. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. 262 THE MOLECULAR PROCESS IN MAGNETIC INDUCTION. till a stage is readied wlien instability begins, and then reversal occurs witli a rush. We thus find a close imitation of all the features tlui^ are actually observed when iron or any of theotlier magnetic metals is carried through a cyclic magnetizing process (Fig 12). The effect of any such process is to form a loop in the curve which expresses the re- lation of the magnetism to the magnet
. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. 262 THE MOLECULAR PROCESS IN MAGNETIC INDUCTION. till a stage is readied wlien instability begins, and then reversal occurs witli a rush. We thus find a close imitation of all the features tlui^ are actually observed when iron or any of theotlier magnetic metals is carried through a cyclic magnetizing process (Fig 12). The effect of any such process is to form a loop in the curve which expresses the re- lation of the magnetism to the magnetizing force. The changes of magnetism always lag behind the changes of magnetizing force. This tendency to lag behind is called magnetic hysteresis. A B. Maanetic Force B A Fig. 12.—Cyclic reversal of magnetization in soft iron (AA), and in the same iron when hardened by stretching (bb). We have a manifestation of hysteresis whenever a magnetic metal has its magnetism clianged in any manner througli changes in the magnetizing force, unless indeed the changes are so minute as to be confined to what I have called the first stage («, Fig. 1). Eesidual magnetism is only a particular case of hi/steresis. Hysteresis comes in whatever be the character or cause of the mag- netic change, provided it involves such deflections on the part of the molecules as make them become unstable. The unstable movements are not reversible witli respect to the agent whicli produces them; that is to say, they are not simply undone step by step as the agent is removed. We know, on quite independent grounds, that wlien the magnetism of a piece of iron or steel is reversed, or indeed cyclically altered in any way, some work is spent in performing the operation—energy is being given to the iron at one stage, and is being recovered from it at another; but when the cycle is taken as a whole there is a net loss, or rather a waste of energy. It may be shown that this waste is proportional to. Please note t
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