The Natural Philosophy of William Gilbert and His Predecessors — Background and Themes

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

Having declared the origin and nature of the loadstone, we hold it needful first to give the history of iron also ... before we come to the explication of difficulties connected with the loadstone ... we shall better understand what iron is when we shall have developed ... what are the causes and the matter of metals ...

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]

[41] Richard Hooker. _Of the laws of ecclesiastical polity_, bk. 1, ch. 3, sect. 4 (_Works_, Oxford, Clarendon Press, 1865, vol. 1, p. 157)

[42] Francis Bacon, _De augmentis scientiarum_, bk. 3, ch. 4, in _Works_, ed. J. Spedding, R. L. Ellis, and D. D. Heath, Boston, n.d. (1900?), vol. 2, p. 267.

[43] _The poems of John Donne_, ed. H. J. C. Grierson, London, Oxford University Press, 1933, p. 175 ("To the Countesse of Bedford, On New Yeares Day").

[45] M: pp. 34, 35. Aristotle, _Works_, ed. W. D. Ross, Oxford, 1908--1952, vol. 2, _De generatione et corruptione_, translated by H. H. Joachim, 1930, vol. 3, _Meteorologica_, translated by E. W. Webster, 1931.

[46] M: pp. 34, 35, 64, 65, 69, 81. Dr. H. Guerlac has kindly brought to my attention the similarity between the explanation given in Gilbert and that given in the _Meteorologica_, bk. 3, ch. 6. p. 378.

[48] A statement of the relation between Aristotle's four elements and place can be found in Maier, _op. cit._ (footnote 17), pp. 143-182.

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]

[49] M: pp. 21, 34, 35, 36, 45.

[50] M: pp. 35, 36, 38, 69; see, however, pp. 42-43: "Iron ore, therefore, as also manufactured iron, is a metal slightly different from the homogenic telluric body because of the metallic humor it has imbibed ..."

[51] M: pp. 19, 34, 36, 37, 42, 69.

[52] M: pp. 35, 36, 37, 38.

[53] M: pp. 38, 63, 69, 84; on p. 34 he says that iron is "more truly the child of the earth than any other metal"; it is the hardest because of "the strong concretion of the more earthy substance."

[54] M: pp. 21, 35, 37, 38.

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.

[57] Gilbert's terminology strongly suggests that he was familiar with alchemical literature, as well as that of medical chemistry. He has been credited as being highly skilled in chemistry. See Sir Walter Langdon-Brown, "William Gilbert: his place in the medical world," _Nature_, vol. 154, pp. 136-139, 1944.

[59] M: pp. 35, 36, 53, 59. See also Galen, _op. cit._ (footnote 15) bk. 2, ch. 3.

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]

[61] M: pp. 20, 21, 32, 61, 63, 66, 70.

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.

[64] M: pp. 310, 311, 312.

[65] M: p. 338. A somewhat different opinion, although not necessarily inconsistent is expressed on p. 66, where he says the surface is due to the action of the atmosphere, the waters, and the radiations and other influences of heavenly bodies.

[66] Aristotle, _op. cit._ (footnote 45), _De generatione et corruptione_, bk. 2, ch. 10.

[67] M: pp. 311, 334, 338.

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:

We see both the finest magnet and iron ore visited as it were by the same ills and diseases, acting in the same way and with the same indications, preserved by the same remedies and protective measures, and so retaining their properties ... they are both impaired by the action of acrid liquids as though by poison[75] ... each is saved from impairment by being kept in the scrapings of the other. [So] ... form, essence and appearance are one.[76]

Any difference between the loadstone proper and the iron proper is due to a difference in the actual power of the magnetic virtue:[77] "Weak loadstones are those disfigured with dross metallic humors and with foreign earth admixtures, [hence one may conclude] they are further removed from the mother earth and are more degenerate."

[68] M: pp. xlvii, 309, 328.

[69] M: pp. 18, 20, 44, 46, 69.

[70] M: pp. 59, 61, 63.

[77] M: pp. 19, 21, 43, 53, 61, 63, 184.

