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Ralph S. (Ralph Stockman) Tarr.

A laboratory manual for physical and commercial geography online

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higher or lower than the mercury column ? Why ?



Why is mercury the best adapted liquid for use in barometers ?



257



For what purpose is the

barometer used? 4



If there is a mercurial barometer in the school, examine it carefully and make a drawing of it,
naming the important parts. Watch the barometer for the next few days to see if the column
of mercury remains always at exactly the same height. Keep a record of your observations.



What do they show about the weight, or pressure, of the air ?



<



258



Materials.



Purpose.



The ther-
mometer.



LIX. — THE THERMOMETER, AND THE DAILY RANGE OF TEMPERATURE

For Each Student. — Ruler. Sharp pencil.

For General Class Use. — One or more thermometers.

To understand the thermometer; to interpret the daily range of temperature; and to
study the effect of inclination of the sun's rays.

Examine the thermometer. What is in the space above the mercury? '_

If air were there, would the mercury rise and fall so easily?

Why does not the mercury rise 30 inches, as in the barometer?



Does the

mercury in the thermometer rise or fall when warmed? Why?



State and explain the movement of the mercury when cooled.



Could other liquids besides

mercury be used for thermometers?

Fill out the following sentence: Liquids expand when warmed and

when cooled. Find out if the same is true of gases and solids.



Fahrenheit
and Centi-
grade
scales.



If your thermometer is graduated according to the Fahrenheit scale, what is its boiling point ?

Its freezing point ? How many degrees are there between the

boiling and freezing points ? By the Centigrade scale, freezing point is called 0°

and boiling point 100°. How many degrees of Centigrade are equal to 1° of Fahrenheit ? 1

Explain why it is true that to change Centigrade to Fahrenheit scale you multiply by 1.8 and add 32.



259



Change 10° Centigrade into Fahrenheit degrees.



Change 25° Centigrade into Fahrenheit.



Making a
curve to
show daily
range of
tempera-
ture.



Below is printed a record of the temperature for every two hours on a winter's day (Feb.
19), in a city in northern United States. In the diagram (Fig. 26) each of the horizontal lines
represent 1°, and each of the vertical lines 2 hours. Make a cross to indicate the degree of
temperature for each two hours (as shown in Fig. 26). Then connect the centers of these
crosses with a line.



A.M.



P.M.



Midnight
21°

2
25°



Temperature record for one day.



20°

4

25.5 C



19°

6
24°



6
18.9°

8
23.2°



18.8°

10

22°



10

20.8°

Midnight
20°



Noon
23°



A.M.



P M.



Study of
the daily



Midnight Noon Midnight

12 2 4 6 8 10 12 2 4 6 8 10 12


















































































































\


f


























/




y


























/


\

















































































Fig. 26.



26°
25°
24°
23°
22°
21°
20°
19°
18°
17°



If possible make a similar curve (on the accompanying sheet of cross-section paper) representing local
conditions. Data can be secured from the nearest Weather Bureau office, or from a self-registering thermom-
eter. Failing such records, the pupils themselves may supply data, one pupil being sent to observe the tem-
perature every two hours, during school hours, and volunteers bringing data from home for the evening and
early morning.

At about what hour of the day was the temperature lowest?

Highest? Why does the



warmest period come after midday ?



260



The coldest after midnight?



Making a On the cross-section paper make a curve similar to that previously made, to show thi

daily curve range of temperature for a summer day. Following are data for such a curve, representinj
for summer. ^ e temperatures for July 10 in a northern city.



A.M.



Midnight
60°



2

56°



4

55.4°



6

57°



65°



10

74°



Noon
80°



P.M.



2

85°



4

83°



6
79°



8
73 c



10

66°



Midnight
61°



Compari-
son of the



Why is it warmer at midday in summer (as shown in the diagram just drawn) than a
two daily midday in winter (as shown in the diagram for the winter day) ?



curves.



Why warmer during the night ?



In which of the diagrams is there greatest range between lowest and highest temperatures



Why is this true ?



