CHAPTER XVI.

WATER ALWAYS TRYING TO BE LEVEL.

If you look at water in a bowl, you see that its surface is smooth and level. If now you stir it about, you make it uneven. Watch it as it becomes still and smooth again. There seems to be a kind of struggle as all the particles of water take their places.

But you will ask me what I mean by the particles of water. We suppose that water is made up of exceedingly fine balls. These balls or particles are so round and smooth that they move among each other very easily. This is the reason that water runs so readily, and so soon becomes level when nothing is disturbing it. If the particles were not so smooth, they would rub each other. They would not roll over each other so freely as they do.

[Sidenote: The particles of water compared to shot.]

To make this plain, we will compare water to small shot. If you put these into a bowl, they will not lie level, as water does. Now what is the reason that these round balls of lead do not act as the smaller round balls of the water do? It is because they are not as smooth. They can not roll over each other easily, for they rub together. They can not in any way be made as smooth as the particles of water are.

If you pour the shot from one bowl into another, they will run somewhat as the water does; but they will not slip along as easily, for they rub each other as they go, while there is almost no rubbing among the particles of water.

[Sidenote: The particles of water round and smooth.]

The balls or particles of water are exceedingly small. They are so small that no one has ever seen them. How, then, you will ask, do we know that they are round and smooth? We say that they are, because we can not see how they could move about among each other so easily if they were rough, or had corners or points on them. You can not roll about blocks or nails as you can roll shot; and the smoother the shot the more easily they will roll. So then we know, from what we see in other things, that the particles of water that roll so easily must be round, and must be smooth also.

If the particles of water were large enough for us to see them, they would look to us, on the surface of still water, as a level layer of little shot or round beads, and we should see them rolling about among each other whenever there is the least motion of the water; but, as we can not see the particles, the surface of the water looks like smooth glass when they are all still.

As water moves so easily, it is almost always in motion. It is moved by the wind, and is raised by it sometimes into very high waves. It runs in the brooks and rivers.

[Sidenote: Why water runs.]

In all its motions the water is always trying to be level; and this is the only reason that water ever runs. Water that is level will not run; it will be still. But, when you disturb this level, it will run till it finds its level again.

I will make this plain to you. Suppose that you have a trough stopped at both ends. Put some water in it as it lies on level ground. The water is level in it, and is quiet. Now raise up one end of the trough a little. The water is at once in motion. Why? Because you have disturbed the level. The water runs from the end that you raise toward the other end. Now hold the trough still a little time with the end raised, and as soon as the water gets its level again, it will be as still as it was before.

[Sidenote: Brooks and rivers.]

Suppose the trough is open at both ends, and water is running in all the time at the raised end. It will keep running toward the lower end. It will be all the time trying to get on a level, but never can. You see here the reason that water runs in a brook or river. You can think of a brook or a river as a trough with one end a little raised; and the water in it is always, as we may say, running after a level, but never finds it. The sea is to a river as a tub would be to the trough that pours its water into it.

[Sidenote: The power of running water.]

There is often great power in the water of a running stream. It works a great deal of machinery in mills of various kinds; and, if the stream be swollen with heavy rains, the water carries away bridges, houses, etc. It does all this in trying to get on a level. If it all could be made level in some way, as you see it in a bowl or a pond, it would do no such violence.

[Sidenote: Dams.]

Sometimes men build a dam across a river. This is for the purpose of turning the water off one side into a canal. The dam stops some of the water running in the river, sometimes all of it. In doing this the water is made about level just above the dam, and so is much more quiet than it is any where else in the river.

Children often build mud dams, and the water that they stop is very still because it is level. When the dams give way, how briskly the water runs to try to get on a level again.

[Sidenote: Pouring from a coffee-pot.]

Water is always on the same level in the spout of a coffee-pot that it is in the pot itself, as represented in the first of these figures. If the coffee-pot be turned up, as seen in the second figure, the level is still preserved. If it be turned up a little more, the liquid in the spout, in trying to be on a level with that in the pot, runs out, as represented in the third figure.

[Sidenote: A supposed discovery of perpetual motion.]

A man once thought that he had discovered a way of keeping up perpetual motion. He thought that he could make a vessel of such a shape that some water in it would never stop moving. The vessel was to be of the shape that you see here. His idea was, that there was so much more water in the vessel than there was in the spout, that it would press the water in the spout up its whole length, and make it run into the vessel. You can see that, if it would operate in this way, the water would be always in motion--it would be going the rounds by way of the spout all the time. But the difficulty is that it would not operate in this way. After the man made his vessel, he found that the water was only as high in the spout as in the vessel, as you see in the figure. It is just as it is with the spout of the coffee-pot.

[Sidenote: Water can rise in the pipes of an aqueduct as high as it is in the fountain.]

In the same way, if an aqueduct pipe extend from a spring, the water will not rise any higher in the pipe than it is in the spring. The pipe is to the spring what the spout is to a coffee-pot. And it makes no difference how long the spout is. The water will stand at the same height in a pipe that extends for miles that it does in one that goes but a little way from the reservoir or fountain. This can be illustrated in a vessel with two pipes, as seen here. The water stands in the branch pipe that is farthest from the vessel at the same height that it does in the near one. Sometimes an aqueduct will supply the lower stories of a building with water, but not the upper stories. The reason is that the upper stories are higher than the level of the water in the fountain from which the water comes.

[Sidenote: The playing of a fountain explained.]

You have often seen a fountain playing. How beautifully the stream rises and spreads out, dropping in a shower all around! Now why is it that the water rises? It is because the spring from which the water comes is so much higher than the pipe of the fountain. The water in the pipe tries, as we may say, to get on a level with the water in the spring. This I will make plain to you by two figures. In the first figure you see represented a vessel of water, with a pipe extending from its lower part up at its side. The water stands at the same level in the pipe that it does in the vessel, as in the case of the coffee-pot. Now suppose, as represented in the second figure, the pipe is quite short. If the vessel be filled with water, the water in the pipe, seeking to get to the same level as that in the vessel, will be thrown up in a stream, as you see. The reason that the stream spreads out and drops in a shower is, that the air resists the stream, and so divides it up, because water is so easily separated into parts.

_Questions._--What is said about water in a bowl? What is said about the particles of water? Give the comparison about shot. Why will not shot run as easily as water from one vessel into another? What is said about the smallness of the particles of water? How do we know that they are round or smooth? If we could see the particles, how would water look to us? What is said about water’s being in motion? What makes it run? Tell about water in a trough. Give the comparison about a trough and a river. What is said about the power of running water? What is said about dams? Tell about the level of water in a coffee-pot. Tell about the man’s contrivance for perpetual motion. What is said about the pipes of an aqueduct? Why will water sometimes come only to the lower story of a building, and not to the upper? Tell about the playing of water from a fountain. Why does the water come down in a shower of drops?