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.