Re: Flat Earth

["John S. Denker" <jsd@MONMOUTH.COM>]

Hugh Haskell wrote:
> Then just what did Eratosthenes measure? Or is that an urban myth? I
> didn't say that it *could* have been known 2350 years ago, I said it
> *was* known 2350 years ago, at least by one man, who was pretty
> well-known in his day, so his result probably would have been known,
> at least to the educated classes at the time.
>
> It is certainly possible that that information could have been lost
> during the first millennium C.E., but if that was the case, the
> knowledge had been recovered, again by the educated classes, by the
> fifteenth century.

Eratosthenes' information was more-or-less lost in antiquity.
A much shorter value was asserted by Poseidonius, confirmed
by Strabo, and adopted by Ptolemy -- and that was the last
word on the subject for 1300 years or so.

> I have read about seafarers in Phoenecian days noting the phenomenon
> of ships disappearing over the horizon by going hull down and
> inferring from that that the earth was not flat. I doubt that this
> lore would have been lost to mariners for over 1000 years,

What reason is there for doubting it?
-- Faith in the goodness of human nature??
-- Faith in the monotonicity of scientific progress??
The overwhelming consensus of scholarly opinion based
on overwhelming evidence is that it WAS lost to western
civilization for nearly 1000 years.

> I suspect that lots of ships seen hull down
> from the crow's nest gave even the lowly able seaman a pretty good
> idea of what the shape of the earth was.

"Should have given" is not the same as "gave".

> I just did a Google search on Ancient Maps and the first item turned
> up was a time line of ancient cartography that showed an awful lot of
> spherical mapping going on from about 400 B.C.E. And then I found
> this:
> <http://www.henry-davis.com/MAPS/Ancient%20Web%20Pages/119D1.html>
> which is a Ptolemaic world projection dating from the 13th century.

Claudius Ptolemy died circa 168 AD.

His approach to mapmaking was not widely known or used
in medieval Europe, not until re-introduced in the 1400s.

> And this one:
> <http://www.brown.edu/Departments/Italian_Studies/dweb/images/maps/decworld/228A.jpg>
> which is dated 1321, and looks pretty global to me.

It looks like a flat disk to me.

If you think it's a map of the whole world, with
periodic boundary conditions, then the Azores are
right next to China, which is pretty absurd.

If you think it's a map of one hemisphere, one
wonders what the author thought was in the other
hemisphere. And why does
the equator run through the mediterranean?  Why is
all of Africa, all of Arabia, and all or most of China
south of the equator?  (My hypothesis is that the
author wanted the equator to run through Jerusalem.)

> I don't know how popular these particular maps were,

That seems like a rather critical point that
shouldn't be passed over lightly.

> but they
> certainly are counterexamples to your claim that 14th century maps
> pushed flatness.

They are at most exceptions, not counterexamples,
and I'm not convinced that they are even significant
exceptions to the point that I was making, namely:

The assertion was earlier made
> > that the idea that the earth was flat was most likely
> > limited to those who lived a goodly distance from the sea, were
> > illiterate, and didn't spend much time looking up.

and I continue to disagree with that assertion.

=======================

The dark ages really were dark!

-- Do not assume that the progress of science (or
of high culture in general) is monotone.

-- Do not assume that scientific observation will
prevail over religious orthodoxy.

-- Do not assume that a cosmopolitan culture will
prevail over parochialism and factionalism.

-- Do not assume that a literate, urbanized culture
will prevail when attacked by hordes who live in
caves and tents and think everybody should live in
caves and tents.

There are counterexamples throughout history.

=============

I think our present scientific and cultural achievements
can be preserved and extended, but we shouldn't
underestimate the effort required.