Dr. William Gilbert,

a distinguished Doctor of Medicine amongst the

Londoners, and Father of Magnetick Philosophy,

an Encomiastic Preface of Edward Wright

on the subject of these books

Magnetical.

hould there by chance be any one, most eminent Sir, who reckons as of small account these magnetical books and labours of yours, and thinks these studies of yours of too little moment, and by no means worthy enough of the attention of an eminent man devoted to the weightier study of Medicine: truly he must deservedly be judged to be in no common degree void of understanding. For that the use of the magnet is very important and wholly admirable is better known for the most part to men of even the lowest class than to need from me at this time any long address or commendation. Nor truly in my judgment could you have chosen any topick either more noble or more useful to the human race, upon which to exercise the strength of your philosophic intellect; since indeed it has been brought about by the divine agency of this stone, that continents of such vast circuit, such an infinite number of lands, islands, peoples, and tribes, which have remained unknown for so many ages, have now only a short time ago, almost within our own memory, been quite easily discovered and quite frequently explored, and that the circuit of the whole terrestrial globe also has been more than once circumnavigated by our own countrymen, Drake and Cavendish; a fact which I wish to mention to the lasting memory of these men. For by the pointing of the iron touched by a loadstone, the points of South, North, East, and West, and the other quarters of the world are made known to navigators even under an overcast sky and in the darkest night; so that thus they always very easily understand to which point of the world they ought to direct their ship's course; which before the discovery of this wonderful virtue of the magnetick βορεοδείξις was clearly impossible. Hence in old times (as is established in histories), an incredible anxiety and immense danger was continually threatening sailors; for at the coming on of a tempest and the obscuring of the view of sun and stars, they were left entirely in ignorance whither they were making; nor could they find out this by any reasoning or skill. With what joy then may we suppose them to have been filled, to what feelings of delight must all shipmasters have given utterance, when that index magnetical first offered itself to them as a most sure guide, and as it were a Mercury, for their journey? But neither was this sufficient for this magnetical Mercury; to indicate, namely, the right way, and to point, as it were, a finger in the direction toward which the course must be directed; it began also long ago to show distinctly the distance of the place toward which it points. For since the index magnetical does not always in every place look toward the same point of the North, but deviates from it often, either toward the East or toward the West, yet always has the same deviation in the same place, whatever the place is, and steadily preserves it; it has come about that from that deviation, which they call variation, carefully noticed and observed in any maritime places, the same places could afterwards also be found by navigators from the drawing near and approach to the same variation as that of these same places, taken in conjunction with the observation of the latitude. Thus the Portuguese in their voyages to the East Indies had the most certain indications of their approach to the Cape of Good Hope; as appears from the narrations of Hugo van Lynschoten and of the very learned Richard Hakluyt, our countryman. Hence also the experienced skippers of our own country, not a few of them, in making the voyage from the Gulf of Mexico to the islands of the Azores, recognized that they had come as near as possible to these same islands; although from their sea-charts they seemed to be about six hundred British miles from them. And so, by the help of this magnetick index, it would seem as though that geographical problem of finding the longitude, which for so many centuries has exercised the intellects of the most learned Mathematicians, were going to be in some way satisfied; because if the variation for any maritime place whatever were known, the same place could very readily be found afterward, as often as was required, from the same variation, the latitude of the same place being not unknown.

