Ralph S. (Ralph Stockman) Tarr.

A laboratory manual for physical and commercial geography online

. (page 14 of 16)
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Of low pressure?

In what direction, in each case, from your home ?

In which direction will they probably move

by to-morrow ?

Using the scale of miles printed on the map, and by comparison with yesterday's map, find
out how far each has moved since yesterday.

How many miles an hour is that?

How far, then, may you expect them to move

by to-morrow?

What change in your local weather should these movements of high and low pressure areas
bring about by to-morrow ?

Now examine the predictions made by the Weather Bureau

and compare them with your own predictions.

To-morrow examine the weather map to see how
nearly the predictions were verified. Record the results.


(This work may be profitably repeated for several successive days, or until the pupil

thoroughly understands the significance of the weather map and is able, from a rapid study

^k of it, to see what it shows as to actual conditions, and the basis upon which predictions are

^^ made. Even after the formal laboratory work on weather maps is completed, the student

should examine the daily weather map, and make his own predictions and^ by examining the

instruments in the school, note how temperature, wind, and precipitation are related to


General From the study of the weather maps, and from the observation of local weather condi-

conclusions. tions, answer the following questions : In which direction do most of the high and low

pressure areas move ?

At about what rate?

When a Low passes over your home, what changes come (a) in pressure,

(6) in temperature,

(c) in wind direction, (d) in wind velocity,

(e) in cloudiness,

(/) in precipitation ? Answer the same questions

for the HiGH-pressure areas.

_ (a)

(6) (c)

(d) (e)


About how much of the United States do the low-pressure areas cover at any one time ?

Give their greatest length and width in miles.

About how far apart are the Lows and Highs ?

About how often does a Low pass over your home ?

Are they always equally well developed ?


When is there most rain, when the low-pressure area is well developed or only

moderately developed ? {

During what conditions of pressure does your coldest weather come ?

Your warmest ?

Explain this in each case.

Cyclonic storms develop in the belt of prevailing west winds. If these winds should blow

every day in your locality, would they be dry or rainy winds ? _'

Cold or warm in winter ? Cool or hot in summer ?

Of what importance, therefore (assuming that
you live in the west-wind belt), are the cyclonic storms to your locality : (a) because of their

influence on temperature ?

(6) because of their influence on rainfall ?



Study of
chart of
the world
for July.


For Each Student. — Colored pencils.

To study and interpret isothermal charts of the world for summer, winter, and the year.

Figure 36 is an isothermal chart of the world for the month of July. With your colored
pencils give different colors to the following parts : (a) all over 80° ; (b) from 70° to 80° ; (c)
50° to 70° ; (d) 30° to 50° ; (e) all below 30°.

In what general direction do most of the isotherms extend?
In which hemisphere (northern or southern) do they follow this direction

with greatest regularity ? Explain the

difference between the isotherms of the northern and southern hemispheres in this respect.

Does the belt of greatest heat coincide with the equator? Draw a line on the

map to show the approximate position of the belt of greatest heat. This will be the heat
equator for July. Mark it so on the map. Where does it lie with reference to the equator ?

Are the warmest areas in the northern or

southern hemisphere? Why

Are they over the water or over the land ? Why

Study of

isothermal Figure 37 is an isothermal chart of the world for the month of January. Color this map

the world as follows: (a) all over 80°; (b) from 70° to 80°; (c) from 50° to 70°; (d) from 30° to 50°;

for January, (e) from 0° to 30° ; (/) from - 30° to 0° ; (g) all below - 30°.


Give two reasons why it is so much colder in the northern than in the southern hemisphere
in January.

Where are the lowest temperatures ?

Why there ?

Where is it warmest ?

Why there ?

Draw in the heat equator on this map. Explain its position.

Fill out this sentence :

The heat equator moves in summer, and . in winter.

Comparison ^ n which hemisphere is there the greatest difference (called range) in temperature between

of January

and July January and July ? _ Account for this difference.

charts. J J




How much is the difference, or range, on the Arctic Circle, on the meridian 120° E. Long. ?

