Transcriber’s Note:

The cover image was created by the transcriber and is placed in the public domain.

GILBERT
WEATHER BUREAU
(METEOROLOGY)
FOR BOYS

BY

ALFRED C. GILBERT

Yale University, 1909

Published by

THE A. C. GILBERT COMPANY

NEW HAVEN, CONN.

New York Chicago San Francisco Toronto London

Copyright, 1920, by

A. C. GILBERT

New Haven, Conn.

WEATHER INDICATIONS
A Study of the Weather

In the minds of most people a very silly notion prevails about the weather and the weather man. They have a general impression that the weather knows no laws—that it is lawless and reckless, fickle and changeable; that the weather man is a sort of conjurer, and by some mysterious gift he is able to prophesy things that most people know nothing about. Nothing could be further from the truth.

After you have carried out the simple experiments described, and have read this text, whether you have a scientific trend of mind or not, you will at least learn that the weather is a science, like electricity, chemistry, or medicine; that its laws are uniform, constant, and unchanging, and there is really nothing mysterious about it. The weather man is a scientist and by means of instruments, which indicate certain things, he comes to definite conclusions. He is not a prophet; he does not prophesy; he forecasts.

If you are interested in having a Weather Bureau station of your own, you will find it one of the most interesting things you ever acquired in your life. You will soon gain a knowledge of a subject that most people are quite ignorant of, and if you desire to stand for leadership among your boy friends, it may be achieved by knowing about those things that to most boys, and in fact to adults, assume a mysterious and magical aspect.

A Weather Bureau station at your home will give you a source of pleasure, fun, and insight into a science that is intensely interesting, easy to understand, fascinating and worth while knowing. The importance of the subject cannot be overestimated. It has an influence on the whole world; it affects our health; it affects our comfort; it means success or failure in farming; it has an immense influence upon transportation. When ready to move perishable goods, the transporter must have indications of what the weather is going to be.

The weather observer is the guardian angel of the ships at sea; some men have doubts as to whether medicine itself has saved more human lives than the study of the weather and the practice of weather observing. It is not unusual for those who live along the coast to see ships hovering into cover long before a storm approaches, for the wonderful weather bureau system operated by the United States Government gives warnings and danger signals all over the country. Statistics show that losses have been reduced seventy-five to eighty per cent through this system. The marine warnings are so perfect, so prompt, and so efficient that for a great many years no long or hard storms have ever reached any part of the United States without advance warnings and danger signals being shown beforehand.

When a storm is brewing, the Government’s wonderful Weather Bureau organization watches every atmospheric change with the greatest care and concern, and takes observations every few hours, and telegraphs the indications to all places where a warning should be given. Thereby perishable goods that need protection can be looked after. When extra hazardous storms and weather changes of a severe character are indicated, hundreds of thousands of telegrams are sent out in a comparatively short time, to all parts of the country, so that interested parties may prepare for such conditions. One can readily see the great service rendered and the satisfaction it must be to the shipper and the farmer to know that his property, which might be destroyed by a bad storm or low temperature, is being constantly and carefully guarded against danger. Not only storms and great cold waves have been forecasted, but floods have been anticipated and warnings given.

This brings us to a study of the subject “Weather,” and the best way to learn about the weather is to first learn about the air.

THE AIR

If you were to ask ninety-nine people out of a hundred to take the stopper out of a bottle, to look into it, and to smell its contents, and then ask them if, in their opinion, it contained anything, the invariable answer would be: “It contains nothing.”

EXPERIMENT NO. 1

Take the stopper out of a bottle and endeavor to pour water into it rapidly and see what happens. (See Fig. [1].) One of the laws in Physics is that no two bodies can occupy the same space at the same time. After doing this experiment, you will come to the conclusion that the bottle does contain something, and that “something” is matter, and that matter is air. There is in the bottle probably as important a thing as you could possibly conceive of, because even this earth without its ocean of air would be a world of desolation; for air sustains life itself, and when agitated, develops great strength. It may be whirled about into a hurricane blast and assume such violent proportions that villages will be swept away, and great waves of water will be raised, upon which ships can be tossed about like so much chaff. We all know that air can become so cold that great suffering will be caused, and so hot that it will make life almost unbearable. We really live in an ocean of air.

Fig. 1

Fig. 2

THE OCEAN OF AIR

As the fishes live at the bottom of the ocean of water, mankind lives at the bottom of an “ocean of air.” (See Fig. [2].) No one is absolutely certain about the depth of this air, but it has been estimated as low as forty miles and as high as two hundred miles. Balloons have gone up to a height of nearly nineteen miles (100,320 feet). We do know that the higher we go, the thinner the air becomes. It is practically impossible for man to ascend into the air more than five or six miles, owing to the fact that the air above that height is so thin that there is not enough to breathe. Naturally, the air at the bottom is more compact because of the vast amount of air above. The air is a great weight lying upon us—14.7 pounds per square inch of surface.

