De Magnete

William Gilbert

• Publisher: Dover Publications
• Year: 2013
• ISBN:
  9780486163017
• Topic: History
• Subtopic: Science History
• Index: History

Much of modern science is based upon the theories and discoveries of William Gilbert, the brilliant English physician and physicist who was the first great experimental scientist. Gilbert was the first to use the word "electricity, " to recognize mass as distinct from weight, to discover the effect of heat upon magnetic bodies, to differentiate clearly between static electricity and magnetism, and to explain phenomena of terrestrial magnetism in terms of the earth as a giant magnet.
In 1600 he published De Magnete in Latin. As lively and entertaining as it was scientifically scrupulous, it summarized everything that had previously been known about electricity and magnetism, founded a new science and earned Gilbert the title of "the father of modern electricity." In it Gilbert explores magnetism and electricity, lodestones, phenomena of magnetism, direction of the earth's magnetic lines of force, variation in the compass, dip, the concept of the earth as a giant magnet, and much else.
This Dover edition is a complete, unabridged reprinting of the definitive English translation of De Magnete prepared by Dr. P. Fleury Mottelay. Dr. Mottelay has added a number of footnotes that explain points that might be obscure to today's readers, who will find in this historically important text invaluable insights into the origins of modern science and physics. Translation by P. F. Mottelay. Biographical introduction. 90 illustrations.

BOOK SECOND.

CHAPTER I.

OF MAGNETIC MOVEMENTS.

OF opinions touching the loadstone and its varieties; of its poles and its recognized faculties (facultatibus); of iron and its properties; of the magnetic substance common to loadstone and iron and the earth itself,—we have treated briefly in the foregoing book. Now remain the magnetic movements and their broader philosophy as developed by experiments and demonstrations. These movements are impulsions of homogeneous parts toward one another or toward the primary conformation of the whole earth. Aristotle admits only two simple movements of his elements—from the centre and toward the centre ; light objects upward, heavy objects downward : so that in the earth there is but one motion of all its parts toward the centre of the world,—a wild headlong falling. We, however, will elsewhere consider what this ‘light’ may be, and will show how erroneously it is inferred by the Peripatetics from the simple motion of the elements; we shall also inquire what ‘heavy’ means.¹¹⁰ But now we have to inquire into the causes of the other movements depending on its true form : these we see clearly in all magnetic bodies; these also we find existing in the earth and all its homogenic parts; further, we find that they are in accord with the earth, and are bound up in its forces. Now five movements or differences of movement are perceived by us : COITION¹¹¹ (commonly called attraction), an impulsion to magnetic union; DIRECTION¹¹² toward the earth’s poles, and verticity of the earth toward determinate points in the universe, and the standstill there; VARIATION,¹¹³ deflection from the meridian,—this we call a perverted motion ; DECLINATION¹¹⁴ (inclination or dip), a descent of the magnetic pole beneath the horizon; and circular movement, or REVOLUTION.¹¹⁵ Of each of these we will treat separately, and will show how they all proceed from a congregant nature, or from verticity or from volubility. Jofrancus Offusius distinguishes several magnetic movements, the first to the centre, the second to the pole, traversing 77 degrees; the third to iron, the fourth to a loadstone. The first is not always to the centre, for only at the poles is it in a right line to the centre, if the motion is magnetic, otherwise it is only the movement of matter toward its mass and toward the earth. The second, of 77 degrees to the pole, is no movement, but a direction or a variation to the earth’s pole. The third and the fourth are magnetic, and are but one movement. Thus this author recognizes no true magnetic movement but coition toward iron or loadstone, commonly known as attraction. There is another movement in the earth as a whole, which does not take place toward the terrella or the parts, i.e., the movement of coacervation and that movement of matter called by philosophers a “right movement:” of that elsewhere.

CHAPTER II.

OF MAGNETIC COITION ; AND, FIRST, OF THE ATTRACTION EXERTED BY AMBER, OR MORE PROPERLY THE ATTACHMENT OF BODIES TO AMBER.

