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 Rh his thoughts and attention to the possibility of reaching India otherwise than through the known routes, and for that purpose established himself on the rocky promontory of Sagres, almost the most western spot on the continent of Europe.

Here he established an observatory, and a seminary for the training of theoretical and practical navigators. He summoned thither astronomers and cartographers and skilled seamen, while he caused stouter and larger vessels to be built for the express purpose of exploration. He perfected the astrolabe (the clumsy predecessor of the modern sextant) by which the latitude could be with some accuracy determined; and he equipped all his ships with the compass, by which the steering was entirely determined. He brought from Majorca (which, as we have seen, was the centre of practical map-making in the fourteenth century) one Mestre Jacme, "a man very skilful in the art of navigation, and in the making of maps and instruments." With his aid, and doubtless that of others, he set himself to study the problem of the possibility of a sea voyage to India round the coast of Africa.

We have seen that Ptolemy, with true scientific caution, had left undefined the extent of Africa to the south; but Eratosthenes and many of the Roman geographers, even after Ptolemy, were not content with this agnosticism, but boldly assumed that the coast of Africa made a semicircular sweep from the right horn of Africa, just south of the Red Sea, with which they were acquainted, round to the north-western shore, near what we now term Morocco. If this were the fact, the voyage by the ocean along this sweep of shore would be even shorter than the