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 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
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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 percent 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 learned about the
air.
THE AIR
If you were 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
NOTE: Many figures have been
relocated from their position in the printed text to make them
more readable on a web page. This may or may not be
indicated in the text.
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
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WEATHER BUREAU 5
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 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, angry waves of
water will be raised, upon which ships can be tossed about like
so much chaff. We all know that
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air can become so cold that great suffering will be caused, and
so hot that it will make life almost unbearable. We really
lived in an ocean of air.
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.
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WEATHER BUREAU 7
[Originally contained Figs. 3 &
4.]
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Of great importance to us in this 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 intverted, the contents do not leave the glass. (See
Fig. 4.)
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 in 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 be
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 on atmospheric pressure.
Guericke is distinguished by his original discoveries of the
properties of the air. He was born at Madgeburg in
Prussian Saxony, November 20, 1602.
He became interested
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WEATHER BUREAU 9
at an early age in the politics of his city, and in 1627 was
elected alderman, and in 1646 Mayor of Madgeburg. 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 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.
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.
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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 anemoscope.
He was interested also in astronomy.
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 eyedropper, 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.
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WEATHER BUREAU 11
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 on 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
learned what causes these changes in the pressure of the
air.
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
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fasten this to a support so that its 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
cause the spiral cardboard to turn in such an attractive
manner.
EXPERIMENT NO. 7
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
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WEATHER BUREAU 13
from below to take the place of the hot air rising and going out
at the top. (See Fig. 9.)
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. The
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 a 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.
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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 the 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.
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WEATHER BUREAU 15
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 percent 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 the 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 and our homes, 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
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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 the 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 become hail-stones.
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 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 a 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.
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WEATHER BUREAU 17
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
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 electricity 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 call
thunder. Often we see several flashes of lightning and
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.
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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 defused 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 report is about twelve
seconds. The longest interval is seventy-two seconds and
the shortest one second. Prolonged peels 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.
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WEATHER BUREAU 19
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; it's diameter sometimes reaching several hundred feet,
being larger above than below, the winds themselves covering a
greater space.
The whirling funnel advances generally to the east or northeast
at a rate of twenty to forty miles an hour, accompanied by a
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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, 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 in near the
surface of the earth for its supply, and this inrush of air 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 in 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, 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[e], 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
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WEATHER BUREAU 21
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 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 defuses 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
Moutain 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.
The
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