HOW TO PROVE BY EXPERIMENT THAT AIR HAS WEIGHT

The air-globe is a piece of apparatus for demonstrating that air has weight. (See Fig. [3].) First, the air-globe is weighed and then the air is pumped into it; its stop-cock is closed and the globe is reweighed. It will be found to have gained in weight. This is conclusive that air is matter and that it has weight.

Fig. 3

Fig. 4

Of great importance to us in the study is the next fact, that air exerts pressure on everything about us and upon ourselves.

EXPERIMENT NO. 2

A tumbler is filled with water and a piece of paper placed over the top of it. The glass is then inverted, holding the hand over the paper so that none of the water will come out. On taking the hand away, although the glass of water is inverted, the contents do not leave the glass. (See Fig. [4].)

Fig. 5

CONCLUSION

It demonstrates that the air is exerting a pressure from below on the paper, which is more than enough to support the weight of the water. The tumbler may be placed in any position and yet the water will stay in. This air pressure is exerted alike from all directions, and this pressure, which is 14.7 pounds to the square inch, is weighed down by the air about it and may be likened very much to ordinary water in that it exerts pressure in all directions.

EXPERIMENT NO. 3

Take an ordinary rubber sucker, such as is used on the end of a dart, and attach it to a string. Force this down on a piece of glass. (See Fig. [5].) The glass can then by lifted by the pressure of the air that holds the rubber to it.

We are indebted to a German experimental philosopher named Otto Von Guericke for knowledge of atmospheric pressure. Guericke is distinguished by his original discoveries of the properties of the air. He was born at Magdeburg in Prussian Saxony, November 20, 1602. He became interested at an early age in the politics of his city, and in 1627 was elected alderman, and in 1646 Mayor of Magdeburg. While serving in the above capacities, he devoted his leisure to science, especially on the creation of a vacuum and the action of bodies in a vacuum. His first experiments were conducted with a pump on a barrel of water. After drawing off all the water, he still found that air permeated the wood of the barrel, so he substituted a globe of copper and pumped out air also. He thus became the inventor of the air pump and illustrated in a simple but effective way the force of atmospheric pressure.

Fig. 6

By placing two hollow hemispheres of copper (see Fig. [6]) together, and exhausting the air, he found that fifteen horses pulling one way and fifteen pulling the opposite were unable to pull the hemispheres apart.

He further demonstrated that in a vacuum all bodies fall equally fast, that animals cannot exist therein, or, in fact, living matter. He is also credited with being the inventor of the air balance and a type of weather cock, called the anemoscope. He was interested also in astronomy.

Fig. 7

EXPERIMENT NO. 4

This experiment should interest you very much, because it is going to lead up to the subject of weather instruments, and is absolutely essential that you understand the fundamental principles in order to intelligently interpret these instruments. This experiment will explain one of the principles of the barometer.

Take a glass tube thirty-two inches long and one-quarter or one-eighth inch in diameter, and fill it with mercury, care being used to get rid of all the air bubbles. The mercury should be poured in with an eye dropper, one end of the tube being sealed, until filled, and then the finger is placed over the open end. (See Fig. [7A]). The tube is inverted and immersed in a reservoir of mercury and clamped to an upright stand. Immediately the mercury falls to about thirty inches. (See Fig. [7B]). Ask yourself what held the mercury up in the tube. Again the answer is that the pressure of the air on the mercury in the reservoir causes it to rise and fall in the tube, as the pressure of the air changes. You will soon learn what causes these changes in the pressure of the air.

Fig. 8

EXPERIMENT NO. 5

Have you ever asked yourself why it is that the wind blows? Why doesn’t it stand still?

Put your hand over a lamp chimney under which the lamp is lighted. You will soon discover that the heat is rising. Four things in connection with this are of great importance:

1. Air has weight. 2. When heated, it rises. 3. Air expands when heated. 4. Warm air will gather and hold more moisture than cold air.

EXPERIMENT NO. 6

Cut a piece of stiff cardboard in a spiral shape. Thread a piece of thread through a pinhole in the center point of the spiral and fasten this to a support so that it swings freely in the air. (See Fig. [8].) Under this put a little alcohol lamp, or put it over a gas jet or radiator.

WHAT HAPPENS

The cardboard will spin around rapidly. Ask yourself what causes this. It is the force of the hot air rising which caused the spiral cardboard to turn in such an attractive manner.

EXPERIMENT NO. 7

Fig. 9

When you are in a warm room, find out which air is the hottest, that in the upper or that in the lower part of the room. This answer you can get by placing the thermometer low down in the room and then putting it up near the ceiling. This is another conclusive proof that hot air rises.

