It is a matter of history how, on the publication of Oersted’s discovery, Ampère leaped forward to generalise on electromagnetic actions, and discovered the mutual actions that may exist between two currents, or rather between two conducting wires that carry currents. They are found to experience mutual mechanical forces urging them into parallel proximity. Biot and Laplace added to these investigations, as also did Arago. Davy discovered that the naked copper wire, while carrying a current, could attract iron filings to itself--not end-ways in adherent tufts, as the pole of a magnet does, but laterally, each filing or chainlet of filings tending to set itself tangentially at right angles to the axis of the wire. [Sidenote: A PARADOXICAL PHENOMENON.] This curious right-angled relation between electric flow and magnetic force came as a complete paradox or puzzle to the scientific world. It had taken centuries to throw off the strange unmechanical ideas of force which had dominated the older astronomy. The epicyclic motions of the planets postulated by the Ptolemaic system were in no way to be accounted for upon mechanical principles. Kepler’s laws of planetary motion were merely empirical, embodying the results of observation, until Newton’s discovery of the laws of circular motion and of the principle of universal gravitation placed the planetary theory on a rational basis. Newton’s laws required that forces should act in straight lines, and that to every action there should be an equal and opposite reaction. If A attracted B, then B attracted A with an equal force, and the mutual force must be in the line drawn from A to B. The discovery by Oersted that the magnet pole was urged by the electric wire in a direction _transverse_ to the line joining them, appeared at first sight to contravene the ideas of force so thoroughly established by Newton. How could this transversality be explained? Some sought to explain the effect by considering the conducting wire to operate as if made up of a number of short magnets set transversely across the wire, all their north poles being set towards the right, and all their south poles towards the left. Ampère took the alternative view that the magnet might be regarded as equivalent to a number of electric currents circulating transversely around the core as an axis. In neither case was the explanation complete. [Sidenote: TWO YEARS WASTED.]