It seems, however, that there has been some inconvenience and hindrance connected with the observation of this variation; because it cannot be observed excepting when the sun or the stars are shining. Accordingly this magnetick Mercury of the sea goes on still further to bless all shipmasters, being much to be preferred to Neptune himself, and to all the sea-gods and goddesses; not only does it show the direction in a dark night and in thick weather, but it also seems to exhibit the most certain indications of the latitude. For an iron index, suspended on its axis (like a pair of scales), with the most delicate workmanship so as to balance in æquilibrio, and then touched and excited by a loadstone, dips to some fixed and definite point beneath the horizon (in our latitude in London, for example, to about the seventy-second degree), at which it at length comes to rest. But under the æquator itself, from that admirable agreement and congruency which, in almost all and singular magnetical experiments, exists between the earth itself and a terrella (that is, a globular loadstone), it seems exceedingly likely (to say the very least), and indeed more than probable, that the same index (again stroked with a loadstone) will remain in æquilibrio in an horizontal position. Whence it is evident that this also is very probable, that in an exceedingly small progress from the South toward the North (or contrariwise) there will be at least a sufficiently perceptible change in that declination; so that from that declination in any place being once carefully observed along with the latitude, the same place and the same latitude may be very easily recognized afterward, even in the darkest night and in the thickest mist by a declination instrument. Wherefore to bring our oration at length back to you, most eminent and learned Dr. Gilbert (whom I gladly recognize as my teacher in this magnetick philosophy), if these books of yours on the Magnet had contained nothing else, excepting only this finding of latitude from magnetick declination, by you now first brought to light, our shipmasters, Britains, French, Belgians, and Danes, trying to enter the British Channel or the Straits of Gibraltar from the Atlantick Ocean in dark weather, would still most deservedly judge them to be valued at no small sum of gold. But that discovery of yours about the whole globe of the earth being magnetical, although perchance it will seem to many "most paradoxical," producing even a feeling of astonishment, has yet been so firmly defended by you at all points and confirmed by so many experiments so apposite and appropriate to the matter in hand, in Bk. 2, chap. 34; Bk. 3, chap. 4 and 12; and in almost the whole of the fifth book, that no room is left for doubt or contradiction. I come therefore to the cause of the magnetick variation, which hitherto has distracted the minds of all the learned; for which no mortal has ever adduced a more probable reason than that which has now been set forth by you for the first time in these books of yours on the Magnet. The ὀρθοβορεοδείξις of the index magnetical in the middle of the ocean, and in the middle of continents (or at least in the middle of their stronger and more lofty parts), its inclining near the shore toward those same parts, even by sea and by land, agreeing with the experiments Bk. 4, chap. 2, on an actual terrella (made after the likeness of the terrestrial globe, uneven, and rising up in certain parts, either weak or wanting in firmness, or imperfect in some other way),—this inclination having been proved, very certainly demonstrates the probability that that variation is nought else than a certain deviation of the magnetick needle toward those parts of the earth that are more vigorous and more prominent. Whence the reason is readily established of that irregularity which is often perceived in the magnetick variations, arising from the inæquality and irregularity of those eminences and of the terrestrial forces. Nor of a surety have I any doubt, that all those even who have either imagined or admitted points attractive or points respective in the sky or the earth, and those who have imagined magnetick mountains, or rocks, or poles, will immediately begin to waver as soon as they have perused these books of yours on the Magnet, and willingly will march with your opinion. Finally, as to the views which you discuss in regard to the circular motion of the earth and of the terrestrial poles, although to some perhaps they will seem most supposititious, yet I do not see why they should not gain some favour, even among the very men who do not recognize a sphærical motion of the earth; since not even they can easily clear themselves from many difficulties, which necessarily follow from the daily motion of the whole sky. For in the first place it is against reason that that should be effected by many causes, which can be effected by fewer; and it is against reason that the whole sky and all the sphæres (if there be any) of the stars, both of the planets and the fixed stars, should be turned round for the sake of a daily motion which can be explained by the mere daily rotation of the earth. Then whether will it seem more probable, that the æquator of the terrestrial globe in a single second (that is, in about the time in which any one walking quickly will be able to advance only a single pace) can accomplish a quarter of a British mile (of which sixty equal one degree of a great circle on the earth), or that the æquator of the primum mobile in the same time should traverse five thousand miles with celerity ineffable; and in the twinkling of an eye should fly through about five hundred British miles, swifter than the wings of lightning, if indeed they maintain the truth who especially assail the motion of the earth). Finally, will it be more likely to allow some motion to this very tiny terrestrial globe; or to build up with mad endeavour above the eighth of the fixed sphæres those three huge sphæres, the ninth (I mean), the tenth, and the eleventh, marked by not a single star, especially since it is plain from these books on the magnet, from a comparison of the earth and the terrella, that a circular motion is not so alien to the nature of the earth as is commonly supposed. Nor do those things which are adduced from the sacred Scriptures seem to be specially adverse to the doctrine of the mobility of the earth; nor does it seem to have been the intention of Moses or of the Prophets to promulgate any mathematical or physical niceties, but to adapt themselves to the understanding of the common people and their manner of speech, just as nurses are accustomed to adapt themselves to infants, and not to go into every unnecessary detail. Thus in Gen. i. v. 16, and Psal. 136, the moon is called a great light, because it appears so to us, though it it is agreed nevertheless by those skilled in astronomy that many of the stars, both of the fixed and wandering stars, are much greater. Therefore neither do I think that any solid conclusion can be drawn against the earth's mobility from Psal. 104, v. 5; although God is said to have laid the foundations of the earth that it should not be removed for ever; for the earth will be able to remain evermore in its own and self-same place, so as not to be moved by any wandering motion, nor carried away from its seat (wherein it was first placed by the Divine artificer). We, therefore, with devout mind acknowledging and adoring the inscrutable wisdom of the triune Divinity (having more diligently investigated and observed his admirable work in the magnetical motions), induced by philosophical experiments and reasonings not a few, do deem it to be probable enough that the earth, though resting on its centre as on an immovable base and foundation, nevertheless is borne around circularly.

