On the Magnet, by William Gilbert

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.


Gilbert’s glossary is practically an apology for the introduction into the Latin language of certain new words, such as the nouns terrella, versorium, and verticitas, and the adjectival noun magneticum, which either did not exist in classical Latin or had not the technical meaning which he now assigns to them. His terrella, or μικρόγη, as he explains in detail on p. 13, is a little magnetic model of the earth, but in the glossary he simply defines it as magnes globosus. Neither terrella nor versorium appears in any Latin dictionary. No older writer had used either word, though Peter Peregrinus (De Magnete, Augsburg, 1558) had described experiments with globular loadstones, and pivotted magnetic needles suitable for use in a compass had been known for nearly three centuries. Yet the pivotted needle was not denominated versorium. Blondo (De Ventis, Venice, 1546) does not use the term. Norman (The Newe Attractiue, London, 1581) speaks of the “needle or compasse,” and of the “wyre.” Barlowe (The Navigators Supply, London, 1597) speaks of the “flie,” or the “wier.” The term versorium (literally, the turn-about) is Gilbert’s own invention. It was at once adopted into the science, and appears in the treatises of Cabeus, Philosophia Magnetica (Ferrara, 1629), and of Kircher, Magnes sive de Arte Magnetica (Coloniæ, 1643), and other writers of the seventeenth century. Curiously enough, its adoption to denote the pivotted magnetic needle led to the growth of an erroneous suggestion that the mariners’ compass was known to the ancients because of the occurrence in the writings of Plautus of the term versoriam, or vorsoriam. This appears twice as the accusative case of a feminine noun versoria, or vorsoria, which was used to denote part of the gear of a ship used in tacking-about. Forcellini defines versoria as “funiculus quo extremus veli angulus religatur”; while versoriam capere is equivalent to “reverti,” or (metaphorically) “sententiam mutare.” The two passages in Plautus are:

Eut. Si huc item properes, ut istuc properas, facias rectius,
Huc secundus ventus nunc est; cape modo vorsoriam;
Hic Favonius serenu’st, istic Auster imbricus:
Hic facit tranquillitatem, iste omnes fluctus conciet.

(in Mercat. Act. V., sc. 2.)

Charm. Stasime, fac te propere celerem recipe te ad dominum domum;
. . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . . .
. . . . . . . . . . . . . . . . Cape vorsoriam
Recipe te ad herum.

(in Trinum. Act. IV., sc. 3.)

The word magneticum is also of Gilbert’s own coinage, as a noun; as an adjective it had been certainly used before, at least in its English form, magneticall, which appears on the title-page of William Borough’s Discourse of the Variation of the Compasse (London, 1596). Gilbert does not use anywhere the noun magnetismus, magnetism. The first use of that noun occurs in William Barlowe’s Magneticall Aduertisements (1616), in the Epistle Dedicatorie, wherein, when speaking of Dr. Gilbert, he says “vnto whom I communicated what I had obserued of my selfe, and what I had built vpon his foundation of the Magnetisme of the earth.” Gilbert speaks of the virtus magnetica, or vis magnetica; indeed, he has a rich vocabulary of terms, using, beside virtus and vis, vires, robur, potestas, potentia, efficientia, and vigor for that which we should now call magnetism or the magnetic forces. Nor does he use the verb magnetisare, or its participle, magnetisatus: he speaks of ferrum tactum, or of ferrum excitatum a magnete. In spite of certain obscurities which occur in places in his work, he certainly shows a nice appreciation of words and their use, and a knowledge of style. One finds occasionally direct quotations from, and overt references to, the classic authors, as in the references to Plato and Aristotle on page 1, and in the passage from the Georgics of Vergil on p. 21. But here and there one finds other traces of unmistakable scholarship, as in the reference to goat’s wool on p. 35, or in the use, on p. 210, of the word perplacet, which occurs in the letter of Cicero ad Atticum, or in that of commonstrabit, occurring on p. 203, and found only in Cicero, Terence and Plautus; whilst the phrase on p. 3, in which Gilbert rallies the smatterers on having lost both their oil and their pains, has a delightfully classical echo. The term orbis virtutis, defined by Gilbert in the glossary, and illustrated by the cuts on pages 76, 77, and 96, might be effectively translated by sphere of influence, or orbit within which there is sensible attraction. It has been preferred, however, to translate it literally as the orbe of virtue, or orbe of magnetick virtue. This choice has been determined by the desire to adopt such an English phrase as Gilbert would himself have used had he been writing English. T. Hood, writing in 1592 in his book The Vse of both the Globes, in using the word orbe, says that the word globe signifies a solid body, while a sphere is hollow, like two “dishes joyned by the brimme”; “The Latines properly call Orbis an Orbe”; “Moreouer the word Sphaera signifieth that instrument made of brasen hoopes (wee call it commonly a ringed Sphere) wherewith the Astronomers deliuer unto the nouices of that Science the vnderstanding of things which they imagine in the heauen.” Further, Dr. Marke Ridley in his Treatise of Magneticall Bodies and Motions (1613), has a chapter (XIIII) “Of the distance and Orbe of the Magnets vertue,” throughout which the term Orbe is retained. Sir Thomas Browne also writes of “the orb of their activities.”

The word Coitio, used by Gilbert for the mutual force between magnet and iron, has been retained in its English form, coition. Gilbert evidently adopted this term after much thought. The Newtonian conception of action and reaction being necessarily equal had not dawned upon the mediæval philosophers. The term attraction had been used in a limited sense to connote an action in which a force was conceived of as being exerted on one side only. Diogenes of Apollonia, Alexander Aphrodiseus, Democritus, and others, conceived the magnet to draw at the iron without the iron in any way contributing to that action. Saint Basil specially affirms that the magnet is not drawn by iron. On the other hand, Albertus Magnus had conceived the idea that the iron sought the magnet by a one-sided effort in which the magnet took no part. Gilbert had the wit to discern that the action was mutual, and to mark the new conception he adopted the new term, and defined it as it stands in his glossary. It is “a concourse or concordancy of both,” and to emphasize his meaning he adds, “not as if there were an ἑλκτικὴ δύναμις but a συνδρομή“ not a tractile power, but a running together. The adjective ἑλκτικὴ is obviously related to the verb ἕλκω, I draw: but its meaning puzzled the subsequent editors of the text, for in the two Stettin editions of 1628 and 1633, the phrase appears in the respective forms of ἑλητικὴ δύναμις and ἑλκυστικὴ δύναμις. In Creech’s English version of Lucretius (edition of 1722, p. 72a, in the footnote) is the commentary “Galen, disputing against Epicurus, uses the term ἑλκεῖν, which seems likewise too violent.” It may be noted that the same verb occurs in the passage from the Io of Plato quoted below. The term συνδρομή applied by Gilbert to explain his term Coitio is used by Diodorus for the mutual onset of two hostile forces.

A picturesque sentence from Sir Thomas Browne’s Pseudodoxia Epidemica (London, 1650, p. 51) sets the matter succinctly forth. “If in two skiffs of cork, a Loadstone and Steel be placed within the orb of their activities, the one doth not move the other standing still, but both hoist sayle and steer unto each other; so that if the Loadstone attract, the Steel hath also its attraction; for in this action the Alliency is reciprocall, which jointly felt, they mutually approach and run into each others arms.” The page and line references given in these notes are in all cases first to the Latin edition of 1600, and secondly to the English edition of 1900.


Last updated Sunday, March 27, 2016 at 11:54