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

Free electricity is always in the air. During clear weather it is generally positive; during cloudy weather it is negative. This electricity is carried in the air by the moisture. As dry air is a non-conductor of electricity, in fair weather the electrified particles of air are insulated and therefore acquire very little intensity. The clouds having been formed and being filled with moisture, form an excellent conductor of electricity, which acquires considerable intensity. It is a well-known physical law that two bodies having opposite electricities attract each other, and those having like charges repel each other. From this, two clouds having opposite charges rush together and produce the phenomena, called lightning, which is accompanied by an explosion called thunder. Often we see several flashes of lightning and then hear several thunder crashes, which is caused by only one section of a cloud discharging its electricity at a time.

As a cloud attracts the opposite charge of electricity from the surface of the earth beneath it by inductive influence, often we see a discharge of electricity from the cloud to the earth, the charge usually being received by such objects as hills, trees, church spires, high buildings, etc. Bodies containing large quantities of moisture are susceptible to strokes of lightning, as the moisture causes them to become good conductors of electricity. Also trees on the outer edge of a forest are more liable to be struck than those farther in.

There are several forms of lightning, such as zigzag, ball, sheet, and heat lightning.

Zigzag lightning, as the name implies, follows an irregular course, producing a long zigzag line of light, sometimes ten miles in length, and is caused by the air producing a field of resistance to the path of electricity, causing it to seek a path of less resistance.

Ball lightning appears like a large ball of fire, usually accompanied by a terrific explosion. This is the result of the bodies being charged with electricity of great intensity, and travels in a straight path, as it has enough strength to oppose any resistance placed in its path.

Heat lightning is usually seen on warm evenings, especially during the summer, and very often unaccompanied by thunder, due to the great distance of the lightning clouds from where we are located, thus diminishing the intensity of the thunder. The electricity of the clouds escape in flashes so feeble as to produce no audible sound.

Sheet lightning is a diffused glare of light sometimes illuminating only the edges of a cloud, and again spreading over its entire surface.

Ordinary flashes of lightning last but the minutest part of a second.

Thunder is the re-entrance of air into an empty space. The vacuum is created by the lightning in its passage through the air. The violence of thunder varies according to the intensity of the electrical flashes.

Because of the fact that light is transmitted almost instantaneously, while sound travels at a speed of eleven hundred feet per second, the sound will not reach the ear for some few seconds after the flash of lightning. Average space of time between a flash and a report is about twelve seconds. The longest interval is seventy-two seconds and the shortest one second. Prolonged peals of thunder are, in some cases, due to the effect of echoes. These peals are especially noticeable in mountainous countries. The echoes are also produced by the reflection of sound from the clouds.

Thunder storms are distributed over certain sections of the globe, occurring most frequently in the equatorial regions and diminishing as we approach the polar regions. Within the tropics, where there are trade winds, thunder storms are rare. Thunder storms are common in warm climates because evaporation supplies electricity in great abundance, and thus precipitation of the air is brought about.

Fig. 11

TORNADOES

Tornadoes are caused by the air becoming abnormally heated over certain areas. Likewise, caused by a difference in pressure. Tornadoes are local whirlwinds of great energy, generally formed within thunder storms. They are most easily distinguished by a funnel-shaped cloud that hangs from the bottom of the larger thunder cloud mass above it. The funnel is formed around a violent ascending mass of whirling winds; its diameter sometimes reaching several hundred feet, being larger above than below, the winds themselves covering a greater space.

Fig. 12

The whirling funnel advances generally to the east or northeast at a rate of twenty to forty miles an hour, accompanied by a deafening noise, destroying everything in its path. The path is usually less than a quarter of a mile in width.

The winds in the vortex (the apparent cavity or vacuum formed in the center of the whirling winds) of the tornado attain an incredible violence, and due to this fact houses are shattered, trees uprooted, and human lives lost, besides other devastation of property and animal life. It is, therefore, the vorticular whirl that causes the destruction produced by tornadoes.

Tornadoes are more frequent in the southern states than anywhere else in the country, and occur in the warmer months.

The velocity of the whirling winds in a tornado increase towards the center, and it is because of this that the point of danger is only a small distance from the funnel cloud. The direction of the whirling motion is from right to left. From the appearance of the funnel formed in a tornado, it looks as though the currents were descending from the cloud to the earth, when in reality the currents are ascending. The ascending current draws on the warm and moist air near the surface of the earth for its supply, and this inrush of air in a spiral form into the low pressure core made by the higher whirl constitutes the destructive blast of the tornado.

Tornadoes approach rapidly, and it is therefore almost impossible for those who happen to be in their path to escape their violence.

A tornado at sea is termed a water spout.

