William Gilbert of Colchester, Physician of London
William Gilbert of Colchester, Physician of London, on the Loadstone and Magnetic Bodies, and on The Great Magnet of the Earth. A New Physiology, Demonstrated with Many Arguments and Experiments "Electrica quae attrahunt eadem ratione ut electricum" A translation of De Magnete by P. Fleury Mottelay. The book also contains Mottelay's Biographical Memoir of Gilbert and an "Address" praising De Magnete, by Edward Wright, a mathematician, cartographer, and contemporary colleague of Gilbert. Published by John Wiley & Sons (1893).
Translator's Preface 
- In the words of the celebrated English mathematician, Edward Wright, I doubt not that our united efforts "will find the heartiest approval among all intelligent men and children of magnetic science."
- Not only does Gilbert frequently make use of what he terms "words new and unheard-of," besides attaching to many others a signification far different from that generally recognized at this day, but, what is worse, he retains to a great extent the terminology of the mediaeval scholastic philosophers.
- It is known that in the philosophy of the schoolmen (as in that of Aristotle) form—forma—means that which added to matter—materia—constitutes the true nature of the thing. Matter per se is indifferent, indefinite; form gives it definiteness. The earth is informed with verticity—that is its prime distinction. When any portion of the earth loses verticity it loses its forma—is deformate. To restore to it verticity, is to reformate it, or to informate it. Portions of the earth that are deformate are, as it were, effete, excrementitious, waste matter.
- England's great poet, John Dryden, tells us: "It is almost impossible to translate verbally and well at the same time; for the Latin (a most severe and compendious language) often expresses that in one word which either the barbarity or the narrowness of modern tongues cannot supply in more. ...But since every language is so full of its own proprieties that what is beautiful in one is often barbarous, nay, sometimes nonsense, in another, it would be unreasonable to limit a translator to the narrow compass of his author's words; it is enough if he choose out some expression which does not vitiate the sense."
Biographical Memoir 
- To give here such an analysis as Gilbert's admirable work merits would be impracticable but the short review of it made by Dr. John Robison deserves... reproduction as follows...
- See John Robison, System of Mechanical Philosophy (1822) Vol.4 p.209
- It is curious to mark the almost perfect sameness of Dr Gilbert's sentiments and language with those of Lord Bacon. They both charge, in a peremptory manner, all those who pretend to inform others, to give over their dialectic labours, which are nothing but ringing changes on a few trite truths, and many unfounded conjectures, and immediately to betake themselves to experiment."
- p.xvi (quoting John Robison)
- He has pursued this method on the subject of magnetism, with wonderful ardour, and with equal genius and success; for Dr. Gilbert was possessed both of great ingenuity, and a mind fitted for general views of things. The work contains a prodigious number and variety of observations and experiments, collected with sagacity from the writings of others, and instituted by himself with considerable expense and labour.
- p.xvi (quoting John Robison)
- It would indeed be a miracle if all Dr. Gilbert's general inferences were just, or all his experiments accurate. It was untrodden ground. But on the whole, this performance contains more real information than any writing of the age in which he lived, and is scarcely exceeded by any that has appeared since. We may hold it with justice as the first-fruits of the Baconian or experimental philosophy.
- p.xvi-xvii (quoting John Robison)
- This work of Dr Gilbert's relates chiefly to the loadstone, and what we call magnets; that is, pieces of steel which have acquired properties similar to those of the loadstone. But he extends the term magnetism and the epithet magnetic, to all bodies which are affected by loadstones and magnets, in a manner similar to that in which they affect each other. In the course of his investigations, indeed, he finds that these bodies are only such as contain iron in some state or other; and in proving this limitation he mentions a great variety of phenomena which have a considerable resemblance to those which he allows to be magnetical, namely, those which he called electrical, because they were produced in the same way that amber is made to attract and repel light bodies. He marks, with care, the distinctions between these and the characteristic phenomena of magnets. He seems to have known, that all bodies may be made electrical, while ferruginous substances alone can be made magnetical.
- p.xvii (quoting John Robison)
- It is not saying too much of this work of Dr. Gilbert's to affirm, that it contains almost everything that we know about magnetism. His unwearied diligence in searching every writing on the subject, and in getting information from navigators, and his incessant occupation in experiments, have left very few facts unknown to him.
