Re: locating buried wires and conduits by holding two metal rods that cross

Dowsing, as "witching" is more widely known, hasn't been taken very seriously by mainstream science and so hasn't been studied much. Most attempts to observe dowsing in a lab have been failures, which is probably why one professor told you it didn't work. There have been enough successes in the field that it warrants further study, but there is no definitive, measurable proof.

The other professor you talked to is right that no one knows how dowsing works. There has been speculation about it, though, and I can list a few of the more common and/or interesting ideas.

1. The person dowsing has learned what kind of ground features are associated with whatever he's trying to find. His hands move with subconscious twitches and muscle adjustments, making the rods move in the way the person subconsciously expects them to move. This is similar to how the puck on a ouija board is supposed to work.
2. The way dowsing rods are held makes them into a sort of sensitive pendulum. As a person walks around, subtle changes in the evenness of the ground which are otherwise unnoticeable cause the rods to move in the direction of the lowest immediate point, which is often associated with water or with buried objects because of ground settling.
3. The rods respond to changes in the electric or magnetic field of the ground. A person holds the rods so they move easily in her hands, and the rods pivot to point towards or away from positive or negative charges or north or south magnetic poles.
4. Some people believe in a mystical "Earth energy" that flows through and around the earth, affecting and being channeled by objects it encounters. This is outside the study of physics, though, and would be difficult at best to prove.

If you would like to see what the people who dowse think, you may want to check out the American Society of Dowsers at http://newhampshire.com/dowsers .org/ or the East Midlands Dowsing Group (a dowsing club near Nottinghamshire, UK) at http://www.oscars.demon.co.uk/ . A fellow at Stanford also has a short page on dowsing at http://taishan.stanford.edu .