The first device which comes to mind from many years ago is the Wimshurst machine
https://en.wikipedia.org/wiki/Wimshurst_machine I doubt if there is rigorous proof… otherwise someone out there would surely try to supersize it… From: Chris Zell the possibility of “sparkgap OU” Has there ever been any rigorous analysis of sparkgaps that might suggest that? It gets claimed from time to time in fringe inventions.
