The Placing of a Loadstone above or below a magnetick body suspended in æquilibrium changes neither the power nor the verticity of the magnetick body.
Q uietly to pass this over would be improper, because a recent error arising from a defective observation of Baptista Porta must be overthrown; on which he (by an unfortunate repetition) even writes three chapters, namely, the 18th, the 31st, and the 42nd. For if a loadstone or a piece of magnetick iron, hanging in æquilibrium or floating on water, is attracted and disposed toward certain definite points, when you bring above it a piece of iron or another loadstone, it will not, if you afterward put the same215 below it, turn round to the contrary parts; but the same ends of the iron or the loadstone will always be directed toward the same ends of the stone, even if the loadstone or the iron is suspended in any way in æquilibrium or is poised on a needle, so that it can turn round freely. He was deceived by the irregular shape of some stone, or because he did not arrange the experiment suitably. Wherefore he is led astray by a vain opinion, and thinks he may infer that, just as a stone has an arctic and antarctic pole, so also it has a western and an eastern, and an upper and a lower pole. So from foolish ideas conceived and admitted arise other fallacies.
The Poles, Æquator, Centre in an entire Loadstone remain and continue steady; by diminution and separation of some part they vary and acquire other positions.
Terrella divided at the arctic circle.
S uppose A B to be a terrella, whose centre is E, and whose diameter (as also its æquinoctial circle) is D F. If you cut off a portion (through the arctic circle, for example), G H, it is demonstrable that the pole which was at A now has a position at I. But the centre and the æquinoctial recede toward B merely so that they are always in the middle of the mass that is left between the plane of the arctick circle G I H and the antarctick pole B. Therefore the segment of the terrella comprised
between the plane of the former æquinoctial (that, of course, which was the æquator before cutting that part away) D E F and the newly acquired æquator M L N will always be equal to the half of that part which was cut off, G I H A. But if the portions have been taken away from the side C D, the poles and axis will not be in the line A B, but in E F, and the axis would be changed in the same proportion as the æquator in the former figure. For those positions of forces and virtues, or rather limits of the virtues, which are derived from the whole form, are moved forward by change of quantity and shape; since all these limits arise from the conspiring together of the whole and of all the parts united; and the verticity or the pole is not a virtue innate in one part, or in some definite limit, or fixed in the substance; but it is an inclination of the virtue to that part. And just as a terrella separated from the earth has no longer the earth's poles and æquator, but individual ones of its own; so also if it again be divided, those limits and distinctions of the qualities and virtues pass on to other parts. But if a loadstone be divided in any way, either along a parallel, or meridionally, so that by the change of shape either the poles or the æquator move to other positions, if the part cut off be merely applied in its natural position and joined to the whole, even without any agglutination or cementing together, the determining points of the virtues return again to their former sites, as if no part of the body had been cut off. When a body is entire, its form remains entire; but when the body is lessened, a new whole is made, and there arises a new entirety, determined for every loadstone, however small, even for magnetick gravel, and for the finest sand.
If the Southern Portion of a Stone be lessened, something is also taken away from the power of the Northern Portion.
N ow although the southern end of a magnetick iron is attracted by a northern end, and repelled by a southern, yet the southern portion of a stone does not diminish, but increases the potency of the boreal part. Wherefore if a stone be cut in two and divided through the arctick circle, or through the tropick of Cancer or the æquator, the southern portion does not attract magnetick substances so strongly with its pole as before; because a new whole arises, and the æquator is removed from its old position and moves forward on account of that cutting of the stone. In the former condition, since the opposite portion of the stone increases the mass beyond the plane of the æquator, it strengthens also the verticity, and the potency, and the motion to unity.
On the Use and Excellence of Versoria: and how iron versoria used as pointers in sun-dials, and the fine needles of the mariners' compass, are to be rubbed, that they may acquire stronger verticity.
