With regards to the difference in frequency of a typical Tesla Coil to the earth resonance frequency, and therefore my total lack of understanding of how Nikola could set up an earth resonant wave with his coil, could two coils be run from the same earth connection but each having a different operating frequency, and generate a low (earth res freq) beat frequency? Steve Bell (UK) steve-at-breakfix.demon.co.uk http://www.breakfix.demon.co.uk