But, within the sphere indicated, Sidonian rovers traversed all parts of the Great Sea, penetrated into every gulf, became familiar sights to the inhabitants of every shore. From timid sailing along the coast by day, chiefly in the summer season, when winds whispered gently, and atmospheric signs indicated that fair weather had set in, they progressed by degrees to long voyages, continued both by night and day,[1426] from promontory to promontory, or from island to island, sometimes even across a long stretch of open sea, altogether out of sight of land, and carried on at every season of the year except some few of special danger. To Sidon is especially ascribed the introduction of the practice of sailing by night,[1427] which shortened the duration of voyages by almost one-half, and doubled the number of trips that a vessel could accomplish in the course of a year. For night sailing the arts of astronomy and computation had to be studied;[1428] the aspect of the heavens at different seasons had to be known; and among the shifting constellations some fixed point had to be found by which it would be safe to steer. The last star in the tail of the Little Bear—the polar star of our own navigation books—was fixed upon by the Phoenicians, probably by the Sidonians, for this purpose,[1429] and was practically employed as the best index of the true north from a remote period. The rate of a ship’s speed was, somehow or other, estimated; and though it was long before charts were made, or the set of currents taken into account, yet voyages were for the most part accomplished with very tolerable accuracy and safety. An ample commerce grew up under Sidonian auspices. After the vernal equinox was over a fleet of white-winged ships sped forth from the many harbours of the Syrian coast, well laden with a variety of wares—Phoenician, Assyrian, Egyptian[1430]—and made for the coasts and islands of the Levant, the AEgean, the Propontis, the Adriatic, the mid-Mediterranean, where they exchanged the cargoes which they had brought with them for the best products of the lands whereto they had come. Generally, a few weeks, or at most a month or two, would complete the transfer the of commodities, and the ships which left Sidon in April or May would return about June or July, unload, and make themselves ready for a second voyage. But sometimes, it appears, the return cargo was not so readily procured, and vessels had to remain in the foreign port, or roadstead, for the space of a whole year.[1431]