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diff --git a/31999.txt b/31999.txt new file mode 100644 index 0000000..3ab7763 --- /dev/null +++ b/31999.txt @@ -0,0 +1,2251 @@ +The Project Gutenberg EBook of The Natural Philosophy of William Gilbert +and His Predecessors, by W. James King + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: The Natural Philosophy of William Gilbert and His Predecessors + +Author: W. James King + +Release Date: April 15, 2010 [EBook #31999] + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK NATURAL PHILOSOPHY--WILLIAM GILBERT *** + + + + +Produced by Chris Curnow, Joseph Cooper and the Online +Distributed Proofreading Team at https://www.pgdp.net + + + + + + + + + + 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 + + Until several decades ago, the physical sciences were + considered to have had their origins in the 17th + century--mechanics beginning with men like Galileo Galilei + and magnetism with men like the Elizabethan physician and + scientist William Gilbert. + + Historians of science, however, have traced many of the 17th + century's concepts of mechanics back into the Middle Ages. + Here, Gilbert's explanation of the loadstone and its powers + is compared with explanations to be found in the Middle Ages + and earlier. + + From this comparison it appears that Gilbert can best be + understood by considering him not so much a herald of the new + science as a modifier of the old. + + THE AUTHOR: W. James King is curator of electricity, Museum + of History and Technology, in the Smithsonian Institution's + United States National Museum. + + +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. + + [1] William Gilbert, _De magnete, magneticisque corporibus + et de magno magnete tellure; physiologia nova, plurimis & + argumentis, & experimentis, demonstrata_, London, 1600, 240 + pp., with an introduction by Edward Wright. All references to + Gilbert in this article, unless otherwise noted, are to the + American translation by P. Fleury Mottelay, 368 pp., + published in New York in 1893, and are designated by the + letter M. However, the Latin text of the 1600 edition has + been quoted wherever I have disagreed with the Mottelay + translation. + + A good source of information on Gilbert is Dr. Duane H. D. + Roller's doctoral thesis, written under the direction of Dr. + I. B. Cohen of Harvard University. Dr. Roller, at present + Curator of the De Golyer Collection at the University of + Oklahoma, informed me that an expanded version of his + dissertation will shortly appear in book form. Unfortunately + his researches were not known to me until after this article + was completed. + +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. Koyre 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. + + [2] Alexandre Koyre, _Etudes galileennes_, Paris, 1939. + + [3] Alfred N. Whitehead, _Science and the modern world_, New + York, 1925, ch. 3; Ernst Cassirer, _Das Erkenntnisproblem_, + ed. 3, Berlin, 1922, vol. 1, pp. 314-318, 352-359. + + [4] However, see M: pp. 161, 162, 168, 335. + +[Illustration: Figure 1.--WILLIAM GILBERT'S BOOK ON THE LOADSTONE, +TITLE PAGE OF THE FIRST EDITION, FROM A COPY IN THE LIBRARY OF +CONGRESS. (_Photo courtesy of the Library of Congress._)] + +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] + + [5] For example, William Whewell, _History of the inductive + sciences_, ed. 3, New York, 1858, vol. 2, pp. 192 and 217; + Charles Singer, _A short history of science to the nineteenth + century_, Oxford, 1943, pp. 188 and 343; and A. R. Hall, _The + scientific revolution_, Boston, 1956, p. 185. + + [6] _Petri Peregrini maricurtenis, de magnete, seu rota + perpetui motus, libellus_, a reprint of the 1558 Angsburg + edition in J. G. G. Hellmann, _Rara magnetica_, Berlin, 1898, + not paginated. A number of editions of Peregrinus, work, both + ascribed to him and plagiarized from him, appeared in the + 16th century (see Heinz Balmer, _Beitraege zur Geschichte der + Erkenntnis des Erdmagnetismus_, Aarau, 1956, pp. 249-255). + + [7] Hellmann, _ibid._, Robert Norman, _The newe attractive, + containyng a short discourse of the magnes or lodestone, and + amongest other his vertues, of a newe discovered secret and + subtill propertie, concernyng the declinyng of the needle, + touched therewith under the plaine of the horizon. Now first + founde out by Robert Norman Hydrographer_. London, 1581. The + possibility is present that Norman's work was a direct + stimulus to Gilbert, for Wright's introduction to _De + magnete_ stated that Gilbert started his study of magnetism + the year following the publication of Norman's book. + + [8] Hellman, _ibid._, William Borough, _A discourse of the + variation of the compasse, or magneticall needle. Wherein + is mathematically shewed, the manner of the observation, + effects, and application thereof, made by W. B. And is to + be annexed to the newe attractive of R. N._ London, 1596. + + [9] Hellman, _ibid._, Simon Stevin, _De havenvinding_, + Leyden, 1599. It is interesting to note that Wright + translated Stevin's work into English. + +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] + + [10] As Edward Wright was to call him in his introduction. + +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. + + [11] Aristotle, _On the soul_, translated by W. S. Hett, Loeb + Classical Library, London, 1935, 405a20 (see also 411a8: + "Some think that the soul pervades the whole universe, whence + perhaps came Thales' view that everything is full of gods"). + + [12] Plato, _Ion_, translated by W. R. M. Lamb, Loeb + Classical Library, London, 1925, 533 (see also 536). + +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. + + [13] Plato, _Timaeus_, translated by R. G. Bury, Loeb + Classical Library, London, 1929, 80. It is difficult to + determine which explanation Plato preferred, for in both + cases the speaker may be only a