Nikola Tesla, with Roger Boskovich's book, “Theoria Philosophiae Naturalis”

Nikola Tesla, with Roger Boskovich's book, “Theoria Philosophiae Naturalis,” in front of the spiral coil of his high-frequency transformer at East Houston St. 46, New York.

Portrait obtained by an exposure of two seconds to the light of a single vacuum tube without electrodes, having a volume of about 90 cubic inches, giving approximately a light of 250 candle-power — photographed by Tonnelé & Co. Copyrighted by the “Electrical Review.”