Divining-rod, often called the Virgula Divina, the Baculus Divinatorius, the Caduceus or wand of Mercury, the Rod of Aaron, is a forked branch, usually of hazel, and sometimes of iron, or even of brass and copper, by means of which minerals and water may be discovered beneath the surface of the earth. The rod, when suspended by the two prongs, sometimes between the balls of the thumbs, indicates by a decided inclination the spot over which the concealed mine or spring is situated. It has often been used also to discover the authors of a crime, as by the famous Jacques Aymar in a case of murder and robbery at Lyons in 1692. Many men, even of some pretensions to scientific knowledge, have been believers in the occult power ascribed to this magic wand. Agricola, Sperlingius, and Kirchmayer all believed in its supernatural influence. Bayle, under the word Abaris, in his Dictionary, gives some ingenious arguments both for and against the divining-rod. It seems to be still believed in, not only by Cornish miners, but even by English civic officials, here and there, in the last decade of the 19th century.
It is hardly necessary to say that men who know anything of scientific method in the examination of nature regard this alleged power of the divining-rod as due either to conscious knavery or to a more or less unconscious delusion, the whole phenomena merely being due to the effect of a strong impression on the mind acting through nerves and muscles.
The divining-rod delusion should for ever have been laid to rest by Chevreul's De la Baguette divinatoire, &c. (1854). See also Lang's Custom and Myth (1884), and Barrett in Proc. Soc. Psychological Research (Oct. 1897).