About how much on the Antarctic Circle on

the same longitude ?

On each of the charts, follow the 40° parallel of north latitude, and in the table set down
the temperatures for the places mentioned. In the lower columns insert the temperature



Central Asia
Long. 80° E.




Long. 40° W.



Central U.S.
Long. 100° W.




Long. 160° W.




Account for the high temperature range in Central Asia.

In central United States.

Contrast these temperature ranges with those in the central Atlantic and Pacific oceans.

How do the temperature ranges on the Atlantic and Pacific coasts of the United States
compare ?


How do those of the Atlantic and Pacific coasts of Eurasia compare ?

Which of the coasts of the United States most nearly resembles eastern Eurasia in tempera-
ture range ? , Western Eurasia ?

How is this to be explained ?

Study of Figure 38 is an annual isothermal chart of the world ; that is, it represents the average

isothermal temperature for the entire year. Color this map as follows : (a) all over 80° ; (6) 70° to 80° ;

woridfor 1 " 5 (c) 50 to 70° ; ((f) 30° to 50° ; (e) 0° to 30° ; (/) below 0°.

the year ^ n *" ne m ap draw in the heat equator. Why should it lie north of the equator ?

Trace the isotherm for 50° in the southern hemisphere. What is its direction?

__._ . Examining the ocean current map (Fig. 22), state why

this isotherm bends northward on the west coast of South America.

Trace the isotherm for

50° in the northern hemisphere. How does it compare in direction with the 50° isotherm in

the southern hemisphere?

Account for its northward bend in crossing the Atlantic.

Account for its southward bend



on the east coast of North America.

Account for its northward bend in central North

America. : •___

Explain the northward bend of isotherms on the west coasts of South America and

The northward bend of isotherms between Iceland and Scandinavia.

_• What countries of west-
ern Europe are crossed by the 50° isotherm? .

Where does this isotherm cross eastern United


How do the latitudes of these two places compare ?

What country of Europe is in the same

latitude as the part of eastern United States that the 50° isotherm crosses ?

What isotherm crosses that part of Europe?

How do you account for these differences

in temperature between eastern United States and western Europe ?


How do the isotherms of western Europe compare with those of western United States in the
same latitude ?■ ._•

Compara- By examining the isothermal charts for July, January, and the year, state, in general

tive study terms and a few sentences, what the summer, winter, and annual temperatures are in the
of isother-
mal charts.

Torrid Zone.

In the North Temperate Zone.

In the South Temperate Zone.

In the North Frigid Zone.

In the South Frigid Zone.


Do the boundaries of these zones seem to be regular, and to follow exactly the circles of

latitude? Where, for instance, do torrid conditions in summer extend into

the temperate zone?

Where do Arctic conditions extend in winter into the temperate zone ?

Which isotherm on the July chart passes nearest your home ? _
Name other places in the northern hemisphere on the same isotherm.

In the southern hemisphere.

Answer the same questions for the January chart.

For the chart of the year.



Study of
an isobaric
chart of
the world.


Colored pencils.

To study the relation between atmospheric pressure and the planetary winds; to note the dis-
tribution of these ivinds; and to consider their effects.

Figure 39 is an isobaric chart of the world for the year. That is, it shows the average
atmospheric pressure for all parts of the earth. With the colored pencils color in : (a) all
the area which has a pressure of over 30.00 inches ; (b) the areas with pressure between 29.90
and 30.00 inches ; (c) the areas between 29.80 and 29.90 inches ; (d) the areas of less than
29.80 inches.

How does the pressure in the equatorial belt compare with the regions immediately to

the north and south of it? t Which way, then,

should the winds blow in these regions?

Make a drawing to show the circulation of the

air between the Tropic of Cancer and the Tropic of Capricorn. In this drawing you should
show four movements of the air: (1) along the surface; (2) a rising; (3) a flowing away
at the higher level ; and (4) a settling of the air.


How does this drawing resemble that of the circulation of air in a room heated by a
stove (Fig. 31) ?

