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Medieval Academy of America
John Buridan on the Habitability of the EarthAuthor(s): Ernest
A. MoodySource: Speculum, Vol. 16, No. 4 (Oct., 1941), pp.
415-425Published by: Medieval Academy of AmericaStable URL:
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JOHN BURIDAN ON THE HABITABILITY OF THE EARTH BY ERNEST A.
MOODY
I. INTRODUCTION PIERRE DUHEM has indicated the importance of the
work of John Buridan of Bethune in laying the foundations of the
modern science of mechanics. Buridan was the senior member, and the
original and constructive genius, of that group of
fourteenth-century moderni described by Duhem as 'the Parisian
precursors of Galileo.' His ideas in dynamics were given
mathematical formulation by Nicholas of Oresme, and were carried to
the new universities of central Europe by such distinguished pupils
as Marsilius of Inghen and Albert of Saxony. In the sixteenth
century, this 'tradition of Buridan' found expositors and defenders
in northern Italy, where it exercised a decisive influence on the
thought of Leonardo da Vinci and of Galileo.1
Little is known of Buridan's life. He was born at Bethune, near
Arras, around 1300 A.D., and was rector of the University of Paris
in the year 1328.2 About this time he visited Avignon on some
mission to the papal court, pausing en route to take meteorological
observations in the Cevennes mountains.3 His name appears in the
university archives, and in the Vatican Register, in connection
with benefices and honours conferred on him between 1328 and 1358,
in the course of a long and distinguished career as teacher on the
Faculty of Arts. These documents refer to Buridan as 'the
celebrated philosopher,' or as 'our most distinguished man,' and
indicate that he was held in high esteem by his colleagues and su-
periors.4
Buridan appears to have had only one scholastic enemy: Nicholas
of Autre- court, the 'mediaeval Hume.' Nicholas' sceptical ideas
are attacked repeatedly in Buridan's writings, and it was Buridan
who signed the prohibitory statute of 1340, in which the Faculty of
Arts condemned the practice of applying strict logical analysis to
scriptural texts, as pursued by Nicholas of Autrecourt and his
disciples.5 The last documentary mention of Buridan is dated July
12, 1358, and consists of a concordat between the Picard and
English nations, signed by Buri- dan as representative of the
Picards.8 It is probable that Buridan's career was
1 P. Duhem, Etudes sur Leonard de Vinci, III' Se'rie: Les
pre'curseurs parisiens de Galilee (Paris: A. Hermann et Fils,
1913).
2 Denifle & Chatelain, Chartularium universitatis
Parisiensis, ii (Paris, 1891), No. 870. Apparently this document
was overlooked by Dr Lynn Thorndike in his History of Magic and
Experimental Sci- ence, iII (New York, 1934), p. 374, Note 14,
where he states that Duhem and Haureau were mis- taken in saying
that Buridan had been rector prior to the year 1340.
3P. Duhem, Le Systeme du Monde, iv (Paris: A. Hermann et Fils,
1916), p. 126. 4Chartul. Univ. Paris, ii, p. 307, Note 1; and Nos
1146, 1156, 1165. See also Denifle & Chatelain,
Auctarium chartularii universitatis Parisiensis, Liber
procuratorum nationis Anglicanae, i (Paris, 1894), col. 41.
6 Buridan deals with Nicholas' doctrines in his Quaestiones in
octo libros Physicorum Aristotelis, I (edited by John Dullaert,
Paris, 1509), Lib. i, Qu. 4, fols 4v-6v, and also in his
Quaestiones in Meta- physicam Aristotelis (edited by J. Badius,
Paris, 1518), Lib. ii, Qu. 1, fol. Ixr.
6 Auctarium chartul. univ. Paris., i, cols. 206, 212, and
233-235.
415
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416 The Habitability of the Earth
terminated in that year by death from the plague, for his name
ceased thence- forth to occur in the university records.
The extant writings attributed to Buridan consist almost
exclusively of Ex- positions and Questions on the treatises of
Aristotle. In this field he was ex- tremely prolific, his lectures
covering the entire corpus of authentic aristotelian writings, with
the exception of the works on animals and the Poetics. These lec-
tures follow the order and subject matter of the aristotelian
treatises, but those which are in the form of Questions are very
independent of the text, and are equivalent in most cases to
original treatises.1
It was in the field of physics, and particularly in dynamics,
that Buridan's thought was most original, constructive, and
influential. This fact was empha- sized by Duhem, who rated Buridan
a mediocre astronomer, and credited Oresme and Albert of Saxony
with the theories and discoveries which mark the beginnings of
modern kinematics and statics. A more careful examination of
fourteenth-century scientific writings shows, however, that most of
the ideas advanced by Oresme and Albert in these fields were
derived from Buridan, wlho in turn seems to have borrowed them from
earlier fourteenth-century teachers at Oxford and Paris. The whole
question of Buridan's originality, and of the signif- icance and
coherence of his work in physical science, requires for its
determina- tion a much greater knowledge of fourteenth century
scientific writings, and a more exhaustive study of Buridan's own
works, than has yet been achieved.2
Quite apart from the question of originality or genius, however,
Buridan's writings have great historical value and interest. For
one thing, they cover practi- cally the whole field of scientific
and philosophical knowledge and opinion, of the fourteenth century,
and thus form a kind of Summa philosophiae for that period. Their
method of discussion, furthermore, gives them particular value as
sources of information concerning the state of fourteenth-century
scientific knowledge as a whole. In his capacity as teacher,
Buridan takes it upon himself to set forth all the diverse views
and arguments of his contemporaries on each problem, and in many
instances he confines himself to such exposition, leaving it to the
auditor or reader to make his choice among the alternative
positions. Such is the case in his treat- ment of the problem of
the rotation of the earth on its own axis, given in Question 22 of
the second book of his Quaestiones super libris de caelo et mundo.
