Among the Forces Part 2

[Ill.u.s.tration: 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...o...b..t (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!

[Ill.u.s.tration: 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 s.p.a.ce 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 a centrifugal (center-fleeing) force. David utilized it to one good purpose. Goliath was greatly surprised; such a thing never entered his head before. Whether a stone or an idea enters one's head depends on the kind of head he has.

We utilize this force in many ways now. Some boys swing a pail of milk over their heads, and if swung fast enough the centrifugal force overcomes the force of gravitation, and the milk does not fall. That is not utilizing the force. It often terrorizes the careful mother, anxious for the safety of the milk.

But in the arts of practical life we do utilize this force, which is only inertia.

Once it took a long time for mola.s.ses to drain out of a hogshead of damp sugar. Now it is put into a great tub, with holes in the side, which is made to revolve rapidly, and the mola.s.ses flies out. In the best laundries clothes are not wrung out, to the great damage of tender fabrics, but are put into such a tub and whirled nearly dry. So fifty yards of woolen cloth just out of the dye vat--who could wring it? It is coiled in a tub called a wizard, and whirled.

Muddy water is put through a process called clarification. It is the same, except that there are no holes in the vessel. The heavier particles of dirt, that would settle in time, take the outside, leaving perfectly clean water in the middle. A perpendicular perforated pipe, with a faucet below, drains off all the clear water and leaves all the mud. Milk is brought in from the milking and put into a separator; whirl it, and the heavier milk takes the outside of the whirling ma.s.s, and the lighter cream can be drawn off from the middle. It is far more perfectly separated than by any skimming.

A rotary snowplow slices off two feet of a ten-foot drift at each revolution, and by centrifugal force flings it out of the cutting with a speed that a hundred navvies or dagos cannot equal.

ONE PLANT HELP

A thousand acres of land on Cape Cod were once blown away. This wind excavation was ten feet deep. It was not an extraordinary wind, but extraordinary land. It was made of rock ground up into fine sand by the waves on the sh.o.r.e.

In all the deserts of the world the wind blows the itinerant sand on its far journeys. If the wind is moderate it heaps the sand up into little hills, some of them six hundred feet high, around any obstruction, and then blows the sand up the slanting face of the hill and over the top, where it falls out of the wind on the leeward side.

In this way the hill is always traveling. In North Carolina hills start inland, and travel right on, burying a house or farm if it be in the way, but resurrecting it again on the other side as the hill goes on. Anyone may see these hills at the south end of Lake Michigan, as he approaches Chicago, west of San Francisco, all along up the Columbia River--the sand having come on the wings of the wind from the coast.

But to see the whole visible world on a march one needs to go to a really large desert. The Pyramids and the Sphinx have been partly buried, and parts of the valley of the Nile threatened, by hordes of sand hills marching in from the desert; cities have been buried and harbors filled up. Many of the harbors of the ancient civilizations are mere miasmatic marshes now. This is partly in consequence of the silt brought in by the rivers; but where the rivers do not flow in it is because the sand blows in along the sh.o.r.e. Harbors are especially endangered when their protection from the waves consists of a bank of sand, as on Cape Cod and the Sandy Hook below the Narrows of the harbor of New York.

How can man combat part of the continent on the move, driven by the ceaseless powers of the air? By a humble plant or two. The movement of the sand hills that threaten to destroy the marvelous beauty of the grounds of the Hotel del Monte at Monterey is stopped by planting dwarf pines. The sand dunes that prevent much of Holland from being reconquered by the sea are protected with great care by willows, etc., and the coast sands of parts of eastern France have been sown with sea pine and broom.

The tract of a thousand acres on Cape Cod had been protected by humble beach gra.s.s. Some careless herder let the cows eat it in places, and away went part of a towns.h.i.+p. It is now a punishable crime on Cape Cod to destroy beach gra.s.s.

GAS HELP

This refers to more than stump speech-making. The old Romans drove through solid rock numerous tunnels similar to the one for draining Lago de Celano, fifty miles east of Rome. This one was three and a half miles long, through solid rock, and every chip cost a blow of a human arm to dislodge it. Of course the process was very slow.

We do works vastly greater. We drive tunnels three times as long for double-track railways through rock that is held down by an Alp. We use common air to drill the holes and a thin gas to break the rock. The Mont Cenis tunnel required the removal of 900,000 cubic yards of rock.

Near Dover, England, 1,000,000,000 tons of cliff were torn down and scattered over fifteen acres in an instant. How was it done? By gas.

There are a dozen kinds of solids which can be handled--some of them frozen, thawed, soaked in water, with impunity--but let a spark of fire touch them and they break into vast volumes of uncontrollable gas that will rend the heart out of a mountain in order to expand.

Gunpowder was first used in 1350; so the old Romans knew nothing of its power. They flung javelins a few rods by the strength of the arm; we throw great iron sh.e.l.ls, starting with an initial velocity of fifteen hundred feet a second and going ten miles. The air pressure against the front of a fifteen-inch sh.e.l.l going at that speed is 2,865 pounds.

That ton and a half of resistance of gas in front must be much more than overcome by gas behind.

But the least use of explosives is in war; not over ten per cent is so used. The Mont Cenis tunnel took enough for 200,000,000 musket cartridges. As much as 2,000 kegs have been fired at once in California to loosen up gravel for mining, and 23 tons were exploded at once under h.e.l.l Gate, at New York.

How strong is this gas? As strong as you please. Steam is sometimes worked at a pressure of 400 pounds to the inch, but not usually over 100 pounds. It would be no use to turn steam into a hole drilled in rock. The ordinary pressure of exploded gas is 80,000 pounds to the square inch. It can be made many times more forceful. It works as well in water, under the sea, or makes earthquakes in oil wells 2,000 feet deep, as under mountains.