Device for demonstrating that a “sinuous” wire and a straight wire exert equal forces on a moving circuit or a compass. It was proposed by Ampere.

(http://www.21stcenturysciencetech.com/articles/spring01/Electrodynamics....)

(http://www.ampere.cnrs.fr/parcourspedagogique/zoom/courant/formule/index...)

(http://www.ampere.cnrs.fr/parcourspedagogique/zoom/video/courantsinu/vid...)