These voyages into the southern hemisphere dealt a damaging blow to the theory of an impassable fiery zone; but as to the circumnavigability of the African continent, the long stretch of coast beyond the equator seemed more in harmony with Ptolemy's views than with those of Mela. The eastward trend of the Guinea coast was at first in favour of the latter geographer, but when Santarem and Escobar found it turning southward to the equator the facts began to refute him. According to Mela they should have found it possible at once to sail eastward to the gulf of Aden. What if it should turn out after all that there was no connection between the Atlantic and Indian oceans? Every added league of voyaging toward the tropic of Capricorn must have been fraught with added discouragement, for it went to prove that, even if Ptolemy's theory was wrong, at any rate the ocean route to Asia was indefinitely longer than had been supposed. But was it possible to imagine any other route that should be more direct? To a trained mariner of original and imaginative mind, sojourning in Portugal and keenly watching the progress of African discovery, the years just following the voyage of Santarem and Escobar would be a period eminently fit for suggesting such a question. Let us not forget this date of 1471 while we follow Prince Henry's work to its first grand climax. [Sidenote: News of Prester John.] About the time that Diego Cam was visiting the tribes on the Congo, the negro king of Benin, a country by the mouth of the Niger, sent an embassy to John II. of Portugal (Prince Henry's nephew), with a request that missionary priests might be sent to Benin. It has been thought that the woolly-haired chieftain was really courting an alliance with the Portuguese, or perhaps he thought their "medicine men" might have the knack of confounding his foes. The negro envoy told King John that a thousand miles or so east of Benin there was an august sovereign who ruled over many subject peoples, and at whose court there was an order of chivalry whose badge or emblem was a brazen cross. Such, at least, was the king's interpretation of the negro's words, and forthwith he jumped to the conclusion that this African potentate must be Prester John, whose name was redolent of all the marvels of the mysterious East. To find Prester John would be a long step toward golden Cathay and the isles of spice. So the king of Portugal rose to the occasion, and attacked the problem on both flanks at once. He sent Pedro de Covilham by way of Egypt to Aden, and he sent Bartholomew Dias, with three fifty-ton caravels, to make one more attempt to find an end to the Atlantic coast of Africa. [Sidenote: Covilham's journey.]