William Gilbert Writes about the Loadstone

William Gilbert's De Magnete, Book One, part 1

In the post Galileo Discusses Magnetism, I showed how Galileo used the results presented in William Gilbert’s De Magnete (On the Magnet¹) to dismantle the Aristotelian arguments put forward against earthly motion. I also mentioned in that same post that I would address the contents of the De Magnete in future posts. In preparation for this series, I have already published two posts:

• On Little Earths and Little Suns

• De Magnete, Nothing Less than the First Ever Work of Experimental Physics

The De Magnete consists of six books, each of which consists of a varying number of chapters. In this post, I will focus on Book One.

In this book, Gilbert introduces key concepts that will be used in the experiments presented in the remaining books. In particular, he discusses at length the loadstone, where it comes from, and its relationship to the Earth. The word loadstone, also spelt lodestone, comes from the Middle English lode (“guide”) + stone, and was first used for a guide tool for mariners.

Gilbert begins by explaining that the loadstone was first discovered by miners who wished to make iron, and who noticed that the loadstone attracts iron. He then gives an extensive overview of writings about the loadstone from antiquity through the Middle Ages. He explains that according to Plato in his dialogue Io, Euripides called the loadstone a magnet. As Gilbert narrates previous writings, he explains that many of these are completely fanciful:

The like of this is found in Pliny, and in Ptolemy's Quadripartitum; and errors have steadily been spread abroad and been accepted — even as evil and noxious plants ever the most luxuriant growth — down to our day, being propagated in the writings of many authors who, to the end that their volumes might grow to the desired bulk, do write and copy all sorts about ever so many things about which they know naught for certain in the light of experience. [pp.2-3]

Among the more serious ancient speculations, Gilbert mentions that Lucretius (99 BCE - 55 BCE), the author of De rerum natura (On the Nature of Things) and one of antiquity’s leading proponents of atomism, proposed a local-motion model of magnetism:

Lucretius Carus, the Epicurean poet, deems the attraction to be due to this, that as there is from all things an efflux of minutest bodies, so there is from iron efflux of atoms into the space betwixt the iron and the loadstone — a space emptied of air by the loadstone's atoms (seeds); and when these being to return to the loadstone, the iron follows, the corpuscles being entangled with each other. [p.5]

Plato, on the other hand, “holds the magnetic virtue to be divine.” [p.5] This is one way of describing action-at-a-distance. So we can see that even in antiquity, this debate between local-motion and action-at-a-distance was very much alive.

Interest for the loadstone increased dramatically with the discovery of the magnetic moment to the north and south:

But when, some three or four hundred years ago, the magnetic movement to the north and the south was discovered or recognized anew, many learned men, each according to his own gifts, strove to honor with admiration and praise or to explain with feeble reasonings a property so curious and so necessary for the use of mankind. [p.5]

This discovery, of course, led to the mariner’s compass, whose importance is underlined by Gilbert:

And that nothing ever has been contrived by the art of man nor anything been of greater advantage to human race than the mariner's compass is certain: but many infer from ancient writings and from certain arguments and conjectures, that the compass was discovered earlier and received among the arts of navigation. [p.8]

As the European “Age of Discovery” of the rest of the world advanced, and as instruments became more precise, it became clear that the needle of a compass did not necessarily point exactly due north and due south:

Sebastian Cabot first discovered that the magnetized iron (needle) varied. [p.8]

In P. Fleury Mottelay’s English translation of De Magnete, there is a footnote to the above line, providing further information:

At page 150 of the 1869 London edition of Mr. J. F. Nicholls' Life of Seb. Cabot, it is said the latter represented to the King of England that the variation of the compass was different in many places, and was not absolutely regulated by distance from any particular meridian; also, that he could point to a spot of no variation, and that those whom he trained as seamen, as Chancellor and Stephen Burrough were particularly attentive to this problem, noting it at one time thrice within a short space. (“Biddle,” Memoir of Sebastian Cabot, 1831; Humboldt, in both his “Examen Critique” and his “Cosmos,” treating of “Oceanic Discoveries”). [p.8, n.1]

Since the compass was so important for navigation, magnetic variation, also known today as magnetic declination, was of serious concern to mariners, and Gilbert mentions several men who wrote about it:

There are other learned men who on long sea voyages have observed the differences of magnetic variation; as that most accomplished scholar Thomas Hariot, Robert Hues, Edward Wright, Abraham Kendall, all Englishmen; other have invented and published magnetic instruments and ready methods of observing, necessary for mariners and those who make long voyages: as William Borough in his little work the Variation of the Compass, William Barlo (Barlowe) in his Supplement, Robert Norman in his New Attractive — the same Robert Norman, skilled navigator and ingenious artificer, who first discovered the dip of the magnetic needle. [pp.14-15]

Once these key concepts have been introduced, the first chapter of Book One ends with a summary of the overall objective of De Magnete:

But when the nature of the loadstone shall have been in the discourse following disclosed, and shall have been by our labors and experiments tested, then will the hidden and recondite but real causes of this great effect be brought forward, proven, shown, demonstrated; then, too, will all darkness vanish; every smallest root of errors, being plucked up, will be cast away and will be neglected; and the foundations, of a grand magnetic science being laid will appear anew, so that high intellects may no more be deluded by vain opinions.