In this Question, Buridan expounds the theory of diurnal rotation
which Copernicus was to defend more than one hundred and fifty
years later, giving excellent argu- ments in its favor. He then
argues against the theory from the standpoint of the
' B. Geyer, Ueberwegs Grundriss der Geschichte der Philosophie,
Band II (1lth edition, Berlin, 1928), p. 595, gives the list of
printed editions. The manuscript texts are discussed by K.
Michalski, 'Les courants critiques et sceptiques dans la
philosophie du XIVe siecle,' in Bulletin International de
l'Acade'mie Polonaise des Sciences et des Lettres, Classe
d'Histoire et de Philosophie, Annee 1925 (Cracow: Imprimerie de
l'Universite, 1927), pp. 202-209.
2 P. Duhem, Le Systeme du Monde, iv, pp. 135-142, discusses
Buridan's astronomy. On the ideas in statics advanced by Albert of
Saxony, see P. Duhem, Les Origines de la Statique, ii (Paris: A.
Her- mann et Fils, 1906), ch. xv. On Oresme, see P. Duhem, Etudes
sur Leonard de Vinci, I1e Sgrie (Paris, 1913), pp. 346-398, and E.
Borchert, 'Die Lehre von der Bewegung bei Nicolaus Oresme,' in
Beitrdge zur Geschichte der Philosophie des Mittelalters, Band
xxxi, Hft. 3 (Muenster, 1934).
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The Habitability of the Earth 417
Ptolemaic astronomy, and indicates his own preference for the
latter system. But he clearly points out to his students that the
newer theory is entirely defensible, since the observed movements
of the heavenly bodies may be described in func- tion of one
hypothesis as well as of the other.1
The text here edited, dealing with the problem of the
habitability of the earth, is based on two manuscripts of Buridan's
Quaestiones super libris de caelo et mundo, where it appears as the
seventh Question of the second book. The two manuscripts utilized
for this edition are from the Bavarian State Library at Munich
(Cod. lat. monac. 19551), and from the library of Bruges (Ms. 477,
anon.). The correspondence of the Questions on the De caelo,
contained in the anonymous Bruges manuscript, with those attributed
by the Munich manuscript to John Buridan, was discovered by the
Abbe Michalski. Since the only copies of this work previously known
were those offered by two manuscripts at Munich, and since the
Bruges text is more complete and more legible than that of the Cod.
lat. monac. 19551, Michalski's identification is of great
value.2
The Munich Codex 19551 contains 149 folios, closely written in
Gothic cursive of the late fourteenth century. The colophon to
Buridan's Questions on the De generatione et corruptione, on fol.
125v, gives 1378 as the date of the copy; and since the handwriting
of this text appears to be the same as that of the copy of
Buridan's Questions on the De caelo et mundo immediately preceding,
we may conclude that both works were transcribed in this manuscript
around the year 1378. The Questions on the De caelo et mundo cover
folios 7Or-105v, and consist of twenty-five Questions on Book i of
Aristotle's treatise, twenty-three on Book ii, two on Book iII, and
eight on Book iv. The colophon, at the foot of the second column on
folio 105v, attributes the text directly to Buridan, as follows:
"Expli- ciunt quaestiones super libris de caelo et mundo Magistri
Johannis Buridani Rectoris Parisius.'
Other works of Buridan are also contained in this Munich codex:
an abbre- viated version of his Questions on Aristotle's Physics, a
set of his Questions on the De generatione et corruptione, and an
incomplete set of his Questions on Aristotle's Parva naturalia.
While Duhem, on the basis of an inaccurate report of the manu-
script transmitted to him by Pere Bulliot, asserted that these
texts were reportata
1 J. Buridan, Questiones de caelo et mundo, ii, Qu. 22 (Cod.
lat. monac. 19551, fol. 99r): 'Et in- dubitanter verum est quod si
esset ita sicut ista opinio ponit, omnia in caelo apparerent nobis
sicut nune apparent.' This Question was edited by J. Bulliot, 'Jean
Buridan et le mouvement de la terre, Question 92e du second livre
du "De Coelo",' in Revue de Philosophie, 14e annee, t. xxv (Paris,
1914). Bulliot's text is that of the Munich Ms 19551.
2 K. Michalski, 'La physique nouvelle et les differents courants
philosophiques au XIVe siecle,' Bulletin International de
l'Academie Polonaise des Sciences et des Lettres, Classe d'Histoire
et de Phi- losophie, Avril-Juin 19Q7 (Cracovie: Imprimerie de
l'Universite, 1928), pp. 114-117. Not having had the opportunity to
examine the Cod. lat. monac. 19551, or Bruges 477, directly, I have
followed the careful report on them given by Michalski in the above
monograph; my edition of the text is based on photo- static copies
of the folios containing Buridan's Qu. de caelo et mundo. I have to
thank the director of the Bayerische Staatsbibliothek for his
courtesy in arranging for the taking of photostats of the cod. lat.
monac. 19551, fols. 70r-125v, in my behalf. The other Munich
manuscript, purporting to contain a copy of this work of Buridan,
is Cod. lat. monac. 761; due to war conditions, I have been unable
to obtain either a photographic reproduction of this manuscript, or
a description of its contents.