The trade winds blow steadily toward the equator from both the south and the north.
By means of arrows indicate these winds on the isobaric chart (Fig. 39). To what part of

the air current in your drawing (Fig. 31) are these winds equivalent?

The belt of calms is the area where the warm air is rising. Indi-
cate its position on both the map and the drawing. The anti-trades are the winds flowing
away from the equator, high above the earth's surface. Indicate these on your drawing.
The horse latitudes are where the air is settling. Mark the position of the two belts of horse
latitudes on both the map and the drawing. In what direction would you expect the winds

to blow on the poleward side of the belts of high pressure?

These are the two belts of prevailing westerlies.

On Figure 39 find several places where the pressure is over 30.10 inches. Which way

must the air be moving in these areas of high pressure ?

Find two areas in the .northern hemisphere where the pressure is as low as 29.70 inches.

How must the winds be blowing in these regions ?

The wind Figure 40 shows the prevailing winds of the earth in the month of January. You wi*l
belts. no te that the wind directions in the regular wind belts do not exactly agree with those you
have drawn in Figure 39. The winds have been deflected from true north and south directions
by the influence of the earth's rotation. On Figure 40 place the following names in their
proper places: northern prevailing westerlies ; southern prevailing westerlies ; belt of north-
ern horse latitudes; belt of southern horse latitudes; belt of northeast trades; belt of south-
east trades; belt of calms, or doldrums. In which two belts is the air settling?

• In which

belt is the air rising?

On page 314 you learned that the heat equator moves north in summer and south in win-
ter. Since the trade winds represent cooler air flowing toward this heated belt, what change

in their position must occur with the changes in season? j


40° East from 80° Greenwich 120°

Fig. 39,

West from 40° Greenwich 0° Longitude 40° East from 80 Greenwich 120 J

Fig. 40.


Deflection Currents of air and water on the earth are turned by the influence of the earth's rotation

of winds by toward the right in the northern hemisphere, and toward the left in the southern hemisphere

the earth's (Text-book, p. 258); that is, if you stand so that a current strikes your back, the current will

be deflected towards your right in the northern hemisphere. Apply this to explain why the

trade winds blow from the northeast and southeast, instead of from due north and south.

What compass direction does the influence of rotation cause winds to have in the northern

hemisphere when blowing from the south?

What direction in the southern hemisphere when blowing from the north ?

How does this apply in explaining the direction of the pre-
vailing westerlies?

Winds in What is the direction of the winds in Eurasia : (a) in the northern part ?

areas of low

and high

pressure. > (&) m the eastern part ?

(c) in the southern part? Why should winter

winds blow outward from the cold interior of a continent?

__1 On the map of the isobars (Fig. 39)

there are three areas of high pressure over the ocean in the southern horse latitude belt, and
two in the northern horse latitude belt. Locate these five areas on Figure 40 and state how

the winds blow in such areas.


Locate the two areas of low pressure (in the North Atlantic

and North Pacific) and state how the winds blow there.


Winds on Is the temperature of water more or less uniform than that of land?

water and

land- Differences in temperature give rise to differences in air pressure,

and these to winds. Where, then, should the winds have a more regular direction, on land or

on water? Examine the map to see if the

trade winds have a more constant direction on land or on water.

How about the belt of northern prevailing westerlies ?

The southern belt

of prevailing westerlies ?

Why do the latter winds blow more regularly than those of the

northern hemisphere ?

and lee-

On which coasts (east-facing or west-facing) do the trade winds blow from the sea?

On which from the land?

On which coasts do the prevailing westerlies blow from the

sea? What effect must this have on the

temperature of the land that they reach ?


temperature of these coasts in summer ?

On which coasts do the westerlies blow from the
.__ What effect must this have on the


In winter ?

Which of the coasts (east or west)

in the westerly belts must therefore have the more equable climate?



Materials. For Each Student. — Colored pencils. Ruler.

For General Class Use. — A rain gauge. (A tinsmith can make a fairly satisfactory rain
gauge. See Text-book, p. 424.)

