A "Kinraide coil", a resonant transformer circuit that generates high voltage, low current, high frequency electricity invented by Thomas Burton Kinraide in 1898. It is similar to a Tesla coil but produces higher currents. Kinraide used it to power x-ray tubes in the early 20th century. It produced more penetrating x-rays than existing induction coil circuits, able to make images of the heavy trunk bones. Information from Kinraide coil, Electrotherapy Museum website