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418 The Habitability of the Earth
rather than literal copies of Buridan's lectures, Michalski
concludes, after careful examination and comparison of extant
manuscript copies, that the Munich text of the Questiones de caelo
et mundo is to be attributed to Buridan.1
The Questiones de caelo et mundo contained in the anonymous
Bruges Ms 477 commence on fol. 164v and end on fol. 21Or, followed
by a table of the Questions, covering fols 21Or-210v. The Questions
contained in this text are identical with those of the Munich
codex, except that it contains an initial Question (Utrum de mundo
debet esse scientia distincta a scientia libri Physicorum) which is
missing from the Munich manuscript. The Bruges copy is in all
respects superior to that of Munich; it is more carefully
transcribed, more free from lacunae, and more legible. Though on
palaeographic grounds it is not to be considered earlier than the
Munich codex, but probably slightly later, its relatively greater
completeness indicates that it is either a more faithful copy of a
common original, or a copy of a more accurate earlier text. The two
manuscript copies are unquestionably of common ancestry, the
variants being quite obviously due to the copyists. In al- most all
instances it is the scribe of the Munich codex who is at fault, by
reason of haste, inattention, or lack of comprehension of the work
being copied.
The seventh Question on the second book of Aristotle's De caelo,
in which Buridan discusses the problem of whether the whole earth
is habitable, is here edited for the first time from the two
manuscripts above mentioned. In Cod. lat. monac. 19551, this
Question extends from fol. 87r, col. A to fol. 88r col. B; in the
Ms. Bruges 477 it runs from fol. 188v col. A to fol. 189v col.
B.
The problem of the habitability of the earth, treated in this
Question, was not new in the mediaeval tradition. The geographical
information and misinforma- tion contained in Pliny's Naturalis
Historia was known to mediaeval writers, and utilized to some
extent in their discussions. But their interest in the problem, and
their methods of seeking its solution, were inspired by Aristotle
rather than by Pliny; they were concerned with the causes which
determine and limit the possi- bilities of human habitation of the
earth, rather than with the mere facts as to how much of the earth
is actually inhabited. Hence little attention is paid to the
descriptive information provided by explorers and travellers,
except insofar as it may confirm the theoretical grounds. The
discussion is pursued in terms of astron- omy and geology, sciences
which underlie geography by exhibiting certain general causes which
limit geographical possibilities. It is because the principles of
the solution of the problem are astronomical and geological, that
Buridan raises the question of the earth's habitability in his
lectures on the De caelo et mundo.2
Buridan's discussion falls into two main divisions: he first
treats of climatic conditions determined by astronomical causes, as
factors limiting the habitability
I Michalski, 'La physique nouvelle, etc.,' loc. cit., pp.
115-116. 2 The aristotelian text of the De caelo does not directly
raise this question at all, though the dis-
cussion in Book ii, ch. 4, fols. 287a 32-287b 21, of the
sphericity of the earth and of the regions of the four elements, is
relevant to the problem, as Buridan's discussion shows. The
traditional locus of this problem of the habitability of the earth
was Aristotle's Meteorologica, ii, ch. 5, 362a 33-362b 29, where
climates and winds are discussed. Thus Aquinas' treatment of the
problem is found in his Expositio in Meteorologicam Aristotelis,
ii, Lect. x (Leonine ed., iii, pp. 419-420), and not in his
commentary on the De caelo.
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The Habitability of the Earth 419
of the earth, and he then deals with the problem of why the dry
land has not long since been washed into the sea. The discussion of
climates involves the traditional distinction of the five zones,
and is chiefly devoted to the problem of whether or not the
equatorial zone, and the south temperate zone, are fitted for human
habi- tation. Most of the arguments invoked are purely
astronomical, but the Arab philosopher Ibn-Sina (Avicenna) is cited
as authority for the theory that the most temperate of all climates
is found at the equator, and for a story that some men had
penetrated to this region and had brought back reports of a great
civilization there, possessed of all the perfections of an earthly
paradise. Buridan's attitude toward this tale of Avicenna, and
toward the Arab philosopher's a priori argu- ments in support of
it, is reserved if not indeed sceptical.'
More interesting, from the scientific point of view, is the
discussion given in the second part of the Question. Since water is
lighter than earth, and since the ele- ments tend toward
equilibrium at their proper levels, it would seem that the whole
earth should be covered by water. This theory is confirmed by the
observed phenomenon of erosion, indicating that over a long period
of time the dry land should have been completely washed into the
sea by the action of rivers and rain. Since this has obviously not
happened, there must be some constant process which counterbalances
erosion, by which the elevation of the continental areas above sea
level is maintained.
Two theories are suggested. The first rests on the postulate
that the sphere of water is eccentric to the earth, so that its
natural center is outside the center of the earth. Several
objections are raised against this view, which seems to Buridan
insufficient because of its failure to give any natural cause of
such eccentricity. He therefore offers another 'more probable'
theory, based on the distinction between center of gravity and
center of magnitude. If we assume a common center of gravity for
both earth and water, the water will always flow to its natural
level with respect to this center, and since it is a fluid its
center of magnitude will al- ways be practically coincident with
its center of gravity. But the center of magni- tude of the earth
need not coincide with its center of gravity, because earth is not
a homogeneous fluid like water. On the contrary, the continental
areas, which are exposed to the heat of the sun and to
pulverization and admixture of air, will be lighter and less dense
than those parts of the earth which are under the sea. Since,
therefore, the earth is not strictly symmetrical but has more dry
land on one side than on the other, it cannot become symmetrical in
this respect, because its center of gravity cannot become
coincident with its center of volume. The proc- esses of erosion
tend to make the dry side of the earth smaller in relative volume;
but in so doing they make it lighter, and thus offset the change
effected in the earth's center of volume, by an equal change in its
center of gravity.