Purpose. To study the distribution of rainfall in the United States, and to discover the reasons for the

differences in amount.

Observing For two weeks keep a record of the amount of rainfall, measuring it after each rain.

amount of Measure the depth of the water in the tube with a ruler, remembering that this depth is ten

rainfall. times the actual rainfall. Why is it advisable to so construct the rain guage that the rain

from an area of ten square inches is collected instead of from only one square inch?

What is meant when one says " an inch of rain has fallen " ?

Is an inch of rain a light or

heavy rainfall? What is meant by saying

"the annual rainfall is 100 inches"? .

1 What is the rainfall of your own region (Fig. 41)?

Has a region with 100 inches of rainfall a

dry or a rainy climate? !_._

Fill the cylinder of the rain gauge with snow to a depth of ten inches (but do not pack
it tightly), and allow the snow to melt. How much water gathers in the bottom of- the

cylinder? What do you conclude therefore as to the amount of

snow that represents an inch of rain?


Rainfall of On the map of the United States (Fig. 41) the lines indicate the amount of rainfall in

the United i nc hes. Color in (with green pencil) the areas with a rainfall of over 60 inches. In what

two parts of the country is there the heaviest rainfall ?

By examining the map showing the
winds of the earth (Fig. 40) account for these two areas of heavy precipitation.

Color in (with blue pencil) the areas with a rainfall of be-
tween 50 and 60 inches. A rainfall of 50 inches or more is heavier rainfall than is common.

What parts of our country have such a condition of rainfall ?

Color in (with brown pencil) those sections with a rainfall of less than 10 inches. Such
a rainfall is altogether too little for agriculture, and deserts commonly exist where there is
such light rainfall. What states and parts of states, therefore, have a desert condition of

rainfall ?

In which of the wind belts are these desert regions located ?

What explanation can you give

for these desert conditions ?






Color in (with yellow pencil) the sections with a rainfall of from 10 to 20 inches. In
general, a rainfall of less than 20 inches is too little for agriculture ; and the country included
in the belt with rainfall between 10 and 20 inches may be called the arid country. What

states, or parts of states, are included in this arid belt?

What explanation can you offer

for the fact that the arid lands are mainly in the interior of the country ?

In the arid belt

you will note on the map that there are small areas with a heavier rainfall. What is the

explanation of these?

Why is there such an abrupt change from heavy rainfall in western

Washington to light rainfall in eastern Washington ?

Fill out the following sentence: On

the windward side of mountains the rainfall is ; on the leeward side

the rainfall is

Why is evaporation greater in the southern than in the northern part of the arid belt ?


How does this help to explain the fact that in some parts of the north, as in eastern Washington
and eastern Dakota, there is extensive wheat raising, although the rainfall is less than 20

inches ?

Color in (with red pencil, in parallel ruled lines) the areas with a rainfall of from 20 to 30
inches. What states are partly included in this belt ?

Account for the fact that in Texas

the western portion of this area has too little rainfall for agriculture.

Color in (with blue

ruling) the areas with a rainfall between 30 and 40 inches ; and the areas (with green ruling)
between 40 and 50 inches. About what proportion of the United States has rainfall enough

for agriculture (20 inches or over)? ' In what

parts of the country is this condition general ?

for agriculture in the arid and desert sections ?

What means are adopted to supply moisture

State how the rainfall varies from the mouth of the Mississippi to northern Minnesota.


From Virginia to southern California.


From the coast of Washington to the coast of Maine.

Following along several lines from the coast to the interior, what do you discover as to the

general change in amount of rainfall? Fill

out the following sentence: In general, the amount of rainfall from

coast to interior. Account for this fact.





Materials For Each Student. — Colored pencils.

Purpose. To study and understand the cause for the distribution of rainfall over the earth.

Belts of Figure 42 is a blank map of the world with the rainfall of the continents indicated by a

heavy rain- series of lines. By reference to the Text-book (Fig. 444), secure data for filling in, with the
fall. green pencil, the areas which have heavy rainfall. In which zone do most of these areas lie ?

