30. When the battery contact was made in one direction, the
galvanometer-needle was deflected on the one side; if made in the other
direction, the deflection was on the other side. The deflection on breaking
the battery contact was always the reverse of that produced by completing
it. The deflection on making a battery contact always indicated an induced
current in the opposite direction to that from the battery; but on breaking
the contact the deflection indicated an induced current in the same
direction as that of the battery. No making or breaking of the contact at B
side, or in any part of the galvanometer circuit, produced any effect at
the galvanometer. No continuance of the battery current caused any
deflection of the galvanometer-needle. As the above results are common to
all these experiments, and to similar ones with ordinary magnets to be
hereafter detailed, they need not be again particularly described.

31. Upon using the power of one hundred pairs of plates (10.) with this
ring, the impulse at the galvanometer, when contact was completed or
broken, was so great as to make the needle spin round rapidly four or five
times, before the air and terrestrial magnetism could reduce its motion to
mere oscillation.

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.