Re: rotation of the earth

Glenn Morton (
Sat, 13 Dec 1997 18:07:43 -0600

At 01:45 PM 12/13/97 -0500, George Murphy wrote:

> First, I think we need something from the historians of science
>about whether or not this aspect of Magellan's voyage _was_ seen as a
>challenge to the Ptolemaic model in the early 16th century. In my own
>rather eclectic reading relative to geocentric-heliocentric debates I've
>never seen anything about this. That itself proves nothing, but some
>reference would be helpful.

Ask and you shall receive. Here is what William Manchester says,

"The full significance of the great voyage was not grasped until
much later, but its most profound implication had begun to emerge
two months before the Victoria's return to Spanish waters, when
she was anchored off Santiago in the Cape Verde Islands. There
the shore party became entangled with the Portuguese over what at
first appeared to be a trivial argument. They disagreed over
which day of the week it was. Throughout their long absence, now
approaching three years, Pigafetta had scrupulously dated each
day's entry, beginning with "Tuesday, Sept. 20, 1519," when the
Armada de Molucca left Sanlucar de Barremeda, and continuing with
"Wednesday," "Thursday," and so on. Arriving here he noted that
the date was Wednesday, July 9, 1522. But crewmen who landed to
pick up supplies reported that in Santiago it was Thursday, July
"Don Antonio was puzzled. It was inconceivable that he
could have missed a day. He checked with Albo, who, on
instructions from Magellan, had also kept a record of the days
in his ship's log. Albo agreed: It was Wednesday, no question
about it. The Cape Verde Portuguese, they decided, had somehow
fallen into error. However, when they reached Sanlucar on what
they knew to be Saturday, September 6, the Spaniards greeting
them insisted that it was Sunday, September 7. Somehow, the
flota had dropped twenty-four hours out of the calendar.
"None of the great geographers, neither Aristotle, Ptolemy,
nor Pierre d'Ailly, had anticipated this riddle. Sixteenth-
century Eurpoean men of science, as startled as Pigafetta and
Albo, toiled over their desks until they came up with what, they
unanimously agreed, was the only possible solution. Copernicus,
they concluded was right. The earth was rolling eastward,
completing a full cycle every day. Magellan and his men had been
sailing westward, against that rotation; having traversed a full
circle, the circumnavigators had gained exactly twenty-four
hours. geocentrism - the age-old conviction that the earth was
the center of the universe - was therefore discredited. The
earth was not only round; it was moving. In fact, it was
revolving around its own axis.
Magellan was not there to savor the moment, but it was his
finest. In many ways it was the crowning triumph of the age, the
final, decisive blow to the dead past. Those with the most to
lose ignored their defeat, denied the discovery, and denounced
those who endorsed it as heretics. Couriers had galloped off to
report both the circumnavigation and the confusion over dates to
the pope. He now rejected the obvious explanation. Actually, he
would have been betraying his predecessors in Saint Peter's chair
if he had accepted it. The Church had always held that whenever
observed experience conflicted with Holy Scripture, observation
had to yield. And the authority of the Bible, historically
interpreted, denied the possibility of a heliocentric system.
"Accordingly, the Holy Office in Rome declared that the
notion of a moving earth circling the sun was 'philosophically
foolish and absurd and formally heretical, inasmuch as it
expressly contradicts the doctrines of Holy Scripture in many
places, both according to their literal meaning and according to
the common exposition and interpreation of the Holy Fathers and
learned theologians.' Twenty-eight successive pontiffs agreed.
It took the Church three hundred years to change its mind.
Copernicus's De revolutionibus was removed from the Catholic
Index in 1758, but the ban on Galileo's Dialogue continued until
1822, exactly three centuries after Albo's log and Don Antonio's
diary had become available to the Holy See.
"Nevertheless, patristic mulishness could not diminish the
glory of the armada's achievement. The power of the medieval
mind was forever broken. Medieval certitude had been weakened by
the Renaissance. Nationalism, humanism, rising literacy, the new
horizons of trade - all these had challenged blind, ritualistic
allegiance to the assumptions of a thousand years. But
Magellan's voyage exposed its central myth. Europe was no longer
the world, and the world was no longer the center of the
universe. Since the earth was revolving daily, heaven and hell
could not be located where they had been thought to be, and in
rational mindes there was a growing skepticism that either of
them existed." ~William Manchester, A World Lit Only By Fire: The
Medieval Mind and the Renaissance: Portrait of an Age, (Boston:
Little, Brown & Co., 1992), p. 290-291

