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Ralph S. (Ralph Stockman) Tarr.

A laboratory manual for physical and commercial geography online

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32


19


6






































24° . . .


87


74


61


48


36


24


11






































26° . . .


88


75


63


51


40


28


17


6




































28° . . .


88


77


65


54


43


33


22


11


1


































30° . . .


89


78


67


57


47


36


26


17


7


































32° . . .


90


79


69


59


50


40


31


21


12


3
































34° . . .


91


81


72


62


53


44


35


26


17


9
































36° . . .


91


82


73


66


56


47


38


30


22


14


6






























38° . . .


92


83


75


67


58


50


42


34


26


18


11


3




























40° . . .


92


84


76


68


60


53


45


38


30


22


16


8


1


























42° . . .


92


84


77


69


62


55


48


40


34


27


20


13


6


























44° . . .


92


85


78


70


63


57


50


43


37


30


24


17


11


5
























46° . . .


93


85


79


72


65


58


52


46


39


33


27


21


15


9


3






















48° . . .


93


86


79


73


66


60


53


48


42


36


30


24


19


13


7


2




















50° . . .


93


87


80


74


67


61


55


50


44


38


33


27


22


16


11


6


1


















52° . . .


94


87


81


75


69


63


57


51


46


40


35


30


24


20


15


10


5


















54° . . .


94


88


82


76


70


64


59


53


48


43


38


32


28


23


18


13


8


4
















56° . . .


91


88


82


77


71


65


60


55


50


44


40


35


30


25


21


16


12


8


3














58° . . .


94


89


83


78


72


67


61


56


51


46


42


37


33


28


24


19


15


11


7


2












60° . . .


94


89


84


78


73


68


63


58


53


48


44


39


34


30


26


22


18


14


10


6


2










62° . . .


95


89


84


79


74


69


64


59


54


50


45


41


37


32


28


24


20


16


13


9


5


1








64° . . .


95


90


85


79


74


70


65


60


56


51


47


43


38


34


30


27


23


19


15


12


8


5


1






66° . . .


95


90


85


80


75


71


66


61


57


53


49


45


40


36


32


29


25


22


18


14


11


8


4


1




68° . . .


95


90


85


81


76


71


67


63


58


54


50


46


42


38


34


31


27


24


20


17


14


10


7


4


1


70° . . .


95


90


86


81


77


72


68


64


60


55


52


48


44


40


36


33


29


26


23


19


16


13


10


7


4


72° . . .


95


91


86


82


77


73


69


65


61


57


53


49


45


42


38


35


31


28


24


22


18


15


12


9


6


74° . . .


95


91


86


82


78


74


70


66


62


58


54


50


47


43


40


36


33


30


26


23


20


18


15


12


9


76° . . .


95


91


87


82


78


74


70


66


63


59


55


52


48


45


41


38


35


31


28


25


22


20


17


14


11


78° . . .


96


91


87


83


79


75


71


67


63


60


56


53


49


46


43


39


36


33


30


27


24


21


19


16


13


80° . . .


96


92


87


83


79


75


72


68


64


61


57


54


51


47


44


41


38


35


32


29


26


23


20


18


15


82° . . .


96


92


88


84


80


76


72


69


65


62


58


55


52


48


45


42


39


36


33


31


28


25


22


20


17


84° . . .


96


92


88


84


80


77


73


69


66


63


59


56


53


49


46


44


41


38


35


32


29


27


24


22


19


86° . . .


96


92


88


84


81


77


73


70


67


63


60


57


54


51


48


45


42


39


36


34


31


29


26


23


21


88° . . .


96


92


88


85


81


77


74


71


67


64


61


58


55


52


49


46


43


40


38


35


32


30


27


25


22


90° . . .


96


92


88


85


81


78


75


71


68


65


62


59


56


53


50


47


44


41


39


36


34


32


29


26


24



281



LXIII. — CONDENSATION OF WATER VAPOR

Materials. For Each Student. — A drinking glass. Water. Either snow or small pieces of ice.

Purpose. To understand the causes leading to the condensation of water vapor, and the consequent

formation of dew, frost, fog, clouds, rain, and snow.

