o the
galvanometer coils KL, so that the one which before carried the current
from the copper now conveyed that from the iron, and vice versa. But the
same striking superiority of the copper was manifested as before. This
precaution was taken in the rest of the experiments with other metals to be
described.

208. I then had wires of iron, zinc, copper, tin, and lead, drawn to the
same diameter (very nearly one twentieth of an inch), and I compared
exactly equal lengths, namely sixteen feet, of each in pairs in the
following manner: The ends of the copper wire were connected with the ends
A and B of galvanometer coil K, and the ends of the zinc wire with the
terminations A and B of the galvanometer coil L. The middle part of each
wire was then coiled six times round a cylinder of soft iron covered with
paper, long enough to connect the poles of Daniell's horse-shoe magnet
(56.) (fig. 33.), so that similar helices of copper and zinc, each of six
turns, surrounded the bar at two places equidistant from each other and
from the poles of the magnet; but these helices were purposely arranged so
as to be in contrary directions, and therefore send contrary currents
through the galvanometer coils K and L,

209. On making and breaking contact between the soft iron bar and the poles
of the magnet, the galvanometer was strongly affected; on detaching the
zinc it was still more strongly affected in the same direction. On taking
all the precautions before alluded to (207.), with others, it was
abundantly proved that the current induced by the magnet in copper was far
more powerful than in zinc.

210. The copper was then compared in a similar manner with tin, lead, and
iron, and surpassed them all, even more than it did zinc. The zinc was then
compared experimentally with the tin, lead, and iron, and found to produce
a more powerful current than any of them. Iron in the same manner proved
superior to tin and lead. Tin came next, and lead the last.

211. Thus the order of these metals is copper, zinc, iron, tin, and lead.
It is exactly their order with respect to conducting power for electricity,
and, with the exception of iron, is the order presented by the
magneto-rotation experiments of Messrs. Babbage, Herschel, Harris, &c. The
iron has additional power in the latter kind of experiments, because of its
ordinary magnetic relations, and its place relative to magneto-electric
action of the kind now under investigation cannot be asce