influenced by the
position of the helix (30.). But on breaking the magnetic contact, the
needle was whirled round in the opposite direction with a force equal to
the former.

48. A piece of copper plate wrapped _once_ round the iron cylinder like a
socket, but with interposed paper to prevent contact, had its edges
connected with the wires of the galvanometer. When the iron was brought in
contact with the poles the galvanometer was strongly affected.

49. Dismissing the helices and sockets, the galvanometer wire was passed
over, and consequently only half round the iron cylinder (fig. 6.); but
even then a strong effect upon the needle was exhibited, when the magnetic
contact was made or broken.

50. As the helix with its iron cylinder was brought towards the magnetic
poles, but _without making contact_, still powerful effects were produced.
When the helix, without the iron cylinder, and consequently containing no
metal but copper, was approached to, or placed between the poles (44.), the
needle was thrown 80 deg., 90 deg., or more, from its natural position. The
inductive force was of course greater, the nearer the helix, either with or
without its iron cylinder, was brought to the poles; but otherwise the same
effects were produced, whether the helix, &c. was or was not brought into
contact with the magnet; i.e. no permanent effect on the galvanometer was
produced; and the effects of approximation and removal were the reverse of
each other (30.).

51. When a bolt of copper corresponding to the iron cylinder was
introduced, no greater effect was produced by the helix than without it.
But when a thick iron wire was substituted, the magneto-electric induction
was rendered sensibly greater.

52. The direction of the electric current produced in all these experiments
with the helix, was the same as that already described (38.) as obtained
with the weaker bar magnets.

53. A spiral containing fourteen feet of copper wire, being connected with
the galvanometer, and approximated directly towards the marked pole in the
line of its axis, affected the instrument strongly; the current induced in
it was in the reverse direction to the current theoretically considered by
M. Ampere as existing in the magnet (38.), or as the current in an
electro-magnet of similar polarity. As the spiral was withdrawn, the
induced current was reversed.

54. A similar spiral had the current of eighty pairs of 4-inch plates sent
through it so as