Contributions from

the Museum of History and Technology:

Paper 8

The Natural Philosophy of
William Gilbert and His Predecessors

W. James King

By W. James King

THE NATURAL PHILOSOPHY OF

WILLIAM GILBERT

AND HIS PREDECESSORS

The year 1600 saw the publication by an English physician, William Gilbert, of a book on the loadstone. Entitled De magnete,[1] it has traditionally been credited with laying a foundation for the modern science of electricity and magnetism. The following essay is an attempt to examine the basis for such a tradition by determining what Gilbert's original contributions to these sciences were, and to make explicit the sense in which he may be considered as being dependent upon earlier work. In this manner a more accurate estimate of his position in the history of science may be made.

One criterion as to the book's significance in the history of science can be applied almost immediately. A number of historians have pointed to the introduction of numbers and geometry as marking a watershed between the modern and the medieval understanding of nature. Thus A. Koyré considers the Archimedeanization of space as one of the necessary features of the development of modern astronomy and physics.[2] A. N. Whitehead and E. Cassirer have turned to measurement and the quantification of force as marking this transition.[3] However, the obvious absence[4] of such techniques in De magnete makes it difficult to consider Gilbert as a founder of modern electricity and magnetism in this sense.

There is another sense in which it is possible to contend that Gilbert's treatise introduced modern studies in these fields. He has frequently been credited with the introduction of the inductive method based upon stubborn facts, in contrast to the methods and content of medieval Aristotelianism.[5] No science can be based upon faulty observations and certainly much of De magnete was devoted to the destruction of the fantastic tales and occult sympathies of the Romans, the medieval writers, and the Renaissance. However, let us also remember that Gilbert added few novel empirical facts of a fundamental nature to previous observations on the loadstone. Gilbert's experimental work was in large part an expansion of Petrus Peregrinus' De magnete of 1269,[6] and a development of works like Robert Norman's The new attractive,[7] in which the author discussed how one could show experimentally the declination and inclination of a magnetized needle, and like William Borough's Discourse on the variation of the compass or magnetized needle,[8] in which the author suggested the use of magnetic declination and inclination for navigational purposes but felt too little was known about it. That other sea-going nations had been considering using the properties of the magnetic compass to solve their problems of navigation in the same manner can be seen from Simon Stevin's De havenvinding.[9]

Instead of new experimental information, Gilbert's major contribution to natural philosophy was that revealed in the title of his book—a new philosophy of nature, or physiology, as he called it, after the early Greeks. Gilbert's attempt to organize the mass of empirical information and speculation that came from scholars and artisans, from chart and instrument makers, made him "the father of the magnetic Philosophy."[10]

Gilbert's De magnete was not the first attempt to determine the nature of the loadstone and to explain how it could influence other loadstones or iron. It is typical of Greek philosophy that one of the first references we have to the loadstone is not to its properties but to the problem of how to explain these properties. Aristotle[11] preserved the solution of the first of the Ionian physiologists: "Thales too ... seems to suppose that the soul is in a sense the cause of movement, since he says that a stone has a soul because it causes movement to iron." Plato turned to a similar animistic explanation in his dialogue, Ion.[12] Such an animistic solution pervaded many of the later explanations.

That a mechanical explanation is also possible was shown by Plato in his Timaeus.[13] He argued that since a vacuum does not exist, there must be a plenum throughout all space. Motion of this plenum can carry objects along with it, and one could in this manner explain attractions like that due to amber and the loadstone.

Another mechanical explanation was based upon a postulated tendency of atoms to move into a vacuum rather than upon the latter's non-existence. Lucretius restated this Epicurean explanation in his De rerum natura.[14] Atoms from the loadstone push away the air and tend to cause a vacuum to form outside the loadstone. The structure of iron is such that it, unlike other materials, can be pushed into this empty space by the thronging atoms of air beyond it.