GREAT has ever been the fame of the loadstone and of amber in the writings of the learned: many philosophers cite the loadstone and also amber whenever, in explaining mysteries, their minds become obfuscated and reason can no farther go.¹¹⁶ Over-inquisitive theologians, too, seek to light up God’s mysteries and things beyond man’s understanding by means of the loadstone and amber: just as light-headed metaphysicians, when they utter and teach their vain imaginings, employ the loadstone as a sort of Delphic sword and as an illustration of all sorts of things. Medical men also (at the bidding of Galen), in proving that purgative medicines exercise attraction through likeness of substance and kinships of juices (a silly error and gratuitous !), bring in as a witness the loadstone, a substance of great authority and of noteworthy efficiency, and a body of no common order. Thus in very many affairs persons who plead for a cause the merits of which they cannot set forth, bring in as masked advocates the loadstone and amber. But all these, besides sharing the general misapprehension, are ignorant that the causes of the loadstone’s movements are very different from those which give to amber its properties; hence they easily fall into errors, and by their own imaginings are led farther and farther astray. For in other bodies is seen a considerable power of attraction, differing from that of the loadstone,—in amber, for example. Of this substance a few words must be said, to show the nature of the attachment of bodies to it, and to point out the vast difference between this and the magnetic actions; for men still continue in ignorance, and deem that inclination of bodies to amber to be an attraction, and comparable to the magnetic coition. The Greeks call this substance

λεκτρον, because, when heated by rubbing, it attracts to itself chaff ; whence it is also called

