Fogs and Clouds.
What is always taking place from the surface of the water in the rivers, lakes, and oceans?
The water is always passing off in the form of vapor.
Where does this vapor go?
It goes into the air so that the air becomes filled with moisture.
What kind of air will hold the most vapor?
Warm air will hold the most vapor.
When warm air becomes colder, what is done with the vapor?
The vapor is condensed into small particles of water.
When this takes place near the earth, what does it produce?
It produces a fog.
Where do fogs mostly occur?
Fogs mostly occur over low grounds and along the course of streams.
When the vapor is condensed higher up in the air, what does it produce?
It produces a cloud.
What is a cloud?
A cloud is only a fog, higher up in the air.
Do fogs ever ascend in the air?
Yes; they often ascend, and thus produce clouds.
What causes the vapor of the air to be condensed into clouds?
Cold causes it to be condensed into clouds.
Does the air grow colder as we ascend?
Yes; the higher we ascend, the colder we find the atmosphere.
What becomes of the vapor in the air, as it ascends from the earth?
The vapor is condensed into clouds in the upper regions of the air.
Why do we mostly see clouds at the top of a mountain?
Because the vapor in the air is condensed into clouds by the cold at the top of the mountain.
When is a cloud formed in the air?
When a warm, damp wind meets with a cold wind, its vapor is condensed and a cloud is formed.
Are clouds often formed in this way?
Yes; clouds are often quickly formed in this way.
When the cloud passes into a warmer current of air, what becomes of it?
It is changed back into vapor, so that it cannot be seen.
How then can a cloud in the sky disappear very quickly?
By passing into a warmer current of air the cloud is changed into a vapor, and may thus quickly disappear.
Are clouds of different heights?
Yes; some clouds touch the earth, while other clouds are high up in the air.
Why are clouds higher on a fine day?
Because there is not so much moisture in the air, and, therefore, it rises higher before its vapor is condensed into clouds.
Why are clouds lower on a rainy day?
Because there is so much moisture in the air, that it is condensed into clouds near the earth.
Are the clouds high during a thunder-storm?
No; during a thunder-storm the clouds are seldom more than one-third of a mile high, and very often are much nearer the surface of the earth.
Is there any difference in the thickness of the clouds?
Yes; some are only a few inches thick, while others are a mile or more in thickness.
When the sun is about to rise, which of the seven colors of light is the first to appear?
The red color appears first.
When the sun sets, which of the seven colors is the last to fade away?
The red color is the last to fade away.
Why are the clouds red just before sunrise?
Because they are tinged by the red ray of light, before the other rays appear.
Why are the clouds red after sunset?
Because they are tinged by the red ray of light, after the other rays have faded away.