foil for Plato's opinion + rather than an expression of these opinions. + +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. + + [14] Lucretius, _De rerum natura_, translated by W. H. D. + Rouse, Loeb Classical Library, London, 1924, bk. VI, lines + 998-1041. + +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. + + [15] Galen, _On the natural faculties_, translated by A. S. + Brock, Loeb Classical Library, London, 1916, bk. 1 and bk. 3. + A view similar to this appeared in Plato, _Timaeus_, 81 (see + footnote 13). + + [16] This same concept was to reappear in the Middle Ages as + the _inclinatio ad simile_. + +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] + + [17] The background for much of the following was derived + from Annaliese Maier, _An der Grenze von Scholastik und + Naturwissenchaft_, ed 2, Rome, 1952. + +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] + + [18] St. Thomas' epistemology for the natural inanimate world + was based upon Aristotle's dictum: that which is in the mind + was in the senses first. + +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." + + [19] Rene Descartes, _Oeuvres_, Charles Adam and Paul + Tannery, Paris, 1897-1910, vol. 2, p. 597 (letter to + Mersenne, 16 Oct., 1639), and vol. 11 (Le Monde), p. 39. The + original definition can be found in Aristotle, _Physics_, + translated by P. H. Wickstead and F. M. Cornford, Loeb + Classical Library, London, 1934, 201a10. Aquinas rephrases + the definition as "_Motus est actus existentis in potentia + secundum quod huius modi._" See St. Thomas Aquinas, _Opera + omnia_, Antwerp, 1612, vol. 2, _Physicorum Aristotelis + expositio_, lib. 3, lect. 2, cap. a, p. 29. + +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] + + [20] St. Thomas Aquinas, _op. cit._ (footnote 19), vol. 9, + _Summa contra gentiles_, lib. 3, cap. 92 (Quo modo dicitur + aliquis bene fortunatus et quo modo adjuvatur homo ex + superioribus causis), p. 343. + + [21] St. Thomas Aquinas, op. cit. (footnote 19), vol. 17 + _Opuscula, De operationibus occultis naturae ad queindam + militem ultramontem_, pp. 213-224. + +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] + + Respondeo dicendum, quod omnibus rebus naturaliter insunt + quaedam principia, quibus non solum operationes proprias + efficere possunt, sed quibus etiam eas convenientes fini suo + reddant, sive sint actiones quae consequantur rem aliquam ex + natura sui generis, sive consequantur ex natura speciei, ut + magneti competit ferri deorsum ex natura sui generis, et + attrahere ferrum ex natura speciei. Sicut autem in rebus + agentibus ex necessitate naturae sunt principia actionum + ipsae formae, a quibus operationes proprie prodeunt + convenientes fini.... + +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] + + Forma enim elementi non habet aliquam operationem nisi quae + fit per qualitates activas et passivas, quae sunt + dispositiones materiae corporalis. Forma autem corporis + mineralis habet aliquam operationem excedentem qualitates + activas et passivas, quae consequitur speciem ex influentia + corporis coelestis, ut quod magnes attrahit ferrum, et quod + saphirus curat apostema. + +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] + + Quod quidem ex propriis formarum operationibus perpendi + potest. Formae enim elementorum, quae sint infimae et + materiae propinquissime, non habent aliquam operationem + excedentem qualitates activas et passivas, ut rarum et + densum, et aliae huiusmodi, qui videntur esse materiae + dispositiones. Super has autem sunt formae mistorum quae + praeter praedictas operationes, habent aliquam operationem + consequentem speciem, quam fortiuntur ex corporibus + coelestibus; sicut quod magnes attrahit ferrum non propter + calorem aut frigiis, aut aliquid huiusmodi; sed ex quadam + participatione virtutis coelestis. Super has autem formas + sint iterum animae plantarum, quae habent similitudinem non + solum ad ipsa corpora coelestia, sed ad motores corporum + coelestium, inquantum sunt principia cuiusdam motus, + quibusdam seipsa moventibus. Super has autem ulterius sunt + animae brutorum, quae similitudinem iam habent ad substantiam + moventem coelestia corpora, non solum in operatione qua + movent corpora, sed etiam in hoc quod in seipsis + cognoscitivae sunt, licet brutorum cognitio sit materialium + tantum et materialiter.... + +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] + + Illud ergo trahere dicitur, quod movet alterum ad seipsum. + Movere autem aliquid secundum locum ad seipsum contingit + tripliciter. Uno modo sicut finis movet; unde et finis + dicitur trahere, secundum illud poetate: "trahit sua quemque + voluptas": et hoc modo potest dici quod locus trahit id, quod + naturaliter movetur ad locum. Alio modo potest dici aliquid + trahere, quia movet illud ad seipsum alterando aliqualiter, + ex qua alteratione contingit quod alteratum moveatur secundum + locum: et hoc modo magnes dicitur trahere ferrum. Sicut enim + generans movet gravia et levia, inquantum dat eis formarum + per quam moventur ad locum, ita et magnes dat aliquam + qualitatem ferro, per quam movetur ad ipsum. Et quod hoc sit + verum patet ex tribus. Primo quidem quia magnes non trahit + ferrum ex quacumque distantia, sed ex propinquo; si autem + ferrum moveretur ad magnetem solum sicut ad finem, sicut + grave ad suum locum, ex qualibet distantia tenderet ad ipsum. + Secundo, quia, si magnes aliis perungatur, ferrum attrahere + non potest; quasi aliis vim alterativam ipsius impedientibus, + aut etiam in contrarium alterantibus. Tertio, quia ad hoc + quod magnes attrahat ferrum, oportet prius ferrum liniri cum + magnete, maxime si magnes sit parvus; quasi ex magnete + aliquam virtutem ferrum accipiat ut ad eum moveatur. Sic + igitur magnes attrahit ferrum non solum sicut finis, sed + etiam sicut movens et alterans. Tertio modo dicitur aliquid + attrahere, quia movet ad seipsum