Rhabdomancy

In addition to prediction, another great divinatory goal is the retrieval of missing objects, lost people, and best of all, precious metals. Rhabdomancy, more commonly known as dowsing, is the art of finding resources -- and humans -- using a divining rod.
This semi-magic(k)al skill has been around for thousands of years, though it probably reached its apex of popularity in Germany in the sixteenth century, when it was vigorously employed to prospect for mines. The divining rod itself is most likely derived from the sorcerer's wand, but it is a more democratic instrument -- almost anyone can use one. The technique is equally foolproof. According to an eighteenth century French dowser and, incidentally, abbot, nothing could be simpler:
A forked branch of hazel, or filbert, must be taken, a foot and a half long, as thick as a finger, and not more than a year old...The two limbs of the fork are held in the two hands, without gripping too tight, the back of the hand being towards the ground. The point goes foremost, and the rod lies horizontally. Then the diviner walks gently over the places where it is believed there is water, minerals, or hidden money. He must not tread roughly, or he will disperse the clouds of vapors and exhalations which rise from the spot where these things are and which impregnate the rod and cause it to start.

Contemporary dowsers are less rigid with regard to the brand of tree necessary for the divining rod: ash, willow, and apple branches are now permissible, and some dowsers even countenance plastic. The physics are inexplicable, but the results are inescapable: the divining rod does indeed lurch upward -- sometimes quite violently -- as it passes over buried spring and minerals.
Rhabdomancy was denounced as the work of the devil at various points in history, but it has been used almost continuously in Europe since the Middle Ages (practical benefits outweigh the maledictions of the Church every time). The French were particularly keen to assert the benign, God-fearing attributes of la baguette, as they call the divining rod, and so were the chief innovators in its development as a policing tool. In 1692, a peasant named Jaques Aymar used his diving rod to track down the murderers of a local wine merchant. His forked stick bobbed up and down dramatically at the murder site and then led Aymar through town, over the Rhone, and all the way to Lyons, where he found a hunchback who confessed to taking part in the deed. Upon the publication of this detective story, judicial rhabdomancy became all the rage in France. In early America, dowsing had the purely pragmatic function of locating well-water. The most fully documented use of rhabdomancy occurred during the mid-nineteenth century by prospectors looking for gold to mine. During the Vietnam war, dowsing was practiced to find land mines. It is now used by oil and gas companies to find caches of those resources.