Among the Forces | Page 7

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.
If we use steel wires instead of gravitation for this purpose, each strong enough to support half a score of people (1,500 pounds), how many would it take? We would need to distribute them over the whole earth: from pole to pole, from side to side, over all the land and sea. Then they would need to be so near together that a mouse could not run around among them.
Here is a measureless power. Can it be gotten to take Pittsburgh coal to New Orleans? Certainly; it was made to serve man. So the coal is put on great flatboats, 36 x 176 feet, a thousand tons to a boat, and gravitation takes the mighty burden down the long toboggan slide of the Ohio and Mississippi Rivers to the journey's end. How easy!
[Illustration: The Head of the Toboggan Slide.]
One load sent down was 43,000 tons. The flatboats were lashed together as one solid boat covering six and one half acres, more space than a whole block of houses in a city, with one little steamboat to steer. There is always plenty of power; just belt on for anything you want done. This is only one thing that gravitation does for man on these rivers. And there are many rivers. They serve the savage on his log and the scientist in his palace steamer with equal readiness.

THE FAIRY WORKS A PUMP HANDLE
The Slave of the Ring could take Aladdin into a cave of wealth, and by speaking the words, "Open Sesame," Ali Baba was admitted into the cave that held the treasures of the forty thieves. But that is very little. I have just come from a cave in Virginia City, Nev., from which men took $120,000,000.
In following the veins of silver the miners went down 3,500 feet--more than three fifths of a mile. There it was fearfully hot, but the main trouble was water. They had dug a deep, deep well. How could they get the water out? Pumps were of no use. A column of water one foot square of that height weighs 218,242 pounds. Who could work the other end of the pump handle?
They thought of evaporating the water and sending it up as steam. But it was found that it would take an incredible amount of coal. They thought of separating it into oxygen and hydrogen, and then its own lightness would carry it up very quickly. But they had no power that would resolve even quarts into their ultimate elements, where tons would be required.
So they asked gravitation to help them. It readily offered to do so. It could not let go its hold of the water in the mine, nor anywhere else, for fear everything would go to pieces, but it offered to overcome force with greater force. So it sent the men twenty miles away in the mountains to dig a ditch all the way to the mine, and then gravitation brought water to a reservoir four hundred feet above the mouth of the mine. Now a column of this water one foot square can be taken from this higher reservoir down to the bottom of the mine and weigh 25,000 pounds more than a like column that comes from the bottom to the top. This extra 25,000 pounds is an extra force available to lift itself and the other water out of the deep well, and they turn the greater force into a pump and work it in the cylinder as if it were steam. It lifts not only the water that works the pump, but the other water also out of the mine by gravitation. So man gets the water out by pouring more water in.

THE HELP OF INERTIA
Since the time of David many boys have swung pebbles by a string, or sling, and felt the pull of what we call