Subject: Re: [HM] Flat earth fallacy
From: Rene Grognard (Rene.Grognard@tip.csiro.au)
Date: Tue Feb 22 2000 - 02:22:42 EST
At 06:26 am 22/02/94 , Vassilis Kyrtatas wrote:
> 1. Is it true that people in the Middle Ages actually believed such a thing?
> 2. If so, would such flat earthers include scientists and other scholars?
> 3. Is it possible that the wisdom of people like Ptolemy, Eratosthenes,
> Aristotle, all of who believed that the Earth is spherical, was lost in the
> Middle Ages?
Quotes from Professor Edward Grant's monumental:
Planets, Stars, & Orbs -- The Medieval Cosmos, 1200-1687
Cambridge University Press 1996, ISBN 0-521-56509-X (paperback)
pp 628-629
Following Aristotle,
"Scholastic authors were unanimous in their acceptance of a round, though
not perfectly spherical, earth. There was, however, a medieval tradition of
a flat earth derived from Lactantius (ca. 250- ca. 325), who rejected a
spherical earth since it necessitated the existence of antipodes, which he
judged absurd, because things on the other side of a spherical earth would
fall off the earth toward the heaven [Lactantius, De divinis
institutionibus, 3:24].
When pious Christians sometimes placed Jerusalem at the center of the
earth, they seemed to imply, if they did not explicitly proclaim, a flat earth.
... the flat-earth theory was dealt a heavy blow by the introduction of
Ptolemy's Geography into the West in 1410 (the first edition was printed
in 1475). Indeed, a few years before its publication in 1475, the Portuguese
had crossed the equator to make many new discoveries along the coast
of Africa and reinforce the concept of a spherical earth.
Whatever may be said about the medieval flat-earth theory with Jerusalem
at its center, it played no role in scholastic questions on the sphericity of
the earth. ... Occasionally scholastic authors alluded [to it] but they did not
associate it with - or even mention, for that matter - Jerusalem or the Bible."
As for Columbus, the relevant debate was not about sphericity but about
the size of the Earth [Grant, pp 620-622].
"In De caelo (2.14.298a.15-16), Aristotle reports ... [an] earth's
circumference
of 400,000 stades. Although the exact value of Aristotle's stade is unknown,
scholars estimate that his value of the earth's circumference was approximately
twice that of the modern value... Eratosthenes' value [252,000 stades] was
popularized in the Middle Ages in Sacrobosco's Sphere and in d'Ailly's Ymago
mundi [Venice, 1531]. ... The method described by Sacrobosco and d'Ailly is
not the one used by Eratosthenes ... but is one devised by the Arabs in the
ninth century. ... [they] reckoned a degree along the meridian ... in miles,
56 2/3 miles, to be precise ... [an] estimate that was considerably less than
the true figure.
...
D'Ailly's report of 20,400 miles as the Arabian value for the earth's
circumference
and his statement shortly afterward in the same chapter about a small
intervening sea [between Spain and India] played a role in making Columbus
conceive of a voyage of discovery ... To buttress his case, however, Columbus
exaggerated Aristotle's support by attributing to him not only the opinion that
a single ocean joined Spain and India but also the belief that it was navigable
in a few days because of its smallness. Far from making a departure from
ancient and medieval opinion, Columbus relied heavily on traditional views
to support his daring proposal."
One can only add that he was lucky America was about at the right place
but on a much larger earth.
By the way Grant's book is otherwise full of unexpected medieval sources
for some of the basic concepts in modern mathematical physics.
But that's another story altogether ...
Regards from DownUnder.
(Sorry, Lactantius !)
(Dr R J-M Grognard)
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