Hi Folks
I haven't been around here much lately (too busy with Heritage Action stuff) so I've pick this thread up rather late.
I have dowsed successfully (finding drains, etc) on many occassions, but as a physicist I look for a scientific explanation. I conclude that the rods, pendulums, hazel twigs, etc are merely "amplifiers" - a means to enhance small muscular movements. I can dowse just by holding my hands out, palm down with my thumb tips pressed together. If you try it you'll find that there's a very sensitibve "balance" position where your thumbs are "wobbling" up and down. A dowsing "hit" causes them to flick up or down into a more stable position.
Obviously the next question is why the body is sensitive to underground entities. My own theory is that we are in some way sensitive to the very small amount of thermal radiation from the hotter regions below the Earth's crust. Water courses and other underground features cast a thermal "shadow" on the surface that we are able to detect. It would be interesting to use a thermal imaging camera on sites with significant "dowse" lines to see if anything can be detected, perhaps with a time exposure.
Others here have dismissed this theory, since it doesn't explain other dowsing phenomena such as dowsing from maps, but I am much more sceptical about such claims.
If you want to read the previous thread on this topic see:
http://www.themodernantiquarian.com/forum/?thread=13084
and for a laugh look for the messages about "the dowsing stance".
Steve