A text-book on chemistryFor the use of schools and colleges . ofpoles are given, and the line joining them is called theaxis. If a bar magnet be rolled iniron filings, they attach them-selves, for the most part, atthe two poles d c?, Fig. 137;or if such a bar be placed under a sheet of pasteboardon the surface of which iron filings are dusted, they ar-range themselves in curved lines, as shown in Fig. 138,which are symmet-rically situated asrespects the polesPP. When, instead ofpresenting to a sus-pended needle apiece of iron, wepresent to it an-other magnet, phe-nomena of repul-sion as well a
A text-book on chemistryFor the use of schools and colleges . ofpoles are given, and the line joining them is called theaxis. If a bar magnet be rolled iniron filings, they attach them-selves, for the most part, atthe two poles d c?, Fig. 137;or if such a bar be placed under a sheet of pasteboardon the surface of which iron filings are dusted, they ar-range themselves in curved lines, as shown in Fig. 138,which are symmet-rically situated asrespects the polesPP. When, instead ofpresenting to a sus-pended needle apiece of iron, wepresent to it an-other magnet, phe-nomena of repul-sion as well as of attraction ensue. If the north poleof one be presented to the north pole of the other, re-pulsion takes place, and the same occurs if two southpoles are presented; but if it be a north and south pole,then attraction takes place. What occurs on presenting a piece of iron to a needle ? Do theseeffects take place through non-conducting substances? Where arethe foci of action in a magnet? What occurs on rolling a bar mag-net in iron filings ? ii Fig. 170 MAGNETISM. These results may be grouped together under thesimple law, Likepoles repel, and unlike ones attract There is therefore an antagonization of effect betweenopposite magnetic poles. If a key be suspended to amagnet by its north pole, on the approach of the southpole of one of equal force it drops off. If we examine the force of a magnet, commencing ateither of its poles and going toward its centre, the in-tensity gradually declines: it ceases altogether aboutmidway between the poles. This point is termed thepoint or line of magnetic indifference. Magnetism may be excited in both iron and steel; inthe former with greater rapidity, in the latter moreslowly. The magnetism which soft iron has received itinstantly loses on being removed from the source whichhas given it magnetism, but steel retains its virtue per-manently. Soft iron is therefore transiently, hard steelpermanently magnetic. When a mass of iron is in co
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