1 This theory of Avicenna is twice mentioned by Roger Bacon, in
the Opus maius (ed. J. H. Bridges, Oxford 1897-1900), Part iv,
Dist. iv, ch. 4, and in the Oputs tertium (ed. J. S. Brewer, London
1859), pp. 119-120. Bacon cites as sources the first book of
Avicenna's Canon, and the first book of his treatise on animals. I
have been unable to locate this second citation in the Venice,
1530, edition of Avicenna; the first refers to the Canon, Lib. I,
Fen ii, Doctrina ii, cap. 8 (Avicennae medicorum arabum principis
Liber Canonis. . . Basileae, per loannes Hervagios, 1556, pp.
62-63).
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420 The Habitability of the Earth
This theory, which seems to please Buridan greatly, affords an
explanation of a number of phenomena. Besides accounting for the
continued existence of dry land despite long continued erosive
processes, it affords an explanation for the forma- tion of
mountains, replacing the numerous fantastic theories advanced by
ancient writers. It likewise explains the presence of fossils in
regions far from the sea, and offers a basis for a mechanical
explanation of earthquakes. Possibly Buridan was aware of these
applications of his theory, for fossils and earthquakes were ob-
served and discussed in mediaeval times. Leonardo da Vinci, in any
case, made the application to the problem of fossils, having become
acquainted with Buri- dan's theory of the movement of the earth by
way of Albert of Saxony.'
The significance of Buridan's discussion and resolution of this
problem of land and sea lies in the fact that he sought, and found,
a strictly mechanical explana- tion of a geological problem. Tbis
explanation was, in essentials, the theory of isostasy which plays
such a basic part in modern physical geology. Whether the theory
was original with Buridan, or taken by him from some unidentified
pred- decessor or contemporary, is a matter of conjecture. Dr Lynn
Thorndike has found a full statement of the theory in an anonymous
treatise on natural phi- losophy written in the fourteenth century;
but the content of this treatise, as described by Dr Thorndike,
indicates that it was written in the latter part of the century,
and probably after Buridan's death.2
It is interesting to compare Buridan's discussion concerning the
habitability of the earth with that which St Thomas Aquinas offers
on the same topic in his commentary on the Meteorologica of
Aristotle.' St Thomas is content to restate Aristotle's conclusions
and arguments as they stand, without seeking to develop the problem
further. Buridan, by contrast, takes the aristotelian text as a
point of departure for independent inquiry - an inquiry primarily
determined by me- chanical principles in relation to observable
phenomena. Arguments of a teleo- logical and analogical order,
though taken into consideration, no longer figure as
'demonstrations,' but only as 'persuasions.' Physical explanation
is conceived in terms of forces, resistances, and measurable or
observable factors.
Is this fourteenth-century shift from a 'metaphysical' to a
'scientific' attitude toward cosmological problems a sign of the
failure of the mediaeval philosophical enterprise, or of its
success? This is a question worthy of our most considered
reflection.
1 P. Duhem, Etudes sur Leonard de Vinci, IlIf Serie, pp. 32-33.
2 L. Thorndike, History of Magic and Experimental Science, III, pp.
580-581. Many of the theories
advanced in this treatise, as described by Dr Thorndike, are
characteristic of Buridan himself. It cannot be a work of Buridan,
however, since its author opposes Buridan, and defends Ockham's
position, on the fundamental problem of whether or not motion is an
absolute entity distinct from the mobile quod movetur. Buridan's
theory of the center of gravity of the earth, in connection with
the maintenance of dry land above sea level, was also stated by
John de Fundis in 1435, according to Dr Thorndike, op. cit., iv, p.
Q39.
3 Thomas Aquinas, Expositio in Meteorologicam Aristotelis, ii,
Lect. x (Leonine ed., iii, pp. 419- 420).
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The Habitability of the Earth 421
II. TEXT (JOHANNIs BURIDANI SUPER LIBRO SECUNDO DE CAELO ET
MUNDO
QUAESTIO SEPTIMA)
Septimo consequenter quaeritur: Utrum tota terra sit
habitabilis. 1
Arguitur primo quod sic, quia communiter dicitur quod una quarta
pars terrae est habitabilis, et non apparet ratio quare magis
debeat esse una quarta habitabilis quam aliae quartae; igitur omnes
quartae debent concedi habitabiles, et per consequens tota terra.
Et 5 hoc etiam apparet per concessionem Aristotelis, qui concedit
ita esse habitabilem terram nobis oppositam sicut istam; de illis
enim dicit quod ipsi habitant sursum et ad dextram, nos autem
deorsum et ad sinistram.'