V ersoria prepared by the loadstone subserve so many actions in human life that it will not be out of place to record a better method of touching them and exciting them magnetically, and a suitable manner of operating. Rich ores of iron and such as yield a greater proportion of metal are recognized by means of an iron needle suspended in æquilibrium and magnetically prepared; and magnetick stones, clays, and earths are distinguished, whether crude or prepared. An iron needle (the soul of the mariners' compass), the marvellous director in voyages and finger of God, one might almost say, indicates the course, and has pointed out the whole way around the earth (unknown for so many ages). The Spaniards (as also the English) have frequently circumnavigated (by an immense circuit) the whole globe by aid of the mariners' compass. Those who travel about through the world or who sit at home have sun-dials. A magnetick pointer follows and searches out the veins of ore in mines. By its aid mines are driven in taking cities; catapults and engines of war are aimed by night; it has been of service for the topography of places, for marking off the areas and position of buildings, and for excavating aqueducts for water under ground. On it depend instruments designed to investigate its own dip and variation.
When iron is to be quickened by the stone, let it be clean and bright, disfigured by no rust or dirt, and of the best steel216. Let the stone itself be wiped dry, and let it not be damp with any moisture, but let it be filed gently with some smooth piece of iron. But the hitting of the stone with a hammer is of no advantage. By these means let their bare surfaces be joined, and let them be rubbed, so that they may come together more firmly; not so that the material substance of the stone being joined to the iron may cleave to it, but they are rubbed gently together with friction, and
(useless parts being rubbed off) they are intimately united; whence a more notable virtue arises in the iron that is excited. A is the best way of touching a versorium when the cusp touches the pole and faces it; B is a moderately good way, when, though facing it, it is a little way distant from the pole; also in like manner C is only moderately good on account of the cusp being turned away from the pole; D, which is farther distant, is hardly so good; F, which is prepared crosswise along a parallel, is bad; of no virtue and entirely irresponsive and feeble is the magnetick index L, which is rubbed along the æquator; oblique and not pointing towards the pole as G, and oblique, not pointing toward but turned away from the pole as H, are bad. These have been placed so that they might indicate the distinct forces of a round stone. But mechanicians very often have a stone tending more to a cone shape, and more powerful on account of that shape since the pole, on which they rub their wires, is at the apex of the projecting part. Sometimes the stone has on the top and above its own pole an artificial acorn or snout made of steel for the sake of its power. Iron needles are rubbed on the top of this; wherefore they turn toward the same pole as if they had been prepared on that part of the stone with the acorn removed. Let the stone be large enough and strong; the needle, even if it be rather long, should be sufficiently thick, not very slender; with a moderate cusp, not too sharp, although the virtue is not in the cusp itself only, but in the whole piece of iron. A strong large stone is not unfit for rubbing all needles on, excepting that sometimes by its strength it occasions some dip and disturbance in the iron in the case of longer needles; so that one which, having been touched before, rested in equilibrium in the plane of the horizon, now when touched and excited dips at one end, as far as the upright pin on which it turns permits it. Wherefore in the case of longer versoria, the end which is going to be the Boreal, before it is rubbed, should be a little lighter, so that it may remain exactly in æquilibrio after it is touched. But a needle in this way prepared does its work worse the farther it is beyond the æquinoctial circle. Let the prepared needle be placed in its capsule, and let it not be touched by any other magneticks, nor remain in the near vicinity of them, lest by their opposing forces, whether powerful or sluggish, it should become uncertain and dull. If you also rub the other end of the needle on the other pole of the stone, the needle will perform its functions more steadily, especially if it be rather long. A piece of iron touched by a loadstone retains the magnetick virtue, excited in it even for ages217, firm and strong, if it is placed according to nature meridionally and not along a parallel, and is not injured by rust or any external injury from the surrounding medium. Porta wrongly seeks for a proportion between the loadstone and the iron: because, he says, a little piece of iron will not be capable of holding much virtue; for it is consumed by the great force of the loadstone. A piece of iron receives its own virtue fully, even if it be only of the weight of one scruple, whilst the mass of the loadstone is a thousand pounds. It is also useless to make the needle rather flat at the end that is touched, so that it may be better and more perfectly magnetick, and that it may best receive and hold certain magnetick particles; since hardly any part will stick on