galvanometer, and it was found that by moving the magnet in the same
direction, and to the same degree on the outside of the helix, no effect on
the needle was produced.

44. The Royal Society are in possession of a large compound magnet formerly
belonging to Dr. Gowin Knight, which, by permission of the President and
Council, I was allowed to use in the prosecution of these experiments: it
is at present in the charge of Mr. Christie, at his house at Woolwich,
where, by Mr. Christie's kindness, I was at liberty to work; and I have to
acknowledge my obligations to him for his assistance in all the experiments
and observations made with it. This magnet is composed of about 450 bar
magnets, each fifteen inches long, one inch wide, and half an inch thick,
arranged in a box so as to present at one of its extremities two external
poles (fig. 5.). These poles projected horizontally six inches from the
box, were each twelve inches high and three inches wide. They were nine
inches apart; and when a soft iron cylinder, three quarters of an inch in
diameter and twelve inches long, was put across from one to the other, it
required a force of nearly one hundred pounds to break the contact. The
pole to the left in the figure is the marked pole[A].

[A] To avoid any confusion as to the poles of the magnet, I shall
designate the pole pointing to the north as the marked pole; I may
occasionally speak of the north and south ends of the needle, but do
not mean thereby north and south poles. That is by many considered the
true north pole of a needle which points to the south; but in this
country it in often called the south pole.

45. The indicating galvanometer, in all experiments made with this magnet,
was about eight feet from it, not directly in front of the poles, but about
16° or 17° on one side. It was found that on making or breaking the