motu locali tantum. Et sic + definitur hic tractio, prout unum corpus trahit alteram, ita + quod trahens simul moveatur cum eo quod trahitur. + +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. + + [22] St. Thomas Aquinas, _op. cit._ (footnote 19), vol 7, + _Scriptum in quartum librum sententiarum magistri Petri + Lombardi_, lib. 4, disq. 33 (De diversis coniugii legibus), + art. 1 (Utrum habere plures uxores sit contra legem naturae), + p. 168. The same statement occurs in one of his most mature + works, _op. cit._ vol. 20, _Summa theologica_, pars 3 + (supplementum), quaestio 65 (De pluralitate uxorum in quinque + articulos divisa), art. 1 (Utrum habere plures uxores sit + contra legem naturae), p. 107. + + [23] St. Thomas Aquinas, _op. cit._ (footnote 19), vol. 8, + _Quaestio unica: de spiritualibus creaturis_, art. 2 (Utrum + substantia spiritualis possit uniri corpori), p. 404. See + also vol. 9, _Summa contra gentiles_, lib. 3, cap. 92 + (Quomodo dicitur aliquis bene fortunatus, et quomodo + adjuvatur homo ex superioribus causis), p. 344; and vol. 17, + _Opuscula, De operationibus occultis naturae ad queindam + militem ultramontem_, pp. 213-214. + + [24] St. Thomas Aquinas, _op. cit._ (footnote 19), vol. 8, + _Quaestio unica: de anima_, art. 1 (Utrum anima humana possit + esse forma et hoc aliquid), p. 437. See also vol. 8, + _Quaestio: De veritate_, quaestio 5 (De providentia), art. 10 + (Utrum humani actus a divina providentia gubernentur mediis + corporibus coelestibus), p. 678. + + [25] St. Thomas Aquinas, _op. cit._ (footnote 19), vol. 2, + _Physicorum Aristotelis expositio_, lib. 7, lect. 3, cap. g + (Probatur in motu locali quod movens et motum oportet esse + simul), p. 97 (quoted in Gilbert, M: p. 104). + +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] + + ... Oportet enim quod illud quod iam conversum est ex duobus + in unum, sit in eadem specie cum agente; quod non esset, si + natura istud impossible eligeret. + +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] + + ... In cuius attractione, lapis fortioris virtutis agens est; + debilioris vero patiens. + +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] + + ... Causa huis est impressio ultimi agentis, confundentis et + alterantis virtutem primi. + +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] + + Huius autem rei causam per hanc viam fieri existimo: agens + enim intendit suum patiens non solum sibi assimilare, sed + unire, ut ex agente et patiente fiat unum, per numerum. Et + hoc potes experiri in isto lapide mirabili in hunc modum.... + Agens ergo, ut vides experimento, intendit suum paciens sibi + unire; hoc autem fit ratione similitudinis inter ea. Oportet + ergo ... virtute attractionis, fiat una linea, ex agente et + patiente, secundum hunc ordinem ... + +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] + + Natura autem, que tendet ad esse, agit meliori modo quo + potest, eligit primum ordinem actionis, in quo melius + salvatur idemptitas, quam in secundo ... + +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] + + Praeterea cum ferrum, vel lapis, vertatur tarn ad partem + meridionalem quam ad partem septemtrionalem ... existima + cogimur, non solum a partem septemtrionali, verum etiam a + meridionali virtutem influi in polos lapidis, magis quam a + locis minere ... Omnes autem orbes meridiani in polis mundi + concurrent; quare, a polis mundi, poli magnetis virtutem + recipiunt. Et ex hoc apparet manifeste quod non ad stellam + nauticam movetur, cum ibi non concurrant orbes meridiani, sed + in polis; stella enim nautica, extra orbem meridianum + cuiuslibet regionis semper invenitur, nisi bis, in completa + firmanenti revolutione. Ex hiis ergo manifestum est quod a + partibus celi, partes magnetis virtutem recipiunt. + +and similarly for the other parts of the heavens and the other parts +of the loadstone.[33] + + Ceteras autem partes lapidis merito estimare potes, + influentiam a reliquis celi partibus retinere, ut non sic + solum polos lapidis a polis mundi, sed totum lapidem a toto + celo, recipere influentiam et virtutem, estimes. + +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] + + Quod tibi tali modo consulo experire: ... Et si tunc lapis + moveatur secundum celi motum, gaudeas te esse assecutum + secretum mirabile; si vero non, imperitie tue, potiusquam + nature, defectus imputetur. In hoc autem situ, seu modo + positionis, virtutes lapidis huius estimo conservari proprie, + et in reliquis sitibus celi virtutem eius obsecari, seu + ebetari, potiusquam conservari puto. Per hoc autem + instrumentum excusaberis ab omni horologio; nam per ipsum + scire poteris Ascensus in quacumque hora volueris, et omnes + alias celi dispositiones, quas querunt Astrologi. + +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. + + [26] Hellmann, _op. cit._ (footnote 6), Peregrinus, pt. 1, + ch. 8. The magnet attracts the iron "secundum naturalem + appetitum lapidis ... sine resistentia." There is no natural + resistence to this motion since it is no longer contrary to + the nature of the iron. The nature of the iron has changed. + + [27] _Ibid._, pt. 1, ch. 9. + + [28] _Ibid._, pt. 1, ch. 9. + + [29] _Ibid._, pt. 1, ch. 8. + + [30] _Ibid._, pt. 1, ch. 9. + + [31] _Ibid._, pt. 1, ch. 9. See also footnote 27. + + [32] _Ibid._, pt. 1, ch. 10. See also ch. 4. + + [33] _Ibid._, pt. 1, ch. 10. See also ch. 4. + + [34] _Ibid._, pt. 1, ch. 10. + + [35] However, he may not always have approved of him. See + M:74; "Overinquisitive theologians, too, seek to light up + God's mysteries and things beyond man's understanding by + means of the loadstone and amber." + +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] + + Si igitur in omni desiderio vitae intellectualis attenderes, + a quo est intellectus, per quod movetur et ad quod, in te + comperires dulcedinem sapientiae aeternae illam esse, quae + tibi facit desiderium tuum ita