But if water keeps evaporating all the time, why doesn't everything dry up? Everything doesn't dry up because of a weather system called the water cycle. Your experiment with the glass placed upside down on the grass helps tell you where the water goes.
The most noticeable features of Mars as seen through a telescope are its north and south poles. These appear just as those on earth would to a man on Mars. Since Mars is tilted at about the same angle that earth is, it has seasons as we do.
How much does air weigh? It depends on when and where you measure it. The air in your living room may weigh as much as you do. Right now there is a column of air resting on your head and shoulders which is several hundred miles high. It weighs hundreds of pounds.
THE SKY around you is like a giant picture which keeps changing as the weather changes. Sometimes the picture has a blue sky with large white clouds floating peacefully through space. Sometimes the picture is a dark one with deep gray clouds and rain.
The brain occupies the upper half of the skull. The largest part of the brain, called the cerebrum, consists of two deeply-wrinkled hemispheres of nerve tissue, one hemisphere on each side of the head. All of man's conscious activities are controlled by his cerebrum.