But passing over these matters (concerning which I believe no one has ever demonstrated anything with greater certainty), without any doubt those matters which you have discussed concerning the causes of the variation and of the magnetick dip below the horizon, not to mention many other matters, which it would take too long to speak of here, will gain very great favour amongst all intelligent men, and especially (to speak after the manner of the Chemists) amongst the sons of the magnetick doctrine. Nor indeed do I doubt that when you have published these books of yours on the Magnet, you will excite all the diligent and industrious shipmasters to take no less care in observing the magnetick declination beneath the horizon than the variation. Since (if not certain) it is at least probable, that the latitude itself, or rather the effect of the latitude, can be found (even in very dark weather) much more accurately from that declination alone, than can either the longitude or the effect of the longitude from the variation, though the sun itself is shining brightly or all the stars are visible, with the most skilful employment likewise of all the most exact instruments. Nor is there any doubt but that those most learned men, Peter Plancius (not more deeply versed in Geography than in observations magnetical), and Simon Stevinus, the most distinguished mathematician, will rejoice in no moderate degree, when they first see these magnetical books of yours, and observe their λιμενευρετική, or Haven-finding Art, enlarged and enriched by so great and unexpected an addition; and without doubt they will urge all their own shipmasters (as far as they can) to observe also everywhere the magnetick declination below the horizon no less than the variation. May your Magnetical Philosophy, therefore, most learned Dr. Gilbert, come forth into the light under the best auspices, after being kept back not till the ninth year only (as Horace prescribes), but already unto almost a second nine, a philosophy rescued at last by so many toils, studyings, watchings, with so much ingenuity and at no moderate expense maintained continuously through so many years, out of darkness and dense mist of the idle and feeble philosophizers, by means of endless experiments skilfully applied to it; yet without neglecting anything which has been handed down in the writings of any of the ancients or of the moderns, all which you did diligently peruse and perpend. Do not fear the boldness or the prejudice of any supercilious and base philosophaster, who by either enviously calumniating or stealthily arrogating to himself the investigations of others seeks to snatch a most empty glory. Verily

but

May your new physiology of the Magnet, I say (kept back for so many years), come forth now at length into the view of all, and your Philosophy, never to be enough admired, concerning the great Magnet (that is, the earth); for, believe me

these books of yours on the Magnet will avail more for perpetuating the memory of your name than the monument of any great Magnate placed upon your tomb.

Interpretation of certain words.^[1]

Terrella, a globular loadstone.

Verticity, polar vigour, not περιδίνησις but περιδίνεισιος δύναμις: not a vertex or πόλος but a turning tendency.

Electricks, things which attract in the same manner as amber.

Excited Magnetick, that which has acquired powers from the loadstone.

Magnetick Versorium, a piece of iron upon a pin, excited by a loadstone.

Non-magnetick Versorium, a versorium of any metal, serving for electrical experiments.

Capped loadstone, which is furnished with an iron cap, or snout.

Meridionally, that is, along the projection of the meridian.

Paralleletically, that is, along the projection of a parallel.

