Strength of Magnet

—The magnetic force exerted by either of the poles of a magnet. The strength of a magnet is not the same thing as its “lifting power.” The strength of a magnet is the strength of its poles. The strength of a magnet pole must be measured by the magnetic force which it exerts. The lifting power of a magnet depends both _ upon the form of the magnet and on its magnetic strength. A horseshoe magnet will lift a load three or four times as great as a bar magnet of the same weight will lift. The lifting power is greater if the area of contact between the poles and the armature be increased. Also the lifting power of a magnet grows in a very curious and unexplained way by gradually increasing the load on its armature, day by day, until it bears a load which at the outset it could not have done. If the load be so increased that the armature is torn off, the power of the magnet falls at once to its original value. The attraction between a powerful electromagnet and its armature may amount to 200 Ibs. per sq. inch. Small magnets lift a greater load in proportion to their own weight than large ones. A good steel horseshoe magnet weighing itself one pound ought to lift twenty pounds weight. Sir Isaac Newton is said to have po e ed a little lodestone mounted in a signet ring which would lift a piece of iron 200 times its own weight.