Galen[15] returned to a quasi-animistic solution in his denial of Epicurus' argument, which he stated somewhat differently from Lucretius. One can infer that Galen held that all things have, to a greater or lesser degree, a sympathetic faculty of attracting its specific, or proper, quality to itself.[16] The loadstone is only an inanimate example of what one finds in nutritive organs in organic beings.

One of the few writers whose explanations of the loadstone Gilbert mentioned with approval is St. Thomas Aquinas. Although the medieval scholastic philosophy of St. Thomas seems foreign to our way of thinking, it formed a background to many of Gilbert's concepts, as well as to those of his predecessors, and it will assist our discussion to consider briefly Thomist philosophy and to make its terminology explicit at this point.[17]

In scholastic philosophy, all beings and substances are a coalescence of inchoate matter and enacting form. Form is that which gives being to matter and which is responsible for the "virtus" or power to cause change, since matter in itself is inert. Moreover, forms can be grasped intellectually, whence the nature of a being or a substance can be known. Any explanation of phenomena has to be based upon these innate natures, for only if the nature of a substance is known can its properties be understood. Inanimate natures are determined by observation, abstraction, and induction, or by classification.[18]

The nature of a substance is causally prior to its properties; while the definition of the nature is logically prior to these properties. Thus, what we call the theory of a substance is expressed in its definition, and its properties can be deduced from this definition.

The world of St. Thomas is not a static one, but one of the Aristotelian motions of quantity (change of size), of quality (alteration), and of place (locomotion). Another kind of change is that of substance, called generation and corruption, but this is a mutation, occurring instantly, rather than a motion, that requires time. In mutation the essential nature is replaced by a new substantial form.

All these changes are motivated by a causal hierarchy that extends from the First Cause, the "Dator Formarum," or Creator, to separate intellectual substances that may be angels or demons, to the celestial bodies that are the "generantia" of the substantial forms of the elements and finally to the four prime qualities (dry and wet, hot and cold) of the substantial forms. Accidental forms are motivated by the substantial forms through the instrumentality of the four prime qualities, which can only act by material contact.

The only causal agents in this hierarchy that are learned through the senses are the tangible qualities. Usually the prime qualities are not observed directly, but only other qualities compounded of them. One of the problems of scholastic philosophy was the incorporation, into this system of efficient agents, of other qualities, such as the qualities of gravity and levity that are responsible for upward and downward motion.

Besides the causal hierarchy of forms, the natural world of St. Thomas existed in a substantial and spatial hierarchy. All substances whether an element or a mixture of elements have a place in this hierarchy by virtue of their nature. If the material were removed from its proper place, it would tend to return. In this manner is obtained the natural downward motion of earth and the natural upward motion of fire.

Local motion can also be caused by the "virtus coeli" generating a new form, or through the qualitative change of alteration. Since each element and mixture has its own natural place in the hierarchy of material substances, and this place is determined by its nature, changes of nature due to a change of the form can produce local motion. If before change the substance is in its natural place, it need not be afterwards, and if not, would then tend to move to its new natural place.

It will be noted that the scholastic explanation of inanimate motion involved the action and passion of an active external mover and a passive capacity to be moved. Whence the definition of motion that Descartes[19] was later to deride, "motus est actus entis in potentia prout quod in potentia."

We have seen above that the "motor essentialis" for terrestial change is the "virtus coeli." Thus the enacting source of all motion and change is the heavens and the heavenly powers, while the earth and its inhabitants becomes the focus or passive recipient of these actions. In this manner the scholastic restated in philosophical terms the drama of an earth-centered universe.

Although change or motion is normally effected through the above mentioned causal hierarchy, it is not always necessary that actualization pass from the First Cause down through each step of the hierarchy to terminate in the qualities of the individual being. Some of the steps could be by-passed: for instance man's body is under the direct influence of the celestial bodies, his intellect under that of the angels and his will under God.[20] Another example of effects not produced through the tangible prime qualities is that of the tide-producing influence of the moon on the waters of the ocean or the powers of the loadstone over iron. Such causal relations, where some members of the normal causal chain have been circumvented, are called occult.[21]

While St. Thomas referred to the loadstone in a number of places as something whose nature and occult properties are well known, it was always as an example or as a tangential reference. One does not find a systematic treatment of the loadstone in St. Thomas, but there are enough references to provide a fairly explicit statement of what he considered to be the nature of the magnet.