- p.xvii (quoting John Robison)
- We ascribe it to the general indolence of mankind, who do not take the trouble of consulting originals, where things are mixed with others which they do not want, or treated in a way, and with a painful minuteness, which are no longer in fashion. We earnestly recommend it [De Magnete] to the perusal of the curious reader. He will (besides the philosophy) find more facts in it than in the two large folios of Scarella.
- p.xviii (quoting John Robison)
- The manner in which "this great man arrived to discover so much of magnetical philosophy" and "all the knowledge he got on this subject," we are told by Sir Kenelm Digby, "was by forming a little load-stone into the shape of the earth. By which means he compassed a wonderful designe, which was, to make the whole globe of the earth maniable; for he found the properties of the whole earth, in that little body; which he therefore called a terrella, or little earth; and which he could manage and try experiences upon, at his will. And in like manner, any man that hath an aim to advance much in natural sciences, must endeavour to draw the matter he enquireth, of into some small modell, or into some kinde of manageable method; which he may turn and wind as he pleaseth. And then let him be sure, if he hath a competent understanding, that he will not misse his mark."
- See Kenelm Digby, Treatise of Bodies (1645) Ch.20 p.225
- Amongst the many other ingenious contrivances frequently alluded to in his book, Gilbert mentions the versorium, an iron needle moving freely upon a point, with which he was enabled to measure excited electricity. He is besides the inventor of "two most ingenious and necessarie Instruments for Sea men to find out thereby the latitude of any place upon sea or land, in the darkest night, that is without the helpe of Sunne, Moone or Starre." These instruments are described in Thomas Blunderville's quarto work entitled "The Theoriques of the seven Planets, shewing their diverse motions... printed at London 1602."
- In the present volume will be found photo lithographic reproductions of three... title-pages. ...The 1628 is the most elaborate of all known Gilbert title-pages. As described by Prof. Sir Wm. Thomson (Lord Kelvin), it is "in the form of a monument, ornamented with commemorative illustrations of Gilbert's theory and experiments, and a fantastic indication of the earliest European mariner's compass, a floated loadstone, but floating in a bowl on the sea and left behind by the ship sailing away from it! In the upper left-hand corner is to be seen Gilbert's terrella and orbis virtutis. The terrella is a little globe of loadstone, which he made to illustrate his idea that the earth is a great globular magnet. ...The meaning of the little bars bordering the terrella is explained in Gilbert's book... where he alludes to the application of bits of fine iron wire as long as a barley-corn, etc., etc.
- The orbis virtutis is simply Gilbert's expression for what Faraday called the field of force, that is to say, the space round a magnet, in which magnetic force is sensibly exerted on another magnet, as, for instance, a small needle, properly placed for the test.
- Gilbert's word virtue expresses even more clearly than Faraday's word force the idea urged so finely by Faraday, and proved so validly by his magneto-optic experiment, that "there is a real physical action of a magnet through all the space round it tho' no other magnet be there to experience force and show its effects."
- The only known writing of Gilbert in English is in the form of a letter dated 14th Februrary (?1602) which appears at the end of William Barlowe's "Magneticall Advertisements or divers observations concerning the loadstone," quarto London 1616, and reads as follows: To the Worshipfull my good friend, Mr. William Barlowe at Easton by Winchester. "...you have shewed mee more—and brought more light than any man hath done. ...Johannes Franciscus Sagredus... a great Magneticall man... writeth that hee hath conferred with divers learned men of Venice and with the Readers of Padua and reporteth wonderfull liking of my booke, you shall have a coppy of the letter: Sir, I propose to adjoyne an appendix of six or eight sheets of paper to my booke after a while, I am in hand with it of some new inventions, and I would have some of your experiments, in your name and invention put into it, if you please, that you may be knowen for an augmenter of that art. So for this time in haste I take my leave the xiiyth of February. Your very loving friend, W. GILBERT." His intention to print the short appendix was never carried into effect.
- In his epistle to Dr. Walter Charleton (physician in ordinary to King Charles I), the celebrated English poet, John Dryden, predicts that "Gilbert shall live till loadstones cease to draw, Or British fleets the boundless ocean awe."
Address by Edward Wright 
- To the most learned Mr. William Gilbert, the distinguished London physician and father of the magnetic philosophy: a laudatory address concerning these books on magnetism, by Edward Wright.
