ent was then employed connecting the former experiments
on volta-electric induction (6-26.) with the present. A combination of
helices like that already described (6.) was constructed upon a hollow
cylinder of pasteboard: there were eight lengths of copper wire, containing
altogether 220 feet; four of these helices were connected end to end, and
then with the galvanometer (7.); the other intervening four were also
connected end to end, and the battery of one hundred pairs discharged
through them. In this form the effect on the galvanometer was hardly
sensible (11.), though magnets could be made by the induced current (13.).
But when a soft iron cylinder seven eighths of an inch thick, and twelve
inches long, was introduced into the pasteboard tube, surrounded by the
helices, then the induced current affected the galvanometer powerfully and
with all the phenomena just described (30.). It possessed also the power of
making magnets with more energy, apparently, than when no iron cylinder was
present.

35. When the iron cylinder was replaced by an equal cylinder of copper, no
effect beyond that of the helices alone was produced. The iron cylinder
arrangement was not so powerful as the ring arrangement already described
(27.).

36. Similar effects were then produced by _ordinary magnets_: thus the
hollow helix just described (34.) had all its elementary helices connected
with the galvanometer by two copper wires, each five feet in length; the
soft iron cylinder was introduced into its axis; a couple of bar magnets,
each twenty-four inches long, were arranged with their opposite poles at
one end in contact, so as to resemble a horse-shoe magnet, and then contact
made between the other poles and the ends of the iron cylinder, so as to
convert it for the time into a magnet (fig. 2.): by breaking the magnetic
contacts, or reversing them, the magnetism of the iron cylinder could be
destroyed or reversed at pleasure.

37. Upon making magnetic contact, the needle was deflected; continuing the
contact, the needle became indifferent, and resumed its first position; on
breaking the contact, it was again deflected, but in the opposite direction
to the first effect, and then it again became indifferent. When the
magnetic contacts were reversed the deflections were reversed.

38. When the magnetic contact was made, the deflection was such as to
indicate an induced current of electricity in the opposite direction to
that fitted to form