32.  By using charcoal at the ends of the B helix, a minute spark could be perceived when the contact of the battery with A was completed.  This spark could not be due to any diversion of a part of the current of the battery through the iron to the helix B; for when the battery contact was continued, the galvanometer still resumed its perfectly indifferent state (28.).  The spark was rarely seen on breaking contact.  A small platina wire could not be ignited by this induced current; but there seems every reason to believe that the effect would be obtained by using a stronger original current or a more powerful arrangement of helices.

33.  A feeble voltaic current was sent through the helix B and the galvanometer, so as to deflect the needle of the latter 30 deg. or 40 deg., and then the battery of one hundred pairs of plates connected with A; but after the first effect was over, the galvanometer-needle resumed exactly the position due to the feeble current transmitted by its own wire.  This took place in whichever way the battery contacts were made, and shows that here again (20.) no permanent influence of the currents upon each other, as to their quantity and tension, exists.

34.  Another arrangement 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.