a sharp point; because he thought that it was by the adhesion of parts of the loadstone (as it were, hairs) that the influence is imparted and conserved, though those particles are merely rubbed off by the rubbing of the iron over the softer stone, and the iron none the less points toward the North and South, if after it is touched it be scoured with sand or emery powder, or with any other material, even if by long rubbing of this kind the external parts of it are lessened and worn away. When a needle is being rubbed, one should always leave off at the end; otherwise, if it is rubbed on the loadstone from the point toward the middle, less verticity is excited in the iron, sometimes none at all, or very little. For where the last contact is, there is the pole and goal of verticity. In order that a stronger verticity may be produced in the iron by rubbing on the loadstone, one ought in northern lands to turn the true northern pole of the loadstone toward the highest part of the sky; on this pole that end of the needle is going to be rubbed, which shall afterwards turn toward the north of the earth; whilst it will be an advantage for the other end of the needle to be rubbed on the southern pole of the terrella turned toward the earth, and this being so excited will incline toward the south. In southern regions beyond the æquator the plan is just the contrary. The reason of this dissimilarity is demonstrated, Book II., chap, xxxiv., in which it is shown (by a manifest combination of a terrella and the earth) why the poles of a loadstone, for different reasons, are one stronger than the other. If a needle be touched between the mutually accordant poles of two loadstones, equal in power, shape, and mass, no strength is acquired by the needle. A and B are two loadstones attracting one another, according to nature, at their dissimilar ends; C, the point of a needle touched by both at once, is not excited (even if those loadstones be connected according to nature), if they are equal; but if they are not equal, virtue is acquired from the stronger. When a needle is being excited by a loadstone, begin in the middle, and draw the needle toward its end; at the end let the application be continued with a very gentle rubbing around the end for some time; that is to say, for one or two minutes; do not repeat the motion from the middle to the end (as is frequently done) for in this way the verticity is injured. Some delay is desirable, for although the power is imparted instantly, and the iron excited, yet from the vicinity of the loadstone and a suitable delay, a more steady verticity arises, and one that is more firmly durable in the iron. Although an armed stone raises a greater weight of iron than an unarmed one, yet a needle is not more strongly excited by an armed stone than by an unarmed one. Let there be two iron wires of the same length, wrought from the same wire; let one be excited by an armed end, the other by an unarmed end; it is manifest that the same needles have a beginning of motion or a sensible inclination at equal distances from the same armed and unarmed loadstone; this is ascertained by measuring with a longish reed. But objects which are more powerfully excited move more quickly; those which are less powerfully excited, more feebly, and not unless brought rather close; the experiment is made on water with equal corks.
On Variation.
D irection has hitherto been spoken of as if in nature there were no variation; for in the preceding natural history we wished to omit and neglect this, inasmuch as in a terrestrial globe, perfect and in every sense complete, there would be none. Since, however, in fact, the earth's magnetick direction, owing to some fault and slip, deviates from its right course and from the meridian, we must extract and demonstrate the obscure and hidden cause of that variance which has troubled and sore racked in vain the minds of many. Those who before us have written on the magnetick movements have made no distinction between direction and variation, but consider the motion of magnetick iron to be uniform and simple. Now true direction is the motion of the magnetick body to the true meridian and its continuance therein with its appropriate ends towards the poles. But it very often happens at sea and on land that the magnetick iron does not point to the true pole, and that not only a versorium and magnetick pieces of iron, and the needle of a compass, or a mariners' compass, but also a terrella in its boat, as well as iron ore, iron stones, and magnetick earths, properly prepared, are drawn aside and deviate towards some point of the Horizon very near to the meridian. For they with their poles frequently face termini away from the meridian. This variation (observed by means of instruments or a nautical variation compass) is therefore the arc of the horizon between the common point of intersecion of it with the true meridian, and the terminus of the deflecion on the horizon or projection of the deviating needle. That arc varies and differs with change of locality. To the terminus of the variation is commonly assigned a great circle, called the circle of variation, and also a magnetick meridian passing through the zenith and the point of variation on the horizon. In the northern regions of the earth this variation is either from the north toward the east or from the north toward the west: similarly in the southern regions it