"It had always been supposed that the immediate areas of the Poles must be the coldest regions of the globe, because the farthest points from the equator. Hence the argument that the higher the latitude the greater must be the difficulties and dangers of navigation. Quite an opposite opinion, however, had begun to prevail among meteorologists on the publication, in 1817, of the Isothermal system of Alexander Von Humboldt, which showed that distance from the equator is no rule for cold, as the equator is not a parallel of maximum heat. The line of maximum heat crosses the Greenwich meridian, in Africa, fifteen degrees north of the equator, and rises, to the eastward, five degrees higher, running along the southern edge of the Desert of Sahara. In 1821, Sir David Brewster pointed out, in a paper on the mean temperature of the globe, the probability of the thermometer being found to range ten degrees higher at the Pole than in some other parts of the Arctic Circle. No new facts have since been discovered to invalidate this conclusion--many, on the contrary, have come to light tending to confirm it."] [Sidenote: POLAR CURRENTS] Bearing these facts in mind, the reader will perceive that it is the surface-water only which ever reaches so low a temperature that it is changed to ice; and he will also perceive that when the wind moves the surface-water, the particles which have become chilled by contact with the air mingle in the rolling waves with the warm waters beneath, and hence that ice can only form in sheltered places or where the water of some bay is so shoal and the current so slack that it becomes chilled to the very bottom, or where the air over the sea is uniformly calm. He will remember, however, that the winds blow as fiercely over the Polar Sea as in any other quarter of the world; and he will, therefore, have no difficulty in comprehending that the Polar ice covers but a small part of the Polar water; and that it exists only where it is nursed and protected by the land. It clings to the coasts of Siberia, and springing thence across Behring Strait to America, it hugs the American shore, fills the narrow channels which drain the Polar waters into Baffin Bay through the Parry Archipelago, crosses thence to Greenland, from Greenland to Spitzbergen, and from Spitzbergen to Nova Zembla,--thus investing the Pole in an uninterrupted land-clinging belt of ice, more or less broken as well in winter as in summer, and the fragments ever moving to and fro, though never widely separating, forming a barrier against which all the arts and energies of man have not hitherto prevailed. [Sidenote: THE ICE-BELT.]