How do the two curves resemble each other ?



Fill out the following sentence : In both summer and winter the temperature is



Variatioo

in amount

of heat at midday than late in the afternoon; and the temperature is

from the j n sumrQ er than in winter. What relation do these facts have to the altitude of the sun
sun.



261



To understand the reason why the altitude of the sun influences the temperature, draw two
diagrams, as follows :

Diagram 1. On the cross-section paper, mark heavily two of the vertical parallel lines an
inch apart down to a certain horizontal line. How many spaces do these vertical parallel lines

include at the horizontal line? Starting from the same horizontal

line, draw parallel lines (an inch apart), each at an angle of 45° with the horizontal liue. How

many spaces are included between these two parallel lines at the horizontal line ?

If these parallel lines in both cases represent rays of the sun, and the horizontal

line the surface of the earth, in which case would a given area receive most rays ?

How does this help to explain the fact that the sun warms the earth more at midday than in
the afternoon ?



In summer more than in winter ?



Diagram 2. In the diagram (Fig. 27) draw two lines, one vertical, the other at an angle
of 45°, both passing through the atmosphere to the same point on the surface of the earth



ATMOSPHERE




Fig. 27.



(marked A). Let each line represent a ray of sunlight. Measure with the ruler to see in
which case the ray passes through a greater thickness of air. Which ray, then, would be most

interfered with in its passage through the air?

How does this help to explain (a) the fact that the sun is warmer at noon than in the after-



noon (•



262



(b) that it is warmer in summer than in winter ?

(c) that you can often look directly at the

sun just before sunset?

Now state, clearly and concisely, why the sun's rays are warmer in

summer than in winter, and at noon than in the afternoon.



263



4



LX.— WEATHER OBSERVATIONS

Materials. For General Class Use. — One or more thermometers. A barometer. If possible, other meteoro-

logical instruments.

Purpose. To study local weather conditions.

Value of Work of this nature will teach the use of the instruments ; it will direct the student's at-

such a tention to the weather phenomena that are always surrounding him ; it will supply original

s u y ' data for later use, especially in the study of weather maps. For a part or all of the time that

the class is studying the atmosphere a weather record may profitably be kept, using such in-
struments as the school possesses.
How to For at least one week, at the same hour if possible, let each student make observations of

keep the ^ e we ather conditions and fill in the blank spaces in the table. After that, let a different
record

student, each day, make the observations and report them to the class for entry in their tables.



265



i



Date


Day of
Week


Hour
of Day


Tem-
pera-
ture


Baro-
metric
Pressure


Wind Direction


Wind Velocity


Kinds of Clouds


Rain or

Snow


Amount of
Precipita-
tion




Mon.














1






Tues.




















Wed.




















Thur.




















Fri.




















Mon.




















Tues.




















Wed.




















Thur.




















Fri.




















Mon.




















Tues.




















Wed.




















Thur.




















Fri.




















Mon.




















Tues.




















Wed.




















Thur.




















Fri.



















267



Date


Day of
Week


Hour
of Day


Tem-
pera-
ture


Baro-
metric
Pressure


Wind Direction


Wind Velocity


Kinds of Clouds


Rain or

Snow


Amount of
Precipita-
tion




Mon.




















Tues.




















Wed.




















Thur.




















Fri.




















Mon.




















Tues.




















Wed.




















Thur.




















Fri.




















Mon.




















Tues.




















Wed.




















Thur.




















Fri.




















Mon.




















Tues.




















Wed.




















Thur




















Fri.



















268



Date


Day ok
Week


Hour
of Day


Tem-
pera-
ture


Baro-
metric
Pressure


Wind Direction


Wind Velocity


Kinds of Clouds


Rain or

Snow


Amount of
Precipita-
tion




Mon.




















Tues.




















Wed.




















Thur.




















Fri.




















Mon.




















Tues.




















Wed.
Thur.


































'•




Fri.




















Mon.










-


-








Tues.




















