Perhaps the reader may have been unfortunate enough to travel by rail in the depth of winter, and to be associated with fellow-passengers who will insist on closing every window, even though the carriage be crowded. Suppose that on such a day, the weather being perfectly fine, the train stops at a station, and the guard outside opens the door to see if another passenger can be accommodated with a place. No sooner is the door opened than a shower of snow at once fills the carriage. This is simply the moisture suspended in the air and generated by human lungs. The rush of cold air at once freezes this moisture and converts it into snow, thus showing those who will condescend to learn, that they have been breathing and re-breathing the air that has passed through a variety of human lungs, and is charged with their different moistures. I have seen the same phenomenon at a dinner party, where, after the withdrawal of the ladies, one of the windows was opened. Now, in Esquimaux-land, it is absolutely necessary to conserve every atom of heat, for the cold is so intense that if a cask of water be near a coal fire, only the part next the fire will be thawed, the rest being ice. Cold, therefore, is a foe which has to be fought and kept away from the household. Then there are other foes--such as Polar Bears, for instance--which would be only too glad to get into an igloo and make a meal of its inhabitants. The Esquimaux architect, therefore, avails himself of an ingenious device by which he can set both foes at defiance. In summer-time he contents himself with a hut made of skins, and merely hangs a skin over the entrance by way of a door. But in the winter, when he is driven to his snow-house for shelter, he acts in a very different manner. Instead of merely cutting an aperture for a door in the side of the igloo, he constructs a long, low, arched tunnel, so small that no one can enter the igloo except by traversing this tunnel on his hands and knees. Sometimes a number of huts are connected with each other, one or two tunnels leading into the air, and the rest serving merely as passages from one hut to the other. [Illustration: NESTS OF FAIRY MARTIN. TOWERS OF SAND-WASP.] [Illustration: HUTS OF ESQUIMAUX.] * * * * * IN Nature are several examples of tunnels constructed on the same principle. There are, for instance, the curious nests of the Fairy Martin of Southern Australia (_Hirundo Ariel_), which bear a singular resemblance to oil-flasks, the body of the nest being rather globular, and the only entrance being through a tolerably long, tunnel-like neck. Then there are the various Weaver-birds of Africa, with their long-necked nests. Some of these strange edifices look almost like horse-pistols suspended by the butt, so round is the nest, and so long and narrow is the tunnel-like entrance. * * * * *