dulce et delectabile, ut in + inerrabili affectu feraris ad eius comprehensionem tanquam ad + immortalitatem vitae tue, quasi ad ferrum et magnetem + attendas. Habet enim ferrum in magnete quoddam sui effluxus + principium; et dum magnes per sui praesentiam excitat ferrum + grave et ponderosum, ferrum mirabili desiderio fertur etiam + supra motum naturae, quo secundum gravitatem deorsum tendere + debet, et sursum movetur se in suo principio uniendo. Nisi + enim in ferro esset quaedam praegustatio naturalis ipsius + magnetis, non moveretur plus ad magnetem quam ad alium + lapidem; et nisi in lapide esset major inclinatio ad ferrum + quam cuprum, non esset illa attractio. Habet igitur spiritus + noster intellectualis ab aeterna sapientia principium sic + intellectualiter essendi, quod esse est conformius sapientae + quam aliud non intellectuale. Hinc irraditio seu immissio in + sanctam animam est motus desideriosus in excitatione. + +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] + + [36] Nicholas of Cusa (Nicolaus Cusaneus), _Nicolaus von + Cues, Texte seiner philosophischen Schriften_, ed. A. + Petzelt, Stuttgart, 1949, bk. 1, _Idiota de sapientia_, p. + 306 (quoted in Gilbert, M:104). It is interesting that Cusa + held that the loadstone has an inclination to iron, as well + as the converse! + + [37] Cusa, _Cusa Schriften_, vol. 8, _De pace fidei_, + translated by L. Mohler, Leipzig, 1943, ch. 12, p. 127. + + [38] Cusa, _Exercitationes_, ch. 7, 563 and 566, quoted in, + F. A. Scharpff, _Des Cardinals und Bischofs Nicolaus Von Cusa + Wichtigste Schriften in Deutscher Uebersetzung_, Freiburg, + 1862, p. 435. See also Martin Billinger, _Das Philosophische + in Den Excitationen Des Nicolaus Von Cues_, Heidelberg, 1938, + and _Cusa Schriften_ (see footnote 37), vol. 8, p. 209, note + 105. Gilbert (M: p. 223) called the compass "the finger of + God." + +The Elizabethan Englishman Robert Norman also turned to the Deity to +explain the wonderful effects of the loadstone.[39] + + Now therefore ... divers have whetted their wits, yea, and + dulled them, as I have mine, and yet in the end have been + constrained to fly to the cornerstone: I mean God: who ... + hath given Virtue and power to this Stone ... to show one + certain point, by his own nature and appetite ... and by the + same vertue, the Needle is turned upon his own Center, I mean + the Center of his Circular and invisible Vertue ... And + surely I am of opinion, that if this would be found in a + Sphericall form, extending round about the Stone in Great + Compass, and the dead body Stone in the middle therof: Whose + center is the center of his aforesaid Vertue. And this I have + partly proved, and made visible to be seen in the same + manner, and God sparing me life, I will herein make further + Experience. + +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. + + [39] Hellmann, _op. cit._ (footnote 6), Norman, bk. 1, ch. 8. + + [40] M: p. 14. + +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: + + This twilight of two yeares, not past or next, + Some embleme is of me, ... + ... of stuffe and forme perplext, + Whose _what_ and _where_, in disputation is ... + +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] + + 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"). + + [44] M: pp. 33, 34. + + [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. + + [47] M: p. 83. + + [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. + + [55] M: pp. 35, 63. + + [56] M: pp. 45, 46. + +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. + + [58] _Ibid._, p. 37. + + [59] M: pp. 35, 36, 53, 59. See also Galen, _op. cit._ + (footnote 15) bk. 2, ch. 3. + + [60] M: pp. 16, 59. + +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. + + [62] M: p. 59. + + [63] M: p. 84. + +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. + + [71] M: pp. 60, 63. + + [72] M: p. 110. + + [73] M: pp. 60, 61. + + [74] M: p. 62. + + [75] M: p. 63. + + [76] M: p. 60. + + [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. + + [78] M: p. 61. + + [79] M: pp. 66, 67. + + [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. + + [87] M: pp. 89, 95. + + [88] M: pp. 83, 86. + + [89] M: pp. 81, 86, 87. + + [90] M: pp. 80, 81, 86, 87. + + [91] M: p. 79. + + [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. + + [95] M: pp. 96, 135. + + [96] M: p. 89. + + [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. + + [99] M: p. 84. + + [100] M: pp. 84, 89. See also Aristotle, _op. cit._ (footnote + 45), _Meteorologica_, bk. 4. + + [101] M: p. 90. + +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] + + [102] M: pp. 84, 85. + + [103] M: p. 84. + + [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). + + [106] M: p. 87. + +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] + + [107] M: p. 92. + + [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. + + [110] M: p. 94. + + [111] M: p. 95. + +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] + + [112] M: p. 93. + + [113] M: pp. 92, 93. + + [114] M: p. 93. + + [115] M: p. 94. + + [116] M: p. 94. + +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] + + [117] M: p. 97. + + [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. + + [126] M: p. 98. + + [127] M: pp. 100, 112, 113, 143, 148. It need hardly be + pointed out that coitus is not an impersonal term. + + [128] M: p. 110. + + [129] M: p. 110. + + [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. + + [137] M: p. 109. + +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. + +Although Gilbert remarked that the cause of magnetic phenomena did +not fall within any of the categories of the formal causes of the +Aristotelians, he did not renounce for this reason the medieval +tradition. Actually there are many similarities between Gilbert's +explanation of the loadstone's powers and that of St. Thomas. Magnetic +coition is not due to any of the generic or specific forms of the +Aristotelian elements, nor is it due to the primary qualities of any +of their elements, nor is it due to the celestial "generans" of +terrestrial change.