These tubes are the muzzles of great air-guns, through which she sends darts loaded with dynamite to fall upon a hostile ship or fort. It would not be safe, to say the least, to fire such bombs with gunpowder; and therefore pumps and engines in her interior compress air until it has acquired an expansive force sufficient for the purpose. When one of the darts has been laid in the breech of the tube, down beneath the deck, and suitably closed in, a valve is opened, the compressed air acts like burning powder, and away goes the dart, in a graceful curve to its target. In this case, of course, it is the vessel rather than the immovable gun that is aimed, and good marksmanship depends upon accurate calculation of distance; but remarkable shooting has been done. This system has never yet been tried in actual warfare, and may prove valuable chiefly in clearing harbors of mines. CHAPTER VII THE MERCHANTS OF THE SEA The history of shipping in an earlier chapter will also answer as a history of early international commerce. It began with the Egyptians and Phenicians, and was confined to their parts of the Mediterranean until after the middle ages, when it moved steadily to the western borders of Europe. How great, rich, and influential were Tyre and its people we have already seen. A thousand years before the Christian era they controlled the commerce of the ancient world by reason of their wisdom as traders and their skill and energy as navigators and seamen. Turn to the twenty-seventh chapter of Ezekiel, and see how the Phenician metropolis was regarded, even in the time of that prophet, six hundred years before Christ. These Syrians had gradually extended their commerce until it took in the whole known world; and by their caravans to and from the interior of Arabia, Persia, India, and the Soudan, by their trains (perhaps of pack-horses) across Europe, by their marine expeditions to the Nile,—which they forced open to trade, for ancient Egypt was much like China in its exclusiveness,—and by their ships to all the Mediterranean ports, and up and down the Atlantic coast, they gathered and exchanged in the bazaars of Tyre and Sidon the products, manufactures, and luxuries of every country that had anything to sell. To the Phenicians, indeed, was ascribed, by the Latin and Greek writers of a few centuries later, the invention of navigation; and even when Phenicia had become of little account as a nation, its conquerors noted with admiration the skill of the men of that coast in seamanship. “They steered by the pole-star, which the Greeks therefore called the Phenician star; and all their vessels, from the common round _gaulos_ to the great Tarshish ships,—the East-Indiamen, so to speak, of the ancient world,—had a speed which the Greeks never rivaled.”