Meaning of In which can there be most vapor, warm air or cold air?

saturation if the relative humidity of the air is 90 % when the temperature is 70°, would the temperature
and dew

poin ' need to be raised or lowered to bring the relative humidity to 100% ?

If the temperature continued to change in the same direction until

after the point of saturation was reached, what would happen ? _>

; What reason can you give

for calling the point of saturation (relative humidity 100%) the dew point f



Formation Breathe against a cold object, like a window pane. What happens ?

of dew.

Explain why the vapor was condensed? ._



Fill the drinking

glass two thirds full of water and ice (or snow) and stir the mixture, being careful not to wet
the outside of the glass. Explain why water begins to appear on the outside of the glass.



In the evening, when the ground cools by radiation, dew often forms. Explain the cause
of the formation of dew.



283



Would dew form most quickly when the relative humidity is high,

or low? When would no dew form?

What forms if the dew point is below the freezing point?



Determina- Again place water and snow (or ice) in the drinking glass and stir the mixture carefully with the ther-

tion of dew mometer. Note when vapor first begins to condense on the outside of the glass and then read the thermometer.
point. The temperature of that reading is the dew point for the air in the room. Determine the dew point by this



method.



Formation When you breathe into the air of a cold winter day, you can "see your breath." What is

of fog.



it that you see ?

Explain what has happened.



What must happen when warm, damp

winds blow over a cold surface?

On this basis, explain why it is that the cold Labrador

current is such a foggy part of the ocean. ■_



Why is it that winds often cause fog on mountains ?



Formation Air that rises above the earth's surface expands ; and when air expands it grows cooler.

of clouds. What then must result if damp air (or air with high relative humidity) rises to a considerable



height ?



If you could see a fog from either above or below, it would look like a cloud.

284



Explain why clouds form every day in the warm, humid belt of calms.



*



Explain why clouds



appear on warm, humid summer days.



Observa-
tion of
clouds.



In the Text-book (p. 248) you will find the names of the principal forms of clouds. What

form have the clouds to-day ? Keep a record

of the clouds for a week, giving their name, form, and a brief description, in the following

table. Erom which kind of cloud does rain or snow fall?



Formation
of rain.



Causes for
differences
in rainfall.



^A differences



Day op Week


Name op Cloud


Description of Clouds


Monday






Tuesday






Wednesday






Thursday






Friday







If condensation continues, will the clouds grow larger or smaller?

What does the fact that the fog particles float in air currents indicate

as to their size? When condensation con-
tinues, what must be the effect on the size of the particle?

What must thenhappen?

Under what conditions is snow formed

instead of rain?

In the belt of calms the air is rising. Would this be a rainy or a dry region ?



State your reasons for this conclusion.

285



In the

horse latitude belt the air is descending. Would this be a rainy or a dry region ?

State your reasons for this conclusion.



Where winds

blow from the ocean against rising land, would there be much or little rain ?
State your reasons for this conclusion.



Where winds blow from the land to the ocean, what condition of rainfall would there be ?
. State your reasons for this conclusion.



286



Materials.



Purpose.



Making an
isothermal
chart.



LXIV. — ISOTHERMAL CHARTS OF UNITED STATES

For Each Student. — Colored pencils.

To make and understand an isothermal chart; to study and interpret a summer and winter
isothermal chart of the United States; and to bring out the fact that temperature conditions are of
great and fundamental importance to vegetation.

On the accompanying map (Fig. 28) are marked the temperatures at a number of localities
in the United States at 8 a.m. on a winter's day. With this data draw in (as directed below)
isothermal lines so as to connect places having the same temperature. Your map then becomes
an isothermal chart. It will be sufficient to draw an isothermal line for every ten degrees ; e.g
for 0°, 10°, 20°, etc.

In making the map start with the isothermal line for 50°. Since the temperature at New
Orleans was 50°, it is evident that the line will have to pass through that city. Will it run



through Mobile? Macon?



Augusta ?



Will it then continue nearer Ealeigh (48°) or Wilmington, N.C. (56°) ?