The following chapters present different aspects of loadstone and iron. Gilbert explains how loadstone can be found around the world, in many different forms, and with many different names. And, despite the numerous writings thereon, the loadstone has in fact been little studied:

The Egyptians, as Manetho related, give it the name of ‘the bone of Horus,’ calling the potency that presides over the revolution of the sun Horus, as the Greeks called it Apollo. But later, as Plato declares, Euripides gave to it the name magnet. It is mentioned and praised by Plato in the Io, by Nicander of Colophon, Theophrastus, Dioscorides, Pliny, Solinus, Ptolemy, Galen, and other investigators of nature. But considering the great differences of loadstones, their dissimilitude in hardness, softness, heaviness, lightness, density, firmness, friableness: in color and in all other qualities: these writers have not handed down any sufficient account of it. The history of the magnet was overlooked by them, or, if written, was incompletely given... [p.17]

Gilbert adds that the diversity of loadstones is probably greater than is currently known, claiming that loadstones of lower strength are probably everywhere:

[F]or in every clime, in every province, in all kinds of land, either the loadstone is found or lies unknown because of its deep site or its inaccessible situation; or, because of its weaker and less potent virtues, it is not recognized by us the while we see it and touch it. [p.18]

Most important for the purpose of his study, however, is that the best loadstones are found in iron mines, and when smelted, produce the best quality steel:

A strong loadstone and one that under experiment resembles unpolished iron and usually is found in iron mines: sometimes it is found also forming a continuous vein by itself:... [p.18]

The metallic loadstones are those which are smelted into the best of iron; the rest are not easily smelted, but are burnt. [p.19]

Gilbert then explains that a loadstone has north and south poles, as does the earth. Therefore it is possible to simulate the magnetism of the earth by creating a miniature earth, called a terrella. I discussed this topic in more detail in the two previous posts, linked above.

The first experiment that Gilbert describes is how to determine which pole of a loadstone is north (boreal) and which is south (austral). The idea is to put the loadstone in a light floating vessel in a bath of water, and to let the vessel move freely. It will naturally turn so that the south pole of the loadstone points north:

[T]here the stone, as if in a boat floating in the middle of an unruffled surface of still water, will straightaway set itself, and the vessel containing it in motion, and will turn in a circle till its south pole shall face north, and its north pole, south. [p.26]

It should be noted that Gilbert’s conclusion was directly in contradiction with the accepted view of the day:

Further, it is to be remembered that all who hitherto have written about the poles of the loadstone, all instrument-makers, and navigators, are egregiously mistaken in taking for the north pole of the loadstone the part of the stone that inclines to the north, and for the south pole the part that looks to the south: this will hereafter prove to be an error. So ill-cultivated is the whole philosophy of the magnet still, even as regards its elementary principles. [p.27]

Gilbert’s conclusion is confirmed by the next experiment: if two loadstones are brought together, one fixed with north (south) pole pointing to the other, the second in a boat, the second will spin around until the south (north) pole points to the first. Furthermore, if a loadstone is cut near its equator, then the southern part of the northern half becomes a south pole, and the northern part of the southern half becomes a north pole, and the two halves will attempt to reunite if brought sufficiently close to each other.

In like manner, if you oppose the north pole of the stone in your hand to the south pole of the floating one, they come together and follow each other. For opposite poles attract opposite poles. But, now, if in the same way you present N. to N. or S. to S., one stone repels the other; and as though a helmsman were bearing on the rudder if is off like a vessel making all sail, nor stands nor stays as long as the other stone pursues. [pp.28-29]

Furthermore, in one same stone we are thus able to demonstrate all this: but also we are able to show how the self-same part of one stone may by division become either north or south. [pp.29-30]

Gilbert then changes his focus from the loadstone to iron. He explains that a loadstone attracts iron, and that this attraction varies in accordance to the quality of the iron:

The most potent virtue of the loadstone and the one valued by the ancients is the attraction for iron; for Plato mentions that the magnet, so called by Euripides, draws to itself iron, and not only attracts iron rings but also endows them with the power of doing as the stone itself, to wit, of attracting other rings, and that thus sometimes a long chain of iron objects, as nails, or rings, is made, the several parts hanging from one another. [pp.31-32]

The best iron (such as that which from its uses is called acies, and from the country of the Chalybes, chalybs) is most readily and strongly attracted by a good magnet; but inferior iron, iron that is impure, rusty, not well purged of dross, and not worked over in the second furnace is attracted more weakly; and any iron is more faintly attracted more weakly; and any iron is more faintly attracted if covered and smeared with thick, greasy, tenacious fluids. [p.32]

These comments about the attraction between the loadstone and iron lead naturally to a discussion about iron itself, and where iron might be found. This discussion is vitally important, as it will lead Gilbert to assert that nowhere is Aristotle’s element ‘earth’ to be found, and will be the focus of a separate post.

---

If you wish to donate to support my work, please use the Buy Me a Coffee app.

1. W. Gilbert. De Magnete. Dover, New York, 1958. Translation by P. Fleury Mottelay of De Magnete, first published in 1600.