Three quarters of a century elapsed between Amp re's definition of electrodynamics and Einstein's reform of the concepts of space and time. The two events occurred in utterly different worlds: the French Academy of Sciences of the 1820s seems very remote from the Bern patent office of the early 1900s, and the forces between two electric currents quite foreign to the optical synchronization of clocks. Yet Amp re's electrodynamics and Einstein's relativity...