Page:A history of the theories of aether and electricity. Whittacker E.T. (1910).pdf/108

 between circuits carrying electric currents may be due to "the reaction of the elastic fluid which extends throughout all space, whose vibrations produce the phenomena of light," and which is "put in motion by electric currents." This fluid or aether can, he says, "be no other than that which results from the combination of the two electricities."

In the second conception, Ampère suggests that the interspaces between the metallic molecules of a wire which carries a current may be occupied by a fluid composed of the two electricities, not in the proportions which form the neutral fluid, but with an excess of that one of them which is opposite to the electricity peculiar to the molecules of the metal, and which consequently masks this latter electricity. In this inter-molecular fluid the opposite electricities are continually being dissociated and recombined; a dissociation of the fluid within one inter-molecular interval having taken place, the positive electricity thus produced unites with the negative electricity of the interval next to it in the direction of the current, while the negative electricity of the first interval unites with the positive electricity of the next interval in the other direction, Such interchanges, according to this hypothesis, constitute the electric current.

Ampère's memoir is, however, but little occupied with the more speculative side of the subject. His first aim was to investigate thoroughly by experiment the ponderomotive forces on electric currents.

"When," he remarks, "M. Oersted discovered the action which a current exercises on a magnet, one might certainly have suspected the existence of a mutual action between two circuits carrying currents; but this was not a necessary consequence; for a bar of soft iron also acts on a magnetized needle, although there is no mutual action between two bars of soft iron."

Ampère, therefore, submitted the matter to the test of the laboratory, and discovered that circuits carrying electric currents exert ponderomotive forces on each other, and that