[138] + + Relictis aliorum opinionibus de magnetis attractione; nunc + coitionis illius rationem, et motus illius commoventem + naturam docebimus. Cum vero duo sint corporum genera, quae + manifestis sensibus nostris motionibus corpora allicere + videntur, Electrica et Magnetica; Electrica naturalibus ab + humore effluviis; Magnetica formalibus efficientiis, seu + potius primariis vigoribus, incitationes faciunt. Forma ilia + singularis est, et peculiaris, non Peripateticorum causa + formalis, et specifica in mixtis, est secunda forma, non + generantium corporum propagatrix; sed primorum et praeciporum + globorum forma; et partium eorum homogenearum, non + corruptarum, propria entitas et existentia, quam nos + primariam, et radicalem, et astream appellare possumus + formam; non formam primam Aristotelis; sed singularem illam, + quae globum suum proprium tuetur et disponit. Talis in + singulis globis, Sole, lunas et astris, est una; in terra + etiam una, quae vera est ilia potentia magnetica, quam nos + primarium vigorem appellamus. Quare magnetica natura est + telluris propria, eiusque omnibus verioribus partibus, + primaria et stupenda ratione, insita; haec nec a caelo toto + derivatur procreaturve, per sympathiam, per influentiam, aut + occultiores qualitates; nec peculiari aliquo astro: est enim + suus in tellure magneticus vigor, sicut in sole et luna suae + formae; frustulumque; lunae, lunatice ad eius terminos, et + formam componit se; solarque; ad solem, sicut magnes ad + tellurem, et ad alterum magnetem, secundum naturam sese + inclinando et alliciendo. Differendum igitur de tellure quae + magnetica, et magnes; tum etiam de partibus eius verioribus, + quae magneticae sunt; et quomodo ex coitione difficiuntur. + +Instead, he declared it to be due to a form that is natural and proper +to that element that he made the primary component of the earth.[139] + +To understand his argument, let us briefly recall the peripatetic +theory of the elements. In this philosophy of nature each element or +simple body is a combination of a pair of the four primary qualities +that informs inchoate matter. These qualities are the instruments of +the elemental forms and determine the properties of the element. Thus +the element fire is a compound of the qualities hot and dry, and the +substantial form of fire acts through these qualities. Similarly for +the other elements, earth, water, and air: their forms determine a +proper place for each element, and a motion to that place natural to +each element.[140] + + [138] M: p. 105, and Gilbert, _De magnete_, London, 1600, bk. + 2 ch. 4, p. 65. + + [139] M: p. 105. + + [140] M: pp. 289, 322. + +Gilbert had previously declared that the primary substance of the +earth is an element. Since it is an element, it has a motion natural +to it, and this motion is magnetic coition. As an Aristotelian +considered the substantial form of the element, fire, to act through +the qualities of hot and dry, and to cause an upward motion; so +Gilbert argued that the substantial form of his element, pure +loadstone, acts through the magnetic qualities and causes magnetic +coition. This motion is due to its primary form, and is natural to the +element earth.[141] It is instilled in all proper and undegenerate +parts of the earth,[142] but in no other element.[143] + + [141] M: pp. 26, 68, 105, 179, 198, 307, 335, 343. For + rotation, see footnote 147. + + [142] M: pp. 67, 71. That each part is informed with the + properties of the whole is an argument favoring an animistic + explanation of the nature of this form. + + [143] M: p. 109. + +To the medieval philosopher, the "generantia" of the occult powers of +the loadstone are the heavenly bodies. Gilbert, however, endowed the +earth with these heavenly powers which were placed in the earth in the +beginning[144] and caused all magnetic materials to conform with it +both physically and formally.[145] Such magnetic powers are the +property of all parts of the earth;[146] they give the earth its +rotating motion[147] and hold the earth together in spite of this +motion.[148] + + [144] M: pp. 111, 188. + + [145] M: pp. 67, 105, 179, 183. + + [146] M: pp. 101, 105, 217. + + [147] M: pp. 179, 304, 305, 311, 322, 326, 328, 330-334, + 338-343. + + [148] M: pp. 142, 179; see also electric attraction, p. 97. + +Indeed, each of the main stellar bodies, sun, moon, stars, and earth, +has such a form or principle unique to itself that causes its parts +not only to conform with itself but to revolve.[149] Thus, if one +removes a piece of the moon from this body, it will tend to align +itself with the moon and then to return to its proper place; and a +fragment of the sun would similarly tend to return after proper +orientation.[150] Moreover, there is a farther-ranging, though weaker, +mutual action of the heavenly bodies so that one has a causal +hierarchy of these specific conforming powers. The form of the sun is +superior to that of the inferior globes and is responsible for the +order and regularity of planetary orbits.[151] In like manner, the +moon is responsible for the tides of the ocean.[152] + + [149] M: pp. 308, 317-343. + + [150] M: pp. 106, 340. + + [151] M: pp. 308, 309, 311, 330, 333, 344, 347. + + [152] M: pp. 136, 334, 345. + +By virtue of the causal hierarchy of forms, the loadstone acquires its +magnetic powers from the earth.[153] As the earth has its natural +parts, so has the stone.[154] Although the geometrical center of a +terrella is the center of the magnetic forces,[155] objects do not +tend to move to the center but to its poles,[156] where the magnetic +energy is most conspicuous.[157] However, in a sense, the energy is +everywhere equal: the virtue is spread throughout the entire mass of +the loadstone,[158] and all the parts direct the forces to the +poles.