Some information on electrical rock disintegration:
http://www.informaworld.com/smpp/conten ... 277~db=allThe plasma explosion, generated by pulses inside the rock fragments, is induced by development of the treelike conductive capillaries which result from application of an electrical field which exceeds the dielectric strength of the rock.
After re-watching the stones-down-the-hole video, I am convinced there is a static electrical charge that increases with depth, perhaps in the same ratio as the above ground charge. This would mean the stone would experience a rapid change in voltage, and being a reasonably good insulator, higher differential between inner and outer voltages.
So now I'm thinking the experiment is not so simple, and am looking at possible experiments.
1) a bare copper wire with a weight of some kind on the end, lowered down so as not to touch the inside of the tube.
2) a coaxial cable with some kind ow a weight on the end. A copper disk or sphere? What about bifilar coils of various wire size and turns?
3) an 'active head' module lowered on a fiber optic cable. The head would be able to compare static charge to a reference voltage source and send data by way of the fiber to topside instrumentation. EM activity might be sampled at numerous levels in the shaft, over a range of frequencies through the use of widely tunable circuitry in the head.
Determining a zero or referece voltage for 3) is perhaps not as easy as one might think, but it might not need to be overly accurate to give polarity and reasonable charge gradient readings.
http://www.advancedphysics.org/forum/sh ... php?t=1985