Hmmmm...if I place an 'electrode' (say a metal bar 1-foot long) in a deep mine and run a wire from the 'bar' to the surface, would I be able to detect a current from the end of that wire and another 'bar' touching the surface/ground ? And, if so, would the current strength increase/vary the deeper the mine 'bar' is placed below the surface? ...And would it work better if the 'bars' were, say, copper for one bar and iron for the other....? (Trivia: You can detect a current between a brass nail and an iron nail driven, say, 2-inches apart AND 3-inches deep into a maple tree -- the only tree I tried.... [Hmm, try this with a forest and wire 'them' in series/parallel......................]) ;0
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