Wed.




















Thur.





















Fri.




















Mon.




















Tues.




















Wed.




















Thur.




















Fri.



















269



Date


Day of
Week


IIOUE

of Day


Tem-
pera-
ture


Baro-
metric
Pressure


Wind Direction


Wind Velocity


Kinds of Clouds


Rain oe

Snow


Amount of
Precipita-
tion




Mon.




















Tues.




















Wed.






*














Thur.




















Fri.




















Mon.




















Tues.




















Wed.
Thur.






































Fri.




















Mon.




















Tues.




















Wed.




















Thur.




















Fri.




















Mon.




















Tues.




















Wed.




















Thur




















Fri.



















270



LXL — THE SEASONAL TEMPERATURE RANGE
Materials. For Each Student. — Colored pencils

Purpose. To study the monthly range of temperature in different regions; to see how it varies from

place to place, and to interpret some of the variations. Also to study the daily range in some of
these same places.

Making of Which is the hottest month in your locality? The coldest

a seasonal

tempera- month? If you had twelve temperature records, one for every two

ture curve. ] 10urs j n ^ ne ( j a y ) how would you obtain the average or mean temperature for that day ?

Knowing the mean temperature for each day in the month, how would you find the mean tem-
perature for the month? 1

There follows a list giving the mean temperature (in Fahrenheit

degrees) for each month of the year at a certain place in northern United States. From this
data construct a curve on the cross-section paper to show the seasonal change in temperature.
Let each vertical line represent a month, and each horizontal line 10°.

Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec.
31° 32° 35° 45° 60° 70° 75° 74° 68° 56° 45° 34°

The teacher may obtain (from the nearest Weather Bureau Station) the monthly mean temperatures
for a place near the school. From this data construct a seasonal curve for your locality over the diagram just
made, using a different colored pencil.

How does the seasonal temperature curve resemble the daily temperature curve?



When is the warmest period? The coldest period?

V

Why do these periods not coincide exactly with the longest and the shortest days?



Clearly state the reasons why summer is the warmest, and winter the coldest period.

271



Seasonal There follows a table giving the monthly mean temperatures (approximate) for a number

tempera- f places in different parts of the world. On the cross-section paper make a diagram to show
th UfVeS ^ e seasoua l temperature curve for each of these places (all on one diagram). Let each hori-
parts of the zou ^ a ^ ^ ne stand for 5° and every second vertical line for a month. Make room for tempera-
world, tures as high as 95° and as low as 45°. For each curve use a differently colored pencil, or
different symbols (such as dots or dashes).



Place


Jan.


Fjsb.


March


April


Mat


June


July


Aug.


Sept.


Oct.


Nov.


Dec.


New York City


37°


31°


35°


52°


62°


72°


75°


75°


70°


56°


45°


33°


Singapore


80°


81°


82°


82°


83°


83°


83°


82°


82°


81.5°


81°


80°


Arctic, Lat. 82°,
Fort Conger


-37°


-43°


-23°


-11°


17°


32°


37°


35°


15°


-10°


-26°


-30°


Key West, Fla.


69°


68°


72°


75°


79°


81°


84°


83°


83°


80°


74°


69°


Yuma, Ariz.


55°


62°


64°


68°


73°


83°


92°


90°


83°


74°


61°


57°


St. Vincent, Minn.


-5°





15°


35°


50°


62°


66°


65°


52°


40°


22°





Central Australia


94°


92°


89°


85°


75°


70°


65°


60°


65°


70°


78°


87°


Central Atlantic
at equator


79°


80°


80.5°


81°


80.5°


80°


79°


80°


80.5°


81°


80.5°


79°



In what one respect are most of these curves alike ?



Why



Why does the curve for Central



Australia differ so widely from the others ?



Which curve is the flattest ?



Why



272



Which region has the coldest summers ?
The coldest winters ?



What does the difference between the curve at St. Vincent and Key West or Singapore
suggest as to the influence of distance from the sea ? 1



Where do you find the highest tempera-



tures ?



