sailing are not to be credited, for they had not and could not have used the needle and the chart. But do you go notwithstanding, and make your voyage without being influenced by their opinions, and, by the grace of God, you will not fail to secure, by your enterprise, both honor and compensation.”[96] Gil Eannes followed the advice of his sanguine patron, and succeeded the same year in doubling Cape Bojador and in exploring a part of the coast beyond it. South of Cape Bojador it was believed that a zone of scorching heat would be entered by vessels sailing toward the equator. Pliny adverts to it in these words: “The middle of the earth, over which is the path of the sun, is parched and set on fire by the luminary, and is consumed by being so near the heat. There are only two of the zones which are temperate—those which lie between the torrid and the frigid zones—and these are separated from each other, in consequence of the scorching heat of the heavenly bodies.”[97] Conceiving this statement to be as fallacious as many other declarations of the early geographers had been, Prince Henry, in 1454, sent Luigi da Cadamosto, a Venetian navigator, to explore the coast beyond Cape Bojador so long invested with so many imaginary terrors. In 1462 Pedro de Cintra sailed three hundred miles beyond Sierre Leone. As it was necessary for seamen to know the latitude and longitude of the places to which they desired to sail, another nautical instrument besides the mariner’s compass was needed by them.[98] The adaptation of an instrument called the astrolabe, by which the latitudes of places could be determined, apparently originated with King John II. of Portugal.[99] It is said that “when Prince Henry began the discovery of Guinea that all mariners were accustomed to sail along the coasts, and that they always steered their courses by observing the physical features of the land, which are still used as guides.”