Cusp, tip of a versorium excited by the loadstone.

Cross, sometimes used of the end that has not been touched and excited by a loadstone, though in many instruments both ends are excited by the appropriate termini of the stone.

Cork, that is, bark of the cork-oak.

Radius of the Orbe of the Loadstone, is a straight line drawn from the summit of the orbe of the loadstone, by the shortest way, to the surface of the body, which, continued, will pass through the centre of the loadstone.

Orbe of Virtue, is all that space through which the Virtue of any loadstone extends.

Orbe of Coition, is all that space through which the smallest magnetick is moved by the loadstone.

Proof, for a demonstration shown by means of a body.

Magnetick Coition: since in magnetick bodies, motion does not occur by an attractive faculty, but by a concourse or concordance of both, not as if there were an ἑλκτικὴ δύναμις of one only, but a συνδρομή of both; there is always a coition of the vigour: and even of the body if its mass should not obstruct.

Declinatorium, a piece of Iron capable of turning about an axis, excited by a loadstone, in a declination instrument.

I N D E X O F C H A P T E R S.

Book 1.

Chap. 1. Ancient and modern writings on the Loadstone, with certain matters of mention only, various opinions, & vanities.

Chap. 2. Magnet Stone, of what kind it is, and its discovery.

Chap. 3. The loadstone has parts distinct in their natural power, & poles conspicuous for their property.

Chap. 4. Which pole of the stone is the Boreal: and how it is distinguished from the austral.

Chap. 5. Loadstone seems to attract loadstone when in natural position: but repels it when in a contrary one, and brings it back to order.

Chap. 6. Loadstone attracts the ore of iron, as well as iron proper, smelted & wrought.

Chap. 7. What iron is, and of what substance, and its uses.

Chap. 8. In what countries and districts iron originates.

Chap. 9. Iron ore attracts iron ore.

Chap. 10. Iron ore has poles, and acquires them, and settles itself toward the poles of the universe.

Chap. 11. Wrought iron, not excited by a loadstone, draws iron.

Chap. 12. A long piece of Iron (even though not excited by a loadstone) settles itself toward North & South.

Chap. 13. Wrought iron has in itself certain parts Boreal & Austral: a magnetick vigour, verticity, and determinate vertices or poles.

Chap. 14. Concerning other powers of loadstone, & its medicinal properties.

Chap. 15. The medicinal virtue of iron.

Chap. 16. That loadstone & iron ore are the same, but iron an extract from both, as other metals are from their own ores; & that all magnetick virtues, though weaker, exist in the ore itself & in smelted iron.

Chap. 17. That the globe of the earth is magnetick, & a magnet; & how in our hands the magnet stone has all the primary forces of the earth, while the earth by the same powers remains constant in a fixed direction in the universe.

Book 2.

Chap. 1. On Magnetick Motions.

Chap. 2. On the Magnetick Coition, and first on the attraction of Amber, or more truly, on the attaching of bodies to Amber.

Chap. 3. Opinions of others on Magnetick Coition, which they call Attraction.

Chap. 4. On Magnetick Force & Form, what it is; and on the cause of the Coition.

Chap. 5. How the Power dwells in the Loadstone.

Chap. 6. How magnetick pieces of Iron and smaller loadstones conform themselves to a terrella & to the earth itself, and by them are disposed.

Chap. 7. On the Potency of the Magnetick Virtue, and on its nature capable of spreading out into an orbe.

Chap. 8. On the geography of the Earth, and of the Terrella.

Chap. 9. On the Æquinoctial Circle of the Earth and of a Terrella.

Chap. 10. Magnetick Meridians of the Earth.

Chap. 11. Parallels.

Chap. 12. The Magnetick Horizon.

Chap. 13. On the Axis and Magnetick Poles.

Chap. 14. Why at the Pole itself the Coition is stronger than in the other parts intermediate between the æquator and the pole; and on the proportion of forces of the coition in various parts of the earth and of the terrella.

Chap. 15. The Magnetick Virtue which is conceived in Iron is more apparent in an iron rod than in a piece of Iron that is round, square, or of other figure.

Chap. 16. Showing that Movements take place by the Magnetical Vigour though solid bodies lie between; and on the interposition of iron plates.