is from the south toward the east or toward the west. Wherefore one should observe in the northern regions of the earth that end of the versorium or compass which turns toward the North; but in the southern regions the other end looking to the south — which seamen and sciolists for the most part do not understand, for in both regions they observe only the boreal lily of the compass (that which faces North). We have before said that all the motions of the magnet and iron, all its turning, its inclination, and its settlement, proceed from bodies themselves magnetical and from their common mother the earth, which is the source, the propagatrix, and the origin of all these qualities and properties. Accordingly the earth is the cause of this variation and inclination toward a different point of the horizon: but how and by what powers must be more fully investigated. And here we must at the outset reject that common opinion of recent writers concerning magnetick mountains, or any magnetick rock, or any phantasmal pole distant from the pole of the earth, by which the motion of the compass or versorium is controlled. This opinion, previously invented by others, Fracastorio himself adopted and developed; but it is entirely at variance with experience. For in that case in different places at sea and on land the point of variation would change toward the east or west in proportion and geometrical symmetry, and the versorium would always respect the magnetick pole: but experience teaches that there is no such definite pole or fixed terminus on the earth to account for the variation. For the arcs of variation are changed variously and erratically, not only on different meridians but on the same meridian; and when, according to this opinion of the moderns, the deviation should be more and more toward the east, then suddenly, with a small change of locality, the deviation is from the north toward the west as in the northern regions near Nova Zembla. Moreover, in the southern regions, and at sea at a great distance from the æquator towards the antarctick pole, there are frequent and great variations, and not only in the northern regions, from the magnetick mountains. But the cogitations of others are still more vain and trifling, such as that of Cortes about a moving influence beyond all the heavens; that of Marsilius Ficinus about a star in the Bear; that of Peter Peregrinus about the pole of the world; that of Cardan, who derives it from the rising of a star in the tail of the Bear218; of Bessardus, the Frenchman, from the pole of the Zodiack; that of Livio Sanuto from some magnetick meridian; that of Franciscus Maurolycus from a magnetical island; that of Scaliger from the heavens and mountains; that of Robert Norman, the Englishman, from a point respective. Leaving therefore these opinions, which are at variance with common experience or by no means proved, let us seek the true cause of the variation. The great magnet or terrestrial globe directs iron (as I have said) toward the north and south; and excited iron quickly settles itself toward those termini. Since, however, the globe of the earth is defective and uneven on its surface and marred by its diverse composition, and since it has parts very high and convex (to the height of some miles), and those uniform neither in composition nor body, but opposite and dissimilar: it comes to pass that the whole of that force of the earth diverts magnetical bodies in its periphery toward the stronger and more prominent connected magnetick parts. Hence on the outermost surface of the earth magnetical bodies are slightly perverted from the true meridian. Moreover, since the surface of the globe is divided into high lands and deep seas, into great continental lands, into ocean and vastest seas, and since the force of all magnetical motions is derived from the constant and magnetick terrestrial nature which is more prevalent on the greater continent and not in the aquæous or fluid or unstable part; 219it follows that in certain parts there would be a magnetick inclination from the true pole east or west away from any meridian (whether passing through seas or islands) toward a great land or continent rising higher, that is, obviously toward a stronger and more elevated magnetick part of the terrestrial globe. For since the diameter of the earth is more than 1,700 German miles, those large lands can rise from the centre of the earth more than four miles above the depth of the ocean bottom, and yet the earth will retain the form of a globe although somewhat uneven at the top. Wherefore a magnetical body is turned aside, so far as the true verticity, when disturbed, admits, and departs from its right (the whole earth moving it) toward a vast prominent mass of land as though toward what is stronger. But the variation does really take place, not so much because of the more prominent and imperfect terrestrial parts and continent lands as because of the inæquality of the magnetick globe, and because of the real earth, which stands out more under the continent lands than under the depths of the seas. We must see, therefore, how the apodixis of this theory can be sustained by more definite observations. Since throughout all the course from the coast of Guinea to Cape Verde, the Canary Isles, and the border of the kingdom of Morocco, and thence along the coasts of Spain, France, England, Belgium, Germany, Denmark, and Norway, there