"Everything," Anton answered, nodding his head. "The heat of the sun is what causes weather changes, because winds are due to the heating of the air, and the sun is the only thing that heats the air. At the equator, where the sun shines nearly overhead all the year round, the air gets to be very hot. Hot air expands, and as it gets bigger, it displaces the cold air above it. Gravity pulls down the colder air on both sides of this belt of rising hot air, and the down-flowing cold air on both sides blows in toward the equator under the warm air, where the heat of the sun warms it again, and, in turn, it rises. This is going on all the time and is one of the chief things that starts the winds blowing." "But winds don't always blow the same way," said the farmer; "you talk as if they did." "Some of them do," Anton replied. "There are lots of places where the winds hardly change, at all, but always blow in the same direction. You read of sailing ships taking the 'trade winds' when coming from Europe to America. Those are all easterly winds and blow towards the American coasts all the year round." "I don't see how they can," the other objected. "They do, Mr. Tighe," the Forecaster interrupted, endorsing Anton's statements; "the trade winds are the downflowing currents of cold air that Anton spoke of, which come down at either side of the equatorial belt to replace the warm air which is rising. The trade winds, however, form only a narrow belt and blow only near the surface of the earth. Above them, you can see the lighter clouds blowing eastward with a westerly wind, so that, quite often, in the trade winds, you can look overhead and see two layers of clouds driving in opposite directions." "You mean to say that there are different layers of wind?" queried the farmer. "Sure," put in Ralph, the cloud expert, "I've got photographs that show that up clearly. You've seen clouds going at different rates, haven't you, Mr. Tighe, some fast and some slowly?" The other nodded and turned to the Forecaster, who continued. "There are always several layers of wind, and, except above the equatorial belt," he said, "the direction of the upper air winds is generally towards the east." "How can you tell that?" "By the clouds, or by kites and balloons. But we don't even need to do this, because there are a few places that rise above the lower layers of the trade winds. Thus, the Peak of Teneriffe, which is in the trade-wind belt, has a continuous easterly wind on its lower slopes and a continuous westerly wind right at the summit.