Deinde arguitur quod nulla pars terrae debeat esse habitabilis,
quia terra est sphaerica 10 et in medio mundi sicut centrum, ut
habetur secundo huius.2 Aqua autem naturaliter sita est supra
terram et fluit semper ad locum decliviorem, propter quod etiam
naturaliter efficitur sphaerica, ut habetur secundo huius ;3 ex quo
sequitur quod ipsa naturaliter debet totam terram circumdare, et
sic nulla pars terrae esset habitabilis propter aquas. Nec valet
dicere quod sunt montes et elevationes in terra, ad quas
elevationes aqua circumdans 15 non attingit, ideo illae elevationes
sunt habitabiles. Contra hoc obicitur fortiter, si mundus fuerit
perpetuus ut ponit Aristoteles, quia omni tempore partes superiores
ex montibus descendunt multae ad valles, et nullae vel paucae
ascendunt; et sic ab infinito tempore illi montes deberent esse
totaliter consumpti et reducti ad planitiem.
90 Similiter, si terra sit elevatior ubi non est mare, et
depressior ubi est mare seu declivior,
tunc manifestum est quod omni tempore multae partes istius
terrae altioris portantur cum fluviis in profundum maris, unde
provenit quod mare efficitur grossum et salsum; et illae partes
terrae non revertuntur de profundo maris ad istam terram, imo quod
elevatur de mari per exhalationem seu evaporationem non est nisi
subtile aquosum, et non grossum 25 terrenum. Ideo videtur quod ab
infinito tempore tota profunditas maris deberet esse re- pleta
terra, et haec elevatio terrae deberet esse consumpta; et sic aqua
naturaliter deberet totam terram circumdare, nec deberent esse
aliquae elevationes discoopertae.
Et hoc etiam confirmatur ex alio, quia sicut sphaera aeris valde
excedit in magnitudine 30 et profunditate sphaeram aquae, ita, ut
sit proportio elementorum, sphaera aquae debet notabiliter excedere
in magnitudine et profunditate sphaeram terrae; et si sit ita, ipsa
debet elevari undique super terram plus quam ad montes altissimos;
ideo nihil debet re- manere habitabile.
5 Oppositum amborum apparet ad sensum. Magna enim pars terrae
habitatur, et magna
etiam est quae non habitatur.
Ista quaestio videtur mihi valde difficilis. Et primitus
notandum est de ea, quod dupli- 39
Varia lectio: [B= Ms. Bruges 477: M= Cod. lat. Monac. 19551) 1.
Septimo om. B. S. pars om. B. 4-5. aliae quartael alia 31. 14.
esset] est M. 19. totaliter] toti B. 24. quod om. M. R5. seu] vel
M. 30. etiam om. 31. 31. debet] deberet M. 36. habitatur]
inhabitatur M. 39. valde om. M. primitus ... ea] primo notandum
M.
1 Aristotle, De caelo, ii, ch. 2, 985b 23-5. 2 Aristotle, De
caelo, ii, ch. 14, 296b 7-298a 20. t Aristotle, De caelo, ii, ch.
4, Q87b 5-8.
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422 The Habitability of the Earth
1 citer terra potest reddi inhabitabilis: uno modo propter
excessum in primis qualitatibus, maxime in calido et in frigido;
alio modo propter impedimentum aquarum. Et primo dicemus de primo
istorum modorum.
5 Notandum est ergo quod terra imaginatur dividi in quinque
zonas secundum exigentiam corporum caelestium. Prima zona est sub
circulo aequinoctiali inter tropicum Cancri et tropicum Capricorni,
et directe super illam zonam decurrunt omni tempore sol et alii
planetae. Et de ista zona dicunt multi quod ipsa est inhabitabilis
propter excessivum calorem ab ipso sole.'
10 Aliae duae zonae sunt sub polis, ita quod una est sub
arctico, alia sub antarctico; et extendunt se usque ad illos parvos
circulos quos circa polos mundi describunt poli zodiaci moti motu
diurno. Et dicitur quod illae duae zonae sunt inhabitabiles ex
nimio frigore propter elongationem a sole.2
Aliae duae zonae sunt una inter tropicum Cancri et parvum
circulum arcticum, in qua i5 habitamus; alia similiter est ad aliam
partem inter tropicum Capricorni et parvum circu-
lum antarcticum. Et istae duae reputantur communiter habitabiles
et satis temperatae, quia nec sunt sub sole nec nimis distant a
sole.3
Ita dicunt multi communiter quantum est ex caliditate et
frigiditate; et omnes, ut mihi videtur, concesserunt quod duae
zonae sub polis sunt inhabitabiles vel nimis difficilis
Ro habitationis propter nimium excessum frigoris et recessum
earum a sole. Omnes etiam con- cesserunt zonam inter tropicum
Cancri et parvum circulum arcticum esse habitabilem, quia experimur
eius habitationem. Sed de aliis duabus zonis fuerunt diversae
magnae opiniones.
25 Et modo dicemus de zona media quae est inter tropicos sub
aequinoctiali. Statim enim prima facie apparet quod illa propter
nimium calorem sit inhabitabilis, quia procedentes usque ad
tropicum Cancri inveniunt tantum calorem, quod ibi homines ultra
communem modum hominum aduruntur et fiunt nigri, sicut apparet de
Indis et Aethiopibus; ideo videtur quod ultra esset tanta caliditas
quod non possent ibi homines habitare. Et hoc con-
s0 firmatur, quia si esset ultra habitatio, aliqui nostrum
venissent ad eos, vel illi venissent ad nos; quod non est auditum,
ut aliqui dicunt.