lie on the right hand and toward the east a continent and extensive connected regions, and on the left extensive seas and a vast ocean lie open far and wide, it is consonant with the theory (as has been carefully observed by many) that magnetical bodies should turn slightly to the East from the true pole toward the stronger and more remarkable elevations of the earth. But it is far otherwise on the eastern shores of northern America; for from Florida by Virginia and Norumbega to Cape Race and away to the north the versorium is turned toward the west. But in the middle spaces, so to speak, as in the more westerly Azores, it looks toward the true pole. That any magnetick body turns itself similarly to the same regions of the earth is not, however, because of that meridian or because of the concordancy of the meridian with any magnetick pole, as the crowd of philosophizers reckon, for it is not so throughout the whole of that meridian. For on the same meridian near Brazil something very different occurs, as we will show further on. The variation (cæteris paribus) is always less near the æquator, greater in higher latitudes, with the limitation that it be not very near the pole itself. Hence the variation is greater on the coast of Norway and Belgium than on the coast of Morocco or Guinea: greater also near Cape Race than in the harbours of Norumbega or of Virginia. On the coast of Guinea magnetick implements deviate by a third part of one rumbe to the East: in Cape Verde Islands by a half: on the coast of Morocco by two thirds: in England at the mouth of the Thames by a whole rumbe: and at London by nearly eleven degrees and one third. For indeed the moving magnetick virtue is stronger in a higher latitude; and the larger regions extending toward the poles dominate the more, as is easily apparent anywhere on a terrella. For as in the case of true Direction magnetick bodies tend toward the pole (namely, toward the stronger end, the whole earth causing the motion), so also do they incline a little toward the stronger and higher parts by the action of the whole along with the conjoint action of iron bodies.
That the variation is caused by the inæquality of the projecting parts of the earth.
D emonstration of this may manifestly be made Variation on imperfect terrella. by means of a
terrella in the following way: let there be a round loadstone somewhat imperfect in some part, and impaired by decay (such an one we had with a certain part corroded to resemble the Atlantick or great Ocean): place upon it some fine iron wire of the length of two barleycorns, as in the following figure. A B, a Terrella in certain parts somewhat imperfect and of unæqual virtue on the circumference. The versoria E, F, do not vary, but look directly to the pole A; for they are placed in the middle of the firm and sound part of the terrella and somewhat distant from the imperfect part: that part of the surface which is distinguished by dots and transverse lines is the weaker. The versorium O also does not vary (because it is placed in the middle of the imperfect part), but is directed toward the pole, just as near the western Azores on the earth. The versoria H and L do vary, for they incline toward the sounder parts very near them. As this is manifest in a terrella whose surface is sensibly rather imperfect, so also is it in others whole and perfect, when often one part of the stone has stronger external parts, which nevertheless do not disclose themselves manifestly to the senses. In such a terrella the demonstration of the variation and the discovery of the stronger parts is on this wise. Let A be the pole, B the place of the variation, C the stronger regions; then the horizontal versorium at B varies from the pole A toward C: so that both the variation is shown and the stronger places of the loadstone recognized. The stronger surface is also found by a fine iron wire of the length of two barleycorns: for since at the pole of the terrella it rears up perpendicularly, but in other places inclines toward the æquator, if in one and the same parallel circle it should be more erect in one place than in another; where the wire is raised more upright, there the part and surface of the terrella is stronger. Also when the iron wire placed over the pole inclines more to one part than to another. Let the experiment be made by means of a fine iron wire of three digits length placed over the pole A, so that its middle lies over the pole. Then one end is turned away from B toward C, and is not willing to lie quietly toward B; but on a terrella which is perfect220 all round and even it rests on the pole directed toward any point of the æquator you please. Otherwise, let there be two meridians meeting in the poles A B, let iron wires be reared just at the ends D and C of the equal arcs D A and C A; then the wire at D (the stronger region) will be more raised up than that at C, the weaker. And thus the sounder and stronger part of the loadstone is recognized, which otherwise would not be perceived by the touch. In a terrella which is perfect, and even, and similar in all its parts, there is, at equal distances from the pole, no variation221. Variation is shown by means of a terrella, a considerable part of which, forming a surface a little higher than the rest, does, although it be not decayed and broken, allure the versorium from the true direction (the whole terrella co-operating).