Gilbert's second induction was that they are "true and intimate parts of the globe,"[78] that is, that they are piece of the "materia prima" of all we see about us. For they "seem to contain within themselves the potency of the earth's core and of its inmost viscera."[79] Whence, in Gilbert's philosophy, the earthy matter of the elements was not passive or inert[80] as it was in Aristotle's, but already had the magnetic powers of loadstone. Being endowed with properties, it was, in peripatetic terms, a simple body.

[80] M: p. 69. Gilbert is confusing Aristotelian matter and an element. He includes cold and dry, with formless and inert! See also Maier, _op. cit._ (footnote 17).

If these pieces of earth proper, before decay, are loadstones, then one may pass to the next induction that the earth itself is a loadstone.[81] Conversely, a terrella has all the properties of the earth:[82] "Every separate fragment of the earth exhibits in indubitable experiments the whole impetus of magnetic matter; in its various movements it follows the terrestial globe and the common principle of motion."[83]

[81] M: p. 63; bk. 1, ch. 17.

[82] M: pp. 67, 181-183, 235-240, 281-289, 313-314.

[83] M: p. 71. See also pp. 314 and 331. It is not clear, at this point, whether he believed a "properly balanced" terrella would be a _perpetuum mobile_.

The next induction that Gilbert made was that as the magnet possesses verticity and turns towards the poles, so the loadstone-earth possesses a verticity and turns on an axis fixed in direction.[84] He could now discuss the motions of a loadstone in general, in terms of its nature, just as an Aristotelian discussed the motion of the elements in terms of their nature.

[84] M: pp. 68, 70-71, 97, 129, 179-180, 311, 315, 317-335 Gilbert implied (M: p. 166), that a terrella does not rotate as Peregrinus said, due to resistance (M: p. 326), or due to the mutual nature of coition (M: p. 166); or even to the rotation of the earth (M: p. 332). However (M: p. 129), he also mentioned that a terrella would revolve by itself!

But before reaching this point in his argument, Gilbert digressed to classify the different kinds of attractions and motions which the elements produce. In particular, he distinguished electric attraction from magnetic coition, and pointed out the main features of electrical attraction. Since the resultant motions were different, the essential natures of electric and magnetic substances had to differ.

Gilbert introduced his treatment of motion by discussing the attraction of amber. All sufficiently light solids[85] and even liquids,[86] but not flame or air[87] are attracted by rubbed amber. Heat from friction,[88] but not from alien sources like the sun[89] or the flame,[90] produce this "affection." By the use of a detector modeled after the magnetic needle, which we would call an electroscope but which he called a "versorium,"[91] Gilbert was able to extend the list of substances that attract like amber.[92] These Gilbert called "electricae."[93]

[85] M: pp. 78, 82, 84, 86.

[86] M: pp. 78, 89, 91.

[89] M: pp. 81, 86, 87.

[90] M: pp. 80, 81, 86, 87.

[92] M: pp. 77-78, 79.

[93] M: p. 78. The definition Gilbert gave of an electric in the glossary at the beginning of his treatise was not an experimental one: "Electricae, quae attrahunt eadem ratione ut electrum."

Possibly as a result of testing experimentally statements like that of St. Thomas, on the effect of garlic on a loadstone, Gilbert discovered that the interposition of even the slightest material (except a fluid like olive oil) would screen the attraction of electrics.[94] Hence the attraction is due to a material cause, and, since it is invisible, it is due to an effluvium.[95] It must be much rarer than air,[96] for if its density were that of air or greater, it would repel rather than attract.[97]

[94] M: pp. 86, 91, 135.

[97] M: pp. 90, 92, 95.

The source of the effluvia could be inferred from the properties of the electrics. Many but not all of the electrics are transparent, but all are firm and can be polished.[98] Since they retain the appearance and properties of a fluid in a firm solid mass,[99] Gilbert concluded that they derived their growth mostly from humors or were concretions of humors.[100] By friction, these humors are released and produce electrical attraction.[101]

[98] M: pp. 83, 84, 85.

[100] M: pp. 84, 89. See also Aristotle, _op. cit._ (footnote 45), _Meteorologica_, bk. 4.