RAINFALL

You will recall a preceding statement that evaporated humidity turns into water when it becomes cool below a certain point. (See page [14], Effect of the Sun.) A given amount of air will hold a certain amount of moisture. For example, let us assume that a cubic foot of air (see Fig. [11]) is saturated, that is, it is holding all the water it will retain. Now if this cubic foot of air is cooled, it will contract, and as a result there will not be enough room to hold both the air and moisture, so the excess moisture will leak out. (See Fig. [12].) The result of this reduction in temperature causes precipitation, simply because the air cannot sustain the water that is in it. Therefor, at any time when moisture in the air has reached the point of saturation and a chilling takes place, due to the air becoming cold, rain follows. This may happen as a result of air rising into higher places or cooler levels, or through its contact with cooler surfaces.

WHY WE GET SUCH HEAVY RAINFALLS SOMETIMES AROUND MOUNTAINS

The air becomes thoroughly saturated. When air is comparatively warm, it will expand, and this air, which is heavily saturated is brought up by breezes onto the mountain range, which is cold, causing the air to lose its heat and contract and really force the water out of the air. The same principle applies to sea breezes bringing rain.

WINDS

Winds are caused as a result of differences in temperature between the various layers of the atmosphere. A certain amount of air becomes heated and rises, and as explained before, expands. As the air expands, it becomes lighter, and because it is light it goes upward toward higher regions. It also flows from hot to cold countries. A good illustration of this is the sea breezes. If you have lived around the seashore in the summer time, you will have observed that during the hot part of the day the winds generally blow from the sea toward the land. At night the direction of the wind is reversed, that is, it blows from the land to the sea. Why? Because the land during the day retains its heat, while the water diffuses it. What is the result? The air on the land expands, becomes light. The air over the water being cool, it does not expand, and the result is that it presses toward the land. At night the land loses its heat more rapidly than the water, so that it is not long before the land is cooler than the water, and when this happens, the air over the land, which has become cooler, presses seaward.

KINDS OF WINDS

Mountain Breezes: Caused by the heating and cooling of the hills and valleys.

Avalanche Winds: Winds that are in front of a landslide, caused by the movement of the snow forcing the air in front of it.

Fig. 13

Fig. 14

Fig. 15

Fig. 16

Fig. 17

Volcanic Winds: Due to volcanic eruption, which produces an outrush of air.

A Squall: Due to the sudden disturbance in temperature.

A Simoon: A desert wind.

VELOCITY OF WIND

The wind blows a great deal harder on water than on land, because on land it meets with various obstacles, whereas it has very little friction on the water.

THE FORCE OF THE WINDS

Wind blowing at 20 miles per hour has a force of 1¼ lbs.

Wind blowing at 35 miles per hour has a force of 6 lbs.

Wind blowing at 50 miles per hour has a force of 13 lbs.

Wind blowing at 75 miles per hour has a force of 28 lbs.

Wind blowing at 90 miles per hour has a force of 40 lbs.

DAY SIGNALS

Fig. 18

Fig. 19

Fig. 20

Fig. 21

Fig. 22

Fig. 23

NIGHT SIGNALS

Fig. 19A

Fig. 20A

Fig. 21A

Fig. 22A

Fig. 23A

NAME OF WINDS

Beaufort’s scale, used in preparation of all Weather Bureau wind forecasts and storm warnings.

The following method of transmitting weather signals by means of flags was used for a number of years, but the newspapers now convey the same news to the interested public:

1. A square white flag indicates fair weather. (See Fig. [13].)

2. A square blue flag indicates rain or snow. (See Fig. [14].)

3. A white and blue flag, half white and half blue, indicates local rain or snow. (See Fig. [15].)

4. Black triangular flag indicates a change in temperature. (See Fig. [16].)

5. White flag with a square black center indicates cold wave. (See Fig. [17].)

When No. 4 is placed above No. 1, 2, or 3, it indicates warmer weather; when below, colder; when not displayed the temperature is expected to remain stationary.

The following flag warnings are used along the Atlantic and Gulf coasts to notify inhabitants of this section of the country of impending danger.

Fig. [18]. The Small Craft Warning. A red pennant indicates that moderately strong winds that will interfere with the safe operation of small craft are expected. No night display of small craft warnings is made.

Fig. [19]. The Northeast Storm Warning. A red pennant above a square red flag with black center displayed by day, or two red lanterns, one above the other, displayed by night (Fig. [19A]), indicates the approach of a storm of marked violence, with winds beginning from the northeast.

Fig. [20]. The Southeast Storm Warning. A red pennant below a square red flag with black center displayed by day, or one red lantern displayed by night (Fig. [20A]), indicates the approach of a storm of marked violence with winds beginning from the southeast.

