the argument about the result begins, because it is the most serious attempt anyone has made to test dowsing under controlled conditions.

Dowsers worked on the upper floor of a barn. Beneath them, on the floor below, a water pipe was moved between runs to a position set at random. The dowser walked the upper floor and marked where they judged the pipe to lie. Neither the dowser nor the attendant with them knew where it had been placed, which is what makes the trials double blind rather than merely blind, and it closes the route by which an experimenter's knowledge can leak to a subject through posture, hesitation or a glance.

The scale matched the seriousness. More than five hundred dowsers took part across 1987 and 1988, and more than ten thousand individual trials were run. The programme was funded by the German federal government, which is unusual for a test of this kind and is part of why the results carried weight when they appeared.

The reason a design like this matters is that dowsing is easy to test and easy to appear to pass. In ordinary conditions a dowser has the ground, the vegetation, local knowledge and the reactions of the people watching, and a practitioner may draw on all of them without being aware of doing so. Removing the target from sight and from anyone present is what separates the claim from everything else that could produce a hit.