A memorable example of an able and acute train of thought, based on observations at sea, was that which led to his last voyage in search of a strait. He had watched the gulf stream constantly flowing in a westerly direction, and he thought that he had ascertained, as the result of careful observation, that the islands in the course of the current had their lengths east and west, owing to erosion on their north and south sides. From this fact he deduced the constancy of the current. His own pilot, Juan de la Cosa, serving under Ojeda and Bastidas, had established the continuity of land from the Gulf of Paria to Darien. The Admiral himself had explored the coast of Cuba, both on the north and south sides, for so great a distance that he concluded it must surely be a promontory connected with the continent. The conclusion was that, as it could not turn to north or south, this current, ever flowing in one direction, must pass through a strait. The argument was perfectly sound except in one point--the continental character of Cuba was an hypothesis, not an ascertained fact. Still, it was a brilliant chain of reasoning, and it led to a great result, though not to the expected result. Just as the search for the philosopher's stone led to valuable discoveries in chemistry, and as the search for El Dorado revealed the courses of the two largest rivers in South America, so the Admiral's heroic effort to discover a strait in the face of appalling difficulties, in advancing years and failing health, made known the coast of the continent from Honduras to Darien.