RELATING TO AFRICA. 
373 
made wholly without some guiding principle. In 
general, every geographical feature was extend- 
ed in the direction which it followed, when it 
first merged into the unknown space. In some 
cases, indeed, a certain flexure is necessary, in or- 
der to complete the figure of a continent, an 
ocean, or other grand geographical feature. Such 
was the line by which, in the system of Ptolemy, 
the African continent was carried round till it 
met the farthest extremity of Asia. The estimate 
of distance was also a point on which the early geo- 
graphers were naturally liable to much error. The 
most usual was that of exaggeration. Astronomi- 
cal observations were yet rare, and very imperfect. 
The materials were derived almost entirely from 
travellers employed on mercantile or military ob- 
jects. The difficulties and dangers of an unknown 
tract, the windings of the road, and the disposition 
to magnify their own achievements, combined in 
inducing such persons to form a high idea of the 
space which they had traversed. Sometimes, how- 
ever, rumour conveys the knowledge of a grand re- 
mote feature, while the intermediate space is but 
imperfectly known. That space then appears less, 
and the distant object nearer, than it really is. 
Thus the pillars of Hercules, made known to the 
early Greeks by the exploits of that celebrated ad- 
venturer, were placed by them very little beyond 
Sicily. Tims, in the system of Eratosthenes, a 
