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Nikola Tesla seated inside a circular framework 51 feet in diameter, which supported the primary and secondary conductors of the largest Tesla coil ever built, at his Colorado Springs experimental station in 1899.  The oscillator is operating at 100 khz, and the discharges occur with a deafening roar striking an unconnected, comparatively smaller diameter coil 22 feet away.  The activity of the oscillator created earth currents of such magnitude that sparks an inch long could be drawn from a water main at a distance of 300 feet from the station.  The inscription on the photograph is addressed to Sir William Crookes and reads; To my illustrious friend Sir William Crookes of whom I always think and whose letters I never answer. June 17, 1901 Nikola Tesla.

The special coil, 8 feet in length and 14 inches in diameter, wound for investigation of the influence of elevation upon the capacity of an elevated conductor, appears to the right in this interior view of the Tesla laboratory.