Chap. 17. On the Iron Cap of a Loadstone, with which it is armed at the pole (for the sake of the virtue), and on the efficacy of the same.

Chap. 18. An armed Loadstone does not indue an excited piece of Iron with greater vigour than an unarmed.

Chap. 19. Union with an armed Loadstone is stronger; hence greater weights are raised; but the coition is not stronger, but generally weaker.

Chap. 20. An armed Loadstone raises an armed Loadstone, which also attracts a third; which likewise happens, though the virtue in the first be somewhat small.

Chap. 21. If Paper or any other Medium be interposed, an armed loadstone raises no more than an unarmed one.

Chap. 22. That an armed Loadstone draws Iron no more than an unarmed one: and that an armed one is more strongly united to iron is shown by means of an armed loadstone and a polished Cylinder of iron.

Chap. 23. The Magnetick Force causes motion toward unity, and binds firmly together bodies which are united.

Chap. 24. A piece of Iron placed within the Orbe of a Loadstone hangs suspended in the air, if on account of some impediment it cannot approach it.

Chap. 25. Exaltation of the power of the magnet.

Chap. 26. Why there should appear to be a greater love between iron & loadstone, than between loadstone & loadstone, or between iron & iron, when close to the loadstone, within its orbe of virtue.

Chap. 27. The Centre of the Magnetick Virtues in the earth is the centre of the earth; and in a terrella is the centre of the stone.

Chap. 28. A Loadstone attracts magneticks not only to a fixed point or pole, but to every part of a terrella save the æquinoctial zone.

Chap. 29. On Variety of Strength due to Quantity or Mass.

Chap. 30. The Shape and Mass of the Iron are of most importance in cases of coition.

Chap. 31. On long and round stones.

Chap. 32. Certain Problems and Magnetick Experiments about the Coition, and Separation, and regular Motion of Bodies magnetical.

Chap. 33. On the Varying Ratio of Strength, and of the Motion of coition, within the orbe of virtue.

Chap. 34. Why a Loadstone should be stronger in its poles in a different ratio; as well in the Northern regions as in the Southern.

Chap. 35. On a Perpetual Motion Machine, mentioned by authors, by means of the attraction of a loadstone.

Chap. 36. How a more robust Loadstone may be recognized.

Chap. 37. Use of a Loadstone as it affects iron.

Chap. 38. On Cases of Attraction in other Bodies.

Chap. 39. On Bodies which mutually repel one another.

Book 3.

Chap. 1. On Direction.

Chap. 2. The Directive or Versorial Virtue (which we call verticity): what it is, how it exists in the loadstone; and in what way it is acquired when innate.

Chap. 3. How Iron acquires Verticity through a loadstone, and how that verticity is lost and changed.

Chap. 4. Why Iron touched by a Loadstone acquires an opposite verticity, and why iron touched by the true Northern side of a stone turns to the North of the earth, by the true Southern side to the South; and does not turn to the South when rubbed by the Northern point of the stone, and when by the Southern to the North, as all who have written on the Loadstone have falsely supposed.

Chap. 5. On the Touching of pieces of Iron of divers shapes.

Chap. 6. What seems an Opposing Motion in Magneticks is a proper motion toward unity.

Chap. 7. A determined Verticity and a disponent Faculty are what arrange magneticks, not a force, attracting them or pulling them together, nor merely a strongish coition or unition.

Chap. 8. Of Discords between pieces of Iron upon the same pole of a Loadstone, and how they can agree and stand joined together.

Chap. 9. Figures illustrating direction and showing varieties of rotations.

Chap. 10. On Mutation of Verticity and of Magnetick Properties, or on alteration in the power excited by a loadstone.

Chap. 11. On the Rubbing of a piece of Iron on a Loadstone in places midway between the poles, and upon the æquinoctial of a terrella.

Chap. 12. In what way Verticity exists in any Iron that has been smelted though not excited by a loadstone.

Chap. 13. Why no other Body, excepting a magnetick, is imbued with verticity by being rubbed on a loadstone, and why no body is able to instil and excite that virtue, unless it be a magnetick.

