A New Theory of Magnetism
The information presented below is drawn from “Ampere’s Electrodynamic Molecular Model” by L.P. Williams, and “A History of the Theories of Aether and Electricity” by E.T. Whittaker.
Ampere radically challenged the two-fluid theory theory, arguing that there were in fact no aural, boreal, or any magnetic fluids at all. As a basis he used the fact he’d observed, that currents running in the same direction attract, and in the opposite repel. He then proposed that each magnet was made up of circular currents running along its length rather than these fluids, with each end of the solenoid positioned where concentrations of the fluids were thought to be. He demonstrated that the effects of these solenoids would be in keeping with the magnetic phenomenon observed and formerly attributed to the magnetic fluids, and that furthermore, his theory would reduce all these phenomenon to one principle. All electromagnetic phenomena were explained by this model for permanent magnets, and could be predicted by his rule for the attraction and repulsion of currents.
When he and his friend Augustin Fresner tried to test this theory by looking for the electric currents, they found none of the traditional effects of currents, such as the production of heat. Thus, they modified the theory by substituting currents circulating around each molecule of the magnet rather than around the magnet as a whole, assuming that heating and other ordinary effects of currents would not be observed with molecular currents. As Ampere did not believe in action at a distance, or objects being able to act upon others without contact, he needed some substance to transmit the effects of the electric currents to the objects around them. Thus, he turned to ether theory. At this time, his contemporaries were working on a wave theory of light, theorizing that there was some substance present everywhere that acted as a medium for light, just as other waves required a medium to travel through. They termed this the “luminiferous ether.” Ampere theorized that it was this same substance that carried the effects of the currents, which propagated through the ether to affect objects around them. Thus, magnets and currents could attract and repel things they themselves were not in contact with, but which the ether was, neatly avoiding the assumption of action at a distance forces.
A translated excerpt from Ampere’s presentation to the Academy of Science on October 2, 1820 can be found here.
Look here for Henry’s explanation of Ampere’s theory.