horseshoe magnet of the Royal Society, and connecting the axis and
the edge of the disk, each by a wire with a galvanometer, he
obtained, when the disk was turned round, a constant flow of
electricity. The direction of the current was determined by the
direction of the motion, the current being reversed when the
rotation was reversed. He now states the law which rules the
production of currents in both disks and wires, and in so doing
uses, for the first time, a phrase which has since become famous.
When iron filings are scattered over a magnet, the particles of iron
arrange themselves in certain determinate lines called magnetic
curves. In 1831, Faraday for the first time called these curves
'lines of magnetic force'; and he showed that to produce induced
currents neither approach to nor withdrawal from a magnetic source,
or centre, or pole, was essential, but that it was only necessary to
cut appropriately the lines of magnetic force. Faraday's first paper
on Magneto-electric Induction, which I have here endeavoured to
condense, was read before the Royal Society on the 24th of November,
1831.

On January 12, 1832, he communicated to the Royal Society a second
paper on Terrestrial Magneto-electric Induction, which was chosen as
the Bakerian Lecture for the year. He placed a bar of iron in a coil
of wire, and lifting the bar into the direction of the dipping needle,
he excited by this action a current in the coil. On reversing the
bar, a current in the opposite direction rushed through the wire.
The same effect was produced when, on holding the helix in the line
of dip, a bar of iron was thrust into it. Here, however, the earth
acted on the coil through the intermediation of the bar of iron.
He abandoned the bar and simply set a copper plate spinning in a
horizontal plane; he knew that the earth's lines of magnetic force