not allow sufficient extent to the great desert of Sahara, while the
southern parts are too much expanded. He places the sources of the Nile,
and the Mountains of the Moon in south latitude thirteen, instead of north
latitude six or seven; but the error of latitude is not so remarkable and
unaccountable as the very erroneous latitude which he assigns to Cape
Aromata, on a coast which was visited every year by merchants he must have
seen at Alexandria. The most difficult point to explain in Ptolemy's
central Africa is the river Gir, which he describes as equal in length to
the Niger, and running in the same direction, till it loses itself in the
same lake. What this river is, geographers have not agreed. It is mentioned
by Claudian, as resembling the Nile in the abundance of its waters.
Agethimedorus, a geographer of the third century, regards it and the Niger
as the same river.

What then was the amount of the knowledge of the ancients, as it existed
among the Romans, in the height of their power, respecting the form,
extent, and surface of the globe? If we view a map drawn up according to
their ideas, we are immediately struck with the form they assigned the
world, and perceive with what propriety they called the extent of the world
from east to west longitude or _length_, and the extent from north to
south latitude, or _breadth_. In some maps, especially that drawn up
from the celebrated Peutingerian Tables, which contain an itinerary of the
whole Roman empire, thirty-five degrees of longitude occupy twenty-eight
feet eight inches, whereas thirteen degrees of latitude are compressed
within the space of one foot. It is easy to conceive how it happened that
too much space is assigned between places situated east and west of each
other, as the latitude of a place is much more easily determined than its
longitude. At the same time, as the routes of the Roman armies generally
were from east to west, the countries lying in that direction were better
known than those lying to the north and south, though the longitudes, and
general space assigned the world, in the former deviation, were erroneous.
It was the opinion of most of the ancient geographers, that there was a
southern continent or hemisphere, to correspond to and balance the
northern; and this they formed by cutting off the great triangle to the
south. The ancients also, while they curtailed those parts of the world
with which they were unacquainted, extended the kno