No. 47: Sep-Oct 1986
The following two paragraphs were taken from a letter to Nature:
"David Marks, in The Skeptical Inquirer, asserts that there are no theories to account for paranormal effects. This is not true for dowsing. Serious dowsing claims, such as those made by Soviet geologists, which are difficult to account for in terms of the reception of normal sensory cues, may be explained by postulating human sensitivity to small magnetic field gradient changes. The theory is supported by a series of tests involving 150 subjects.
"The magnetic theory predicts that dowsers can achieve above-chance re sults only if the features they claim to detect are associated with magnetic gradients of at least one nanotesla per metre. This was not the case in Randi's recent experiments, so his chance results are therefore consistent with the magnetic theory, which merits further investigation."
(Williamson, Tom; "Dowsing Explained," Nature, 320:569, 1985.)