[159] The poles become the "thrones" of the magnetic +powers.[160] On the other hand, the directive force is stronger where +coition is weaker and accordingly, verticity is most prominent at the +equator.[161] + + [153] M: pp. 184-186, 190, 232. This is not quite the same + argument as that the powers of the loadstone are identical + with those of the earth. See footnote 78. + + [154] M: pp. 125, 180. + + [155] M: p. 151. + + [156] M: pp. 121, 150. + + [157] M: pp. 115, 151, 165. + + [158] M: pp. 106, 118, 151, 191, 205, 221, 243. + + [159] M: pp. 116, 117, 119, 131, 183, 188, 221. + + [160] M: p. 31. + + [161] M: pp. 116, 151, 200. + +The strength of a loadstone depends upon its shape and mass. A bar +magnet has greater powers than a spherical one because it tends to +concentrate the magnetic powers more in the ends.[162] For a given +purity and shape, the heavier the loadstone, the greater its +strength.[163] A loadstone has a maximum degree of magnetic force that +cannot be increased.[164] However, weaker ones can be strengthened by +stronger ones.[165] Similarly, the shape and weight of the iron +determine the magnetic force in coition.[166] + + [162] M: pp. 131, 132, 153-158. + + [163] M: pp. 141, 152, 153, 158, 161, 191, 222. + + [164] M: p. 146. + + [165] M: p. 165. + + [166] M: p. 153. + +The formal forces of a loadstone emanate in all directions from +it,[167] but there is a bound to it that Gilbert called the "orbis +virtutis."[168] The shape of this "orbis virtutis" is determined by +the shape of the stone.[169] This insensible effusion is analogous +to the spreading of light that reveals its presence only by opaque +bodies.[170] Similarly, the magnetic forms are effused from the +stone,[171] and can only reveal their presence by coition with +another loadstone or by "awakening" magnetic bodies within the +"orbis virtutis."[172] Unmagnetized iron that comes within the "orbis +virtutis" is altered, and the magnetic virtue renews a form that is +already potentially in the iron.[173] The formal energy is drawn not +only from the stone but from the iron.[174] This is not generation, or +alteration in the sense of a new impressed quality, but alteration in +the sense of the entelechy or the activation of a form potentially +present.[175] Those bodies magnetized by coming within the "orbis +virtutis" have in turn an efflux of their own.[176] Iron can also +receive verticity directly from the earth without the intervention of +an ordinary loadstone.[177] Such verticity can be expelled and +annulled by the presence of another loadstone.[178] + + [167] M: pp. 121, 123, 124, 304, 305, 306, 307, 309. + + [168] Gilbert defined the _orbis virtutis_ in the glossary at + the beginning of his treatise as, "... totum illud spatium, + per quod quaevis magnetis virtus extenditur." This is the + core of the difference between electric and magnetic forces. + The substantial form of an electric could not be "effused," + but was "imprisoned" in matter (as the Neoplatonic soul in + the human body); while the primary form of a magnet did not + require a material carrier and its effusion was similar to + the propagation of a species in light. + + [169] M: pp. 124, 150, 151. + + [170] M: pp. 123, 307. + + [171] M: pp. 304-307. See also p. 310, where it is stated + that the sun and earth could awaken souls. + + [172] M: pp. 101, 110, 112, 123, 148, 149, 304, 305. This + awakening of the iron within the "orbis virtutis" is + comparable (pp. 216, 350) to the birth of a child under the + influence of the stars. + + [173] M: pp. 110, 111, 112, 189, 216, 217. See also footnote + 36. + + [174] M: p. 106. + + [175] M: pp. 106, 109, 110. + + [176] M: pp. 113, 114. + + [177] M: pp. 190, 192, 210-216. + + [178] M: p. 209. + +Although one does not normally find iron to be magnetized, a loadstone +always has some magnetism. That two bodies such as iron and loadstone +should have different properties is the result of the loss of a form +by the iron, but this form is still potentially present in the iron. +The iron that has been obtained from an ore has been deformed,[179] +for it has been placed "outside its nature" by the fire.[180] The +nature has not been removed, since, once the iron has cooled, the +confused form can be reformed by a loadstone. [181] The latter +"awakens" the proper form of iron.[182] After smelting, the magnetized +iron may manifest stronger powers than a loadstone of equal weight, +but this is because the primary matter of the earth is purer in the +iron than in the loadstone.[183] If fire does not deform a loadstone +too much, it can be remagnetized,[184] but a burnt loadstone cannot be +reformed.[185] Corruption from external causes may also deform a +loadstone or iron so that it can not be magnetized.[186] Bodies mixed +with the degenerate substance of the earth or with aqueous humor +spoilt by contamination with earth, do not show either electric +attraction or magnetic coition.[187] + + [179] M: pp. 107, 110, 111. + + [180] M: p. 108. + + [181] M: pp. 111, 112, 113. + + [182] M: pp. 109, 111, 112, 148, 149. + + [183] M: pp. 112, 149. + + [184] M: pp. 142, 189. + + [185] M: p. 190. + + [186] M: pp. 85, 105, 113, 143, 226. + + [187] M: p. 84. + +In a manner suggestive of Peregrinus, Gilbert wrote that, "magnetic +bodies seek formal unity."[188] Thus a dissected loadstone not only +tends to come back together, as in the unordered coacervation of +electric attraction, but to restore the organization it had before +dissection.[189] Accordingly, opposite poles appear on the interfaces +of the sections, not "from an opposition" but from "a concordance and +a conformance."[190] This ensures that when the parts are joined +together again, they have the same orientation as before. Gilbert +compared this power of restoring the original loadstone with that of a +plant's vital power under the process of cutting and grafting; the +plant can be revived only when the parts are in a certain order.