But the improvements which took place in the art of navigation, the more accurate measurement of time, and, above all, the discovery of the polarity of the magnet, greatly advanced the cause of geographical knowledge. Instead of creeping timidly along the coast, or limiting his expeditions to the narrow basins of inland waters, the voyager might now spread his sails boldly on the deep, secure of a guide to direct his bark unerringly across the illimitable waste. The consciousness of this power led thought to travel in a new direction; and the mariner began to look with earnestness for another path to the Indian Spice-islands than that by which the Eastern caravans had traversed the continent of Asia. The nations on whom the spirit of enterprise, at this crisis, naturally descended, were Spain and Portugal, placed, as they were, on the outposts of the European continent, commanding the great theatre of future discovery. Both countries felt the responsibility of their new position. The crown of Portugal was constant in its efforts, through the fifteenth century, to find a passage round the southern point of Africa into the Indian Ocean; though so timid was the navigation, that every fresh headland became a formidable barrier; and it was not till the latter part of the century that the adventurous Diaz passed quite round the Stormy Cape, as he termed it, but which John the Second, with happier augury, called the Cape of Good Hope. But, before Vasco de Gama had availed himself of this discovery to spread his sails in the Indian seas, Spain entered on her glorious career, and sent Columbus across the western waters. The object of the great navigator was still the discovery of a route to India, but by the west instead of the east. He had no expectation of meeting with a continent in his way, and, after repeated voyages, he remained in his original error, dying, as is well known, in the conviction that it was the eastern shore of Asia which he had reached. It was the same object which directed the nautical enterprises of those who followed in the Admiral's track; and the discovery of a strait into the Indian Ocean was the burden of every order from the government, and the design of many an expedition to different points of the new continent, which seemed to stretch its leviathan length along from one pole to the other. The discovery of an Indian passage is the true key to the maritime movements of the fifteenth and the first half of the sixteenth centuries. It was the great leading idea that gave the character to the enterprise of the age.