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Page 12
A very strong current of heat may be sent right through the heart
of a block of ice without melting the ice at all or cooling off
the heat in the least. It is done in this way: Send the beam of
heat through water in a glass trough, and this absorbs all the heat
that can affect water or ice, getting itself hot, and leaving all
other kinds of heat to go through the ice beyond; and appropriate
tests show that as much heat comes out on the other side as goes
in on this side, and it does not melt the ice at all. Gunpowder
may be exploded by heat sent through ice. Dr. Kane, years ago,
made this experiment. He was coming down from the north, and fell
in with some Esquimaux, whom he was anxious to conciliate. He said
to the old wizard of the tribe, "I am a wizard; I can bring the
sun down out of the heavens with a piece of ice." That was a good,
deal to say in a country where there was so little sun. "So," he
writes, "I took my hatchet, chipped a small piece of ice into the
form of a double-convex lens, [Page 33] smoothed it with my warm
hands, held it up to the sun, and, as the old man was blind, I
kindly burned a blister on the back of his hand to show him I could
do it."
These are simple illustrations of the various kinds of heat. The
best furnace or stove ever invented consumes fifteen times as much
fuel to produce a given amount of heat as the furnace in our bodies
consumes to produce a similar amount. We lay in our supplies of
carbon at the breakfast, dinner, and supper table, and keep ourselves
warm by economically burning it with the oxygen we breathe.
Heat associated with light has very different qualities from that
which is not. Sunlight melts ice in the middle, bottom, and top at
once. Ice in the spring-time is honey-combed throughout. A piece
of ice set in the summer sunshine crumbles into separate crystals.
Dark heat only melts the surface.
Nearly all the heat of the sun passes through glass without hinderance;
but take heat from white-hot platinum and only seventy-six per cent.
of it goes through glass, twenty-four per cent. being so constituted
that it cannot pass with facility. Of heat from copper at 752�
only six per cent. can go through glass, the other ninety-four per
cent. being absorbed by it.
The heat of the sun beam goes through glass without [Page 34] any
hinderance whatever. It streams into the room as freely as if there
were no glass there. But what if the furnace or stove heat went
through glass with equal facility? We might as well try to heat our
rooms with the window-panes all out, and the blast of winter
sweeping through them.
The heat of the sun, by its intense vibrations, comes to the earth
dowered with a power which pierces the miles of our atmosphere,
but if our air were as pervious to the heat of the earth, this
heat would flyaway every night, and our temperature would go down
to 200� below zero. This heat comes with the light, and then,
dissociated from it, the number of its vibrations lessened, it is
robbed of its power to get away, and remains to work its beneficent
ends for our good.
Worlds that are so distant as to receive only 1/1000 of the heat
we enjoy, may have atmospheres that retain it all. Indeed it is
probable that Mars, that receives but one-quarter as much heat
as the earth, has a temperature as high as ours. The poet drew on
his imagination when he wrote:
"Who there inhabit must have other powers,
Juices, and veins, and sense and life than ours;
One moment's cold like theirs would pierce the bone,
Freeze the heart's-blood, and turn us all to stone."
The power that journeys along the celestial spaces in the flashing
sunshine is beyond our comprehension. It accomplishes with ease
what man strives in vain to do with all his strength. At West Point
there are some links of a chain that was stretched across the river
to prevent British ships from ascending; these links were made
of two-and-a-quarter-inch iron. A powerful locomotive might tug
in vain at one of them and not stretch it the thousandth part of
an inch. But the heat of a single gas-burner, that glows with the
preserved sunlight of other ages, when suitably applied to the
link, stretches it with ease; such enormous power has a little
heat. There is a certain iron bridge across the Thames at London,
resting on arches. The warm sunshine, acting [Page 35] upon the
iron, stations its particles farther and farther apart. Since the
bottom cannot give way the arches must rise in the middle. As they
become longer they lift the whole bridge, and all the thundering
locomotives and miles of goods-trains cannot bring that bridge down
again until the power of the sunshine has been withdrawn. There is
Bunker Hill Monument, thirty-two feet square at the base, with an
elevation of two hundred and twenty feet. The sunshine of every
summer's day takes hold of that mighty pile of granite with its
a�rial fingers, lengthens the side affected, and bends the whole
great mass as easily as one would bend a whipstock. A few years ago
we hung a plummet from the top of this monument to the bottom. At 9
A.M. it began to move toward the west; at noon it swung round toward
the north; in the afternoon it went east of where it first was, and
in the night it settled back to its original place.
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