[191] + + [188] M: p. 186. + + [189] M: pp. 185-188. See also footnote 31. + + [190] M: pp. 186, 193. + + [191] M: pp. 199-200. + +A hypothesis similar to that used to explain electric attraction lay +beneath the explanation of magnetic coition: that bodies brought into +contact will move together. In electric attraction, the contact is +material and due to the "spiritus" from the electric body; in magnetic +coition, it is formal and depends on the action of a primary form that +spreads from a magnetized body to its limit of effusion, the "orbis +virtutis." If iron is inside the "orbis virtutis," the two bodies +"enter into alliance and are one and the same"[192] for within it +"they have absolute continuity, and are joined by reason of their +accordance, albeit the bodies themselves be separated."[193] + +Gilbert's treatment of coition can be analyzed into the same two steps +as can electric attraction. First occurs a contact, which in this case +is not physical but formal, and from this initial formal contact +follows movement to a more complete unity. Both the contact and the +movement to unity are described on the same level of abstraction, +instead of on two different levels as in electric attraction. Again +one does not find any clear-cut concept of force as a push or +pull,[194] but instead, a motion to a formal unity, this time a +cooperative motion. The parts of a magnetic body are in greater +harmony when they are assembled in a certain pattern and so they move +accordingly. + + [192] M. p. 111. + + [193] M: p. 112. + + [194] See, however, M: pp. 112, 113. + +As to the nature of the primary form itself, Gilbert agreed with +Thales that it is like a soul,[195] "for the power of self-movement +seems to betoken a soul."[196] With Galen and St. Thomas he placed the +form of the loadstone superior to that of inanimate matter.[197] In a +sense, Gilbert even made it superior to organic matter, for it is +incapable of error.[198] Like the soul, the primary form cannot be +fragmented; when a loadstone is divided, one does not separate the +poles but each part acquires its own poles and an equator. + + [195] M: pp. 109, 312. + + [196] M: p. 109. + + [197] M: p. 309. + + [198] M: pp. 311-312. + +Like the soul, fire does not destroy it.[199] Like the soul of astral +bodies, and of the earth itself, it produces complex but regular +motions; the motion of two loadstones on water offers such an +example.[200] Like the soul of a newborn child, whose nature depends +on the configuration of the heavens, the properties in the newly +awakened iron depend upon its position in the "orbis virtutis."[201] + +Whence Gilbert declared: + + ... the earth's magnetic force and the animate form of the + globes, that are without senses, but without error ... exert + an unending action, quick, definite, constant, directive, + motive, imperant, harmonious through the whole mass of + matter; thereby are the generation and the ultimate decay of + all things on the superficies propagated.[202] The bodies of + the globes ... to the end that they might be in themselves, + and in their nature endure, had need of souls to be conjoined + to them, for else there were neither life, nor prime act, nor + movement, nor unition, nor order, nor coherence, nor + _conactus_, nor _sympathia_, nor any generation nor + alteration of seasons, and no propagation; but all were in + confusion....[203] Wherefore, not with reason, Thales ... + declares the loadstone to be animate, a part of the animate + mother earth and her beloved offspring.[204] + +Gilbert ended book 5 of his treatise on the magnet with a persuasive +plea for his magnetic philosophy of the cosmos, yet his conceptual +scheme was not too successful an induction in the eyes of his +contemporaries. In particular the man from whom the Royal Society took +the inspiration for their motto, "Nullius in verba," did not value his +magnetic philosophy very highly. Whether Francis Bacon was alluding to +Gilbert when he expounded his parable of the spider and the ant[205] +is not explicit, but he certainly had him in mind when he wrote of +the Idols of the Cave and the Idols of the Theater.[206] + + [199] M: p. 108. + + [200] M: p. 110. + + [201] M: p. 216. + + [202] M: p. 311. + + [203] M: pp. 310, 311. + + [204] M: p. 312. + + [205] Francis Bacon, _op. cit._ (footnote 42), vol. 1, + _Novum organum_, bk. 1, ch. 95, p. 306. + + [206] _Ibid._, ch. 54 and ch. 64 (pp. 259 and 267). + +Few of the subsequent experimenters and writers on magnetism turned to +Gilbert's work to explain the effects they discussed. Although both +his countrymen Sir Thomas Browne[207] and Robert Boyle[208] described +a number of the experiments already described by Gilbert and even used +phrases similar to his in describing them, they tended to ignore +Gilbert and his explanation of them. Instead, both turned to an +explanation based upon magnetic effluvia or corpuscles. The only +direct continuation of Gilbert's _De magnete_ was the _Philosophia +magnetica_ of Nicolaus Cabeus.