Draw the line at what you think is the proper distance from

Ealeigh. At Norfolk the temperature was 54°. Will the 50° isotherm pass on the cold side

(north) or on the warm side (south) of Norfolk?

Continue the 50° isothermal line southeastward from New Orleans. On which side of Galves-
ton does it extend? On which side of Corpus

Christi, Tex. ? ._'_

Now draw the 60° and 70° isothermal lines across the Florida peninsula. Then draw in
the other isotherms down to 20° below zero. Shade (with blue pencil) the part of the map
with a temperature below 30° ; this is (approximately) the area of the country where the tem-
perature is below freezing point on that day.



Questions
on the
isothermal
chart.



Where is the coldest area ?



Why should it be coldest there ?



28T



Why does the 30°

isotherm extend farther south in the interior than on the east and west coasts ?



Why should it be farther north on the west than on the east coast ?



Study of
isothermal
charts of
United
States for
January
and July.



Fill out this sentence:



This isothermal chart shows that in winter the temperature from south

to north ; and it also shows that the temperature from seacoast to

interior.

The isothermal chart that you have just made represents the conditions in the country at
8 o'clock on a single day. If all the temperature records at each locality for a month were
averaged together, an isothermal chart could be made for that month. This is what has been
done in the two charts (Figs. 29 and 30), one for the month of January, the other for July.

With the colored pencils shade in the following areas : (a) those with temperatures below
0°; (b) those with temperatures between 0°and 30°; (c) those with temperatures between 30°
and 50° ; (d) those with temperatures between 50° and 70° ; (e) those above 70°.

What is the general direction that the isotherms follow ?

Where is there the greatest departure from this direction?



What is the explanation of this ?



On which coast, the Atlantic or the Pacific, is there the

greatest difference in temperature in going from north to south?

How much difference in temperature is there between the north and

south ends of each coast in summer ?



In winter ?



288




289



130___\?Al£o 120° W 110° 1062 IS^l 95° 90° 8a" 80" 75 70° 65° 00°




108° Longitude 100° West 95° from 90° Greemrieh 85° 70



Fig. 29. — Isothermal Chart of United States for January.



125° 120° 116° 110° 105° 100° 95° 90° 85° 80



70° 66°




105° Longitude 100° Wert 95° from 90° Greenwioh 85



Fig. 30. — Isothermal Chart of United States for July.

291



Why is there a marked difference of temperature range



on the two coasts ?



Which of these two monthly charts does Figure 28 most resemble?

Do Figures 28, 29, and 30 show the same general features?

In what part of the country is there the greatest difference in tem-
perature between summer and winter?



Why is this so ?



ence?

Explain this also.



Where is there the least differ-



Which is the most southern point in the country ?
Is it the warmest place in the country in summer ?



Account for this.



What is the warmest place in the country in winter ?
Which is the most northern point in the country ? ._
Is it also the coldest part of the country in winter ?



Explain.



293



LXV. — THE RELATION OF WINDS TO ATMOSPHERIC PRESSURE

Purpose. To show that winds are caused by the flowing of air from regions of high pressure to regions

of lower pressure.

Movement The air near a hot stove, a radiator, or lamp, is warmed. Hold a light, downy feather

of light and near one of these and then release it. What is the movement of the current of air near this
heavy air.

heated object? Why is this so?



Could



the air rise against gravity unless something were pushing it up ? When the

warm air near a stove is rising, what is the movement of the cooler, heavier air in other parts



of the room ?



What effect has this movement on the warm, lighter air?












- m-


1




W




rl


■<p- —






• A




J



3



Fig. 31. — Diagram for showing Circulation of Air in Room heated by a Stove.

295



In the diagram

(Fig. 31) draw arrows to show the circulation of the air in a room warmed by a stove. Fill
in the following sentence, putting the words " lighter " or " heavier " in their proper places.

Warm air is than cool air ; the cool air

settles and forces up the warm air. This causes the cool

air to flow toward places of warm air.

Is it true on the earth, as well as in a room, that heavy air will flow toward regions of

light air and force the light air to rise ? What is the instrument that is used

to measure the weight or pressure of the air? Recalling your study

of the barometer, which, heavy or light air, makes the mercury rise higher in the instrument?