Fig. [21]. The Southwest Storm Warning. A white pennant below a square red flag with black center displayed by day, or a white lantern below a red lantern displayed by night (Fig. [21A]), indicates the approach of a storm of marked violence, with winds beginning from the southwest.

Fig. 24

Fig. [22]. The Northwest Storm Warning. A white pennant above a square red flag with black center displayed by day, or a white lantern above a red lantern displayed by night (Fig. [22A]), indicates the approach of a storm of marked violence, with winds beginning from the northwest.

Fig. [23]. Hurricane, or Whole Gale Warning. Two square flags, red with black centers, one above the other, displayed by day, or two red lanterns, with a white lantern between, displayed by night (Fig. [23]), indicate the approach of a tropical hurricane, or of one of the extremely severe and dangerous storms which occasionally move across the Great Lakes and Atlantic Coast.

Fig. 25

We have installed at our manufacturing plant a high-class weather station, with equipment of the latest United States Weather Bureau standard pattern, and are able to send out weather signals by wireless from our own wireless station twice daily, at 4 P. M. and 7 P. M., to all boys owning a wireless outfit. The indications are taken from our own instruments. A description of these instruments and the method of recording the indications will give you an insight into how the various government weather stations arrive at their forecasts.

Fig. 26

On the roof of the factory is a weather vane (Fig. [34]) twenty feet high, which is connected electrically with a register in our weather office. The register is of the quadruple type (Fig. [45]), and is capable of recording wind direction, wind velocity, rainfall, and sunshine on the same form or sheet. Thus, we know the wind direction and can deduce certain things relating to the weather. Mounted on the wind vane support is an anemometer (Fig. [36]), an instrument for measuring the velocity of the wind. A rain gauge (Fig. [49]) on the roof catches the precipitation, and for every one hundredth of an inch of rainfall, a small tipping bucket empties its contents into a receiver and a record is made on the form in the quadruple register.

The same pen that records the rainfall also records the number of hours of sunshine during a day, for it is not a common thing to have rain and sunshine at the same time.

A hygrothermograph (Fig. [43]) records on a form the temperature and amount of humidity in the atmosphere.

A barograph (Fig. [44]) records the pressure of the atmosphere. For determining the pressure, we also have a mercurial and aneroid barometer, which will be described later on.

You can readily see that it is a simple matter to obtain the weather indications.

Fig. 27

CLOUDS

The numberless kinds of clouds makes it quite difficult to describe and arrange them or illustrate them in any manner that makes it easy to recognize them. Although some may be recognized from description and with a fair amount of observation, you will be able to classify them in their proper place. For instance, the thunder clouds most anyone recognizes without any experience whatever.

Fig. 28

There are really four simple cloud formations and three compound formations:

1. The Cirrus Cloud. (Fig. [24].)

The Cirrus cloud is always seen high in the sky and at a great elevation. Its formation is fibrous and it is particularly characterized for its many varieties of shapes. It also has a marked delicacy of substance and it is pure white.

2. The Cumulus Cloud. (Fig. [25].)

The Cumulus cloud is of moderately low elevation. It is a typical cloud of a summer day. It may be recognized by little heaps or bushes rising from a horizontal base. In summer-time we are all familiar with the cumulus clouds rising with the currents of air in huge masses. They form one of the most accurate indications of fair weather when you see them gradually dissolving. Sometimes these clouds become very large, and, while the texture is generally of a woolly white, naturally, when they assume such large sizes, they gradually change in color to a darkish tint.

3. The Stratus Cloud. (Fig. [26].)

This is the opposite of the Cirrus cloud, because it hangs the lowest of all, in gray masses or sheets, with a poorly-defined outline.

4. The Nimbus Cloud. (Fig. [27].)

Any cloud can be classed as a nimbus cloud from which rain or snow is falling.

Of the Compound Clouds we have:

Fig. 29

1. The Cirro-Cumulus Cloud (Fig. [28]), which has all the characteristics of both the Cirrus and the Cumulus. The most characteristic form of this cloud, and the one most commonly known, is when these clouds form small round masses, which appear to be cirrus bands broken up and curled up. This is what people call the “mackerel” sky.

2. The Cirro-Stratus Cloud (Fig. [29]), which is known when the clouds arrange themselves in thin horizontal layers at a great elevation.

Fig. 30

3. The Cumulo-Stratus (Fig. [30]) is the cumulus and the stratus blended together. Their most remarkable form is in connection with approaching thunder storms, and are often called thunder heads. They rapidly change their outline and present a beautiful spectacle in the sky at times.

The Cirrus, Cirro-Cumulus and Cirro-Stratus are known as the upper clouds and the others are known as the lower.

ATMOSPHERIC DISTURBANCES

Disturbances of the atmosphere are classified as follows: Cyclonic, or low area storms, or anti-cyclonic, or high area storms.

Fig. 31

The word “cyclone” to most people immediately means a terrific storm, whereas in weather observing the cyclonic storm is not really a cyclone or hurricane at all. It is a storm with an atmospheric pressure below average. Particularly important is the wind that blows about this area, which is always spirally inward, due to the rotation of the earth on its axis. This is probably why it is given the name of cyclonic storm, for it bears one of the important characteristics of a real cyclone. As the wind is deflected and moves into the storm center, it turns to the right and in the form of a whirlwind, spirally, moves around the storm center. (See Fig 31.) It is this whirling process that has given it the name, cyclonic storm.

As the air rises over the point of low storm area, or, in other words, the area of low pressure, and travels into the atmosphere, it is not permitted to rise to any great height, because it is always acted upon by the force of gravity and is being pulled back to earth again. We assume that because of this fact, this rising air which has been pulled back to the earth again piles up in certain places, causing the barometer to rise. Such a center as this is known as a high barometric center or the anti-cyclonic area. Here the circulation of the air is exactly opposite to that of the cyclonic area.

Fig. 32

We are all more or less acquainted with these anti-cyclonic storms, because in winter these great masses of air rise up from the warm areas, pile up, and form high pressure areas over the mountains of Canada, and soon this high pressure works down upon us as blizzards and cold waves.

We have described quite minutely the movement of the wind about these points of high pressure and low pressure and have shown you the map and have illustrated the high pressure and low pressure areas, but there is still another feature that is of great importance to us, and that is the movement of the storms and the fact that storms have a progressive movement from west to east.

These storms move more rapidly in the United States than elsewhere, and are more rapid in their movement in winter than in summer. Their speed is almost one half again as great. The average velocity of the low area storm in the United States is about twenty-five miles an hour in June, July, August, and September, and from October on they continue to increase.

LOW PRESSURE

We can summarize low pressure storms generally in the following manner: They have a wind circulation inward and upward and are elliptical in form. Their velocity varies from six hundred to nine hundred miles per day, moving in the same general direction. They are characterized in their eastern quadrants by cloudy weather, southerly and easterly winds, precipitation, temperature oppressive in summer and abnormally high in winter, falling barometer, increasing humidity and followed by clear weather, rising barometer, decreasing humidity and falling temperature in the western quadrants.

Buys Ballot’s law of winds is, that in the Northern Hemisphere if one stands with his back to the wind, the low barometric pressure will be invariably to the left hand; in the Southern Hemisphere the lowest pressure is always to the right. This law explains one of the characteristics of low pressure storms.

AREAS OF HIGH PRESSURE

In speaking of low pressure storms we called them storm centers, because nearly always they are of sufficient intensity to bear that name, but in high pressure areas we do not speak of them as storm centers.

The Buys Ballot’s law applies to anti-cyclonic as well as cyclonic storms, that is, when one’s back is to the wind, the lowest barometric pressure is at the left and the highest at the right. This is probably understood by saying that in the cyclonic storms, the winds blow inward, contrary to the hands of a watch, and in the anti-cyclonic they blow outward, that is, in the same direction to the direction of the hands of the watch.

In the United States, the cyclonic storms are not as frequent as low pressure storms, and it is safe to say that probably not more than one-third of the entire anti-cyclonic areas can be classed as storm areas.

WHY AIR RISES

Another very interesting experiment is to secure a long-stemmed glass bulb (see Fig. [32]). Arrange this apparatus as illustrated, with the stem of the bulb immersed in the water. The glass bulb condenses the air. When you first put it into the water nothing happens, but as soon as you apply heat the air bubbles come out of the end of the tube. This means that the air in the tube has expanded and part of it has come out through the stem of the tube and the remainder is lighter. It is well to remember, when air is heated it expands and becomes lighter. This fact is extremely important to remember, because it has a great deal to do with the important instrument, the barometer, which is used to measure the pressure of the atmosphere and is an important element in the question of humidity, as you will learn later. By this time you no doubt have learned that:

1. Air has weight.

2. Heated air expands, becomes lighter, and exerts less pressure.

3. Cold air comes from the side to take the place of hot air that rises.

When the rays of the sun heat an area of the earth, the air over such a place expands and becomes lighter, naturally rising, and the result of this is that the winds are produced by cool air moving in to take the place of the heated air. This cool air moves in from all directions. When such a thing happens at any point on the earth’s surface, it is known as a storm center, an area of low pressure.

WHAT IS A CYCLONIC STORM?

Because of the rotation of the earth on its axis, a force arises which tends to deflect to the right all motions in the northern hemisphere, and to the left all motions in the southern hemisphere. The winds flowing toward the storm center are turned to the right or left and move in a spiral around the storm center. This system of whirling winds around a central region of low pressure produce what is termed a cyclonic storm. Storms have a tendency to move in an easterly or northeasterly direction, and at a rate of from five hundred to seven hundred miles a day. Cyclonic storms, although we look upon them as being very severe, are very often mild and not of an intensive character.

WHICH WAY DOES THE WIND BLOW AFTER A STORM?

From the descriptions and experiments preceding, which illustrate the development of storms, reference was made only to the winds blowing in toward the storm center. Naturally the question comes to your mind: What happens to them after the cold air has taken the place of the warm air? They change to other directions when the storm has passed away. It is because of this fact that we look for a change in weather conditions when the wind changes—a very important sign that you will be interested in later on.

It is well to mention here a thing that is going to be very important to us when we study the barometer, that is, the pressure of the atmosphere. Should the pressure of the air, which is normally at sea level 14.7 pounds to the square inch, change, that is, become lighter, it would not exert so much pressure on the column of mercury in the tube of the barometer and the mercury would drop in the tube. (See Fig. [7].) On the other hand, if the weight of the air was increased, that is, if it became heavier, it would force the mercury to rise in the tube. This should be quite clear to you, because it is the lightness and heaviness of the air that is going to interest us more particularly than any other part of the subject when we get into the study of the atmospheric changes, what causes them, and the indications that lead up to our conclusions. In order that this principle is absolutely clear to you, you should perform Experiment 4, or if you have not facilities for doing it, it is well to see it performed in any physics laboratory.

Immediately you ask yourself: If air has such a tremendous pressure as 14.7 pounds to the square inch, why is it that a weight of air amounting to thirty-five thousand pounds bearing down on the average individual does not cave the body in? Simply because air penetrates the body so easily that it exerts as much pressure on the inside as on the outside, and thereby equalizes itself. For instance, if you go down into a subway or a caisson (a water-tight box or chamber within which submarine construction is carried on under great air pressure to keep out the water), where the pressure is sometimes greater than it is outside, have you noticed the effect this pressure exerts on the ear drums? As it becomes greater, you may equalize it by swallowing, which allows the air to get back of the ear drums through the Eustachian tubes, which lead from the mouth to the inner ear.

MOISTURE

Water vapor is always present in the air.

EXPERIMENT NO. 10

Expose a piece of dry potash to the air. You will soon discover that the potash will dissolve. It has taken up water from the air.

EXPERIMENT NO. 11

Put a piece of ice in a pitcher of water and allow it to stand in a warm room. You will soon notice that little beads of perspiration collect on the outside of the pitcher. This moisture is air being condensed.

Water vapor is part of the atmosphere. Some of it is always present in the air. The amount of vapor that the air can hold depends upon the temperature. When the temperature is warm, the air will hold more water. For instance, at 100° F. a cubic foot of air will hold 19.79 grains of vapor; at 80° F., 10.95 grains; at 50° F., 4.09 grains, and 32° F., 2.17 grains. At 32° F. is the freezing point on the Fahrenheit scale.

Air containing as much water vapor as it can hold is saturated. If the air is suddenly cooled down, that is, if the temperature falls when the air is saturated, air molecules are contracted, and it must give up the water, which produces rain. The ocean and the Great Lakes are the source from which the air gets its water. It rises into the air in the form of vapor, that is, vapor rising from the surface of the water, and the wind distributes it over the land. Condensation turns it into clouds, and when it is over-saturated, or rather, when the temperature drops and the air is unable to retain any more water, then it forms into drops of water and falls as rain. When the clouds get into the air, below the freezing point of the water, the drops of water are changed into ice crystals or snow flakes.

When the ice crystals are just at the point of melting into water, due to the rise in temperature, the snowflakes lose their form and the result is sleet.

HOW CAN WE USE THESE FACTS?

So far we have described, in a general way, certain facts about the elements of the air, such as temperature, pressure, humidity, precipitation, evaporation, clouds, winds, etc., and these facts of the elements enter into a very interesting phase of weather observation which we will designate as prophesying without instruments or forecasting by physical science. When we come to the more interesting and scientific part of weather observation, we will drop the word “prophecy,” because the instruments that are used to measure these elements are going to indicate certain things to us that will lead you to more definite conclusions. Hence, the following observations are what have given an opportunity to the weather prophet or to those people who have been credited with some mysterious power to prophesy what the weather is going to be. They are not definite or conclusive, and they cannot always be depended upon, but they certainly are significant and interesting, and a description of weather would not be complete without a list in chronological order of a series of phenomena or physical signs of this character that have lead certain men to gain quite a reputation for prophesying what the weather is going to be.

Fig. 33

APPEARANCES

Various appearances that come in the sky.

For instance, a good example is in the case of the thunder storm, which can be determined at least a few hours in advance, by the movement of the clouds and the forms they take. In every locality there is a direction that clouds take that forecasts bad weather, and there is a direction that clouds take that forecasts fair weather.

When you see a halo about the top of a mountain, you know that bad weather is expected. The same is true when a halo appears about the moon. This indicates rain, or if the lower clouds break up and the upper clouds, or a second light covering of clouds, are seen above the lower ones, it speaks for continued bad weather. In some localities if rainy weather is continuing for some time, and a certain change in wind sets in, it will indicate that good weather is coming.

These observations will be readily understood as being adapted for certain localities and are not general. It is always necessary that the observer adapt himself to these localities and study them, so that he can make prophecies accordingly. It should be borne in mind that these prophecies are only possible from one day to another.

WHAT THE CLOUDS INDICATE

When high clouds are seen crossing the sun or the moon in a different direction from the lower clouds, this indicates change of wind toward the direction of the higher clouds. When you see hard-edged clouds, look for wind. When you see delicate soft clouds, look for fine weather and probably moderate breeze or high breeze. When you see gloomy dark clouds in a blue sky, look for slight winds. When you see a bright blue sky through fine clouds that are soft and delicate, this indicates fine weather. When you see soft-looking clouds, you can expect less wind, but probably rain. But when the clouds become hard and ragged, tufted and rolling in appearance, stronger winds are coming. When you see small clouds that are inky looking, look for rain. When you see light clouds traveling across heavy hard masses of clouds, this indicates both wind and rain, but if the light scud clouds are alone, you may expect wind only. Misty clouds forming or hanging over the peaks of hills indicate both wind and rain. If during a rainy spell they ascend or disperse the weather is pretty certain to clear up. If there has been fine weather and you begin to see light streaks in the sky which are distant clouds, and they continue to increase and grow into cloudiness, this indicates rain.

SUNSET AS AN INDICATION

When the sun is setting and the sky in the west presents a color of whitish yellow or radiates out at a great height, rain can be looked for during the next night or day. Gaudy colors where clouds are definitely outlined indicate probably wind and rain.

Before setting, if the sun looks diffused and the color is a brilliant white, this forecasts storms. When the sun sets in a slightly purple sky and the color at the zenith is a bright blue, this indicates fine weather. A red sunset generally indicates good weather, whereas a ruddy or misty sunset indicates bad weather.

WHAT THE SKY INDICATES

When you see a dark, dismal sky, look for rain. A sky with a greenish hue, described as a sickly-looking sky, is an indication of both rain and wind. A sailor’s sky, which is red in the morning, means either wind or rain, and it makes no difference if the sky is cloudy or clear, if at sunset it is rosy, it indicates fine weather. A gray sky in the morning indicates fine weather. When daylight is first seen above a bank of clouds, look for a good stiff wind. Wind is indicated if we have a bright yellow sky in the morning, and rain is indicated if the sky takes on a pale yellow hue. If the sky turns bright yellow late in the afternoon, it generally indicates that rain is near at hand. Unusual colorations, particularly of deep intense color, indicate wind or rain.

The following appearances indicate a change in the weather: When the atmosphere is clear and crystalline and the stars appear extremely bright; when the background of the horizon seems to be pinned up against the foreground; when the clouds form into delicate white film-like mist way up overhead. (Fig. [33].)

WHAT FOG AND DEW INDICATE

Locality has considerable to do with what the fog indicates. As a rule, where you have fog, there is not much wind, and as a result it does not indicate stormy weather, unless the fog becomes heavy with overhanging sky, then it is apt to turn into rain, but a heavy fog with a light sky indicates fine weather. A fog in the morning generally indicates a fair day. A rising fog is a good indication for fair weather.

Courtesy Julien Friez & Sons, Baltimore, Md.
Fig. 34

Fig. 35

Dew is a pretty good sign of fine weather. When you can see and hear with remarkable clearness, and everything is calm and still, it is a pretty infallible sign that cold weather is due.

Frost may be looked for on clear, calm, cloudless nights, when the ground is apt to be cooler than the air.

INDICATIONS FROM CIRRUS CLOUDS

When these clouds suddenly appear in the sky on a clear summer day, they indicate wet weather. Especially if the weather ends turn upward, which means that the clouds are coming down. When moisture in the form of little drops cling to vegetation, it is a pretty good indication that there is apt to be more rain.

When the sky assumes the appearance of a gray mass and the sun is observed shining through, it is a pretty good indication that it will rain before night.

When overhead clouds are thick and grayish and the lower surface of them is lumpy, this is an indication of rain.

Whirlwinds of dust are also indications of rain.

THE MOON

The rings that we see formed about the moon are caused by the delicate white clouds through which the moon is shining.