[209] The latter sought to bring +Gilbert's explanation of magnetism more directly into the fold of +medieval substantial forms. + + [207] Sir Thomas Browne, _Pseudodoxia epidemica_, ed. 3, + London, 1658, bk. 2, ch. 2, 3, 4. + + [208] Robert Boyle, _Experiments and notes about the + mechanical production of magnetism_, London, 1676. + + [209] Nicolaus Cabeaus, _Philosophia magnetica_, Ferarra, + 1629. + +However, Gilbert's efforts towards a magnetic philosophy did find +approval in two of the men that made the seventeenth century +scientific revolution. While Galileo Galilei[210] was critical of +Gilbert's arguments as being unnecessarily loose, he nevertheless saw +in them some support for the Copernican world-system. Johannes +Kepler[211] found in Gilbert's explanation of the loadstone-earth a +possible physical framework for his own investigations on planetary +motions. + + [210] Galileo Galilei, _Dialogue on the great world systems_, + in the translation of T. Salusbury, edited and corrected by + G. de Santillana, University of Chicago Press, 1953, pp. + 409-423. + + [211] Cassirer, _op. cit._ (footnote 3), vol. 1, p. 359-367. + +Yet Galileo and Kepler had moved beyond Gilbert's world of +intellectual experience. They were no longer concerned with +determining the nature of material things in order to explain their +qualities. Instead, they had passed into the realm of the mathematical +relations of kinematics: quantitative law had replaced qualitative +experience of cause and effect. Gilbert had some intimations of the +former, but he was primarily concerned with explaining magnetism in +terms of substance and attribute. He had to ascertain the nature of +the loadstone and of the earth in order to explain their properties +and their motions. He even went further and explained the nature of +the form of the loadstone. + +His method of determining the nature of a substance was a rather +primitive one--it was not by a process of induction and deduction, nor +by synthesis and analysis, nor by "resolutio" and "compositio," but by +the use of analogies. He compared the natural history of metals and +rocks with that of plants, and gave the two former the same kind of +principle as the last. He determined the nature of the entity behind +electric attraction by finding that such attractions could be +screened, and hence it had to be corporeal. After comparing this +"corporeal" attraction with that of the surface forces of a fluid, he +concluded that the entity was a subtle fluid. He determined the nature +of the entity behind magnetic coition by (incorrectly) finding that it +cannot be screened, and hence the cause had to be a formal one. Since +both stars and the loadstone can carry out regular motions, and stars +had souls, the form of the loadstone had to be a soul. The method of +analogy was used again in his comparison of the properties of a +magnetized needle placed over a terrella with the properties of a +compass placed over the earth, whence he concluded the earth to be a +giant loadstone. Since the earth resembled the other celestial globes, +it had to have, the circular inertia of these globes.[212] As for his +magnetic experiments to show physically that the earth moved, and his +unbridled speculations on the "animae" of the celestial globes, one is +inclined to agree with Bacon's estimate of his magnetic philosophy. + +One might consider Gilbert's book as a Renaissance recasting of +Aristotle's _De caelo_ with the earth in the role of a heavenly body. +So it might well be, for Gilbert was still concerned with +distinguishing the nature of the heavenly body, earth, that caused the +coitional and revolving motions, from those natures for which up and +down, and coacervation were the natural motions. Because the natural +motions were different, the natures had to be different, and these +different natures led to a universe and a concept of space neither of +which were Aristotelian. One no longer had a central reference point +for absolute space; there was no "motor essentialis" focused upon the +earth but one had only the mutual motion of the heavenly bodies. The +natural distinction between heaven and earth was gone, for the earth +was no longer an inert recipient but a source of wonder, and so the +stage was set for the universe of Giordano Bruno.[213] The +Aristotelian philosophy of nature was used to justify a new cosmology, +but there was no break with the past such as one finds in Galileo and +Kepler. Instead he followed the chimera of the world organism, as +Paracelsus had, and of the world soul, as Bruno had. Consequently +Gilbert's physiology did not enter into the main stream of science. + + [212] Because the earth has the same nature as a celestial + globe, its revolution and circular inertia require no more + explanation than those of any other heavenly body. + + [213] One wonders if Bruno might not have been another of the + stimuli for Gilbert. The latter's interest in magnetism began + shortly before Bruno visited England and lectured on his + interpretation of the Copernican theory. + +Yet this is not to deny Gilbert's services to natural philosophy. +Although not all of his experimental distinction between electric and +magnetic forces has been retained, still, some of it has. His "orbis +virtutis" was to become a field of force, and his class of electrics, +insulators of electricity. His practice of arming a loadstone was to +be of considerable importance in the period before the invention of +the electromagnet. His limited recognition of the mutual nature of +forces and their quantitative basis in mass was ultimately to appear +in Newton's second and third laws of motion. In spite of the +weaknesses of the method of analogy, Gilbert's experimental model of +the terrella to interpret the earth's magnetism was as much a +contribution to scientific method as to the theory of magnetism. + +Consequently, in spite of an explanation of electricity and magnetism +that one would be amused to find in a textbook today, we can still +read his _De magnete_ with interest and profit. But more important +than his scientific speculations, is the insight he can give us into a +Renaissance philosophy of nature and its relation to medieval thought. +One does not find in _De magnete_ a prototype of modern physical +science in the same sense one can in the writings of Galileo and +Kepler. Instead one finds here a full-fledged example of an earlier +kind of science, and this is Gilbert's main value to the historian +today. + + + + + +End of the Project Gutenberg EBook of The Natural Philosophy of William +Gilbert and His Predecessors, by W. 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