At about what height does the mercury stand

in the barometer tube ? Does a reading of the

barometer of 29.8 inches mean heavier or lighter air than a reading of 30.2 inches?

Which of these two would be called high pressure?

Which low pressure ?

Figure 32 is a map of the United States showing the pressure of trie air for a certain day
in winter. The lines are called isobars (meaning equal weight), and each line passes through
places having the same air pressure, or weight. The figures on each line show the pressure in
inches of mercury in the barometer on this day. Find the place with the lowest pressure and

write in the words "low pressure." Is this a region of light air or of heavy air?

On the map mark in the words " high pressure " where

they belong.

From the center of which of these areas will the air flow outward? ,__

What would you call this flowing of the air?

Toward the center of which of the areas will the wind blow ?

With arrows mark in the winds as you think they would go with

such a condition of pressure as shown on this map.

Water running down a slope is often said to flow down grade. The winds shown on your
map are not flowing down a slope, but the air is flowing from a region of high barometric pres-
sure to one of low barometric pressure. What reason can you give for calling the difference

in pressure between two places a barometric gradient?



296




297



Is the barometric gradient steepest

where the isobars are close together or far apart?

Where is it gentlest? On what kind

of a grade does water flow most swiftly? On

what kind of a barometric gradient will air flow most swiftly ?

. ; On your map mark places where the air must be moving swiftly. Would

these regions have strong or light winds?

What would be the case where the barometric gradient is gentle?

On Figure 33 the arrows represent winds observed on a certain day in a part of the United
States. On this map sketch in a number of isobars to show the location of the area of low
pressure and the area of high pressure.




Fig. 33. — Map to show Wind Directions observed on a Certain Day in Part of the United States.

299



#



Materials.
Purpose.



Making a

weather

map.



Observa-
tion of the
weather
map.



LXVL— THE WEATHER MAP

Colored pencils.

To understand the meaning of the symbols on a weather map ; to appreciate the method of con-
structing such a map; and to study the relations between air ])ressure and weather, under cyclonic
and anticy clonic conditions.

On the map of the United States (Fig. 34) are data from observations made by the United
States Weather Bureau at 8 a.m. on a winter's day. At this hour the observers at each of the
places marked on the map made observations of their thermometers, barometers, etc., and tele-
graphed the results to Washington. There a weather map was made to show the weather con-
ditions over the entire country at that hour. The data that were telegraphed to Washington
are printed on the map. You are to construct the weather map.

First draw the isothermal lines (using a red pencil) as directed on page 289. Next draw in
the isobars, using a blue pencil. To do this, follow the same method as in drawing the iso-
thermal lines, showing differences for each tenth of an inch by a separate isobar. Draw
each of the isobars through places having the same barometric pressure ; or on the proper side
of those places where the pressure was not exactly a tenth of an inch. For instance, the isobar
would be drawn through a place having 29.9 inches ; but it must go to one side of a place
having a reading of 29.93, or of a place having a reading of 29.89. Having completed the isobars,
mark the word High in the place where the lines inclose an area of high pressure ; and mark
the word Low in the place where the lines inclose an area of low pressure.

With black pencil or ink, draw arrows to show the wind direction at each place, remem-
bering that the letters N.W., N., etc., refer to the compass directions from which the winds
blow. Place the point of the arrow on the end toward which the wind is blowing. Finally,
color (with green pencil) the area where rain (r) or snow (s) are falling, making the snow
area a heavier green than the rain. In this shading you can color in the area between places
that have the same letters.

Is it colder within the area of the high or of the low pressure?

In which of the two areas is there clear weather ?

In which is there rain or snow ?



In what part of the low-pressure area is rain falling ?



.. In what part



snow?







Using the scale of miles (printed on the map), measure the distance from east to



west in which there is precipitation. Measure the diameter of the

301



area of precipitation along a north-south line. Do the winds blow

toward or away from the area of high pressure ?

Do they blow toward or away from the area of low pressure?



Interpreta- If winds blow from all sides toward a center, what must become of the air as it flows

tion of the

weather toward the center ? If the relative humidity

map.



of the air is high, what must happen as it rises ?



