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Page 7
We want a steady, unswerving force that will pull our clock hands with
an exact motion day and night, year in and year out. We hang up a
string, and ask gravitation to take hold and pull. We put on some lead
or brass for a handle, to take hold of. It takes hold and pulls,
unweariedly, unvaryingly, and ceaselessly.
It turns single water-wheels with a power of more than twelve hundred
horses.
It holds down houses, so that they are not blown away. It was made to
serve man, and it works without a grumble.
Thus the higher force in nature always prevails over the lower, and the
greater amount over the less amount of the same force. What is the
highest force?
THE FAIRY PULLS GREAT LOADS
Far back in the hills west of Mauch Chunk, Pa., lie great beds of coal.
They were made under the sea long ages ago, raised up, roofed over by
the Allegheny Mountains, and kept waiting as great reservoirs of power
for the use of man.
But how can these mountains be gotten to the distant cities by the sea?
Faith in what power can say to these mountains, "Be thou removed far
hence, and cast into the sea?" It is easy.
Along the winding sides of the mountains have been laid two rails like
steel ribbons for a dozen miles, from the coal beds to water and
railroad transportation. Put a half dozen loaded cars on the track,
and with one man at the brake, lest gravitation should prove too
willing a helper, away they go, through the springtime freshness or the
autumn glory, spinning and singing down to the point of universal
distribution.
[Illustration: Incline at Mauch Chunk.]
On one occasion the brake for some reason would not work. The cars
just flew like an arrow. The man's hair stood up from fright and the
wind. Coming to a curve the cars kept straight on, ran down a bank,
dashed right into the end of a house and spilled their whole load in
the cellar. Probably no man ever laid in a winter's supply of coal so
quickly or so undesirably.
But how do we get the cars back? It is pleasant sliding down hill on a
rail, but who pulls the sled back? Gravitation. It is just as willing
to work both ways as one way.
Think of a great letter X a dozen miles long.
Lay it down on the side against three or four rough hills. Bend the X
till it will fit the curves and precipices of these hills. That is the
double track. Now when loaded cars have come down one bar of the X by
gravity, draw them up by a sharp incline to the upper end of the other
bar, and away they go by gravity to the other end. Draw them up one
more incline, and they are ready to take a new load and buzz down to
the bottom again.
I have been riding round the glorious mountain sides in a horseless,
steamless, electricityless carriage, and been delighted to find
hundreds of tons of coal shooting over my head at the crossings of the
X, and both cars were drawn in opposite directions by the same force of
gravity in the heart of the earth.
If you do not take off your hat and cheer for the superb force of
gravitation, the wind is very apt to take it off for you.
THE FAIRY DRAWS GREATER LOADS
Pittsburg has 5,000,000 tons of coal every year that it wishes to send
South, much of it as far as New Orleans--2,050 miles. What force is
sufficient for moving such great mountains so far? Any boy may find it.
Tie a stone to the end of a string, whirl it around the finger and feel
it pull. How much is the pull? That depends on the weight of the
stone, the length of the string, and the swiftness of the whirl. In
the case of David's sling it pulled away hard enough to crash into the
head of Goliath. Suppose the stone to be as big as the earth (8,000
miles in diameter), the length of the string to be its distance from
the sun (92,500,000 miles), and the swiftness of flight the speed of
the earth in its orbit (1,000 miles a minute). The pull represents the
power of gravitation that holds the earth to the sun.
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