galvanometer. But the moment the motion became transverse, the needle was
deflected.

111. These effects were also obtained from _electro-magnetic poles_,
resulting from the use of copper helices or spirals, either alone or with
iron cores (34. 54.). The directions of the motions were precisely the
same; but the action was much greater when the iron cores were used, than
without.

112. When a flat spiral was passed through edgewise between the poles, a
curious action at the galvanometer resulted; the needle first went strongly
one way, but then suddenly stopped, as if it struck against some solid
obstacle, and immediately returned. If the spiral were passed through from
above downwards, or from below upwards, still the motion of the needle was
in the same direction, then suddenly stopped, and then was reversed. But on
turning the spiral half-way round, i.e. edge for edge, then the directions
of the motions were reversed, but still were suddenly interrupted and
inverted as before. This double action depends upon the halves of the
spiral (divided by a line passing through its centre perpendicular to the
direction of its motion) acting in opposite directions; and the reason why
the needle went to the same side, whether the spiral passed by the poles in
the one or the other direction, was the circumstance, that upon changing
the motion, the direction of the wires in the approaching half of the
spiral was changed also. The effects, curious as they appear when
witnessed, are immediately referable to the action of single wires (40.
109.).

113. Although the experiments with the revolving plate, wires, and plates
of metal, were first successfully made with the large magnet belonging to
the Royal Society, yet they were all ultimately repeated with a couple of