The Turn Of The Century Electrotherapy Museum
(C) Jeff Behary 2007

And sometimes they just

Tonight I feel as I did when I first tested the "Prague Coils", my first twin Pancake unit.  Here is a single 9" Pancake Coil yielding 9" discharges
to a variac nearby.  Power consumption was 1/2 - 1 kW, 4000V transformer, 3 series 1/2" tungsten spark gap, .016 mfd condenser.
In complete darkness negative discharges surround the coil - note the corona on the primary winding (2 1/2 turns of 1/8" thick x  3/4" wide pure silver).
When power is off 1/4" static sparks can be drawn from the secondary, primary, spark gap, or all of the above...

These photos are higher resolution than most on the site, but I think they are well worth the time to load them.