If you have the time, consider how you would go
about charting time, without much to go on but the sun, moon, and seasons. You
could do this at a surf beach, a sports field during half-time, or in the library
on a spare afternoon. You could be Eratosthenes of Cyrene, a hero just for one
day. Determining the years since you were born would be child’s play compared
with calculating the years since the last small ice age in your local area. When
you write ‘Chronographies’, in between duties as the Alexandria librarian, you
want to date everything since the Trojan War. This is a good genesis point, but
Homer was not specific (none of the Homers, in fact), and was the Trojan horse
just for one day? Or you can pre-empt encyclopedists by writing, in similar
vein, a chronology of the winners of the Olympic Games. It was worth all the
sweat they gave just to have their names dated in Eratosthenes’ ‘Olympic
Victors’.
Your knowledge of Homer tells you that Greece and
Anatolia are big chunks, but let’s not get into particulars. This annoyed
Eratosthenes (circa 276 BC-circa 194 BC), who was interested in inventing
Geography. None of the Homers were interested in geographic signposts. Ithaca,
for example, is probably an island in the Aegean, or Adriatic maybe, when it
isn’t 7 Eccles Street, Dublin 1. You know that, but then you don’t read
literature for the literal landmarks much, even while Jerusalem in the Bible is
generally meant to indicate the city called Jerusalem. You don’t have to devise
maps for climate zones, place grids over land drawings to find the quickest way
home, or draw lines in proverbial sand to say where one country stops and
another starts. Because Eratosthenes did it for you in his 3-volume
‘Geographika’, when he wasn’t working the circulation desk of the Alexandria
Library. Your cartographic skills rarely extend beyond sketching directions to
the party on a coaster, or swearing at the GPS as you drive into a lake. You
don’t have to reinvent the wheel, just make it stop. Nor do you need to reinvent
the globe of the world.
It is but a small step for a man of Geography
then to calculate the circumference of the Earth. You will find though it is a
giant leap from Alexandria to the Upper Nile. When you stare down a well there
at noon on the solstice, as you may do, your head blocks the reflection of the
sun on the water below. While at the same time in Alexandria, the sun casts a
slight shadow. By measuring the giant leap and the angle of the sun’s rays,
Eratosthenes calculated that the Earth’s circumference was fifty times that
distance. His margin of error was only 10%, because of his assumptions about
distance and about light rays being parallel. Another assumption that was not
exactly right was that the Earth is a perfect sphere. We believe it’s roundy,
but not flat. Flat Earthers have a psychological block that has nothing to do
with Geography. You can be a Flat Earther, if you choose, but don’t blame
someone else. A repeat of Eratosthenes’ calculation in 2012 using more accurate
data came within 0.16% accuracy of the accepted circumference of the Earth.
Then again, if you have the time, consider how
you would go about measuring the distance from the Earth to the sun. You could
do this by googling, asking someone with primary school education, or going to
the local library and finding out. None of these options were available to
Eratosthenes. Or the tilt of the Earth’s axis? He was quite accurate, nor had he
ever met anyone who had navigated the said globe. Later critics nicknamed him
Beta because he was a jack-of-all-trades, with the implication, master of none.
Strabo (circa 64 BC-24 CE), who knew a thing or two, called Eratosthenes a
mathematician among geographers and a geographer among mathematicians, which is
a case of stating the obvious when Eratosthenes is the father of Geography. You
and I look at the sun, not too long, in the context of the universe, and it is
too close for comfort. We are bound to it by gravitational pull in ways
Eratosthenes could not imagine, though he would have grasped the meaning once
explained, probably faster than Strabo. You and I teach ourselves not to fear
the heat of the sun, given we face a new small ice age in our local
area.
Beta version is perhaps the ultimate compliment
and badge of honour for someone with this list of trial achievements. Anyone can
get an A for repeating what Eratosthenes proposed. It takes an Eratosthenes to
say that this angle or that distance or that leap (miles or years) is as good as
he can get, for now, and stand by the results. Meanwhile, in the A for
Alexandria Library he was scrolling and texting every other bit of the day,
which may have left him, as it leaves you and me, wondering just how many days
he had, anyway. His answer, produced well advance of the naysayers and
newspapers, was 365 days in a year. With an extra day every fourth year. This
calculation is slightly better than beta. He figured this out because he was not
superstitious about eclipses, and because he wanted to know. Time moves slowly
in a library, or quickly, quicker than light, but that has nothing to do with
the library.
As you know, you see every kind of person visit a
library. There are the highly read and the illiterate, specialists and
polymaths, autodidacts and true believers. There are visitors from every nation
and those who’ve never even been around the block. The Greek word for blockheads
is idiota. Eratosthenes was a polymath, hence the description of him amongst his
friends as pentathlos, though he was not a library visitor. He was the
librarian, which means he observed the varieties of visitor. It could well be
for this reason that he objected to Aristotle (384-322 BC). Aristotle argued
that humanity was divided into Greeks and barbarians, the conclusion to be
reached being that Aristotle was a Greek. He believed that Greeks should keep
themselves racially pure. This either/or thinking, not remote from alpha/beta
thinking, is impossible to sustain in a library that is open most days of the
year. Eratosthenes believed there was good and bad in every nation and people,
and rebuked Aristotle for being so black and white.
This seventh and ultimate paragraph is dedicated
to the inventor of prime numbers. Opinion remains undivided on who this person
is. Eratosthenes, a mere beta male by contrast with his alpha critics, proved
that two is the same as one in regard to primes. He proposed a simple algorithm
for finding prime numbers, which is known in mathematics as the Sieve of
Eratosthenes. By iteratively marking the composites (the multiples of each
prime, starting with 2) the Sieve shakes out all the wash of composites, leaving
only the primes gleaming in the Sieve. This image though can serve also to
describe what remains of his work. You are warned before you begin your own work
in these fields of endeavour. For all the works of his that we have, that
precious minority of prime material, the majority of Eratosthenes’ composite
production was lost with the destruction of the Library of Alexandria.
Troublingly, this occurs during the lifetime of the aforementioned Strabo.
No comments:
Post a Comment