Eratosthenes
Syene*
sitting on the Nile and
more significantly on the Tropic of Cancer:
an obelisk at noon on the longest day in June
cast no shadow
Alexandria
on the coast five hundred of our miles north:
an obelisk at noon on the longest day in June
cast a shadow out of plumb
seven-and-a-half degrees
Eratosthenes
with facts like these
linked to his hypotheses
(a round earth travels round a very distant sun)
performed a circumcomputation of our globe
Earth’s circumference
is five hundred miles
times what three hundred sixty is to seven-and-a-half
about twenty-four thousand miles?
Columbus would have stayed home had he guessed that
* the ancient name for Aswan, see Ezek. 29:10