By examining the map of winds of the earth

(Fig. 40), determine in which of the wind belts the largest areas of heavy rainfall lie?

How do you account for this fact ?

There is heavy rainfall

also in some small sections of the temperate zones. On which coasts of the continents are these

located? In what wind belts ?

Account for these areas of heavy rainfall.

Desert Color in (with brown pencil) the areas which have desert conditions. In which zones are


these located? !__

Why should there be arid conditions in the horse latitude belts ?



coasts (east or west facing) have desert conditions in the trade wind belts ? _""

Why is there heavy rainfall on the opposite coasts in these
belts? •_..

Till in this sentence : Windward coasts in the trade wind belts have

rainfall; leeward coasts have rainfall. Cuba and Porto Rico lie in

the path of the northeast trade winds. What must be the condition of rainfall on the north-

east side? On the southwest side ?

Account for the arid regions in the west wind belts of North America and South America.

Which continents have the largest area of desert land ?

How do you account for this in each


Regions of Color in (with yellow pencil) the regions of light rainfall. What portions of the
light rain-
fall, northern continents are included?

Why should there be less rainfall in the cold north than

in the warm south?







Why are regions of light rainfall extensive in the continent interiors f

Would these regions of light rainfall be better suited for grazing or for agriculture ?
Why would this be less true in the cool north ?

As the belt of calms shifts northward in summer and southward in winter, how would
the rainfall vary with the season in that part of Africa that lies south of the Desert of

Sahara ? (Text-book, p. 283.)

How would the rainfall vary with the season in the southern
part of Africa?

At what season would agriculture be possible in each of these two regions ?

Why are these regions (the savannas) grass
lands and not forest-covered lands ?

Regions of Color in the remainder of the map (with blue pencil) to show the areas of moderate rain-
rainfall. f a |] What parts of North America are included ?


Of Eurasia?

Europe, eastern United

States, and southeastern Asia are the most densely settled parts of the earth. What is the

condition of rainfall in each of these sections ?

Why are desert countries sparsely


Why are the warm regions of heavy rainfall also unsuited to dense settlement ?

What reasons can you give for the fact that the most densely settled parts of the earth are
mainly located in those parts of the temperate zone in which there is moderate rainfall ?

Compar- How does North America compare with other continents in amount of desert ?

ison of



with other



In extent of country having heavy rainfall ?

In extent of country having moderate rainfall ?

In which of these respects is North America favored as compared with other continents ?

Write a brief statement as to the advantages that North America has as to rainfall and
temperature as compared with (a) Eurasia; (6) South America; (c) Africa; (d) Australia-




Purpose. To understand the relation between climate and the plant zones of the earth; and the chief

reasons for the distribution of animal life on the earth.

Fig. 43. — Zones of Plant Life in the United States as influenced by Temperature.

Plant zones Figure 43 shows the different zones of plant life in the United States as influenced by

of the the temperature. In what three sections of the country are tropical conditions found ?

United J r


Explain the presence of tropical conditions in each of these three places.



^ V






Where are cold north-temperate conditions found?

f Explain the presence of cold climate plants so far to the south in western United States.

In what portions of the country are warm temperate plants found?

Cool temperate plants ?

Distribu- Trace the northern limit of trees (Fig. 44). Why cannot trees grow north of this line ?
tion of

P lantsin . To the north of the tree line is the tundra

e wor ' region. What countries of Eurasia and North America are partly within the tundra belt ?

Why is there so little tundra in the southern hemisphere ?

Trace the northern and southern limits of palms. What kind of climate do they require ?

What countries of Europe and North America

are included in the belt of palms?

Why does the limit of palms extend so much farther

north in Europe than in America?

What two continents are almost wholly in the belt of palm growth ?

In which continents are the tropical forests most extensive ?

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Online LibraryRalph S. (Ralph Stockman) TarrA laboratory manual for physical and commercial geography → online text (page 14 of 16)