While, therefore, it appears that the one place of all others at which it would be exceedingly easy to determine one's position from the observation of the sun is the region of the pole, it must be borne in mind that the low elevation of the sun, and the extreme cold may make accurate instrumental observations difficult; and it is conceivable that the explorer who had the misfortune to encounter cloudy weather, and who therefore gained only a brief view of the sun, might be left in doubt as to whether he had really reached the goal of his ambition. Fortunately, however, the explorers who thus far claim to have reached the pole record uninterruptedly fair weather, enabling observations to be taken hour after hour. Under these circumstances, there could be no possibility of mistake as to the general location, although perhaps no observation, under the existing conditions, could make sure of locating the precise position of the pole within a few miles. A curious anomaly incident to the unique geographical location of the pole is that to the observer stationed there all directions are directly south. Yet of course all directions are not one, and the query may arise as to how an explorer who has reached the pole may know in what direction to start on his return voyage. The answer is supplied by the compass, which--perforce pointing straight south--indicates the position of the magnetic pole and so makes clear in which direction lies the coast of Labrador. Moreover if the explorer is provided with reliable chronometers, which of course record the time at a given meridian--say that of Greenwich--these will enable him to determine by the simplest calculation what particular region lies directly beneath the sun at any given time. If, for example, his chronometer shows five o'clock Greenwich time, he knows that the sun's position, as observed at the moment, marks the meridian five hours (_i.e._, 75° of longitude) west of Greenwich. While the arctic region appears thus to have given up its last secret, this is not as yet true of the antarctic. The expedition of Lieutenant (now Sir Ernest) Shackleton, in 1908, approached within about one hundred and eleven miles of the South Pole. The intervening space--less than two degrees in extent--represents, therefore, the only stretch of latitude on the earth's surface that has not been trodden by man's foot or crossed by his ships. More than one expedition is being planned to explore this last remaining stronghold, and in all probability not many years--perhaps not many months--will elapse before the little stretch of ice that separated Lieutenant Shackleton from the South Pole will be crossed, and man's conquest of the zones will be complete. II THE HIGHWAY OF THE WATERS