André-Marie Ampère, the ''Newton of electricity'' and how the simplicity criterion resulted in the disuse of his formula (Q2717922)

André-Marie Ampère considered his formula for the magnetic force between two current elements as his most important contribution to the new science of ``electrodynamics''. He coined the latter name following Oersted's discovery in 1820 of the magnetic force exerted by the current in a wire on a compass needle. Ampère's most famous paper details the 4 equilibrium experiments which he selected as the experimental foundation of his central formula. The author discusses these experiments and how they lead to Ampère's formula. The author also discusses why this formula, originally hailed by Maxwell as ``the cardinal principle of electricity'' never achieved that role, and instead became a historical curiosity piece.