Tamen hoc non obstante Avicenna4 opinabatur contrarium, dicens
quod sub aequinoc- tiali erat summe bona et temperatissima
habitatio; et dicebat se audivisse quod aliqui venerunt ad illum
locum qui reversi erant et narrabant de una maxima et
nobilissima
35 civitate quae erat sub circulo aequinoctiali. Et Avicenna
habet plures rationes per se. Prima est, quod semper illic sunt
dies aequales noctibus, et ideo frigiditas noctis tem-
perat calorem diei et e contrario. Secunda ratio est, quod licet
sol transeat directe super capita eorum, tamen statim
transit et non multo tempore manet ibi. In sphaeris autem
declivibus dies sunt valde longi 40 et sol, licet non directe
veniat super capita hominum, tamen venit prope et non cito
transit, imo longo tempore girat circa capita hominum. Et ideo
non oportet quod sub
5. est ergo] igitur M. I. describunt om. M. 12. moti] in M. 14.
Cancri om. B. 18. multi om. M. 20. etiam] autem M. 25. enim om. M.
26. sit] est M. 30. aliqui ... venissent] aliquis vestrum venisset
B. 33. dicebat] dixit M. 34. venerunt] fuerunt B. 34. qui . . .
erant om. B. et nobilissima om. M. 38. est om. Ml. 38. tamen] cum
B. 41. longo tempore] longe B.
I Cf. Aristotle, Meteorologica ii, ch. 5, 362b 5-8. 2 Cf.
Aristotle, Meteorologica ii, ch. 5, 362b 8-9. 3 Ibid., 362b 5. 4
Avicennae medicorum arabum principis Liber Canonis, de medicinis
cordialibus, et Cantica.
Basileae, per loannes Hervagios, 1556, Lib. i, Fen ii, Doctrina
ii, cap. 8 (pp. 62-63). Cf. Roger Bacon, Opus maius, Part iv, Dist.
iv, cap. 4 (ed. J. H. Bridges, Ox. 1897-1900), and Opus tertium
(ed. J. S. Brewer, London 1859), pp. 119-120, who also cites
Avicenna's first book on animals as source of this opinion.
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The Habitability of the Earth 423
aequinoctiali sit tanta caliditas quanta est hie aliquando in
aestate, nec unquam est ibi 1 intensa frigiditas; ideo locus est
ibi temperatissimus.
Tertia ratio est, quia supponimus caelum et astra esse
perfectissime ordinata ad guber- nandum istum mundum, et maxime
homines et animalia et plantas, de quibus natura propter eorum
nobilitatem debet esse maxime sollicita; ideo rationabile est quod
ad illum 5 locum sit perfectissima hominum habitatio ad quem omnes
stellae caeli ordinatae sunt et simul habent aspectum; sed hoe est
ad locum sub aequinoctiali. Illis enim omnes stellae oriuntur et
occidunt, nobis autem nunquam oriuntur stellae quae sunt iuxta
polum ant- areticum; ergo illic debet esse summe bona habitatio.
Unde Avicenna sub aequinoctiali dicit esse paradisum terrestrem in
quo semper omni tempore plantae frondent et florent et 10
fructificant, et omni tempore blada matura colliguntur et alia
seminantur.
Sicut dubitatum est de zona media, ita aliqui dubitant de illa
zona quae est inter tropi- cum Capricorni et parvum eirculum
antareticum. Dicunt enim aliqui quod licet ista zona quam habitamus
sit temperata et habitabilis, tamen non sequitur quod illa alia
zona sit 15 temperata vel habitabilis, propter unam imaginationem
de sole. Astrologi enim ponunt solem habere eceentricum, et ita sol
multo remotior est a terra quando est in auge eceen- trici, et est
multo propinquior terrae quando est in opposito augis. Modo agens
naturale, quanto est propinquius passo, tanto fortius agit in
ipsum; et quanto est remotius a passo, tanto debilius agit in
ipsum. Modo ultra dicunt isti quod in Cancro sol est in auge eccen-
20 trici, et in Capricorno est in opposito augis; et ideo sequitur
quod ista zona nostra efficitur temperatior quia in aestate, sole
existente in Cancro et quasi supra nos, sol est valde remo- tus a
terra, propter quod calor est minus intensus. Sed in hieme, sole
existente in Capri- corno, fit nobis frigiditas quia sol est nobis
valde obliquus; tamen quia sol tune est pro- pinquus terrae non fit
nobis tanta frigiditas sicut si esset remotus. E contrario autem
est de 25 illa alia zona quae est ultra tropicum Capricorni; quia
cum sol est in Capricorno ipse est quasi supra capita eorum, et cum
hoc est propinquus terrae; ideo nimis intense calefacit, et non
potest habitari vel male potest habitari illa regio propter nimium
calorem. Sed quando sol est in Cancro, tune est illis valde
obliquus, et cum hoc est multum a terra re- motus; ideo valde
modicam virtutem habet super illos, ideo efficitur ibi frigiditas
nimis 30 intensa et prohibens bonam habitationem.
Nunc restat dicere de inhabitatione propter aquas. Et sunt de
hoc tres magnae opiniones. Aliqui ponunt unam solam quartam vel
quasi habitabilem, et alii ponunt omnes quartas terrae habere
habitationes. Et de ista opinione erit primo dicendum. 85
Isti ergo dicunt tam terram quam aquam esse concentricas mundo,
ita quod centrum mundi sit centrum earum ambarum; tamen dicunt in
qualibet quarta terrae esse multas plagas discoopertas aquis,
propter multas terrae gibbositates et quasi montium eleva- tiones
eminentes super aquas. Et dicunt multas alias partes terrae esse
coopertas aquis propter earum depressiones, ad modum vallium inter
praedictas elevationes. Et hoc dicunt 40 ita esse in qualibet
quarta terrae, cuius signum est quod de una plaga valde magna dis-
cooperta nos pertransimus valde magnum et longumn mare et venimus
ad aliam plagam discoopertam valde magnam, et verisimile est quod
ita esset circumeundo terram totam.