In one of his earliest writings, St. Thomas argued that the magnet attracts iron because this is a necessary consequence of its nature.[22]

Due to its generic form, the loadstone is subject to natural motion of place of up and down. However, the "virtus" of its specific form enabled it to produce another kind of motion—it could draw iron to itself.

Normally the "virtus" of a substance is limited to those contact effects that could be produced by the form operating through the active qualities of one substance, on the relatively passive qualities of another. St. Thomas asserted the loadstone to be one of these minerals, the occult powers of whose form goes beyond those of the prime qualities.[23]

That this occult power of the loadstone is a result of the direct influence of the "virtus coeli" was expounded at greater length in his treatise on the soul.[24]

St. Thomas placed the form of the magnet and its powers in the hierarchy of forms intermediate between the forms of the inanimate world and the forms of the organic world with its hierarchy of plant, animal and rational souls. The form of the loadstone is then superior to that of iron, which can only act through its active and passive qualities, but inferior to the plant soul, that has the powers of growth from the "virtus coeli." This is similar to Galen's comparison of the magnet's powers to that of the nutritive powers of organic bodies.

In his commentary on Aristotle's Physics, St. Thomas explained how iron is moved to the magnet. It is moved by some quality imparted to the iron by the magnet.[25]

As the "generans" of terrestrial change moves what is light and heavy to another place by implanting a new form in a substance, so the magnet moves the iron by impressing upon it the quality by which it is moved. By virtue of the new quality, the iron is not in its natural place and moves accordingly. St. Thomas proved that the loadstone acts as a secondary "generans" in three ways: (1) the loadstone produces an effect not from any distance but only from a nearby position (showing that this motion is due to more than place alone), (2) rubbing the loadstone with garlic acts as if it impedes or alters the "virtus magnetis," and (3) the iron must be properly aligned with respect to the loadstone in order to be moved, especially if the loadstone is small. Thus the iron is moved by the magnet not only to a place, but also by changing and altering it: one has not only the change of locomotion but that of alteration. Moreover the source of this alteration in the iron is not the heavens but the loadstone. Accordingly the loadstone could cause change in another substance because it could influence the nature of the other substance.

About the time that St. Thomas was writing his letter De operationibus occultis naturae to a certain knight, Petrus Peregrinus was writing from a military camp a letter in which he showed how certain relatively new effects could be produced by the loadstone. He was more interested in what he could do with the magnet than in explaining these effects. However, he discussed it at sufficient length for one to find that his explanation of magnetic phenomena was basically similar to that of his contemporary, St. Thomas.

Peregrinus based his discussion of the loadstone upon its nature and analyzed magnetic phenomena in terms of the change of alteration. In magnetic attraction, the nature of the iron is altered by having a new quality impressed upon it,[26] and the loadstone is the agent that makes the iron the same species as the stone.[27]

This impressed similarity to the agent, Peregrinus realized, is not a pole of the same polarity but one opposite to that of the inducing pole. To produce this effect, the virtue of the stronger agent dominates the weaker patient and impresses the virtue of the stronger on the weaker so that they are made similar.[28]

A further instance of alteration occurs in the reversal of polarity of magnetized iron when one brings two similar poles together. Again, the stronger agent dominates the weaker patient and the iron is left with a similarity to the last agent.[29]

In this assimilation of the agent to the patient, another effect is produced: the agent not only desires to assimilate the patient to itself, but to unite with it to become one and the same. Speaking of the motion to come together, he says:[30]

The nature of the magnet, as an active cause, tends to enact, and since it acts in the best manner in which it is able, it acts so as to preserve the similarities of opposite poles.[31]

Thus unlike poles tend to come together when a dissected magnet is reassembled.

