It is no modern idea, this search for the North Pole. King Alfred the Great is credited with having sent expeditions towards it, and long before his day men had sailed as far as they could to the North, far enough for them to return with marvellous tales of wonder and mystery. The earliest of whom there is any record is an ancient Greek mariner, Pytheas, who sailed North until he came to an island which he named the Land of Thule. This may have been the Shetlands; it may have been Iceland; but whatever it was, this ancient mariner was by no means pleased with it, in spite of the fact that the sun never set all the time he was there. This prolonged daylight caused him considerable uneasiness, and he hastened away from it farther to the North, and the farther he went the more curious he found the region to be. The sun, which at first refused to set, now refused to rise, and he found himself in perpetual darkness instead of perpetual day. More than that, he tells how he came to a great dark wall rising up out of the sea, beyond which he could discern nothing, while at the same time something seized and held his ship motionless on the water, so that the winds could not move it and the anchor would not sink. He was quite convinced in his own mind where he had come; the wall in front of him was the parapet which ran round the edge of the world to prevent people from falling over, and, like a wise man, he hastened home and told his friends that he had penetrated to the limits of the earth. What the Arctic regions were then, they are to-day; but we, with a greater knowledge, are able to understand what was incomprehensible to the ancient Greek navigator. At the North Pole itself it is known the sun rises and sets only once in twelve months. From March 21 to September 23 daylight continues; from September 23 to March 21 the sun is never visible. The heat at midsummer is probably never above freezing point; at midwinter the cold is so intense that one's eyes would freeze in their sockets if exposed to it. At the limit of the ice two phenomena are met with which explain the fanciful legend of Pytheas. As summer gives place to the cold of autumn, and as winter gives way to the mild temperature of spring, there comes down upon the water a dense mass of fog, to which the name "frost-smoke" is given. It would appear, as it rolled along the surface of the ocean, a veritable wall to one accustomed to the clear atmosphere of the Mediterranean, and a thin sheet of ice might give the meaning to the "something" which held the ship stationary. Modern explorers have known the sea to freeze an inch thick in a single night, and ice an inch thick would probably be enough to check the progress of such a vessel as Pytheas would command.