The above pictures are of a double coned coil I acquired on eBay. The seller purchased it from the estate of a deceased FBI agent. I was informed by one of the bidders, who owns a similar coil without the wires that it was designed by Nikola Tesla, himself. The wooden frame he owns was given to his father by Nikola Tesla as payment (Tesla had no money at the time).
Each cone is 6" in diameter and 6" in height. Each cone has approx. 127ft of wire. The end to end inductance of the secondary is 2.36mH. The quarter wave length frequency calculates to 1.937MHz for a straight solenoid but this coil resonates at about 1.12MHz as determined by a frequency counter and oscilloscope.
The two cones are connected in the middle such that the entire length is one wire. There is no tapping point between the two coils. I had to replace the copper primary due to age and wear but I am keeping the old copper tubing as verification for the coil's age. This coil was likely built in the early 1900s and is identical in layout to Tesla's patent schematics from the late 1890s.
Rumor has it that this coil exhibits antigravity properties. I have not seen antigravity effects when applying a standard spark gap discharge to the primary.