Like St. Thomas, Peregrinus argued that the magnet receives its powers from the heavens. But he further specified this by declaring that different virtues from the different parts of the heavens flow into their counterpart in the loadstone—from the poles of the heavens the virtue flows into the poles of the magnet,[32]

and similarly for the other parts of the heavens and the other parts of the loadstone.[33]

Physical proof for such influences was adduced by Peregrinus from the motions of the loadstone. That the poles of the loadstone receive their virtue from the poles of the heavens follows experimentally from north-south alignment of a loadstone. That not only the poles but the entire loadstone receives power from corresponding portions of the heavens follows from the fact that a spherical loadstone, when "properly balanced," would follow the motion of the heavens.[34]

As the heavens move eternally, so the spherical loadstone must be a "perpetuum mobile".

Another of the scholars whose explanation of the loadstone Gilbert noted with approval was Cardinal Nicholas of Cusa.[35] The latter's references to it were not as direct as those of St. Thomas, but he did use it as an image several times to provide a microcosmic example of the relation of God to his creation. From this one can infer that he explained the preternatural motion of the magnet and the iron by impressed qualities, the heavens being the agent for the loadstone, and the loadstone, the agent for iron.

In the Idiota de sapientia the Cardinal used the image of the magnet and the iron to provide a concrete instance of his "coincidentia oppositorum," to illustrate how eternal wisdom, in the Neoplatonic sense, could, at the same time, be principle or cause of being, its complement and also its goal.[36]

By virtue of the principle that flows from the magnet to the iron—which principle is potentially in the iron, for the iron already has a foretaste for it—the excited iron could transcend its gravid nature and be preternaturally moved to unite with its principle. Reciprocally, the loadstone has a greater attraction to the iron than to other things. Just as the power of attraction comes from the loadstone, so the Deity is the source of our life. Just as the principle implanted in the magnet moves the iron against its heavy nature, so the Deity raises us above our brutish nature so that we may fulfill our life. As the iron moves to the loadstone, so we move to the Deity as to the goal and end of our life.

In De pace fidei, Cusa[37] again used the iron and magnet as an example of motion contrary to and transcending nature. He explained this supernatural motion as being due to the similarity between the nature of the iron and the magnet, and this in turn is analogous to the similarity between human spiritual nature and divine spiritual nature. As the iron can move upward to the loadstone because both have similar natures, so man can transcend his own nature and move towards God when his potential similitude to God is realized. Another image used by Cusa was the comparison of Christ to the magnetic needle that takes its power from the heavens and shows man his way.[38]

The Elizabethan Englishman Robert Norman also turned to the Deity to explain the wonderful effects of the loadstone.[39]

Again, one can infer that the heavens impart a guiding principle to the iron which acts under the influence of this Superior Cause.

One of the points made in St. Thomas' argument on motion due to the loadstone was that there is a limit to the "virtus" of the loadstone, but he did not specify the nature of it. Norman refined the Thomist concept of a bound by making it spherical in form, foreshadowing Gilbert's "orbis virtutis."

Gilbert's philosophy of nature does not move far from scholastic philosophy, except away from it in logical consistency. As the concern of Aristotle and of St. Thomas was to understand being and change by determining the nature of things, so Gilbert sought to write a logos of the physis, or nature, of the loadstone—a physiology.[40] This physiology was not formally arranged into definitions obtained by induction from experience, but nevertheless there was the same search for the quiddity of the loadstone. Once one knew this nature then all the properties of the loadstone could be understood.

Gilbert described the nature of the loadstone in the terms of being that were current with his scholarly contemporaries. This was the same ontology that scholasticism had taught for centuries—the doctrine of form and matter that we have already found in St. Thomas and Nicholas of Cusa. Thus we find Richard Hooker[41] remarking that form gives being and that "form in other creatures is a thing proportionable unto the soul in living creatures." Francis Bacon,[42] in speaking of the relations between causes and the kinds of philosophy, said: "Physics is the science that deals with efficient and material causes while Metaphysics deals with formal and final causes." John Donne[43] expressed the problem of scholastic philosophy succinctly:

As we shall see, Gilbert continued in the same tradition, but his interpretation of form and formal cause was much more anthropomorphic than that of his predecessors.

