Electricity for public schools and colleges . es of force that lie in theplane of the glass. The accompanying figures show us the general aspect of thecurves thus obtained. In fig. ii. we have respectively the cases of a bar-magnet ; ahorseshoe-magnet ; two bar-magnets with unlike poles opposed ;and the same with similar poles opposed. § 12. Magnetic Induction takes place along the Lines ofForce.—It is along these lines of force that we must consider ourmolecules, regarded as small magnetic needles, urged to directthemselves. Hence, if these molecules were perfectly free to move, anymass of ir
Electricity for public schools and colleges . es of force that lie in theplane of the glass. The accompanying figures show us the general aspect of thecurves thus obtained. In fig. ii. we have respectively the cases of a bar-magnet ; ahorseshoe-magnet ; two bar-magnets with unlike poles opposed ;and the same with similar poles opposed. § 12. Magnetic Induction takes place along the Lines ofForce.—It is along these lines of force that we must consider ourmolecules, regarded as small magnetic needles, urged to directthemselves. Hence, if these molecules were perfectly free to move, anymass of iron would by the rearrangement of its molecules becomemagnetised along the lines of force of the inducing field. But as the molecules are subject internally to mechanical con-straint as well as to each others action, the resulting magnetisationis determined by the combined influences, internal and external. If the bar or needle lies so that its greatest length is along thelines of force, and if the form of the bar is symmetrical about this. axis, then the magnetisation should be—whether weak or strong—along the lines of force. But if the bar be unsymmetrically situated with respect to thelines of force, the resulting magnetisation may be quite unsym-metrical and be oblique to the lines of force. c 2 20 ELECTRICITY CH. III. CHAPTER III. MAGNETIC MEASUREMENTS. THE EARTHs MAGNETISM. § I. Coulombs Torsion Balance.—In considering the subjectof magnetic measurements we shall first describe the torsionbalance. This instrument deserves notice as the earliest by whichexact magnetic and electrostatic measurements were obtained, and some study of it will be in-structive. In practice it has,however, been now super-seded by other figure represents oneform of the instrument. Arectangular or cylindricalglass case is provided, eitherwith a graduated scale roundthe sides, as here shown, or,what is better, with a planemirror at the bottom, onwhich is marked a circle 4 gr
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