Flattening that Earth

July 7, 2009

by Gene Callahan

This is a pet peeve of mine, and it just won’t go away. Today, in a nice mathematics book called Journey through Genius, I found this:

“Skepticism aside, Eratosthenes’s reasoning is noteworthy not only for its cleverness but also for the striking fact that he entertained no doubts whatever that our planet was a sphere. In striking contrast, European sailors some 15 centuries later would fear plunging off the edge of a flat earth. We sometimes forget that the ancient Greeks were fully aware of the earth’s spherical shape, and if later sailors kept a keen eye peeled for the horizon’s edge, it was a symptom not of knowledge yet to be acquired but of knowledge lost.”

Well, folks, this passage is a symptom of knowledge ignored. It’s been a standard conclusion of all mainstream historians of the Middle Ages, for at least the past sixty years, that “[essentially] no educated person in the history of Western Civilization from the third century B.C. onward believed that the earth was flat.” (Quoted from here.) What’s really amazing is that this author, if he had stopped to think about this for a moment, would have realized that the Copernican model of the solar system had to defeat… the Ptolemaic model, in which the earth was at the center of a series of concentric spheres.

So how did this idea of the flat earth model get started? It turns out that it was almost entirely an invention of 18th and 19th century rationalists, eager to portray an inherent conflict between religion and science. For instance:

“In Book III, Chapter II of this biography, [Washington] Irving gave a largely fictional account of the meetings of a commission established by the Spanish sovereigns to examine Columbus’s proposals. One of his more fanciful embellishments was a highly unlikely tale that the more ignorant and bigoted members on the commission had raised scriptural objections to Columbus’s assertions that the Earth was spherical.”

The actual issue at stake was the diameter of the earth. The Jesuit advisers to the king and queen had roughly the correct idea of how far Columbus had to sail to reach Japan, and knew he’d never make it. Columbus had under-estimated the distance he had to travel by about a factor of four, and merely got lucky that America happened to be where he thought Japan was!

4 Responses to “Flattening that Earth”

  1. Naska Says:

    Stopping to think a moment does not yield a clear victory for the Copernican system. Ptolemy thought about it for more than a moment and plunked down for geocentrism.
    The heliocentric victory was brought on by Kepler, who produced a much more reliable epehemeris than the two competing regular circular motion models.
    The nested spheres model is Eudoxean/Aristotleian and did not find a strong adherent in Ptolemy, whose construction is far more flexible.
    Ptolemy’s number for the earth’s size is about 70% of Erastosthens’ estimate, and is likely the one Columbus relied on.

  2. Vichy Says:

    “Well, folks, this passage is a symptom of knowledge ignored. It’s been a standard conclusion of all mainstream historians of the Middle Ages, for at least the past sixty years, that “[essentially] no educated person in the history of Western Civilization from the third century B.C. onward believed that the earth was flat.””

    Don’t you hate things ‘everybody knows’?

  3. Lee Kelly Says:

    Well, if there is always at least some idiot who has got it wrong, then anything that everybody knows must be known by some idiot who is wrong. Therefore, whatever everybody knows is false.


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