RELATING TO AFRICA. 
379 
in the south, is swelled to a great height by the 
summer rains, and forms then almost the main 
body of the Nile. He describes also the bend 
which it makes in its passage through Nubia. The 
source of this great stream being conceived to lie 
in these regions rendered inaccessible by extreme 
heat, was considered as beyond the reach of dis- 
covery. The idea, however, of its coming from 
the west still prevailed ; and Strabo mentions a re- 
port of its flowing from the remote boundary of 
Mauritania. This idea is followed at greater length 
by Mela and Pliny, whose speculations on the sub- 
ject will find a place in the following chapter. 
Equal in fame with the geographical school of 
Eratosthenes, was that of Ptolemy, who did not, 
however, flourish till the second century of the 
Christian era. This school displays a great acces- 
sion of actual knowledge with regard to all the re- 
mote quarters of the world ; but this, in many in- 
stances, was not accompanied with sounder views 
as to those parts which lay still beyond the sphere 
of observation. It was ascertained, that the bound- 
ing ocean of Asia did not exist at the point fixed 
by Eratosthenes ; hence it was rashly inferred, that 
Asia was not bounded by an ocean, but stretched 
on every side into an expanse of unknown conti- 
nent. The enterprise of , the Alexandrian mer- 
chants made them acquainted also with a large ex- 