I want to point out that Ted Davis, (if I recall correctly) and I discussed
this thing at length a while ago. His concern was that Manchester was
wrong. I was able to point him to contemporary literature about the
puzzelment of the crew. Here it is,

"Finally, constrained by our great extremity, we went to the
islands of Capo Verde. Wednesday, July nine, we reached on of
those islands called Sancto Jacobo, and immediately sent the boat
ashore for food, with the story for the Portuguese that we had
lost our foremast under the equinoctial line (although we had
lost it upon the cape of Bonna Speranza), and when we were
restepping it, our captain-general had gone to Spagnia with the
other two ships. With those good words and with our merchandise,
we got two boatloads of rice. We charged our men when they went
ashore in the boat to ask what day it was, and they told us that
it was Thursday with the Portuguese. We were greatly surprised
for it was Wednesday with us, and we could not see how we had
made a mistake; for as I had always kept well, I set down every
day without interruption. However, as was told us later, it was
no error, but as the voyage had been made continually toward the
west and we returned to the same place as does the sun, we had
made that gain of twenty-four hours, as is clearly seen."~Antonio
Pigafetta, First Voyage Around the World, in Charles E. Nowell,
Editor, Magellan's Voyage around the World, Northwestern
University Press, 1962, p. 256.

What I have still been unable to find are contemporary records of the
reaction of the church. I probably will be unable to get those since I am
not a historian.

> It seems to me you've made things more complicated than
>necessary by introducing 4 motions. The essence of the problem can be
>seen just with the rotation of the "fixed stars" and the motion of the
>sun around the earth in an approximately circular orbit. The epicycles
>& deferent are unneeded refinements for this purpose.

If one is going to see if the voyage of Magellan had any implication for
Ptolemy, one must use the system that Ptolemy and the Medievals used. Their
system was a whole bunch of complicated cycles and epicycles etc. Mercury
rotated around an epicycle, which in turn rotated around a center which also
rotated around its own circle. I would refer you to A.C. Crombie, "Medieval
and Early Modern Science, Vo. 2, (new York: Doubleday, 1959) p. 171

This is what most modern people miss about Ptolemy's system the complexity
of it. You simply can't simplify it in the fashion you do. It was somewhat
of a clockwork mechanism in which the ratios of the epicycles to the
deferents were set to fit the observational data. Messing with those ratios
messed up the ability of the model to predict things.

> Then IMHO Don is correct. Moving (generally) west, the ship
>sees a smaller angular speed of the sun & a solar day longer by a factor
>ws/(ws-wm). The ship returns to the island after sidereal time T (which
>both agree on, since they see the sun in the same position relative to
>the stars) & N days have passed for the islanders. Thus Tws = 2Np where
>p = pi = 3.14... & N is the # of solar days which have passed on the
>island. The number of solar days passed for the ship is N'
>(ws-wm)/Nws = [(ws-wm)/ws][Tws/2p] = N - Twm/2p. But Twm = 2p (since
>the ship has just gone around the earth once) so N' = N - 1. One gets
>the same result with a heliocentric model.

By simplifying the problem like you do you miss the subtlety. The Medieval
church's view of the system was that God imparted motion to the parts from
the outside. I found this this morning on the web,

"The heavens, on the other hand, were made up of an entirely different
substance, the aether [1] or quintessence (fifth element), an immutable
substance. Heavenly bodies were part of spherical shells of aether. These
spherical shells fit tightly around each other, without any spaces between
them, in the following order: Moon, Mercury, Venus, Sun, Mars, Jupiter,
Saturn, fixed stars. Each spherical shell (hereafter, simply, sphere) had
its particular rotation, that accounted for the motion of the heavenly body
contained in it. Outside the sphere of the fixed stars, there was the prime
mover (himself unmoved), who imparted motion from the outside inward. All
motions in the cosmos came ultimately from this prime mover. The natural
motions of heavenly bodies and their spheres was perfectly circular, that
is, circular and neither speeding up nor slowing down."

By traveling west, they went IN the direction of the stellar sphere but
against the direction of the motion of the spheres carrying the planets.
Once again, I try to point out that this means that one sphere is moving
slower and the other faster relatively, yet the epicycles remain constant.
The causality of this as, I think, was generally envisioned by them is shown
to be erroneous.

> People in the early 16th century may have been puzzled by
>"losing a day" but I can't see why a thoughtful geocentrist would have
>any basic problem with it. &, as I said, it would be helpful to have
>some refernce to any who did have such a problem.

You got it.


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