The Turn Of The Century Electrotherapy Museum http://www.electrotherapymuseum.com    Quadpolar Tesla Coil Tests 4 Pancake Coils - 48" long! 2 Bipolar Coils - primaries in antiparellel. 1st and 4th coils have same polarity; 2nd and 2rd coils have same polarity. 2nd and 3rd coils grounded.  2nd and 3rd innermost secondaries connected together. Tripolar Tesla Coil - 1st and 3rd Coils have the same polarity, middle coil has the opposing pole. On taking a discharge from either pole to the centre, the end pole of the same polarity bursts into a brush discharge. (C) Jeff Behary, 2008