This humoric source of the effluvia was substantiated by Gilbert in a number of ways. Electrics lose their power of electrical attraction upon being heated, and this is because the humor has been driven off.[102] Bodies that are about equally constituted of earth and humor, or that are mostly earth, have been degraded and do not show electrical attraction.[103] Bodies like pearls and metals, since they are shiny and so must be made of humors, must also emit an effluvium upon being rubbed, but it is a thick and vaporous one without any attractive powers.[104] Damp weather and moist air can weaken or even prevent electrical attraction, for it impedes the efflux of the humor at the source and accordingly diminishes the attraction.[105] Charged bodies retain their powers longer in the sun than in the shade, for in the shade the effluvia are condensed more, and so obscure emission.[106]

[104] M: p. 90. See also p. 95.

[105] M: pp. 78, 85-86, 91. (see particularly the heated amber experiment described on p. 86).

All these examples seemed to justify the hypothesis that the nature of electrics is such that material effluvia are emitted when electrics are rubbed, and that the effluvia are rarer than air. Gilbert realized that as yet he had not explained electrical attraction, only that the pull can be screened. The pull must be explained by contact forces,[107] as Aristotle[108] and Aquinas[109] had argued. Accordingly, he declared, the effluvia, or "spiritus,"[110] emitted take "hold of the bodies with which they unite, enfold them, as it were, in their arms, and bring them into union with the electrics."[111]

[108] Aristotle, _Physics_, translated by P. H. Wicksteed and F. M. Cornford, Loeb Classical Library, London, 1934, bk. 7, ch. 1, 242b25.

[109] St. Thomas Aquinas, _op. cit._ (footnote 19), vol. 2, _Physicorum Aristotelis expositio_, lib. 7, lect. 2 (In moventibus et motis non potest procedi in infinitum, sed oportet devenire ad aliquid primum movens immobile), cap. d, p. 96.

It can be seen how this uniting action is effected if objects floating on water are considered, for solids can be drawn to solids through the medium of a fluid.[112] A wet body touching another wet body not only attracts it, but moves it if the other body is small,[113] while wet bodies on the surface of the water attract other wet bodies. A wet object on the surface of the water seeks union with another wet object when the surface of the water rises between both: at once, "like drops of water, or bubbles on water, they come together."[114] On the other hand, "a dry body does not move toward a wet, nor a wet to a dry, but rather they seem to go away from one another."[115] Moreover, a dry body does not move to the dry rim of the vessel while a wet one runs to a wet rim.[116]

By means of the properties of such a fluid, Gilbert could explain the unordered coming-together that he called coacervation.[117] Different bodies have different effluvia, and so one has coacervation of different materials. Thus, in Gilbert's philosophy air was the earth's effluvium and was responsible for the unordered motion of objects towards the earth.[118]

[118] M: p. 92 (see also p. 339). Although Gilbert does not make it explicit, this would solve the medieval problem of gravitation without resorting to a Ptolemaic universe. In addition, since coacervation is electric, and electric forces can be screened, it should have been possible to reduce the downward motion of a body by screening!

The analogy between electric attraction and fluids is a most concrete one, yet lying beneath this image is a hypothesis that is difficult to fix into a mechanical system based upon contact forces. This is the assumption that under the proper conditions bodies tend to move together in order to participate in a more complete unity.[119] The steps in electrical attraction were described as occurring on two different levels of abstraction: first one has physical contact through an effluvium or "spiritus" that connects the two objects physically. Then, as a result of this contact, the objects somehow sense[120] that a more intimate harmony is possible, and move accordingly. Gilbert called the motion that followed contact, attraction. However, this motion did not connote what we would call a force:[121] it did not correspond directly to a push or pull, but it followed from what one might term the apprehension of the possibility of a more complete participation in a formal unity. The physical unity due to the "spiritus" was the prelude to a formal organic unity, so that _humor_ is "rerum omnium unitore." Gilbert's position can be best seen in the following:[122]

Spiritus igitur egrediens ex corpora, quod ab humore aut succo aqueo concreverat, corpus attrahendum attingit, attactum attrahenti unitur; corpus peculiari effluviorum radio continguum, unum effecit ex duobus: unita confluunt in conjunctissimam convenientiam, quae attractio vulgo dicitur. Quae unitas iuxta Pythagorae opinionem rerum omnium principium est, per cuius participationem unaquaeque res una dicitur. Quoniam enim nullo actio a materia potest nisi per contactum, electrica haec non videntur tangere, sed ut necesse erat demittitur aliquid ab uno ad aliud, quod proxime tangat, et eius incitationis principium sit. Corpora omnia uniuntur & quasi ferruminantur quodammodo humore ... Electrica vero effi via peculiaria, quae humoris fusi subtilissima sunt materia, corpuscula allectant. Aer (commune effluvium telluris) & partes disjunctis unit, & tellus mediante aere ad se revocat corpora; aliter quae in superioribus locis essent corpora, terram non ita avide appelerent.

