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.
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.
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.
Why water runs.