EVOLUTION OF ELECTRICITY FROM MAGNETISM. 
133 
that already described (6.) was constructed upon a hollow cylinder of paste¬ 
board : 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.), but magnets could be made by the in¬ 
duced 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 arrange¬ 
ment was not so powerful as the ring arrangement already described ( 27 -). 
36. Similar effects were then produced by ordinary magnets : thus the hol¬ 
low 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 in¬ 
dicate an induced current of electricity in the opposite direction to that fitted to 
form a magnet having the same polarity as that really produced by contact with 
the bar magnets. Thus when the marked and unmarked poles were placed as in 
fig. 3, the current in the helix was in the direction represented, P being sup- 
