On the Magnet, by William Gilbert

Chap. xxxii.

Certain Problems and Magnetick Experiments about the Coition, and Separation, and regular Motion of bodies magnetical.

E qual loadstones come together with equal incitation. *

Also magnetick bodies of iron, if alike in all respects, * come together when excited with similar incitation.

Furthermore, bodies of iron not excited by a * loadstone, if they are alike and not weighed down by their bulk, move towards one another with equal motion.

Two loadstones, disposed on the surface of some water in suitable skiffs, if they are drawn up suitably within their orbes of virtue, incite one another mutually to an embrace. So a proportionate * piece of iron in one skiff hurries with the same speed towards the loadstone as the loadstone itself in its boat strives towards the iron. From their own positions, indeed, they are so borne together, that they are joined and come to rest at length in the middle of the space. Two iron wires magnetically excited, floating in water by means of * suitable pieces of cork, strive to touch and mutually strike one another with their corresponding ends, and are conjoined.

Coition is firmer and swifter than repulsion and separation in * equal magnetick substances. That magnetick substances are more sluggishly repelled than they are attracted is manifest in all magnetical experiments in the case of stones floating on water in suitable skiffs; also in the case of iron wires or rods swimming (transfixed through corks) and well excited by a loadstone, and in the case of versoria. This comes about because, though there is one faculty of coition, another of conformation or disposition, repulsion and aversion is caused merely by something disposing; on the other hand, the coming together is by a mutual alluring to contact and a disposing, that is, by a double vigour.

A disponent vigour is often only the precursor of coition, in order that the bodies may stand conveniently for one another before conjunction; wherefore also they are turned round to the corresponding ends, if they can [not]181 reach them through the hindrances.

figure

If a loadstone be divided through a meridian into two equal parts, the separate parts mutually repel one another, the poles being * placed directly opposite one another at a convenient and equal distance. They repel one another also with a greater velocity than when pole is put opposite pole incongruously. Just as the part B of the loadstone, placed almost opposite the part A, repels it floating in its skiff, because D turns away from F, and E from C; but if B is exactly joined with A again, they agree and become one body magnetical; but in proximity they raise enmities. But if one part of the stone is turned round, so that C faces D and F faces E, then A pursues B within its orbe until they are united.

The Southern parts of the stone avoid the Southern parts, and the Northern parts the Northern. Nevertheless, if by force you move up the Southern cusp of a piece of iron too near the Southern part of the stone, the cusp is seized and both are linked together in friendly embraces: because it immediately reverses the implanted verticity of the iron, and it is changed by the presence of the more powerful stone, which is more constant in its forces than the iron. For they come together according to their nature, if by reversal and mutation true conformity is produced, and just coition, as also regular direction. Loadstones of the same shape, size, and vigour, attract one another mutually with like efficacy, and in the opposite position repel one another mutually with a like vigour.

Iron rods not touched, though alike and equal, do yet often act * upon one another with different forces; because as the reasons of their acquired verticity, also of their stability and vigour, are different, so the more strongly they are excited, the more vigorously do they incite.

Pieces of iron excited by one and the same pole mutually repel * one another by those ends at which they were excited; then also the opposite ends to those in these iron pieces raise enmities one to another.

In versoria whose cusps have been rubbed, but not their cross-ends, * the crosses mutually repel one another, but weakly and in proportion to their length.

In like versoria the cusps, having been touched by the same * pole of the loadstone, attract the cross-ends with equal strength.

In a somewhat long versorium the cross-end is attracted rather * weakly by the cusp of a shorter iron versorium; the cross of the shorter more strongly by the cusp of the longer, because the cross of the longer versorium has a weak verticity, but the cusp has a stronger.

The cusp of a longer versorium drives away the cusp of a * shorter one more vehemently than the cusp of the shorter the cusp of the longer, if the one is free upon a pin, and the other is held in the hand; for though both were equally excited by the same loadstone, yet the longer one is stronger at its cusp on account of its greater mass.

The Southern end of an iron rod which is not excited attracts * the Northern, and the Northern the Southern; moreover, also the Southern parts repel the Southern, and the Northern the Northern.

If magnetick substances are divided or in any way broken in pieces, each part has a Northern and a Southern end.

A versorium is moved as far off by a loadstone when an obstacle * is put in the way, as through air and an open medium.

Rods rubbed upon the pole of a stone strive after the same pole * and follow it. Therefore Baptista Porta errs when he says, chapter 40182, "If you put that part to it from which it received its force, it will not endure it, but drives it from it, and draws to it the contrary and opposite part."

The principles of turning round and inclining are the same in the case of loadstone to loadstone, of loadstone to iron, of iron also to iron.

When magnetick substances which have been separated by force and dissected into parts flow together into a true union and are suitably connected, the body becomes one, and one united virtue, nor have they diverse ends.

The separate parts assume two opposite poles, if the division has * not been made along a parallel: if the division has been made along a parallel, they are able to retain one pole in the same site as before.

Pieces of iron which have been rubbed and excited by a loadstone are more surely and swiftly seized by a loadstone at fitting ends than such as have not been rubbed.

If a spike is set up on the pole of a loadstone, a spike or style * of iron placed on the upper end is strongly cemented to it, and draws away the erect spike from the terrella when motion is made.

If to the lower end of the erect spike the end of another spike * is applied, it does not cohære with it, nor do they unite together.

As a rod of iron draws away a piece of iron from a terrella, so is it also with a minute loadstone and a lesser terrella, though weaker in strength.

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The piece of iron C comes into conjunction with the terrella A, and the vigour in it is magnetically exalted and excited, both in the adjoining end and in the other also which is turned away through its conjunction with the terrella. The end that is turned away also conceives vigour from the loadstone B; likewise the pole D of that loadstone is powerful on account of its suitable aspect and the nearness of the pole E of the terrella. Several causes therefore concur why the piece of iron C should cleave to the terrella B, to which it is joined more firmly than to the terrella A; the vigour excited in the rod, the vigour also excited in the stone B, and the strength implanted in B concur; therefore D is more firmly cemented magnetically with C than E with C.

But if you were to turn the vertex F round to the iron C, C would not adhære to F as formerly to D; for stones so arranged being within the orbe of virtue are placed contrary to natural order; wherefore F does not receive power from E.

Two loadstones or excited pieces of iron, duly cohæring, fly * asunder on the approach of another more powerful loadstone or magnetized piece of iron. Because the new-comer repels the other with its opposing face, and dominates it, and ends the relationship of the two which were formerly joined. So the forces of the other are lessened and succumb; but if it conveniently could, being diverted of its association with the weaker, and rolling round, it would turn about to the stronger. Wherefore also magnetick bodies suspended in the air fall when a loadstone is brought near them with an opposing face, not (as Baptista Porta teaches) because the faculty of both those which were joined before grows faint and torpid, for no face can be hostile to both the ends which cohære, but to one only; and when the stronger loadstone, coming fresh with opposing face, impels this further from it, it is put to flight by the friendly reception of the former.

181 Page 100, line 20. Page 100, line 24. si per impedimēta . . . pervenire possunt.— All editions agree in this reading, but the sense undoubtedly requires non possint. Compare p. 91, line 21.

182 Page 102, line 4. Page 102, line 4. capite 4. — This is a misprint for capite 40, and is retained in the later editions. In the quotation from Baptista Porta, where the English version of 1658 is adhæred to, the words "& deturbat eam" have been omitted by the translator.

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Last updated Friday, March 14, 2014 at 22:17