In this drawing it was definitely an artist's sketch.
In reality, a completely flat spiral Tesla transformer did exist. It
is clearly visible in the rear of the photograph of Tesla's Houston
Street Laboratory in New York City. It was visible behind Tesla's
"spinning egg" exhibit he was developing for the Columbian Expo
World's Fair in Chicago. A portion of this coil was tapped across as
a primary, thus the partial primary drives the secondary --- very
similar to the way a Variac can produce 140 or 280 vac from only 120
vac or 240 vac input.
Dr. Resonance
Hi Doc,
I was not doubting the existence of a flat spiral Tesla coil, only
the accuracy of the operation as depicted in this "artist's concept".
Matt D.