Sed contra istam opinionem sunt duae magnae dubitationes. Prima
est, quia omnia maria quae ab aliquibus poterunt transiri, et omnes
terrae habitabiles quae poterunt in- 45 veniri, continentur in ista
quarta terrae quam habitamus. Et aliqui laboraverunt in mari ad
permeandum mare in aliis quartis, et nunquam potuerunt pervenire ad
aliquam terram 47
6-7. ordinatae ... habent] habent ordinate et simul B. 10.
semper om. M. 14. quod omn. B. 18. terrae om. M. 21. ideo] tunc B.
22. et ... nos] est quasi nos supra B. valde om. B. 28. habitari]
inhabitari M. 34-35. omnes ... habitationes] habere alias quartas
M. 37. am- barum om. B., add. in marg. M. 39. coopertas]
discoopertas M. 43. esset] accideret M. 47. terram] partem M.
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424 The Habitability of the Earth
1 habitabilem; et ideo dicitur quod Hercules in finibus huius
quartae infixit columnas, in signum quod ultra eas non erat terra
habitabilis nec mare permeabile.
Alia dubitatio difficilior est, quae dicta fuerit prius, quia
haec opinio non potest salvare, si mundus fuerit aeternus, quo modo
istae elevationes terrae possunt salvari ab aeterno,
5 cum semper ex eis fluant multae partes terrae cum fluviis ad
fundum maris. lam enim ab infinito tempore deberent tales fundi
marium esse repleti, et deberent elevationes terrarum esse
consumptae; quod non est conveniens dicere volentibus tenere
perpetuitatem mundi in statu prospero animalibus et plantis sicut
nunc est.
Ideo alia fuit opinio, quae ponebat quod ad salutem animalium et
plantarum Deus et 10 natura ab aeterno ordinaverunt aquam
eccentricam, ita quod centrum terrae sit centrum
mundi, sed centrum aquae sit extra centrum mundi. Et sic dicunt
aquam semper defluere ad locum decliviorem non respectu centri
terrae vel mundi sed respectu proprii centri aquae. Et sic potest
esse una pars terrae quasi quarta discooperta aquis, omnibus aliis
existentibus coopertis aquis. Et sic isti salvant quod non sit nisi
una quarta terrae, vel
15 quasi, discooperta et habitabilis. Sed contra istam opinionem
remanent iterum duae dubitationes. Prima est, quia iste
mundus regitur a Deo, sed tamen mediante caelo si volumus loqui
naturaliter. Et ideo ex parte caeli oportet assignare causam illius
eccentricitatis. Non enim posset bene assignari ex parte terrae,
cuius partes sunt consimiles et homogeniae; nec etiam ex parte
aquae cum
0 eius partes sint etiam consimiles et homogeniae; nec ex parte
caeli moti, quia illud indif- ferenter et undique volvitur circa
terram et circa aquam, ideo ex parte ipsius non potest poni ratio
quare centrum aquae esset extra centrum terrae magis ad unam partem
quam ad aliam.
Secunda dubitatio est, quo modo montes sic possent infinito
tempore salvari, cum 25 omni tempore multae partes de locis
altioribus descendant ad loca inferiora, et paucae
ascendant vel portentur de locis bassis ad loca alta, maxime si
velimus loqui de valde altis montibus; ideo in infinito tempore
illi montes alti deberent esse consumpti.
Propter hoc est tertia opinio, quae videtur mihi probabilis, et
per quam perpetuo sal- varentur omnia apparentia, ponendo quod tam
terra quam aqua sunt concentricae mundo,
30 ita quod tota terra est innata congregari circa centrum
mundi, et etiam omnis aqua est innata fluere ad locum decliviorem
respectu centri mundi. Sed multa aqua est in visceribus terrae, et
multa etiam est commixta aeri per evaporationes; ideo non oportet
tantam aquam esse in mari quod excedat elevationes terrae.
Sed tunc quaeritur quo modo aeternaliter salvabuntur illae
elevationes terrae. Re- 35 spondetur, si secundum Aristotelem
poneretur mundus aeternus, quod ab aeterno ad salu-
tem animalium et plantarum mundus est ordinatus quod una pars
terrae, quasi una quarta, est discooperta aquis et eminens super
aquas; et semper manet et manebit etiam naturaliter discooperta,
non obstante concentricitate et licet etiam circumscriberemus
montes.
Et est talis imaginatio, quod terra in parte discooperta
alteratur ab aere et a calore solis, 40 et commiscetur sibi multus
aer, et sic fit illa terra rarior et levior et habens multos
poros
repletos aere vel corporibus subtilibus; pars autem terrae
cooperta aquis non sic alteratur ab aere et sole, ideo remanet
densior et gravior. Et ideo qui divideret terram (1. si dividere-
tur terra) per medium suae magnitudinis, una pars esset valde
gravior quam alia, illa enim
44 pars in qua terra esset discooperta esset multo levior. Et
sic apparet quod aliud est cen-
1. infixit] fixit M. 2. erat] esset M. 3. fuerit] fuit M.
salvare] salvari B. 4. ab aeterno] ex terra M. 9. salutem] saltum
M. 19. non] in M. sed] sed non M. 13. quar- ta] esse add. B. 14.
terrae om. M. 15. et] etiam M. 16. opinionem om. M. quia] quod M.
