388 
GEOGRAPHICAL SYSTEMS. 
was rashly inferred, that Asia was not bounded 
by an ocean, but stretched on every side into an 
expanse of unknown continent. The enterprise 
of the Alexandrian merchants made them ac- 
quainted also with a large extent of the eastern 
coast of Africa, the farthest explored portion of 
which took an easterly direction. This direction 
was hypothetically extended, till it was made to 
join the eastern extremity of Asia. Thus the 
Indian, or Erythrean sea, was enclosed as in a 
vast basin ; and in Africa, as in Asia, an expanse 
of Terra Incognita became on every side the limit 
of the known world. This school, however, shook 
off entirely the previous belief of an uninhabitable 
zone. Ptolemy gives numerous positions under 
and beyond the equator, and even approaching to 
the southern tropic. Admitting that many, or all 
of them, are extended too far to the south, this 
does not the less indicate his own conviction, that 
the region immediately under the line could be 
passed through and inhabited. 
Ptolemy appears to have been the first who 
formed a correct idea of the whole course of the 
Nile. He throws up entirely its western deriva- 
tion, and assigns to its fountains their proper place 
in the vast range of the Mountains of the Moon. 
He represents also, like Eratosthenes, the rivers 
Astapus and Astaboras, (the modern Bahr-elr 
Azrek and Tacazze), as falling into it from th^ 
