Up to the 15th Century the science of navigation was unknown. Before that time mariners occasionally ventured out of sight of land, for short passages during which, because they had no compasses, they attempted to guide themselves by reference to the sun or stars. When clouds obscured the sky, however, they usually lost their direction, and even when the sky was clear they knew no way of ascertaining anything more than rough approximations of the cardinal points. It seems just a bit strange that sailors were so backward in developing means of determining their positions at sea by reference to the sun and stars, while even the ancients were fairly accurate in their ability to locate their positions ashore by such methods. This undoubtedly was as much due to the lack of general knowledge among sailors as it was to the unsteadiness of the ships themselves which made it difficult for careful astronomical observations to be made. But whatever the reason, the fact remains that it was not until after the introduction of the compass that navigation began to make its first faltering advances. [Illustration: USING A CROSS STAFF _This crude instrument was used in an attempt to work out problems in latitude. After holding one end of the staff to the eye and sliding the cross staff along until the observer sighted over one end at the sun and under the other at the horizon, the instrument was placed on a circle marked in degrees, and the angle was determined._ ] That this beginning was made during the period in which Portugal expanded her commerce only goes again to show that the application of new minds to old problems results, almost invariably, in progress. Columbus, of course, did not begin the era of discovery. Prince Henry, the “navigator,” sent out an expedition from Portugal in 1432 which rediscovered the Azores—an astonishing thing for times so early, for the Azores lie 830 miles west of Portugal and are farther from a continental mainland than any other of the islands of the Atlantic. That the islands were known to the ancients, however, is proved by numerous Carthaginian coins found on the island of Corvo, but their location and practically everything else concerning them seems to have been lost until Henry the Navigator attached them to Portugal. But the rediscovery of the Azores proves only that the sailors put great faith in their compasses, and sailed, despite their fears, out to the west where all of them _knew_ (it was no matter of mere _belief_) that the sea ended somewhere suddenly, and that their cockleshell ships would, if they but sailed to the edge, fall down the smooth green cataract of an awful, endless waterfall, into limitless space, or, mayhap, to the vast foundations upon which the world was built. To them it was as if a canoe were being paddled downstream to the brink of a cataract to which Niagara itself would be but a raindrop falling from the eaves.