State what you observe from the study of the diagrams (a) as to the influence of latitude on
the seasonal temperature curve ;



(&) as to the influence of distance from the sea.







Daily
changes in
tempera-
ture in
different
eg ions.



The temperature

falls on the average of 1° for every 300 feet of altitude. On the diagram (just drawn), dot in
a curve to show a theoretical seasonal curve at an elevation of 3000 feet above New York

City.

On the cross-section paper plot the data in the following table to show the daily changes
in temperature at some of the places for which the seasonal curves have just been drawn.
Use colored pencils ; use dots to represent the winter days and continuous lines for summer
days. Let every other vertical line represent 3 hours of the day, and each horizontal line 5°
of temperature. Make room for temperatures as high as 95° and as low as — 30°. ■



273



Place


Mid-
night


3 A.M.


6 A.M.


9 A.M.


Noon


3 P.M.


6 P.M.


9 P.M.


Mid-
night


New York City. Summer


62°


58°


59°


65°


72°


79°


78°


72°


60°


New York City. Winter


10°








12°


24°


30°


25°


18°


10°


Arctic. Winter


-10°


— 12°


-14°


-15°


-17°


-19°


-22°


-24°


-26°


Key West, Fla. Summer


80°


77°


80°


84°


89°


90°


87°


82°


79°


Key West, Fla. Winter


69°


65°


69°


73°


78°


79°


75°


71°


69°


St. Vincent, Minn. Summer


60°


55°


59°


69°


78°


85°


78°


69°


60°


St. Vincent, Minn. Winter


— 22°


—27°


-29°


-19°


-12°


-11°


-13°


-20°


-23°


Central Atlantic at Equator.
Summer


79.8°


79.5°


79.3°


80°


80.5°


81°


80.5°


80°


79.8°


Central Atlantic at Equator.
Winter


79.9°


79.6°


79.3°


80°


80.5°


81°


80.6°


80.1°


79.9°



In what respect are all but one of these daily curves alike ?



. Which one does not show

the midday rise? Why does it not?



Which curve shows the greatest change between day and night ?
Explain.



W r hich the least ?



Explain.



Where is it coldest? Where warmest?



274



What evidence do you find of (a) influence

of ocean?



(b) of influence of distance from sea ?



(c) of influence of latitude ?



275



i



Materials.



Purpose.



Note.



Water
vapor in
the air.



Experi-
ments to
illustrate
variation in
the rate of
evapora-
tion.



LXII. — MOISTURE IN THE AIR

For Each Student. — Two small pieces of cheese cloth, two or three inches square.
For General Class Use. — A fruit jar. (A small vial of alcohol or ether.) A small piece of
muslin. Two thermometers.

To understand the four different conditions which affect the rate of evaporation ; the meaning
of relative and absolute humidity ; and the use of the table for determining the relative humidity,
on the basis of observations of temperature with the dry and wet bidb thermometers.

Note : — To save time the teacher will probably direct that two or more of these experiments be carried
on at the same time.

After it has stopped raining the sidewalks soon become dry. What has become of the

water ?

What term is applied to the change from water to water vapor ?

Is the water vapor a liquid or a gas ? Is it visible or invis-
ible? _ All over the earth water is evaporating, and the water vapor

is rising into the air ; but the rate at which evaporation takes place varies greatly under dif-
ferent conditions. The following experiments are intended to illustrate this fact.

Wet both the pieces of cheese cloth. Put one on the radiator, or in the sun, or in some
other warm place. Put the other on your desk, and not in the sun. Which piece of cloth

becomes dry first ? From this experiment

what do you conclude as to the rate of evaporation at different temperatures?



Would evaporation therefore be more rapid in the frigid zone or in the torrid zone ?

In summer or in winter?

Again wet each piece of cloth, wringing out the surplus water. Pin one of the pieces on
each end of your desk. With a book or piece of paper, fan one of the pieces of cloth.

