"I PASS to other examples. To keep the contents of a soup-tureen warm, what do we do? We enclose the tureen in a woolen coverlet; we wrap it in several thicknesses of a soft material which acts as a very poor heat-conductor because of its fibrous texture.

"But suppose, on the other hand, we wish to keep something at a low temperature; we again avail ourselves of this same quality possessed by fibrous substances. In summer, to exclude the heat from our ice-creams and sherbets we use a jar set into another of much greater size, filling the intervening space with wool, cotton, or rags. Thus the same wool, cotton, or other filling that maintains the warmth of the soup in the tureen will also serve to maintain the coldness of the frozen preparation in the jar.

"Ice, which is one of the most urgently needed supplies in warm countries, is sometimes transported long distances under the burning sun. The United States, for example, ships every year great quantities of ice to China and the Indies, and the vessels engaged in this traffic cross seas where the highest temperature prevails. Nevertheless the cargo reaches its destination almost intact, thanks to the non-conducting material protecting it from the heat, this material being sawdust, straw, dry leaves, or shavings, with which care is taken to cover completely the cakes of ice heaped up in the hold.

"An ice-house for keeping through even the hottest summer weather the ice gathered in winter consists of a deep excavation lined with brick in preference to stone, because the former is a much poorer heat-conductor. A thick layer of straw is also placed next to the bricks. The ice is stored when the weather is very cold, the cakes being packed closely and then flushed with water, which freezes and renders the whole one compact mass. Over all is laid a bed of straw, and on top of this are put planks loaded with stones. Finally the ice-house is roofed with thatch. The very same procedure would be adopted if it were desired to keep from escaping the warmth present in the excavation."

"Then," said Marie, "this thatched roof and layer of straw would be just the thing for making a snug retreat that would keep out the cold."

"Yes, this snug retreat, made of straw and similar material to withstand the severities of winter, is exactly what we find in the extreme north of Europe, where the cold season is so rigorous. Houses of masonry like ours would there be inadequate, because brick and stone would offer but an imperfect obstacle to the dissipation of the interior warmth. For those arctic habitations some building material is required of less conducting power than brick and stone, some material that will retain the interior warmth just as ashes retain the heat of the live coals that they cover. To this end masonry gives place to walls of thick planks or even of logs laid lengthwise one upon another. So far so good, since wood conducts heat much less readily than stone; but it is not enough. A double enclosure or wall is built of these planks or logs, and the space between the two single walls is filled with moss, leaves, or straw. Thanks to this multiple enclosure made of materials that act as very poor heat-conductors, the warmth given out by a stove always alight is kept from escaping even when the severest cold prevails outside.

"The most curious application of powdery substances as a protection against cold is found in the use of snow for constructing winter dwellings."

"What," cried Claire, "do they build houses of snow?"

"Not exactly houses like ours, but huts in which the occupants are very well sheltered."

"And where is that?"

"In Greenland, to the northeast of America, in the frigid zone, as we have already seen. There, where the rigors of the climate are well-nigh inconceivable to us, the Eskimos live in huts built of regular blocks of hardened snow laid in circular courses and rounding toward the top, with a sheet of ice capping the dome to admit the light. A bench of snow next to the wall encircles the interior and is provided with rude bedding of heather and reindeer skins for the repose of the inmates at night. No fireplace is ever found in these abodes, since there is no wood for fuel; and, moreover, a fire would melt the snow hut. A wick of moss fed with seal oil burns in a little stone pot and serves both to melt snow when water is needed for drinking and to maintain an endurable temperature in the hut, thanks to the very slight conductivity of the snow walls. Outside, meanwhile, the cold is of an intensity such that even our severest winters offer no comparison. If one leaves the hut, immediately face and hands turn blue and become quite numb; the skin cracks open under the action of the frost; the breath forms needles of hoar-frost around the nostrils, and the tears freeze on the edges of the eyelids."

"What a frightful country!" Claire exclaimed. "And do people really live there?"

"Yes, there are people who give the sweet name of home to that forbidding land. They live there the year round, in summer under skin tents, and when winter comes in snow huts."

"But why don't they build themselves houses of stone?" asked Jules.

"Because they would freeze in them," was the reply, "for lack of fuel to keep a hot fire going all the time. Snow is the only available material that can conserve the heat of the little lamp and maintain an endurable temperature in the hut; and this it does by reason of the poor conducting power of its powdery mass.

"The various powdery or fibrous substances, such as snow, ashes, shavings, straw, moss, wool, cotton, feathers, all well adapted to the keeping out of either cold or heat, owe this peculiar property in great part to the air held prisoner in their interstices. The air imprisoned in the foam of beaten eggs prevents the heat of the oven from penetrating to the frozen cheese that I told you about in relating a curious experiment. The same foam, inflated with air, would protect from the cold any heated body that it might envelop. Air by itself can be used to prevent the dissipation of heat if it is so placed that it cannot be renewed and mix with the free air of the atmosphere. I will now call your attention to an instance in which this property of air is turned to account in our houses where the climate is severe.

"The warmth in a room escapes to the outside through the walls, floor, and ceiling, these never being perfect non-conductors. For this waste of heat there is hardly any remedy in our dwellings of brick and stone. But there is one avenue of escaping heat that can be easily closed. I refer to the windows. The panes of glass offer but a very imperfect obstacle to the outflow of heat. In order to supply a more efficacious barrier without lessening the transparency of the windows and their admission of light, it is customary to build, as it were, a wall of air behind the panes; that is to say, we fill the opening in the wall with two windows, one on the outside and the other on the inside, thus obtaining in the space between the two similarly glazed frames a layer of immobile air, a sort of transparent wall which the heat from within cannot pass through. That is what we call a double window."

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