CHAPTER II.
AIR IN MOTION.
How a ship is moved along by air.
The air, when it is in motion, does a great deal of work for us. It pushes along the ships in the water. Perhaps you think that it hardly sounds right to say that the air pushes the ships; but it really does push them. The sails are large, broad handles for the air to press against in pushing the vessels along in the water. On the preceding page is a ship with many sails, and most of them are unfurled, or put out for the breeze to press upon.
The air would push a vessel along to some extent, even if there were no sails, by pressing or blowing against the body of the vessel; but, unless the wind blew very strong, the air would not push it along very fast in this way. And so sails are put up on masts, that more of the air may get hold, as we may say, so as to press on the vessel.
A coat used as a sail.
Sometimes the wind helps you along as you are walking. Now, if you take hold of your coat, and spread it out wide, as you see this boy is doing, it will be like a sail, and the wind will carry you along faster, because there is more for the air to press upon. So, too, if you have an umbrella open when the wind is blowing on your back, it will be to you as the sail is to the ship. But if you are going against the wind, the outspread coat and the open umbrella would prevent your getting along fast.
Trees blown by the wind.