Electrica effluvia ab aere multum differunt, & u aer telluris effluvium est, ita electrica suahabent effluvia & propria; peculiaribus effluviis suus cuique; est singularis ad unitatem ductus, motus ad principium, fontem, & corpus effluvia emittens.

A similar hypothesis will reappear in his explanation of magnetic attraction.

[119] M: pp. 91, 92: "This unity is, according to Pythagoras, the principle, through participation, in which a thing is said to be one" (see footnotes 30 and 122).

[120] "Sense" is probably too strong a term, and yet the change following contact is difficult to describe in Gilbert's phraseology without some such subjective term. See Gilbert's argument on the soul and organs of a loadstone, M: pp. 309-313.

[121] M: pp. 112, 113.

[122] Gilbert, _De magnete_, London, 1600, bk. 2, ch. 2, pp. 56-57.

Following the tradition of the medieval schoolmen Gilbert started his examination of the nature of the loadstone by pointing out the different kinds of motion due to a magnet. The five kinds (other than up and down) are:[123]

(1) coitio (vulgo attractio, dicta) ad unitatem magneticam incitatio.

(2) directio in polos telluris, et telluris in mundi destinatos terminos verticitas et consistentia.

(3) variatio, a meridiano deflexio, quem motum nos depravatum dicimus.

(4) declinatio, infra horizontem poli magnetici descensus.

(5) motus circularis, seu revolutio.

Of the five he initially listed, three are not basic ones. Variation and declination he later explained as due to irregularities of the surface of the earth, while direction or verticity is the ordering motion that precedes coition.[124] This leaves only coition and revolution as the basic motions. How these followed from "the congregant nature of the loadstone can be seen when the effusion of forms has been considered."

Coition (he did not take up revolution at this point) differed from that due to other attractions. There are two and only two kinds of bodies that can attract: electric and magnetic.[125] Gilbert refined his position further by arguing that one does not even have magnetic attraction[126] but instead the mutual motion to union that he called coition.[127] In electric attraction, one has an action-passion relation of cause and effect with an external agent and a passive recipient; while in magnetic coition, both bodies act and are acted upon, and both move together.[128] Instead of an agent and a patient in coition,[129] one has "conactus." Coition, as the Latin origin of the term denoted, is always a concerted action. [130] This can be seen from the motions of two loadstones floating on water.[131] The mutual motion in coition was one of the reasons for Gilbert's rejection of the perpetual motion machine of Peregrinus.[132]

[123] _Ibid._, ch. 1, pp. 45-46.

[124] M: pp. 110, 314.

[125] M: pp. 82, 105, 170, 172, 217.

[127] M: pp. 100, 112, 113, 143, 148. It need hardly be pointed out that coitus is not an impersonal term.

[130] M: pp. 109, 115, 148, 149, 155, 166, 174.

[131] M: pp. 110, 155.

[132] M: pp. 166, 332. See also footnote 84.

Magnetic coition, unlike electric attraction, cannot be screened.[133] Hence it cannot be corporeal for it travels freely through bodies[134] and especially magnetic bodies;[135] one can understand the action of the armature on this basis.[136] Since coition cannot be prevented by shielding, it must have an immaterial cause.[137]

[133] M: pp. 90, 106, 107, 108, 113, 132, 135, 136, 158. This is, of course, contrary to modern experience.

[134] M: pp. 106, 107, 108, 114, 134, 136, 140, 162.

[135] M: pp. 106, 109, 114, 159, 162.

[136] M: pp. 137-140.

Yet, unless one has the occult action-at-a-distance, change must be caused by contact forces. Gilbert resolved the paradox of combining contact forces with forces that cannot be shielded, by passing to a higher level of abstraction for the explanation of magnetic phenomena: he saw the contact as that of a form with matter.