Gilbert began his De magnete by expounding the natural history of that portion of the earth with which we are familiar.[44]

His treatment of the origin of minerals and rocks agreed in the main with that of Aristotle,[45] but he departed somewhat from the peripatetic doctrine of the four elements of fire, air, water, and earth.[46] Instead, he replaced them by a pair of elements.[47] (If the rejection of the four Aristotelian elements were clearer, one might consider this a part of his rejection of the geocentric universe but he did not define his position sufficiently.)[48]

According to Gilbert the primary source of matter is the interior of the earth, where exhalations and "spiritus" arise from the bowels of the earth and condense in the earth's veins.[49] If the condensations, or humors, are homogeneous, they constitute the "materia prima" of metals.[50] From this "materia prima," various metals may be produced,[51] according to the particular humor and the specificating nature of the place of condensation.[52] The purest condensation is iron: "In iron is earth in its true and genuine nature."[53] In other metals, we have instead of earth, "condensed and fixed salts, which are efflorescences of the earth."[54] If the condensed exhalation is mixed in the vein with foreign earths already present, it forms ores that must be smelted to free the original metal from dross by fire.[55] If these exhalations should happen to pass into the open air, instead of being condensed in the earth, they may return to the earth in a (meteoric) shower of iron.[56]

Gilbert was indeed writing a new physiology, both in the ancient sense of the word and the modern. The process of the formation of metals had many biological overtones, for it was a kind of metallic epigenesis.[57] "Within the globe are hidden the principles of metals and stones, as at the earth's surface are hidden the principles of herbs and plants."[58] In all cases, the "spiritus" acts as semen and blood that inform and feed the proper womb in the generation of animals.[59] "The brother uterine of iron,"[60] the loadstone, is formed in this manner. As the embryo of a certain species is the result of the specificating nature of the womb in which the generic seed has been placed, so the kind of metal is the result of a certain humor condensing in a particular vein in the body of the earth.

Gilbert developed this biological analogy further by ascribing to metals a process of decay after reaching maturity. Once these solid materials have been formed, they will degenerate unless protected, forming earths of various kinds as a result.[61] The "rind of the earth"[62] is produced by this process of growth and decay. If these earths are soaked with humors, transparent materials are formed.[63]

As we shall see below, the ultimate cause of this internal and superficial life is the motion of the earth, which animation is the expression of the magnetic soul of this sphere.[64] As the life of animals results from the constant working of the heart and arteries,[65] so the daily motion of the earth results in a constant generation of mineral life within the earth. In contrast to Aristotle's[66] making the motion of the heavens the cause of continuous change, Gilbert made that of the earth the remote cause.[67] However, unlike the constant cyclical transmutation of substances in Aristotle, there is only generation and decay.

Gilbert made a number of successive generalizations in order to arrive at the induction that the form of the loadstone is a microcosmic "anima" of that of the earth.[68] After comparing the properties of the loadstone and of iron, his first step in this induction was that the two materials, found everywhere,[69] are consanguineous:[70] "These two associated bodies possess the true, strict form of one species, though because of the outwardly different aspect and the inequality of the selfsame innate potency, they have hitherto been held to be different ..." Good iron and good loadstone are more similar than a good and a poor loadstone, or a good and a poor iron ore.[71] Moreover, they have the same potency,[72] for the innate potency of one can be passed to the other:[73] "The stronger invigorates the weaker, not as if it imparted of its own substances or parted with aught of its own strength, nor as if it injected into the other any physical substance; but rather the dormant power of the one is awakened by the other's without expenditure." In addition, the potency can be passed only to the other.[74] Finally they both have the same history: