Part 3

Another experiment that is quite familiar to all of us is that of opening the windows of a heated room a few inches top and bottom, and holding a lighted match or smoke paper at the bottom, when you will find that it blows the flame or smoke inward. Then put it near the top of the window and it will be drawn out. The same answer is true; the cold air is rushing in from below to take the place of the hot air rising and going out at the top. (See Fig. 9.)

Fig. 10 ]

EXPERIMENT NO. 8

This experiment is even more important than the preceding one, and you should by all means do it, for it is going to prove more conclusively than anything else what causes the wind, and in miniature it is a real storm.

Place a little alcohol lamp on the table, or a wax candle will do. Over this place an ordinary lamp chimney, lifting it a short distance off the table, and it can be held in position by any little object. (See Fig. 10.) Over the chimney hold some smoke paper. (Smoke paper is nothing more than filter paper, or brown wrapping paper of a soft texture.) From the experiments already visualized to you, you should know what to expect. You will again see that the heated air is rising; it has expanded and become light. Now what becomes of the air that is rising and where does it go? In doing this experiment be careful not to make any unnatural movements that will change the current of wind. Stand perfectly still so that the experiment will be perfect, because you are now producing in miniature a real storm, or demonstrating the cause of wind.

The next observation—what happens at the bottom of the chimney? Here you will find the outside air is coming in, the same as it did in the window experiment. Particularly, notice however, that the smoke enters underneath the chimney from all directions, and the smoke paper should be moved away from the glass chimney to determine the distance at which the smoke flames will still be drawn into the chimney.

You now produced for yourself in miniature a storm and wind. The air that has been heated rises over a heated area, and cooler air from all directions around is passing into the space underneath the chimney and taking the place of the heated air that has gone up. This experiment illustrates what takes place, except on a smaller scale, out in the atmosphere when a portion of the earth becomes heated. If this is clear to you, it will help you to understand the main principles underlying storms and winds, which will be given later on.

EXPERIMENT NO. 9

Equally important is the last part of the experiment, which consists in lifting the lamp chimney off the table altogether and continuing with the smoke paper. Note results that you get now. The smoke will spread out over a large area.

WHAT IS THE WEATHER?

By the weather we mean the temperature, the amount of moisture in the air, the pressure of the air, the movement of the air, and all the conditions that have to do with the atmosphere, such as heat, cold, rain, snow, sleet, fog, frost, dew, etc. It has to do with everything, from calmness and clearness to cloudiness and blizzards.

THE EFFECT OF THE SUN

The sun has a great deal to do with the regulation of the weather. Its heat causes evaporation; it is the rays of the sun that raises the vapor from the water and brings it into the air; it is the cooling of this vapor that produces the rain, hail and sleet storms, and its brilliancy causes a difference in air pressure at times. It is this difference in air pressure that produces winds, as you will learn later.

HUMIDITY

The state of the air with respect to the vapor that it contains is called its humidity. The humidity is said to be high when the air is damp, and low when the air is dry. Humidity and moisture in the air are important factors about the weather. It is lack of humidity that has more to do with poor health, colds, and catarrh than anything else. The importance of proper humidity in houses and buildings cannot be emphasized too greatly. Proper humidity will save twelve and one-half per cent in the cost of heating. The great majority of people are under the impression that colds are caused by sudden change in temperature, but the most colds are actually caused by stuffy, hot rooms. The reason that some people complain that 70° is not hot enough is because the humidity is too low, but if the moisture is brought into the air at a proper degree, the humidity is maintained. You will find that 68° will be a proper temperature to maintain in a room. The reason for this is that the air in the room is dry and the heat actually goes through it. In other words, it does not warm it; moist air stops radiation. Consequently, the result is that it warms it. In other words, moisture is nothing more than clothing, and this accounts for the fact that in a hot room, where there is no moisture, we heat our rooms beyond the degree that is necessary in order to feel any reasonable amount of comfort. Dry air allows too much radiation from the body and too rapid evaporation, which makes us cold.

The following experiment illustrates the above statement. Place a few drops of water on a smooth surface, such as a table top or ordinary board, and over this a watch glass, containing a small quantity of ether. In order to hasten evaporation, blow a current of air across it, and it will be found that the glass will be frozen to the board. This is caused by the evaporation of the ether, which uses up heat.

You know a great many times when you go out into the wind how cold it feels, and yet if the wind would actually stop, you would think it warm. It is the wind that causes the rapid evaporation and makes the surface of the skin feel cold. As it is true that the moisture in the air acts as a blanket to us in our homes, it is likewise as true that the vapor in its natural form outside of the house acts as a blanket for the earth. Do you realize that without this blanket we would burn up in the summer and freeze to death in the winter?

FOGS

Water vapor in the air is transparent, but when this water vapor becomes cooled, a portion of it becomes precipitated, which is no more or less than drops of water that are extremely small, but yet large enough to become transparent, and the atmosphere in this state is called fog. In reality, fogs are nothing more than clouds near the surface of the earth. When the ground is at a higher temperature than the air, it produces fogs. They are also produced when a current of moist air and a current of hot air pass over a body of water at a lower temperature. Consequently, you can easily see that fog will never form when it is dry.

HAIL

After rain drops have been formed and they freeze in their passage through the air, they then become hailstones.

SNOW

When condensation of vapor in the air takes place at a temperature below 32° F., a deposit is made in a solid condition, either in the form of snow or hail. Snow is made up of crystals, most of which have great beauty. Everyone should observe either by the naked eye or by a magnifying glass the little crystals caught before they are broken. When you see extremely large snowflakes in the sky, you can be sure the temperature is very near freezing, for at this point the flakes are more or less damp and the snow is heavy and wet. Now if there is a slight wind, the crystals become broken and separate flakes unite to form large masses of snow. Generally speaking, ten inches of snow makes one inch of rain.

DEW

If the temperature of the ground falls below the dew point of the air, the air deposits on the cooler surface moisture in the form of small drops of water, which we call dew drops. Where the temperature of the ground becomes cooler than the air above it, a rapid cooling by radiation on a clear night has taken place; and if the dew point or frost point has been reached by the ground, the air just above the point is several degrees warmer.

FROST

When the moisture in the air that is in contact with the earth is condensed above the freezing point, dew is formed. When below the freezing point, frost is formed or deposited on the earth. It is readily understood from this that the surface on which the frost is deposited is at a freezing temperature, while the air above it may not be freezing. Naturally, you can expect frost when the temperature falls to a point 8° or 10° above the freezing point. Clear, calm nights are favorable for frost, because the absence of clouds helps radiation, that is, it draws heat away from the earth. If there are clouds, it prevents this radiation.

THUNDER AND LIGHTNING