_Father._ When you say, in asking about the smoke that sometimes appears to accompany the northern lights, that you think it more likely that the smoke comes from heat than from cold, I agree with you. But you must also know that wherever the earth is thawed under the ice, it always retains some heat down in the depths. In the same way the ocean under the ice retains some warmth in its depths. But if the earth were wholly without warmth or heat, it would be one mass of ice from the surface down to its lowest foundations. Likewise, if the ocean were without any heat, it would be solid ice from the surface to the bottom. Now large rifts may appear in the ice that covers the land as well as openings in the ice upon the sea. But wherever the earth thaws out and lies bare, whether in places where there is no ice or under the yawning rifts in the glacier, and wherever the sea lies bare in the openings that have formed in the ice, there steam is emitted from the lower depths; and it may be that this vapor collects and appears like smoke or dark fog; and that, whenever it looks as if the lights are about to be quenched by smoke or fog, it is this vapor that collects before them. In reply to your remark about the climate of Greenland, that you think it strange that it is called a good climate, I shall tell you something about the nature of the land. When storms do come, they are more severe than in most other places, both with respect to keen winds and vast masses of ice and snow. But usually these spells of rough weather last only a short while and come at long intervals only. In the meantime the weather is fair, though the cold is intense. For it is in the nature of the glacier to emit a cold and continuous breath which drives the storm clouds away from its face so that the sky above is usually clear.[231] But the neighboring lands often have to suffer because of this; for all the regions that lie near get severe weather from this ice, inasmuch as all the storms that the glacier drives away from itself come upon others with keen blasts. Now if this is clear to you, I believe there is no need of giving any further explanation of the subject than what you have now heard. Footnote 231: By glacier the author evidently means the great inland ice masses. On the effect of this inland ice on the climate of Greenland and neighboring regions, see Nansen, _In Northern Mists_, II, 247. ------------------------------------------------------------------------ XXI THE ZONES OF HEAT AND COLD