A terrella uneven in surface.
It is shown by a small spike placed over a terrella or by a small versorium; for they are turned by the terrella toward the mass that stands out and toward the large eminences. In the same way on the earth the verticity is perturbed by great continents, which are mostly elevated above the depths of the seas and make the versorium deviate sometimes from the right tracks (that is, from the true meridians). On a terrella it is thus demonstrated: the end of the versorium A is not directed straight to the pole P, if there be a large protuberance B on the terrella; so also the cusp C deviates from the pole because of the eminence F. In the middle between the two eminences the versorium G collimates to the true pole because, being at equal distances from the two eminences B and F, it turns aside to neither, but observes the true meridian, especially when the protuberances are of equal vigour. But the versorium N on the other side varies from the pole M toward the eminences H, and is not held back, stopped, or restrained by the small eminence O on the terrella (as it were, some island of land in the ocean). L, however, being unimpeded, is directed to the pole M. The variation is demonstrated in another way on a terrella, just as on the earth. Let A be the pole of the earth, B the equator, C the parallel circle of latitude of 30 degrees, D a great eminence spread out toward the pole, E another eminence spread out from the pole toward the æquator. It is manifest that in the middle of D the versorium F does not vary; while G is very greatly deflected: but H very little, because it is further removed from D. Similarly also the versorium I placed directly toward E does not deviate from the pole: but L and M turn themselves away from the pole A toward the eminence E.
The variation in any one place is constant.
unless there should be a great dissolution of a continent and a subsidence of the land such as there was of the region Atlantis of which Plato and the ancients tell, the variation will continue perpetually immutable; the arc of the variation remains the same in the same place or region, whether it be at sea or on land, as in times past a magnetick body has declined toward the East or the West. The constancy of the variation and the pointing of the versorium to a definite point on the horizon in individual regions is demonstrated by a small versorium placed over a terrella the surface of which is uneven: for it always deviates from the meridian by an equal arc. It is also shown by the inclination of a versorium toward a second magnet; although in reality it is by the turning power of the whole, whether in the earth or in a terrella. Place upon a plane a versorium whose cusp is directed toward the north A: place beside it a loadstone, B, at such a distance that the versorium may turn aside toward B to the point C, and not beyond. Then move the needle of the versorium as often as you will (the box and the loadstone not being moved), and it will certainly always return to the point C. In the same manner, if you placed the stone so that it may be truly directed toward E, the cusp always reverts to E, and not to any other point of the compass. Accordingly, from the position of the land and from the distinctive nature of the highest parts of the earth (certain terrene and more magnetick eminences of the regions prevailing), the variation indeed becomes definite in one and the same place, but diverse and unæqual from a change of place, since the true and polar direction originating in the whole terrestrial globe is diverted somewhat toward certain stronger eminences on the broken surface.
The arc of variation is not changed equally in proportion to the distance of places.
