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Treatises on electricity, galvanism, magnetism, and electro-magnetism

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Peter Mark Roget

Treatises on electricity, galvanism, magnetism, and electro-magnetism

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1832 Excerpt: ...direction. (215.) Two plates of very soft iron must next be provided, equal in breadth to the surfaces containing the poles, and a little longer than those surfaces; so that, when applied to them, a portion of each plate shall project beyond the loadstone to a small extent. In fig. 58, Rr represents the sections of these iron plates affixed to the opposite sides of the loadstone L; and P p the projecting pieces. These projecting pieces should be much narrower than the other portion of the plates. For loadstones weighing less than an outice, the lower surfaces of the projections need not exceed the tenth of an inch; and so in proportion for larger loadstones. The thickness of the plates, also, must be regulated by the strength of the loadstone, and can scarcely be determined without previous trial in each particular case. The best way, therefore, is to make them tolerably thick at first; and then file off successive layers, until we And, by actual experiment on the power of the loadstone after each reduction, that we cease to obtain any advantage; for the power increases gradually to a certain limit, at which the filing ought to be discontinued. The armature of a loadstone should be fixed on it very firmly, by wires, or by an external case, which should be made of any metal which is not susceptible of magnetism. Loadstones are sometimes cut into a spherical shape, in imitation of the earth, and are then called terrellar. Their armatures should, in that case, be adapted to the curvature of the surface, and should each cover about a quarter of that surface. (216.) The addition of armatures to a loadstone is found to have a very favourable effect in augmenting its strength, and this increase of strength goes on for a considerable time after they have been appli...

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