It was doubtless while at Porto Santo that Columbus had thought out his theories, aided by not a little evidence of the material order, such as floating logs and other objects, which had sailed, wind and current borne, from the unknown lands across the Atlantic. Columbus, of course, was not actually the first to feel convinced of the possibility of gaining India by sailing to the West; the theory had been held by Aristotle, Seneca, Strabo, and others. The sole mistake Columbus made in his calculations was concerning the size of the world. He had overestimated the extent of the Continent of Asia, and underestimated the extent of the Atlantic Ocean; he seems to have been convinced that a very few days' sailing to the west of Madeira would bring him to the shores of India. It was this error in calculation that undoubtedly was responsible for many long and agonizing hours spent on the actual voyage. [Illustration: JORGE CABRAL. _From a coloured drawing in a Spanish MS. in the Sloane Collection in the British Museum._] Columbus's proposals, it is true, were received with a certain interest by the Portuguese; but for the jealousy of some officials it is very probable that he would, in the first instance, have seen his cherished plans carried into effect. As it was, a vessel was secretly fitted out, and was sent in command of a rival navigator to test the theories of Columbus. After a while the ship returned, battered and worn, having discovered nothing beyond a series of exceptionally violent tempests. This attempt was in any case destined to prove equally adverse to the fortunes of Columbus. Had it succeeded, he would have undoubtedly been deprived of the credit which should have been his by right; since it failed, the venture was considered to have proved the fallacy of Columbus's theories. When, disgusted with experiences such as these, Columbus left Portugal and took up his residence near the Court of Spain in company with this great idea of his, which followed him everywhere, and was in a sense bigger than himself, he met with an equal lack of success in the first instance. Queen Isabella was sympathetic, but her cautious husband Ferdinand showed himself cold. Dreading the utter destruction of his plans, Columbus determined to wash his hands of the Iberian Peninsula and its over-cautious rulers and statesmen. He was actually on his way to England, whither one of his brothers had already preceded him, when a message from the Court of Spain caused him to hasten back. It is possible that the Court had been in a haggling mood, and had given the discoverer credit for a similar phase; at all events, it was not until his person was almost out of reach that the now complaisant authorities called him back.