Chap. 14. The Placing of a Loadstone above or below a magnetick body suspended in æquilibrio changes neither the power nor the verticity of the magnetick body.

Chap. 15. 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.

Chap. 16. If the Southern Portion of a Stone be lessened, something is also taken away from the power of the Northern Portion.

Chap. 17. 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.

Book 4.

Chap. 1. On Variation.

Chap. 2. That the variation is caused by the inæquality of the projecting parts of the earth.

Chap. 3. The variation in any one place is constant.

Chap. 4. The arc of variation is not changed equally in proportion to the distance of places.

Chap. 5. An island in Ocean does not change the variation, as neither do mines of loadstone.

Chap. 6. The 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.

Chap. 7. Why the variation from that lateral cause is not greater than has hitherto been observed, having been rarely seen to reach two points of the mariners' compass, except near the pole.

Chap. 8. On the construction of the common mariners' compass, and on the diversity of the compasses of different nations.

Chap. 9. Whether the terrestrial longitude can be found from the variation.

Chap. 10. Why in various places near the pole the variations are much more ample than in a lower latitude.

Chap. 11. Cardan's error when he seeks the distance of the centre of the earth from the centre of the cosmos by the motion of the stone of Hercules; in his book 5, On Proportions.

Chap. 12. On the finding of the amount of variation: how great is the arc of the Horizon from its arctick to its antarctick intersection of the meridian, to the point respective of the magnetick needle.

Chap. 13. The observations of variation by seamen vary, for the most part, and are uncertain: partly from error and inexperience, and the imperfections of the instruments: and partly from the sea being seldom so calm that the shadows or lights can remain quite steady on the instruments.

Chap. 14. On the variation under the æquinoctial line, and near it.

Chap. 15. The variation of the magnetick needle in the great Æthiopick and American sea, beyond the æquator.

Chap. 16. On the variation in Nova Zembla.

Chap. 17. Variation in the Pacifick Ocean.

Chap. 18. On the variation in the Mediterranean Sea.

Chap. 19. The variation in the interior of large Continents.

Chap. 20. Variation in the Eastern Ocean.

Chap. 21. How the deviation of the versorium is augmented and diminished by reason of the distance of places.

Book 5.

Chap. 1. On Declination.

Chap. 2. Diagram of declinations of the magnetick needle, when excited, in the various positions of the sphere, and horizons of the earth, in which there is no variation of the declination.

Chap. 3. An indicatory instrument, showing by the virtue of a stone the degrees of declination from the horizon of each several latitude.

Chap. 4. Concerning the length of a versorium convenient for declination on a terrella.

Chap. 5. That declination does not arise from the attraction of the loadstone, but from a disposing and rotating influence.

Chap. 6. On the proportion of declination to latitude, and the cause of it.

Chap. 7. Explanation of the diagram of the rotation of a magnetick needle.

Chap. 8. Diagram of the rotation of a magnetick needle, indicating magnetical declination in all latitudes, and from the rotation and declination, the latitude itself.

Chap. 9. Demonstration of direction, or of variation from the true direction, at the same time with declination, by means of only a single motion in water, due to the disposing and rotating virtue.

Chap. 10. On the variation of the declination.

Chap. 11. On the essential magnetick activity sphærically effused.

Chap. 12. Magnetick force is animate, or imitates life; and in many things surpasses human life, while this is bound up in the organick body.

Book 6.

Chap. 1. On the globe of the earth, the great magnet.

Chap. 2. The Magnetick axis of the Earth persists invariable.

Chap. 3. On the magnetick diurnal revolution of the Earth's globe, as a probable assertion against the time-honoured opinion of a Primum Mobile.

Chap. 4. That the Earth moves circularly.

Chap. 5. Arguments of those denying the Earth's motion, and their confutation.

Chap. 6. On the cause of the definite time of an entire rotation of the Earth.

Chap. 7. On the primary magnetick nature of the Earth, whereby its poles are parted from the poles of the Ecliptick.

Chap. 8. On the Præcession of the Æquinoxes, from the magnetick motion of the poles of the Earth, in the Arctick & Antarctick circle of the Zodiack.

Chap. 9. On the anomaly of the Præcession of the Æquinoxes, & of the obliquity of the Zodiack.