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.

{102} 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 40[182], "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 cohaere 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.

[Illustration]

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 {103} 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 adhaere 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 cohaering, 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 cohaere, 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.

CHAP. XXXIII.

On the Varying Ratio of Strength, and of the Motion _of coition, within the orbe of virtue_.

Should a very large weight, which at a very small distance is drawn towards a loadstone, be divided into ever so many equal parts, and should the radius of the orbe of magnetick attraction be divided into the same number of parts, the like named parts of the weight will correspond to the intermediate parts of the radius.

The orbe of virtue extends more widely than the orbe of motion of any magnetick; for the magnetick is affected at its extremity, even if it is not moved with local motion, which effect is produced {104} by the loadstone being brought nearer. A small versorium also is turned when a good distance off, even if at the same distance it would not flow towards the loadstone, though free and disengaged from impediment.

The swiftness of the motion of a magnetick body to a loadstone is dependent on either the power of the loadstone, on its mass, on its shape, on the medium, or on its distance within the magnetick orbe.

A magnetick moves more quickly towards a more powerful * stone than towards a sluggish one in proportion to the strength, and [as appears] by a comparison of the loadstones together. A lesser mass of iron also is carried more quickly towards a loadstone, just as also one that is a little longer in shape. The swiftness of magnetick motion towards a loadstone is changed by reason of the medium; for bodies are moved more quickly in air than in water, and in clear air than in air that is thick and cloudy.

By reason of the distance, the motion is quicker in the case of bodies near together than when they are far off. At the limits of the orbe of virtue of a terrella a magnetick is moved feebly and slowly. At very short distances close to the terrella the moving impetus is greatest.

A loadstone which in the outmost part of its orbe of virtue * hardly moves a versorium when one foot removed from it, doth, if a long piece of iron is joined to it, attract and repel the versorium more strongly with its opposite poles when even three feet distant. The result is the same whether the loadstone is armed or unarmed. Let the iron be a suitable piece of the thickness of the little finger.

For the vigour of the loadstone excites verticity in the iron and proceeds in the iron and through the iron much further than it extends through the air.

The vigour proceeds even through several pieces of iron (joined * to one another end to end), not so regularly, however, as through one continuous solid.

Dust of steel placed upon paper rises up when a loadstone is moved near above it in a sort of steely hairiness; but if the loadstone is placed below, such a hairiness is likewise raised.

Steel dust (when the pole of a loadstone is placed near) is cemented * into one body; but when it desires coition with the loadstone, the mass is split and it rises in conglomerated parts.

But if there is a loadstone beneath the paper, the mass is split in the same way and many portions result, each of which consists of very many parts, and remains cemented together, as individual bodies. Whilst the lower parts of these pursue greedily the pole of the loadstone placed directly beneath, even they also are raised up as magnetick wholes, just as a small iron wire of the length of a grain or two grains of barley is raised up, both when the loadstone is moved near both beneath and above.

{105} CHAP. XXXIIII.

Why a Loadstone should be stronger in its poles in a different ratio; as well in the Northern _regions as in the Southern_.

The extraordinary magnetick virtue of the earth is * remarkably demonstrated by the subtility of the following magnetical experiment. Let there be given a terrella of no contemptible power, or a long loadstone with equal cones as polar extremities; but in any other shape which is not exactly round error is easy, and the experiment difficult. In the Northern regions, raise the true North pole of the terrella above the horizon straight toward the zenith; it is demonstrable that it raises up a larger iron spike on its North pole, than the South pole of the same terrella is able to raise, when turned in the same way toward the highest point of the sky. The same thing is shown by a small terrella placed in the same way above a larger.

[Illustration]

Let _a b_ be the earth or a somewhat large terrella, also _a b_ a smaller terrella. There is set up above the Northern pole of the smaller terrella a spike larger than the pole _b_ of the smaller terrella can raise, if it is turned round to the higher parts. And the pole _a_ of the {106} smaller terrella has its strength from the larger, declining from the Zenith to the plane of the horizon or to the level. But now, if, * leaving the terrella disposed in the same way, you bring a piece of iron to the lower and Southern pole, it will attract and retain a greater weight than the Boreal pole could, if it were turned round to the lower parts. Which thing is demonstrated thus: let A be the earth or a terrella; E the Boreal pole or some place in some great latitude; B a rather large terrella above the earth or a smaller terrella on the top of a larger; D its Southern pole. It is manifest that D (the Southern pole) attracts a larger piece of iron, C, than F (the Boreal pole) will be able to, if it is turned round downward to the position D, toward the earth or the terrella in the Northern regions.

[Illustration]

Magneticks acquire strength through magneticks, if they are properly placed according to their nature, in near neighbourhood and within the orbe of virtue. Wherefore when a terrella is placed on the earth or on a terrella, so that its Southern pole is turned round toward the Northern pole, its Northern pole, however, turned away from the Northern pole, the influence and strength of {107} its poles are increased. And so the Northern pole of a terrella in such a position lifts up a larger spike than the Southern pole, if the Southern pole is turned away. Similarly the Southern pole in a proper and natural arrangement, acquiring strength from the earth or from a larger terrella, attracts and retains larger rods of iron. In * the other part of the terrestrial globe toward the South, as also in the Austral portion of a terrella, the reasoning is converse; for the Southern pole of the terrella being turned away is more robust, as also the Northern pole when turned round. The more a region on the earth is distant from the aequinoctial (as also in a larger terrella), the larger is the accession of strength perceived; near the aequator, indeed, the difference is small, but on the aequator itself null; at the poles finally it is greatest.

CHAP. XXXV.

On a Perpetual Motion Machine, mentioned by authors, by means of the attraction _of a loadstone_.

Cardan writes[183] that out of iron and the Herculean stone can be made a perpetual motion machine; not that he himself had ever seen one, but only conceived the idea from an account by Antonius de Fantis[184], of Treves.

Such a machine he describes, Book 9, _De Rerum Varietate_. But they have been little practised in magnetick experiments who forge such things as that. For no magnetick attraction can be greater (by any skill or by any kind of instrument) than the retention. Things which are joined and those which are approaching near are retained with a greater force than those which are enticed and set in motion, and are moved; and that coition is, as we have shown above, a motion of both, not an attraction of one. Such a machine Peter Peregrinus feigned many centuries before or else depicted one which he had received from others, and one which was much better fitted for the purpose. Johannes Taysnier published it also, spoiled by wretched figures, and copied out the whole theory of it word for word. O that the gods would at length bring to a miserable end such fictitious, crazy, deformed labours, with which the minds of the studious are blinded!