The Bedouin Arab is the chief trial of the caravans. He is always a foe to them; and although he ostensibly herds camels and horses, his real occupation is robbery and pillage. For days nomadic Arabs will follow a caravan, keeping always out of sight. Most likely a band of a dozen or more mounted on swift horses will survey the caravan from a distance at which they are not likely to be discovered. Then they make their way ahead of it to some point where a dune or a gully will conceal them. Then, just as the end of the caravan drags by, there is a sudden sortie and a rattling musket fire. And before the guards can gather to the defence half a dozen camels are cut out of the train, a driver or two is shot down or pierced with assegais, and both the robbers and their loot are beyond the reach of the guards. But perhaps the greatest value of the desert is its effect upon the climate of Europe. Hot winds blow from the Sahara in all directions; the northerly winds, crossing the Mediterranean, are not only tempered thereby, but the desert blasts tempered and filled with moisture finally reach the southern slopes of Europe, where they convert the nutrition of the soil into bountiful crops of corn, wine, and oil. The conquest of the great African desert is already in sight, and the railway will be its master. The Cape to Cairo line is no longer a vision of the future; the ends of its two parts are rapidly shortening the interval that separates them and they are almost in sight of each other. When the lines that are projected from the Mediterranean coast shall have traversed the stronghold of the Tuaregs to penetrate the wealth of the Sudan and the Kongo, the Sahara will have become merely an incident. CHAPTER XI POLAR REGIONS--THE CONQUEST OF THE ARCTIC Excepting the arctic and the antarctic regions, with their fortifications of eternal ice and snow, intrepid explorers have made known nearly every part of the world. There Giant Frost guards his frozen secrets and defies man to wrest them from him. Many a hero has perished in endeavoring to solve the Sphinx-like riddle of northern lands and seas. Many a gallant ship has found its grave in northern ice-clad waters. Yet there has never been a lack of adventurous spirits to continue the work. But one after another the strongholds of nature have gradually yielded to persistent attacks. Especially is this true of the arctic regions, of which not more than two million square miles of sea and land remain to be explored. Buffeted by adverse winds and floating ice-fields, venturous explorers have drawn nearer and nearer to the north pole. Again and again, the attack has been renewed, until, after half a lifetime, Robert E. Peary, an officer of the United States navy, made a brilliant dash and planted the national ensign at the pole.