Huh.... We were discussing that locally on 10M SSB over the weekend. And, I seem to remember CQ magazine, (Or, was it Popular Communications?), covering a story, where around 1900, an experimenter in Belmont, NY was listening to sound signals from a ground rod. This dude believed that he was hearing industrial noises from Hornell, NY. What's there??? A train refurbishing facility, for one. Now, Alstom Transportation, Inc. (I contracted to work there in 2005, for 8 months, for the MARTA, WMATA, NJ Transit, NYC's R160, and a couple others.) Now, let's see if I can find that article. It was a fascinating read.