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to and fro above a needle resting upon the smooth top of a table, we will find that the needle will follow the magnet energetically or otherwise, according to the proximity of the magnet; that is to say, the farther the magnet is away the less its power over the needle.
It may be well to state here, that, when speaking of the action of the magnet upon any object, we wish it to be under-
Fig. 1.
stood that the object is presented to the ends of the magnet, as it is in its ends that its greatest strength lies. The relative conditions of the different parts of a straight-bar magnet are shown in Fig. 1, the brush-like lines at the ends giving a clear idea by their number and length, of the different degrees of magnetism existing at various points in the magnet;