I n the open sea, when a vessel is borne by a favourable wind along the same parallel, if the variation be changed by one degree in the course of one hundred miles, the next hundred miles do not therefore lessen it by another degree; for the magnetick varies erratically as respects position, form, and vigour of the land, and also because of the distance. As, for example, when a course from the Scilly Isles to Newfoundland has proceeded so far that the compass is directed to the true pole, then, as the vessel proceeds, in the first part of the course the variation increases toward the north-west222, but rather indistinctly and with small difference: thence, after an equal distance, the arc is increased in a greater proportion until the vessel is not far from the continent: for then it varies most of all. But before it touches actual land or enters port, then at a certain distance the arc is again slightly diminished. But if the vessel in its course should decline greatly from that parallel either toward the south or the north, the magnetick will vary more or less, according to the position of the land and the latitude of the region. For (cæteris paribus) the greater the latitude the greater the variation.
An island in Ocean does not change the variation223, as neither do mines of loadstone.
Islands, although they be more magnetick than the sea, yet do not change the magnetick directions or variations. For since direction is a motion derived from the power of the whole earth, not from the attraction of any hill but from the disposing and turning power of the whole; so variation (which is a perturbation of the direction) is an aberration of the real turning power arising from the great inequalities of the earth, in consequence of which it, of itself, slightly diverts movable magneticks toward those which are the largest and the more powerful. The cause now shown may suffice to explain that which some so wonder at about the Island of Elba (and although this is productive of loadstone, yet the versorium (or mariners' compass) makes no special inclination toward it whenever vessels approach it in the Tyrrhenian sea); and the following causes are also to be considered, viz.: that the virtue of smaller magnetick bodies extends scarcely or not at all of itself beyond their own mines: for variation does not occur because of attraction, as they would have it who have imagined magnetick poles. Besides, magnetick mines are only agnate to the true earth, not innate: hence the whole globe does not regard them, and magneticks are not borne to them, as is demonstrated by the diagram of eminences.
That variation and direction arise from the disponent power of the earth, and from the natural magnetick tendency to rotation, not from attraction, or from coition, or from other occult cause.
O wing to the loadstone being supposed (amongst the crowd of philosophizers) to seize and drag, as it were, magnetick bodies; and since, in truth, sciolists have remarked no other forces than those so oft besung of attractive ones, they therefore deem every motion toward the north and south to be caused by some alluring and inviting quality. But the Englishman, Robert Norman, first strove to show that it is not caused by attraction: wherefore, as if tending toward hidden principles, he imagined a point respective224, toward which the iron touched by a loadstone would ever turn, not a point attractive; but in this he erred greatly, although he effaced the former error about attraction. He, however, demonstrates his opinion in this way:
Let there be a round vessel filled with water: in the middle of the surface of the water place a slender iron wire on a perfectly round cork, so that it may just float in æquilibrium on the water; let the wire be previously touched by a magnet, so that it may more readily show the point of variation, the point D as it were: and let it remain on the surface for some time. It is demonstrable that the wire together with the cork is not moved to the side D of the vessel: which it would do if an attraction came to the iron wire by D: and the cork would be moved out of its place. This assertion of the Englishman, Robert Norman, is plausible and appears to do away with attraction because the iron remains on the water not moving about, as well in a direction toward the pole itself (if the direction be true) as in a variation or altered direction; and it is moved about its own centre without any transference to the edge of the vessel. But direction does not arise from attraction, but from the disposing and turning power which exists in the whole earth, not in the pole or in some other attracting part of the stone, or in any mass rising above the periphery of the true circle so that a variation should occur because of the attraction of that mass. Moreover, it is the directing power of the loadstone and iron and its natural power of turning around the centre which cause the motion of direction, and of conformation, in which is included also the motion of the dip. And the terrestrial pole does not attract as if the terrene force were implanted only in the pole, for the magnetick force exists in the whole, although it predominates and excels at the pole. Wherefore that the cork should rest quiescent in the middle and that the iron excited by a loadstone should not be moved toward the side of the vessel are agreeable to and in conformity with the magnetick nature, as is demonstrated by a terrella: for an iron spike placed on the stone at C clings on at C, and is not pulled further away by the pole A, or by the parts near the pole: hence it persists at D, and takes a direction toward the pole A; nevertheless it clings on at D and dips also at D in virtue of that turning power by which it conforms itself to the terrella: of which we will say more in the part On Declination.