The Turn Of The Century Electrotherapy Museum http://www.electrotherapymuseum.com "Phantom Streamers" Experiments with Series Spark Gap (grounded on the far end with my thumb) being charged and discharged from Phantom Steams...  They're visible to the naked eye but extremely hard to photograph.  Here is a series gap (normally used to reduce inverse-current with X-Ray Coils).  The gap fires continuous at 1.25" on setting 2 of the spark gap, and up to about 2" on full power (gap 4).  The distance between the spark balls is 1/8".

Photos lightened to show streamers - blurry here, these phantoms extend out a foot or more from the 2" ball.

The spheres on top of the coil started off as chrome plated steel machinist knobs - "ball knobs". As you can see they're not perfectly polished, but have little (if any) rust...to start off with... Today, I was surprised to see the finish on them after less than 30 minutes of Phantom Streamers...

Geez!  So much for Chrome!