[A] The relative position of an electric current and a magnet is by
most persons found very difficult to remember, and three or four helps
to the memory have been devised by M. Ampère and others. I venture to
suggest the following as a very simple and effectual assistance in
these and similar latitudes. Let the experimenter think he is looking
down upon a dipping needle, or upon the pole of the north, and then
let him think upon the direction of the motion of the hands of a
watch, or of a screw moving direct; currents in that direction round a
needle would make it into such a magnet as the dipping needle, or
would themselves constitute an electro-magnet of similar qualities; or
if brought near a magnet would tend to make it take that direction; or
would themselves be moved into that position by a magnet so placed; or
in M. Ampère's theory are considered as moving in that direction in
the magnet. These two points of the position of the dipping-needle and
the motion of the watch hands being remembered, any other relation of
the current and magnet can be at once deduced from it.

39. But as it might be supposed that in all the preceding experiments of
this section, it was by some peculiar effect taking place during the
formation of the magnet, and not by its mere virtual approximation, that
the momentary induced current was excited, the following experiment was
made. All the similar ends of the compound hollow helix (34.) were bound
together by copper wire, forming two general terminations, and these were
connected with the galvanometer. The soft iron cylinder (34.) was removed,
and a cylindrical magnet, three quarters of an inch in diameter and eight
inches and a half in length, used instead. One end of this magnet was
introduced into the axis of the helix (fig. 4.), and then, the
galvanometer-needle being stationary, the magnet was suddenly thrust in;
immediately the needle was deflected in the same direction as if the magnet