19-20. cum ... homogeniae] propter eandem rationem M. 20. illud]
non M. 24. est om. M. ?6. vel ... alta] e contrario M. ?7. in om.
M. 29. quod] quoddam M. 31. fluere] defluere M. 41. repletos ...
subtilibus] corporibus subtilibus vel ipso aere M. 4e. ter- ram om.
M. 44. qua terra] aqua Ml. discooperta] illa autem add. M.
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The Habitability of the Earth 425
trum magnitudinis terrae, et aliud est centrum gravitatis eius;
nam centrum gravitatis I est ubi tanta est gravitas ex una parte
sicut ex altera, et hoc non est in medio magnitudinis ut dictum
est. Modo ultra, quia terra per suam gravitatem tendit ad medium
mundi, ideo centrum gravitatis terrae est medium mundi, et non
centrum suae magnitudinis, propter quod terra ex una parte est
elevata supra aquam et ex alia parte est tota sub aqua. 5
Sed tune cum quaeris ultra, cum partes illius terrae elevatae
fluant cum fluviis ad aliam partem ad fundum maris, quo modo potest
salvari ista elevatio; respondetur quod si mul- tae partes terrae
elevatae moventur ad aliam partem ad fundum maris, tune gravificant
illam partem ad quam fluunt, et tune semper in residuum quod manet
discoopertum agunt sol et aer, et reddunt illam partem leviorem, et
ita illa pars quae prius erat centrum 10 gravitatis non amplius
erit centrum gravitatis. Ideo oportet quod totalis terra moveatur
et elevetur versus plagam discoopertam; et tune ex hoc sequitur
ultra, per processum tem- poris, quod partes quae sunt in centro
terrae tandem venient ad superficiem terrae habita- bilis, propter
hoc quod continue removentur de ista terra partes quae fluunt ad
partem oppositam; et sic semper salvatur elevatio terrae. 15
Sic etiam salvatur generatio altissimorum montium, quia intra
terram sunt partes terrae bene dissimiles, prout experiuntur
fodientes; aliquae sunt lapidosae et durae, aliae sunt magis
tenerae et citius divisibiles. Cum ergo illae partes interiores
terrae elevantur modo praedicto ad superficiem terrae, illae quae
sunt tenerae et divisibiles per ventos et pluvias et fluvios,
iterum inoventur ad profundum maris; aliae autem magis durae et 90
lapidosae non possunt sic dividi et fluere, ideo manent et continue
per longissima tem- pora elevantur per totalem terrae elevationem;
et ita possunt fieri montes altissimi. Et si nulli essent modo
montes, adhuc per istum modum fierent in futuro; nec apparent alii
modi per quos possent generari et manere tales montes. Aliqui enim
ponunt quod ex motibus terrae, per exhalationes, generantur montes.
Sed si hoc esset verum de aliquibus 25 parvis montibus, tamen de
altissimis montibus et longissimis non possit hoc esse verum; quia
ubi esset tanta exhalatio inclusa, quae tantam terram posset
elevare, non apparet bene; et si esset tanta terra elevata, tamen
exeunte exhalatione caderet iterum in foveam suam.
Et sic patet quaestio. 30
COLUMBIA UNIVERSITY.
1. eius om. M. ?. altera] alia M. 4. est medium] fit in centro
B. 5. supra] extra M. 9. discoopertum] indiscoopertum B. 10. erat]
fuit M. 11. erit] manet M. 18. ergo] igitur M. 20. magis] nimis M.
21. et fluere] nec fluere M. 22-23. Et ... montes] Et simili modo
essent montes M1. 24. tales] tanti M. Q6. possit. . . esse] esset
M. 28. terra om. M. exhalatione] sua add. M. 30. Et ... quaestio
om. B.
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Article Contentsp. 415p. 416p. 417p. 418p. 419p. 420p. 421p.
422p. 423p. 424p. 425
Issue Table of ContentsSpeculum, Vol. 16, No. 4 (Oct., 1941),
pp. 389-512Front MatterBishop Benno II of Osnabrck[pp. 389-403]The
Historical Background of the King of Tars [pp. 404-414]John Buridan
on the Habitability of the Earth [pp. 415-425]The One Hundred and
Three Names of Noah's Wife [pp. 426-452]De Opere Lemoviceno [pp.
453-458]Some Legends Concerning Eleanor of Aquitaine [pp.
459-468]The Tropology of Mediaeval Dedication Rites [pp.
469-479]Passages from the Coutume de Bretagne [pp. 480-484]The
Dates of Three Letters of Petrarch [pp. 485-486]The Date of John
the Scot's Annotationes in Marcianum [pp. 487-488]A Note on the
Vision of a Certain English Prior [pp. 488-489]ReviewsReview:
untitled [pp. 490-491]Review: untitled [pp. 491-492]Review:
untitled [pp. 492-493]Review: untitled [pp. 494-496]Review:
untitled [pp. 496-497]Review: untitled [pp. 497-499]Review:
untitled [pp. 499-501]Review: untitled [pp. 501-503]Review:
untitled [pp. 504-505]Review: untitled [pp. 505-506]Review:
untitled [pp. 506-507]
Bibliography of Periodical Literature [pp. 508-510]Books
Received [pp. 510-511]Communication [pp. 511]Announcement [pp.
512]Back Matter