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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
"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 dwelling."
"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?"
"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
"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."