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and His Predecessors, by W. James King
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Title: The Natural Philosophy of William Gilbert and His Predecessors
Author: W. James King
Release Date: April 15, 2010 [EBook #31999]
Language: English
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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. Koyré considers the Archimedeanization of space as one of the
necessary features of the development of modern astronomy and
physics.[2] A. N. Whitehead and E. Cassirer have turned to measurement
and the quantification of force as marking this transition.[3]
However, the obvious absence[4] of such techniques in _De magnete_
makes it difficult to consider Gilbert as a founder of modern
electricity and magnetism in this sense.
[2] Alexandre Koyré, _Études galiléennes_, 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, _Beiträge 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] René 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. Aër (commune
effluvium telluris) & partes disjunctis unit, & tellus
mediante aëre ad se revocat corpora; aliter quae in
superioribus locis essent corpora, terram non ita avide
appelerent.
Electrica effluvia ab aëre multum differunt, & u aër 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.
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Gilbert and His Predecessors, by W. James King
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