HISTORY OF DISCOVERY. 7 



It also assigned southern limits to the Atlantic Ocean 

 on the west coast of Africa. Neither was Ptolemy the 

 first to give expression to this view ; his predecessors in 

 the field of scientific geography — Seleucus, Eratosthenes, 

 Hipparchus and Strabo — had at least held no different 

 conception of the outlines of the Indian Ocean, and 

 according to the opinion of many the conjecture can 

 be traced back even to Aristotle. But the earlier 

 geographers are justified by the fact that the outlines 

 of the east coast of Africa were known to them only as 

 far as the region of the lower ranges of the Spice 

 mountains, at present known as Cape Gardafui, and 

 they might therefore assume that the coast stretched 

 still farther away to the east, an impression doubtless 

 strengthened by the situation of the outlying island of 

 Socotra. These conjectures, however, must have been 

 given up in the case of Ptolemy ; he knew from the 

 singularly accurate sailing hand-books of the Greek and 

 Arabian mariners who visited the east coast of Africa 

 from Adana — the modern Aden — that the coast line ran 

 not only south, but south-west, in their voyages to the 

 extreme southern stations at which they stopped. These 

 voyages generally ceased at the promontory of Rhaptum, 

 probably the modern Kilwa on the coast of German East 

 Africa. Concerning this promontory, some ancient sail- 

 ing rules which have been preserved since the first 

 century of the Christian era— the Periplus Maris Ery- 

 thraei — state that "the universal and unexplored ocean 

 stretches away beyond Rhaptum to the west, where, to 

 the south of Ethiopia, Lybia and Africa, it unites with 

 the western [i.e., the Atlantic) ocean ". The general 

 direction of the African coast was therefore very well 

 known, whether the knowledge was derived from the 

 accounts of Arabian mariners, or from the traditions of the 

 circumnavigation of Africa by Phoenician vessels in the 

 sixth and seventh centuries before the Christian era. In 



