Showing posts with label Eratosthenes. Show all posts
Showing posts with label Eratosthenes. Show all posts

Saturday, December 8, 2012

The Ring of Fire vs. The Flood

15th century portrayal of Ptolemy's map
Prior to the Age of Exploration, human beings in the western hemisphere did not attempt to travel long distances by sea and discover distant lands.* This was partially because ships that could handle a very long voyage were not able to be built or provisioned easily for such a journey.** Another reason is that the world was "known" to be shaped so that long voyages were fruitless.

Eratosthenes (c.276-c.195 BCE) had established in the Classical Era the spherical nature of the Earth through simple and clear experimentation; no one disputed that. (His math on Earth's diameter was probably a little off: the unit of measurement he used probably gave him an Earth 4000 miles larger around than it is.) What was up for debate was the question of what existed "over the horizon."

Aristotle (384-322 BCE), upon whose scholarly shoulders the Middle Ages tried to stand, loved symmetry. It made sense to him that there were five zones (from the Greek word meaning "girdle") around the Earth. The extreme top and bottom were icy cold and uninhabitable. Just inside of them were the temperate zones where humans and animals lived—note: he believed both temperate zones were inhabited. In the middle it was so hot—and clearly, the further south you go from Greece and the Mediterranean the hotter it got—that it was uninhabitable. Pliny (23-79) said that this central zone was so hot that it was actually a ring of fire and was unlivable and impassable, so we would never be able to visit the people living in the southern hemisphere.

Wait, said Christianity. That can't be. The Flood covered the whole world, and when the waters receded, the Ark of Noah came to rest on Mt. Ararat in Turkey, from which all the animals strolled away and repopulated the world. If the ring of fire at the equator is impassable, how can there be animals living beyond it? Worse, if there are people living in the southern temperate region, how are we going to reach them with the Word of God?

Proving that classical scholars did not always agree, Ptolemy presented different problems in geography. His Geography was translated and made available to Western Europe in 1406. His map (depicted above in a 15th century version printed in Ulm) showed that all you had to do was sail far enough south to reach the southern lands in the world, but he also extended the bottom of Africa eastward, enclosing the Indian Ocean. This meant you could not sail to the Indian Ocean and therefore to India, but would forever have to use the Silk Road (and incidentally pay tolls at every border crossing, something sailors get to avoid).

The Age of Exploration changed all this. In 1473, Aristotle was proved wrong with a Portuguese ship exploring the west coast of Africa passed south of the Equator. In 1488, another Portuguese ship sailed around the Cape of Good Hope and reached the Indian Ocean. India and the east were accessible by ship after all, and the Portuguese quickly established those shipping routes.

Ptolemy's Geography was erroneous in another way. He estimated the Earth's circumference at thousands of miles smaller than Eratosthenes. Since no one cared to duplicate Eratosthenes' experiments and determine the distances involved, Ptolemy might have been taken as truth by some. His estimates of the size of a spherical Earth would put Asia thousands of miles closer to Europe by sailing west. With Portugal dominating southern routes to the East, was it Ptolemy's miscalculation that prompted Spain's Columbus to try a bold plan to establish a different and (he thought) shorter route?

*Perhaps some day we'll get to some of the rare cases of accidental discovery of previously unanticipated lands.
**I have been aboard replicas of Columbus' ships; they are frighteningly small considering the journey they made.

Tuesday, November 13, 2012

The Flat Earth

In 1620, Sir Francis Bacon published Novum Organum ("The New Organon," by which he meant a new interpretation of nature). In it, he claimed that the ancient fathers of the Christian church did not tolerate a belief in a round Earth. It is probably this work that influenced the popular belief ever since that the Middle Ages, or religion, were steadfast in their belief in a flat Earth.

There is plenty of evidence to the contrary, however. True, there was "evidence" in the Middle Ages of a flat Earth. The Mappa Mundi (Map of the World), meant to portray the part of the world believed to be habitable, does make the world look flat and finite. Way back in he 3rd century BCE, however, Eratosthenes had coined the term "geography" and measured the circumference of the clearly round Earth by noting the difference in shadows of a stick at noon on two points many miles apart; the angles and length of the shadows told him that the sun was shining down on the surface at different angles, and the surface was therefore curved.

As revered an early christian as Boethius (480-524, mentioned here) in De consolatione philosophiƦ (The Consolation of Philosophy) reminds us of how small we are in the grand scheme of things with this:
It is well known and you have seen it demonstrated by astronomers, that beside the extent of the heavens, the circumference of the earth has the size of a point; that is to say, compared to the magnitude of the celestial sphere, it may be thought of as having no extent at all.
Medieval sources even quote Pliny the Elder's figure of 29,000 miles for the circumference, a remarkably accurate figure.*

So was there a conflict between science and Christianity? Depends who you talk to, I suppose. William of Conches (1085-1154), who may have been a tutor to the young man who became King Henry II of England, wrote extensively on reconciling the origin of the cosmos in Plato's Timaeus with Genesis. The Bible may have described the earth as flat, but William knew this should not be taken literally, explaining:
The authors of Truth are silent on matters of natural philosophy, not because these matters are against the faith, but because they have little to do with the upholding of such faith, which is what those authors were concerned with.
As learning spread—specially with the advent of mass printing—perceptions of the Earth's shape would have spread thanks to re-printed classical works. Columbus' idea to go west to arrive at an eastward point was not a risky gamble or a brilliant insight. Other "facts" in the Bible were also understood to be not literal: Pope Innocent III, for instance, knew that the Moon shone with reflected light, even though the Bible refers to the Sun and Moon as "two lights."

So what account for the learned Bacon's statement? It may have something to do with the conflict between Galileo and the Church. Although the famous trial would not take place until 1633, Galileo had received a formal Admonition in 1616, warning him:
to relinquish altogether the said opinion that the Sun is the center of the world and immovable and that the Earth moves; nor further to hold, teach, or defend it in any way whatsoever, verbally or in writing; otherwise proceedings would be taken against him by the Holy Office; which injunction the said Galileo acquiesced in and promised to obey.  [link]
It is very likely that Bacon and the rest of Europe's scientific community was aware of this growing conflict. In this historical context, Bacon's statement can be seen as a condemnation of the Church because of a recent action—even though for centuries the knowledge of a round Earth was common.

*In fact, the original figure might have been more accurate than we suspect: it was given in Greek stadia, a measurement which meant different things to different users. Our best interpretation is 29,000 miles, but if Pliny were using stadia of a slightly shorter length... .