Tesla electrical oscillator
A compact Tesla coil invented by Nikola Tesla in the late 1890s. A technical article describing how these compact coils work and giving circuit diagrams is "Tesla circuit controllers for obtaining oscillatory currents of high frequency" in The Electrical Engineer, New York, Vol. 26, No. 538, August 25, 1898, p. 180-182
Caption: An Early "Tesla" High Frequency Oscillator Developing 2 Sq. Ft. of Streamers With 25 Watts Input. First Used in Europe by the Late Lord Kelvin in His Lectures Before the British Association for the Advancement of Science.