DISCOVERIES OF THE PORTUGUESE. 51 
inferred, incorrectly indeed, yet not unplausibly, 
that an empire, which stretched so far inward from 
the eastern coast, must approximate to the west- 
ern ; and that, by penetrating deep on that side, 
they could scarcely fail at length to reach its fron- 
tier. For this reason, whenever an expedition 
w r as sent out to any part of the coast, the first in- 
struction given was, to inquire diligently if the in- 
habitants knew any thing of the monarch in ques- 
tion. Every opportunity was also to be embra- 
ced, of penetrating into the interior \ and, on hear- 
ing the name of any sovereign, an embassy was to 
be sent to ascertain, if he either was Prester John, 
or could throw any light as to where that person- 
age might be found. 
So long as the naval career of the Portuguese 
extended along the shores of the Sahara, and they 
saw nothing before them but a "wild expanse of 
lifeless sand and sky no temptation was felt to 
form a permanent settlement. After passing Cape 
Blanco, however, the coast began to improve ; and 
when they came to the fertile shores of the Sene- 
gal and Gambia, and saw ivory and gold brought 
down in considerable quantities from the interior, 
these regions began to excite the ambition of set- 
tlement and of conquest. The undertaking, how- 
ever, was beyond the force of any expedition that 
had yet sailed from Portugal. Nunez Tristao, in 
attempting to ascend a small river near the Rio 
