English: Heinrich Daniel Ruhmkorff's induction coil. The mechanisms at the ends are interrupters, vibrating switches that interrupt the DC current flowing in the primary winding of the coil to create the flux changes necessary to induce high voltage in the secondary winding. This coil has two interrupters; the one at the right end is a common "hammer" interrupter with metal contacts. The one on the left is a type invented by Fizeau that uses a metal needle dipping into mercury, covered by a layer of alcohol to suppress the formation of sparks, resulting in higher voltages.