- In truth, in my opinion, there is no subject-matter of higher importance or of greater utility to the human race upon which you could have brought your philosophical talents to bear. For by the God-given favor of this stone has it come about that the things which for so many centuries lay hid—such vast continents of the globe, so infinite a number of countries, islands, nations, and peoples—have been, almost within our own memory, easily discovered and oft explored, and that the whole circle of the globe has been circumnavigated more than once by our own Drake and Cavendish.
- Sailors of old were often beset, as we learn from the histories, by an incredible anxiety and by great peril, for, when storms raged and the sight of sun and stars was cut off, they knew not whither they were sailing, neither could they by any means or by any device find out.
- Since the magnetic pointer does not always regard the same northern spot in every locality, but usually varies therefrom, either to the east or to the west, tho' it nevertheless hath and holds ever the same variation in the same place, wherever that may be; it has come about that by means of this variation (as it is called) closely observed and noted in certain maritime regions, together with an observation of the latitude, the same places can afterward be found by navigators when they approach and come near to the same variation. ...Thanks to this magnetic indication, that ancient geographical problem, how to discover the longitude, would seem to be on the way to a solution.
- The iron pointer suspended freely and with the utmost precision in equilibrium on its axis, and then touched and excited with a loadstone, dips down to a fixed and definite point below the horizon (e.g. in the latitude of London it dips nearly 72 degrees) and there stands. But because of the wonderful agreement and congruency manifested in nearly all and singular magnetic experiments, equally in the earth itself and in a terrella, (i.e. a spherical loadstone), it seems (to say the least) highly probable and more than probable that the same pointer... will at the equator stand in equilibrium on the plane of the horizon.
- It is highly probable that in proceeding a very short distance from south to north (or vice versa) there will be a pretty sensible change in the dip; and thus the dip being carefully noted once and the latitude observed, the same place and the same latitude may thereafter be very readily found by means of a dip instrument even in the darkest night and in the thickest weather.
- If these books of yours on the Loadstone contained nought save this one method of finding the latitude from the magnetic dip, now first published by you, even so our British mariners as well as the French, the Dutch, the Danes, whenever they have to enter the British sea or the strait of Gibraltar from the Atlantic Ocean, will justly hold them worth no small sum of gold.
- Hardly twenty years after the English artificer, Robert Norman, had in 1576, devised the inclinatorium, which enabled him to determine the dip or inclination of the magnetic needle, Gilbert boasted that, by means of this instrument, he could ascertain a ship's place in dark starless nights. Gilbert commends the method as applicable aere caliginoso [dark atmosphere]; and Edward Knight, the English mathematician, in the introduction which he added to his master's great work, describes this proposal as "worth much gold." Having fallen into the same error with Gilbert of presuming that the isoclinal lines coincided with the geographical parallel circles, and that the magnetic and geographical equators were identical, he did not perceive that the proposed method had only a local and very limited application.
- See Humboldt, Cosmos (1849) Vol.1 p.172 and Vol.2 p.658
- Footnote to p.xl
- That discovery of yours, that the entire globe is magnetical, albeit to many it will seem to the last degree paradoxical, nevertheless is buttressed and confirmed by so many and so apposite experiments... that no room is left for doubt or contradiction.
- I come therefore to the cause of magnetic variation—a problem that till now has perplexed the minds of the learned; but no one ever set forth a cause more probable than the one proposed now for the first time in these your books on the Loadstone. The fact that the magnetic needle points due north in the middle of the ocean and in the heart of continents—or at least in the heart of their more massive and more elevated parts—while near the coasts there is, afloat and ashore, an inclination of the needle toward those more massive parts, just as happens in a terrella that is made to resemble the earth globe in its greater elevation at some parts and shows that it is weak or decayed or otherwise imperfect elsewhere: all this makes exceedingly probable the theory that the variation is nothing but a deviation of the magnetic needle to those more powerful and more elevated regions of the globe.
- All those who have imagined or accepted certain "respective points" as well as they who speak of magnetic mountains or rocks or poles, will begin to waver as soon as they read these your books on the Loadstone and will of their own accord come over to your opinion.
- As for... the circular motion of the earth and the terrestrial poles, though many will deem it the merest theorizing, still I do not see why it should not meet with indulgence even among those who do not acknowledge the earth's motion to be spherical, seeing that even they cannot readily extricate themselves from the many difficulties that result from a diurnal motion of the whole heavens.