Apply this in explanation of the large

area in which there is precipitation around the Low. •_



Where does the air obtain its vapor?



What bearing has this on the fact that there is a larger area of precipitation on the east and
south sides of the Low than on the north and west?



Why is it warmer on the south and

east sides of the low-pressure area than on the north and west sides ?



What bearing has this

on the distribution of rain and snow in the area of precipitation ?



302




303



If the winds blow outward from an area of high pressure, where does the air come from ?

Is air above the earth warmer or colder than

that at the surface? (Text-book, p. 240.) How does this help to

explain the temperature within the high-pressure area?



Air settling from above the surface

grows warmer; does it then cause clear or cloudy weather ?

Apply this in explanation of the conditions in the high-pressure area.



Making a Figure 35 gives data for the weather map at 8 a.m. on the next day to the one just studied,

weather these data having been obtained by the Weather Bureau observers, as before. On this map

map for the (j raw { n (&$ on the previous map) the isotherms, isobars, and wind directions ; color in the areas

next day. Q £ ra - n an( ^ snow . an( j ma rk the areas of high and low pressure.

Compari- In which direction has the low-pressure area moved in the t wenty -four hours ?

son of the

two maps. j n which direction has the high-pressure area moved?

Mark their courses on Figure 35 by means of

a colored line (brown). Do the winds still blow in the same way (as in Fig. 34) around the

high and low pressure areas? Is there still the same relation between pre-
cipitation and barometric pressure ? Between

areas of pressure and temperature?







By examining and comparing the two maps, state what changes have occurred at Chicago
in (a) barometric pressure



; (6) wind directions
305



; (c) precipitation



; (d) temperature.



Make the same comparison for New York.



For your own home.



306



LXVII. — STUDY OF THE WEATHER MAP

Materials. For Each Student. — A copy of a weather map (any date will do).

For General Class Use. — Thermometer. Barometer. The daily weather map.

(The daily weather map will be sent on application from the nearest Weather Bureau
. station, and it should be posted in a prominent place.)

Purpose. To study the local weather changes and note their relation to high and low pressure areas.

The infor- Each student is given a copy of a weather map.

mation on

a weather what do the dotted lines represent ?

map.

Where is the coldest weather ?

The warmest?

What do the continuous lines

represent? What do the figures at their

ends (29.9, 30.2, etc.) indicate ? Where is the

pressure highest? ;

Where lowest?

What word is printed in the anticyclonic area or areas?

In the cyclonic? What do the arrows represent?

In what directions are the winds blowing in

the low-pressure areas?



In the regions of high pressure ?



What symbols are used to

represent clear, partly clear, and cloudy sky?



307



In which of the areas, the cyclonic or the

anticyclonic, is there the greatest extent of clear weather?



Of cloudy weather ?



In what manner are rain and snow recorded ?

When, with reference to the high and low

pressure areas, is there most rain in a given region ?



When (if at all) is there snow ?



What symbol is used for thunder storms?

Do you find any on your map ? If so, where do they occur with reference

to the pressure conditions?



What data are printed in the columns in the right-hand half of the bottom of the map ?

From these columns find out and record the temperature, wind velocity, and precipitation at
Washington, D.C.

At the Weather Bureau

station nearest your own home.

308



Head the printed matter on the left-hand part of the bottom half of the weather map.
^| What kinds of information are given there ? .__.



Study of Observe and make a record of the local weather conditions of this day, as follows :

the local

weather. The temperature. The barometric pressure.

Direction of wind. Velocity of wind (light, strong, etc.)

Condition of sky (clear, cloudy, or partly cloudy). .__

Precipitation (rain, snow, or clear). Is the barometer low or high?

What relation, if any, do you see between the

pressure and the cloudiness or precipitation?







Is the temperature higher or lower than

yesterday? Is there any noticeable relation between this change in

temperature and the pressure and wind direction ?



Make a prediction, as best you can,

for to-morrow, — do you expect it to be warmer or colder?

Rainier or clearer?

Examine the weather map for to-day. Where is the nearest area of high pressure ?


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