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).
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