- Which theory is the more probable, that the equinoctial circle of the earth may make a rotatary movement of one quarter of an English mile, (60 miles being equal to one degree on the earth's equator in one second of time... or that the equator of the primum mobile in the same time, with inexpressible celerity, makes 5,000 miles and that in the twinkling of an eye it makes about 50 English miles, surpassing the velocity of a flash of lightning, if they are in the right who most strenuously deny the earth's motion?
- It does not seem to have been the intention of Moses or the prophets to promulgate nice mathematical or physical distinctions: they rather adapt themselves to the understanding of the common people and to the current fashion of speech, as nurses do in dealing with babes.
- While we devoutly acknowledge and adore the inscrutable wisdom of the triune Godhead, having with all diligence investigated and discerned the wondrous work of his hands in the magnetic movements, do hold it to be entirely probable, on the ground of experiments and philosophical reasons not few, that the earth while it rests on its centre as its basis and foundation, hath a spherical motion nevertheless.
- Your work, I say, that has been kept back for so many years, your New Physiology of the Loadstone and of the Great Magnet (i.e. the Earth)—a philosophy never to be sufficiently admired; let it go forth into the light of publicity; for believe me... these your books on the Loadstone (De Magnete) will do more to perpetuate your memory than would the monument of any Magnate (Magnatis cujusvis) erected over your grave.
Author's Preface 
- Every day, in our experiments, novel, unheard-of properties came to light: and our Philosophy became so widened, as a result of diligent research, that we have attempted to set forth, according to magnetic principles, the inner constitution of the globe and its genuine substance, and in true demonstrations and in experiments that appeal plainly to the senses, as though we were pointing with the finger, to exhibit to mankind Earth, mother of all.
- Even as geometry rises from certain slight and readily understood foundations to the highest and most difficult demonstrations, whereby the ingenious mind ascends above the aether: so does our magnetic doctrine and science in due order first show forth certain facts of less rare occurrence; from these proceed facts of a more extraordinary kind; at length, in a sort of series, are revealed things most secret and privy in the earth, and the causes are recognized of things that, in the ignorance of those of old or through the heedlessness of the moderns, were unnoticed or disregarded.
- Why should I, in so vast an ocean of books whereby the minds of the studious are bemuddled and vexed; of books of the more stupid sort whereby the common herd and fellows without a spark of talent are made intoxicated, crazy, puffed up; are led to write numerous books and to profess themselves philosophers, physicians, mathematicians, and astrologers, the while ignoring and contemning men of learning: why, I say, should I add aught further to this confused world of writings, or why should I submit this noble and (as comprising many things before unheard) of this new and inadmissible philosophy to the judgment of men who have taken oath to follow the opinions of others, to the most senseless corrupters of the arts, to lettered clowns, grammatists, sophists, spouters, and the wrong-headed rabble to be denounced, torn to tatters, and heaped with contumely.
Explanation of some Terms used in this Work 
- Armed loadstone. One that is furnished with an iron helmet or cap.
- Cuspis (point). The end of a magnetized versorium.
- Crotch. Name sometimes given to the end not touched and excited, although in some instruments both ends are commonly so designated, according as they are most convenient for excitation by the loadstone.
- Declinatorium. A bar or needle movable vertically on its axis and that is excited with a loadstone; used in the dip instrument.
- Electrics. Bodies that attract in the same way as amber.
- Excited magnetic body. One such as iron or steel that acquires magnetism from a loadstone or natural magnet.
- Magnetic coition. This phrase is used rather than attraction because magnetic movements do not result from attraction of one body alone but from the coming together of two bodies harmoniously (not the drawing of one by the other)... the coition is always vigorous, even though heavy substances make opposition.
- Magnetized versorium. An iron bar or needle resting on a point (electroscope) and put in motion—excited—by the loadstone or natural magnet.
- Ostensio. Physical demonstration (opposed to theory).
- Paralleletically. In the direction of a parallel of latitude.
- Sphere of influence. The entire space over which the force of a loadstone extends.
- Sphere of coition. The entire space over which the smallest magnetic body moves toward a loadstone.
- Verticity. Polar strength—activity (or what in Gilbert's day was understood as energy); not gyrating, vertiginous, but turning power: nor is it polar revolution, but a directing virtue, an innate turning vigor (virtus convertens).