current consists in a transport of one kind of electricity with a definite velocity relative to the wire, it might be expected that a coil rotated rapidly about its own axis would generate a magnetic field different from that produced by the same coil at rest. Experiments to determine the matter were performed by A. Föppl[1] and by E. L Nichols and W. S. Franklin,[2] but with negative results. The latter investigators found that the velocity of electricity must be such that the quantity conveyed past a specified point in a unit of time, when the direction of the current was that in which the coil was travelling, did not differ from that transferred when the current and coil were moving in opposite directions by as much as one part in ten million, even when the velocity of the wire was 9096 cm./sec. They considered that they would have been able to detect a change of deflexion due to the motion of the coil, even though the velocity of the current had been considerably greater than a thousand million metres per second.
During the decades in the middle of the century consider-
able progress was made in the science of thermo-electricity,
whose beginnings we have already described.[3] In Faraday's
laboratory note-book, under the date July 28th, 1836, we
read[4]:—"Surely the converse of thermo-electricity ought to be
obtained experimentally. Pass current through a circuit of
antimony and bismuth."
Unknown to Faraday, the experiment here indicated had already been made, although its author had arrived at it by a different train of ideas. In 1834 Jean Charles Peltier[5] (b. 1785, d. 1845) attempted the task, which was afterwards performed with success by Joule,[6] of measuring the heat evolved by the passage of an electric current through a conductor. He found that a current produces in a homogeneous conductor an elevation
