inducing magnetization in iron. The question naturally suggested itself as to whether the similarity of properties between currents and magnets extended still further, e.g. whether conductors carrying currents would, like magnets, experience ponderomotive forces when placed in a magnetic field, and whether such conductors would consequently, like magnets, exert ponderomotive forces on each other.
The first step towards answering these inquiries was taken by Oersted[1] himself. "As," he said, "a body cannot put another in motion without being moved in its turn, when it possesses the requisite mobility, it is easy to foresee that the galvanic arc must be moved by the magnet"; and this he verified experimentally.
The next step came from André Marie Ampère (b. 1775, d. 1836), who at the meeting of the Academy on September 18th, exactly a week after the news of Oersted's first discovery had arrived, showed that two parallel wires carrying currents' attract each other if the currents are in the same direction, and repel each other if the currents are in opposite directions. During the next three years Ampère continued to prosecute the researches thus inaugurated, and in 1825 published his collected results in one of the most celebrated memoirs[2] in the history of natural philosophy.
Ampère introduces his work by proclaiming himself a follower of that school which explained all physical phenomena in terms of equal and oppositely directed forces between pairs of particles; and he renounces the attempt to seek more speculative, though possibly more fundamental, explanations in terms of the motions of ultimate fluids and aethers. Nevertheless, he indicates two conceptions of this latter character, on which such explanations might be founded.
In the first[3] he suggests that the ponderomotive forces
