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Page 14
Air so much enjoys its free, agile state, leaping over hills and
plains, kissing a thousand flowers, that it greatly objects to being
condensed to a liquid. First we must take away all the heat. Two
hundred and ten degrees of heat changes water to steam filling 1,728
times as much space. No amount of pressure will condense steam to
water unless the heat is removed. So take heat away from air till it
is more than two hundred degrees below zero, and then a pressure of
about two hundred atmospheres (14.7 pounds each) changes common air to
fluid. It fights desperately against condensation, growing hot with
the effort, and it maintains its resilience for years at any point of
pressure short of the final surrender that gives up to become liquid.
Perhaps sometime we shall have the pure air of the mountains or the sea
condensed to fluid and sold by the quart to the dwellers in the city,
to be expanded into air once more.
The marvel is not greater that gas is able to sustain itself under the
awful pressure with its particles in extreme dispersion, than that what
we call solids should have their molecules in a mazy dance and yet keep
their strength.
Since this world, in power, fineness, finish, beauty, and adaptations,
not only surpasses our accomplishment, but also is past our finding out
to its perfection, it must have been made by One stronger, finer, and
wiser than we are.
MOBILITY OF SEEMING SOLIDS
When a human breath, or the white jet of a steam whistle, or the black
cough of a locomotive smokestack is projected into the air it is easy
to see that the air is mobile. Its particles easily roll over one
another in voluminously infolding wreaths. The same is seen in water.
The crest of a wave falls over a portion of air, imprisoning it for a
moment, and the mingled air and water of different densities prevent
the light of the sun or sky from going straight down into the black
depths and being lost, but by being reflected and turned back it shows
like beautiful white lace, constantly created and dissolved with a
thousandfold more beauty than any that ever came from human hands. All
the three shifting elements of the swift creations are mobile. This
seems to be the case because these elements are not solid. The
particles have plenty of room to play about each other, to execute mazy
dances and minuets with vastly more space than substance.
Extend the thought a little. Things that seem to us most solid are
equally mobile. An iron wire seems solid. It is so; some parts much
more so than others. The surface that has been in closest contact with
the die as the wire was drawn through, reducing its size by one half,
perhaps, is vastly more dense than the inner parts that have not been
so condensed. File away one tenth of a wire, taking it all from the
surface, and you weaken the tensile strength of the wire one half.
But, dense and solid as this iron is, its particles are as mobile
within certain limits as the particles of air. An electric message
sent through a mile of wire is not anything transmitted; matter is not
transferred, but the particles are set to dancing in wavy motion from
end to end. Particles are leaping within ordered limits and according
to regular laws as really as the clouds swirl and the air trembles into
song through the throat of a singer. When a wire is made sensitive by
electricity the breath of a child can make it vibrate from end to end,
ensouled with the child's laughter or fancies. Nay, more, and far more
wonderful, the wire will be sensitive to the number of vibrations of a
certain note of music, and no receiver at the other end will gather up
its sensitive tremblings unless it is pitched to the keynote of the
vibrations sent. In this way eight sets of vibrations have been sent
on one wire both ways at the same time, and no set of signals has in
any way interfered with the completeness and audibility of the rest.
Sixteen sets of waltzes were being performed at one and the same time
by the particles of one wire without confusion. Because the air is
transmitting the notes of an organ from the loft to the opposite end of
the church, it is not incapable of bringing the sound of a voice in an
opposite direction to the organist from the other end of the church.
The extreme mobility of steel is seen when the red-hot metal is plunged
into water. Instantly every particle takes a new position, making it a
hundredfold more hard than before it was heated. But these particles
of transferred steel are still mobile. A man's razor does not cut
smoothly. It is dull, or has a ragged edge that is more inclined to
draw tears than cut hairs. He draws the razor over the tender palm of
his hand a few times, rearranges the particles of the edge and builds
them out into a sharper form. Then the razor returns to the lip with
the dainty touch of a kiss instead of a saw. Or the tearful man dips
the razor in hot water and the particles run out to make a wider blade
and, of course, a thinner, sharper edge. Drop the tire of a wagon
wheel into a circular fire. As the heat increases each particle says
to its neighbor, "Please stand a little further off; this more than
July heat is uncomfortable." So the close friends stand a little
further apart, lengthening the tire an inch or two. Then, being taken
out of the fire and put on the wheel and cooled, the particles snuggle
up together again, holding the wheel with a grip of cold iron. Mobile
and loose, with plenty of room to play, as the particles have, neither
wire nor tire loses its tensile strength. They hold together, whether
arms are locked around each other's waist, or hand clasps hand in
farther reach. What change has come to iron when it has been made red
or white hot? Its particles have simply been mobilized. It differs
from cold iron as an army in barracks and forts differs from an army
mobilized. Nothing has been added but movement. There is no caloric
substance. Heat is a mode of motion. The particles of iron have been
made to vibrate among themselves. When the rapidity of movement
reaches four hundred and sixty millions of millions of vibrations per
second it so affects the eye that we say it is red-hot. When other
systems of vibration have been added for yellow, etc., up to seven
hundred and thirty millions of millions for the violet, and all
continue in full play, the eye perceives what we call white heat. It
is a simple illustration of the readiness of seeming solids to vibrate
with almost infinite swiftness.
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