ρπαξ, and from its golden color, χρυσοφóρον.¹¹⁷ But the Moors call it carabe, because they used to offer it in sacrifices and in the worship of the gods ; for in Arabic carab means oblation, not rapiens paleas (snatching chaff), as Scaliger would have it, quoting from the Arabic or Persian of Abohali (Hali Abbas).¹¹⁸ Many call this substance ambra (amber), especially that which is brought from India and Ethiopia.¹¹⁹ The Latin name succinum appears to be formed from succus, juice.¹²⁰ The Sudavienses or Sudini call the substance geniter, as though genitum terra (produced by the earth). The erroneous opinion of the ancients as to its nature and source being exploded, it is certain that amber comes for the most part from the sea: it is gathered on the coast after heavy storms, in nets and through other means, by peasants, as by the Sudini of Prussia ; it is also sometimes found on the coast of our own Britain. But it seems to be produced in the earth and at considerable depth below its surface, like the rest of the bitumens ; then to be washed out by the sea-waves, and to gain consistency under the action of the sea and the saltness of its waters. For at first it was a soft and viscous matter, and hence contains, buried in its mass forevermore (œternis sepulchris relucentes), but still (shining) visible, flies, grubs, midges, and ants. The ancients as well as moderns tell (and their report is confined by experience) that amber attracts straws and chaff. The same is done by jet, a stone taken out of the earth in Britain, Germany, and many other regions: it is a hard concretion of black bitumen,—a sort of transformation of bitumen to stone. Many modern authors have written about amber and jet as attracting chaff and about other facts unknown to the generality, or have copied from other writers: with the results of their labors booksellers’ shops are crammed full. Our generation has produced many volumes about recondite, abstruse, and occult causes and wonders, and in all of them amber and jet are represented as attracting chaff ; but never a proof from experiments, never a demonstration do you find in them.¹²¹ The writers deal only in words that involve in thicker darkness subject-matter; they treat the subject esoterically, miracle-mongeringly, abstrusely, reconditely, mystically. Hence such philosophy bears no fruit; for it rests simply on a few Greek or unusual terms—just as our barbers toss off a few Latin words in the hearing of the ignorant rabble in token of their learning, and thus win reputation—bears no fruit, because few of the philosophers themselves are investigators, or have any first-hand acquaintance with things; most of them are indolent and untrained, add nothing to knowledge by their writings, and are blind to the things that might throw a light upon their reasonings. For not only do amber and (gagates or) jet,¹²² as they suppose, attract light corpuscles (substances) : the same is done by diamond, sapphire, carbuncle, iris stone, opal, amethyst, vincentina, English gem (Bristol stone, bristola ), beryl, rock crystal.¹²³ Like powers of attracting are possessed by glass, especially clear, brilliant glass; by artificial gems made of (paste) glass or rock crystal, antimony glass, many fluor-spars, and belemnites. Sulphur also attracts, and likewise mastich, and sealing-wax [of lac], hard resin, orpiment (weakly).¹²⁴ Feeble power of attraction is also possessed in favoring dry atmosphere by sal gemma [native chloride of sodium], mica, rock alum.¹²⁵ This we may observe when in mid-winter the atmosphere is very cold, clear, and thin; when the electrical effluvia of the earth offer less impediment, and ∗ electric bodies are harder: of all this later. These several bodies (electrics) not only draw to themselves straws and chaff, but all metals, wood, leaves, stones, earths, even water and oil ; in short, whatever things appeal to our senses or are solid : yet we are told that it attracts nothing but chaff and twigs. Hence Alexander Aphrodiseus incorrectly declares the question of amber to be unsolvable, because that amber does attract chaff, yet not the leaves of basil ; but such stories are false, disgracefully inaccurate.¹²⁶ Now in order clearly to understand by experience how such attraction takes place, and what those substances may be that so attract other bodies (and in the case of many of these electrical substances, though the bodies influenced by them lean toward them, yet because of the feebleness of the attraction they are not drawn clean up to them, but are easily made to rise), make yourself a rotating-needle (electroscope—versorium) of any sort of metal,¹²⁷ three or four fingers long, pretty light, and poised on a sharp point after the manner of a magnetic pointer. Bring near to one end of it a piece of amber or a gem, lightly rubbed, polished and shining : at once the instrument revolves. Several objects are seen to attract not only natural objects, but things artificially prepared, or manufactured, or formed by mixture. Nor is this a rare property possessed by one object or two (as is commonly supposed), but evidently belongs to a multitude of objects, both simple and compound, e.g., sealing-wax and other unctuous mixtures. But why this inclination and what these forces,—on which points a few writers have given a very small amount of information, while the common run of philosophers give us nothing,—these questions must be considered fully. Galen recognizes in all three kinds of attractions in nature : first, the attraction exercised by those bodies which attract by an elemental quality—heat, to wit ; secondly, by those which attract by the in-rush into a vacuum ; thirdly, by those which attract through a property pertaining to their entire mass: and these three kinds are enumerated by Avicenna and others. This division cannot by any means content us, nor does it define the causes (causas) of amber, jet, diamond, and other like substances, which owe to the same virtue the forces they possess; nor of loadstone or of other magnetic bodies, which possess a force altogether different from that of those other bodies, both in its efficiency and in the sources whence it is derived. We must, therefore, find other causes of movements, or must with these stray about as it were in darkness, never at all reaching our goal. Now amber does not attract by heat, for when heated at a fire and brought near to straws, whether it is merely warm, or whether it is hot, even burning hot, or even brought to the flaming point, it has no attraction. Cardan (and Pictorius too) is of opinion that the attraction of amber is much like that seen in the cupping-glass: yet the attractional force of the cupping-glass does not really come from igneous force; but he had already said that a dry body is eager to drink up one that is moist and juicy, and therefore such bodies are drawn to it. These two explications are inconsistent, and they are without ground in reason also. For were amber to move toward its sustenance, or other bodies to turn to amber, as to their food, the one, being swallowed up, would disappear, while the other would increase in size. And then why seek in amber the attractive force of fire? If fire attracts, why do not many other bodies heated by the fire, the sun, or by friction attract also? Nor can attraction, because of air displaced, occur in open air, though this is the cause Lucretius assigns for magnetic movements; nor in the cupping-glass can heat or fire feeding on the air attract: the air in the cupping-glass rarefied to flame, when again it becomes dense and is compressed into small space, causes the skin and flesh to rise, because nature avoids a vacuum. In open air, heated objects cannot attract, not even metals or stones brought to a very high temperature by fire. For an iron rod at white heat, a flame, a candle, a flaming torch, or a red-hot coal when brought near to straws or to a revolving pointer (versorium) does not attract; and yet plainly all these cause the air to come to them in a current, for they consume air as a lamp consumes oil. But of heat, and how very different is the view held by the whole crowd of the philosophers, as to its attractive power in natural bodies and materia medica, from the fact as seen in nature, we will treat elsewhere when we come to explain what heat and cold really are. They are very general properties or close appurtenances of substances, but are not called true causes; and if I may use the expression, they utter certain words, but in fact they show nothing specifically. Nor does the supposed attractive force of amber arise from any peculiar property of its substance or from any special relation between it and other bodies; for in many other substances, if we but search with any diligence, we see the same effect, and, by them, all other bodies, of whatever properties possessed, are attracted. And likeness is not the cause of amber’s attracting, for all things that we see on the globe, whether similar or dissimilar, are attracted by amber and such like ; hence no strong analogy is to be drawn either from likeness or from identity of substan...

Table of contents

• Title Page
• Copyright Page
• TRANSLATOR’S PREFACE.
• BIOGRAPHICAL MEMOIR.
• Table of Contents
• AUTHOR’S PREFACE. - TO THE CANDID READER, STUDIOUS OF THE MAGNETIC PHILOSOPHY.
• EXPLANATION OF SOME TERMS USED IN THIS WORK.
• BOOK FIRST.
• BOOK SECOND.
• BOOK III.
• BOOK IV.
• BOOK V.
• BOOK VI.
• GENERAL INDEX.