Eventually, Tesla got things tuned, keeping it at low power.

But, in the spirit of a true hacker, just once, he decided to run it wide open, just to see what would happen. What was the upper limit of the wave he would build up, bouncing back and forth in the planet below?

Wearing three-inch rubber soles, Tesla and his assistant, Kolman Czito, hooked the coil to the ground below it, the 200 feet antenna with a huge copper sphere on top of it. Getting as much electricity as he wanted, right off the city power supply mains, he turned the coil on.

At first, there was nothing. Then, slowly, a buzz from rows of oil capacitors turned into a roar as the spark - gap opened and a wrist - thick arc jumped across it. "Inside the lab the noise was deafening". Mr. Czito recollects later in January 1943, as he was interrogated by E.J.Hoover personally in the FBI headquarters in Washington DC, after the great inventor was found dead in his hotel room in New York. "But Tesla was outside, watching it, oblivious for everything else around him. Any surge that bounced back would run up the antenna and jump off as lightning. Off the top of the antenna shot a six - foot lightning bolt, which kept going in a steady arc though, unlike a single lightning flash. It was amazing. Tesla watched carefully, wanted to see if the power would build up, if his wave theory would work."

It worked.

"Soon, the ligtning was twenty feet long, then fourty, sixty, eighty, a hundred feet... The surges were growing more powerful, thunder was following each lightning bolt. Hundred and twenty feet... hundred and thirty feet - Then the lightning shot upwards off the antenna. Thunder was booming around, the earth was radiating an eery blue glow" (the deafening sound was heard 22 miles away, in the town of Cripple Creek)

Then everything halted and all was still once more.