e immediately swerves to the east: he bends
his loop to the east, and the north poles moves to the west. Suspending
a common bar magnet in a vertical position, he causes it to spin round
its own axis. Its pole being connected with one end of a galvanometer
wire, and its equator with the other end, electricity rushes round the
galvanometer from the rotating magnet. He remarks upon the "_singular
independence_" of the magnetism and the body of the magnet which carries
it. The steel behaves as if it were isolated from its own magnetism.

And then his thoughts suddenly widen, and he asks himself whether the
rotating earth does not generate induced currents as it turns round its
axis from west to east. In his experiment with the twirling magnet the
galvanometer wire remained at rest; one portion of the circuit was in
motion _relatively_ to _another portion_. But in the case of the
twirling planet the galvanometer wire would necessarily be carried along
with the earth; there would be no relative motion. What must be the
consequence? Take the case of a telegraph wire with its two terminal
plates dipped into the earth, and suppose the wire to lie in the
magnetic meridian. The ground underneath the wire is influenced like the
wire itself by the earth's rotation; if a current from south to north be
generated in the wire, a similar current from south to north would be
generated in the earth under the wire; these currents would run against
the same terminal plates, and thus neutralize each other.

This inference appears inevitable, but his profound vision perceived its
possible invalidity. He saw that it was at least possible that the
difference of conducting power between the earth and the wire might
give one an advantage over the other, and that thus a residual or
differential current might be obtained. He combined wires of different
materials, and caused them to act in opposition to each other, but found
the combination ineffectual. The more copious flow in the better
conductor was exactly counterbalanced by the resistance of the worst.
Still, though experiment was thus emphatic, he would clear his mind of
all discomfort by operating on the earth itself. He went to the round
lake near Kensington Palace, and stretched four hundred and eighty feet
of copper wire, north and south, over the lake, causing plates soldered
to the wire at its ends to dip into the water. The copper wire was
severed at the middle, and the severed ends con