The Turn Of The Century Electrotherapy Museum

Tesla Coil with 2000 turns

XI. Exhibition of a Tesla Coil. By Prof. Silvanus Thompson, D.Sc., FM.S*


This apparatus is intended to replace the two induction coils and spark-gap arrangements used by Mr. Tesla for high frequency experiments. It consists of an induction-coil, with a separate self-inductance coil in the primary circuit. This self-inductance coil is also used as an electromagnet for the separate interrupter of the primary circuit. A condenser of 2.27 microfarads capacity is connected between one end of the primary coil and one terminal of the interrupter, so as to include hoth of them between its terminals. The primary consists of 5 turns of copper strip. The secondary has 2000 turns of thick wire. The supply current, about half an ampere, may be taken from the electric-light mains at almost any voltage from 50 to 200, direct or alternating.


Prof. Lodge said that he believed Sir W. Crookes had found it work quite well at 10 volts. He pointed out also that if the straight discharge rods at the spark-gap were free to slide, the discharge drove them back into their sockets.

Prof. Fitzgekald said it was stated at Toronto that the spark was broken at the interrupter when the condenser was charged, and that by the time the condenser was ready to discharge, the contact at the interrupter had been made again. It had seemed to him at first that the condenser discharges and surgings must take place at a rate far higher than the period of the mechanical movement of the interrupter ; but he perceived afterwards that it was not so.

Prof. Herschel asked if such an apparatus was suitable for work with Rontgen rays.

Dr. Thompson, in reply, congratulated Mr. Tesla upon the perfect working and compactness of his invention. The present form was not suited for Rontgen ray experiments, with ordinary focus-tubes, but Mr. Tesla had designed a special tube that was excellent for that purpose.

* January 21, 1898

Testing idea first with a small cylindrical coil

Winding 2000 turns of 34 AWG...tedious!

Housing plus primary winding

Flaming arc...coil is positioned vertically for the first tests.

Hot ribbon

Long jagged sparks

Pseudo static sparks...

(C) Jeff Behary, 2010