THE ORIGIN OF THE IDEA 7 
Perioken and Antipodes. Strabo and Pomponius Mela 
at a much later date gave expression to this view. 
But the rival philosophers following the lead of Hip- 
parchus ridiculed a theory founded on no better basis 
than the principle of symmetry, and relying on a state- 
ment of the Chaldean astronomer, Seleukos, that the 
Indian ocean was tideless (a statement entirely contrary 
to fact) argued that the land was really continuous and 
the seas occupied enclosed basins within it, of which the 
Caspian was one of the smallest. How this idea of 
Seleukos outweighed the historical circumstance men- 
tioned by Herodotus that a Phoenician expedition had 
circumnavigated Africa by the south we cannot tell. 
The fact remains that the Alexandrian School took up 
the theory of continuous land and that Ptolemy, the 
greatest teacher of that School, and the ultimate reposi- 
tory of the Geography of the Greeks, embodied it in his 
celebrated map. Thus it happened that his error changed 
the direction and retarded the progress of geographical 
discovery for twelve hundred years after his death. 
Anyone who reads the laborious arguments by which 
the ancient philosophers buttressed their fancies as to 
other habitable worlds and their people must be struck 
by the v^st amount of admirable controversy which might 
have been rendered unnecessary by a few expeditions 
carried out with the determination which characterised 
the Greek wars. One reason of this apparent lack of 
enterprise was undoubtedly the general acceptance of the 
existence of zones of climates, which was an important 
truth but poisoned by the exaggerated intensity of the 
climates attributed to the extreme zones. 
Without going fully into the question of the zones it is 
enough to say that even when the flat-Earth theory pre- 