Which dries the more quickly? What do

you conclude from the results of this experiment as to the rate of evaporation where the wind

is blowing, as compared to the rate where it is calm ?

Would evaporation, therefore, be more rapid

277



on a windy day or on a day when there is no wind ?

Would it be more rapid in the trade wind belt, or in the belt of calms?

Once more wetting the two pieces of cloth, spread one out on the desk and make a small

roll of the other. Which dries the more quickly?

What do you conclude from this experiment as to the relation between the amount of evapo-
ration and the amount of surface exposed?



1 Would there, therefore, be more water vapor

rising from a large body of water (such as the ocean) or from a small body (such as a pond) ?

Which would probably have more vapor,

winds from the land or winds from the ocean?

While these experiments were being carried on, the teacher has placed a small amount of
water in* the bottom of a fruit jar and, putting on the cover, has set it in a warm place.
Evaporation has caused much water vapor to rise into the air in the jar, and this air is there-
fore very damp. Now suspend a piece of wet cloth (by a string) in the jar, and put back the
cover. At the same time spread out another piece of wet cloth on the desk. When the cloth

on the desk is dry, take out the piece of cloth from the jar. Is it dry ?

What do you conclude as to the rate of evaporation in dry air as compared to that in damp



air r



Would evaporation, therefore, be more rapid on a damp day or on a dry day
In a desert or in a humid region?



Meaning of A quart dish half full of water has |, or 50%, as much water as it can hold. This per-

absolute centage represents the relative amount of water in the glass compared with what the dish
and relative

Umi 1 y * might hold. What would be the percentage if the dish were full? .



What if § full ?



You could state the amount of water in the dish in two ways : that is, you could say, when
the dish was half full, that the absolute amount was a pint ; or, you could say that the amount
relative to what the dish might hold was 50%.

It is important sometimes to speak of the absolute and relative amounts of vapor in the
air. If you had a given quantity of perfectly dry air, and let one pint of water evaporate

into it, what would be the absolute amount of vapor in the air ? '_'__

This would be called its absolute humidity. To determine the relative
278



UM1VERSU*

OF

humidity you would need first to know how much vapor could possibly pass into that quan-
tity of air. Suppose the amount of water that this quantity of air could hold was 4 pints ;

what would be the relative humidity when its absolute humidity was 1 pint?

What would be its relative humidity if there were 2 pints

in it? What if there were 4 pints in it?

Could it then take any more water vapor?

What, then, is meant by saturated air?

Was the air saturated when the water

was being evaporated from the pieces of cloth on the desk ? If it had been,

could there have been any evaporation ?

Determin- Evaporation is a cooling process, because in evaporation heat must be used. This can be proved by

ing relative placing a drop of ether or alcohol on the back of the hand. As it evaporates it takes some heat from the

humidity. hand and therefore feels cool. Take two thermometers and hang them side by side. Tie (with thread) a

small piece of muslin around the bulb of one, with one end of the muslin hanging down like a wick. Read

the two thermometers. Now saturate the muslin with alcohol and watch the mercury of this thermometer.

Why does this thermometer register a lower temperature than the other ?

See if water has the same effect

as alcohol, saturating the muslin and letting the wick end rest in a glass of water ; but, since water does not
evaporate as fast as alcohol, fan the muslin to make the water evaporate more rapidly.

It is possible to determine the relative humidity of the air by using two such thermometers — a dry bulb
and a wet bulb thermometer. The principle is that the evaporation lowers the temperature. The tempera-
ture is lowered more if evaporation is rapid than if slow. Which is dryest, air with low relative humidity, or

air with high relative humidity? In which will evapo-
ration be more rapid, air with high or low relative humidity ?

From this do you conclude that the difference in temperature as shown by the dry and wet bulb thermome-
ters would be greater when the relative humidity is high, or when low ?



Following is a table which can be used to determine the relative humidity. First find the difference in
temperature of the dry and wet bulb thermometers. Suppose it to be 3°. Find the number 3 (the third figure
from the left) at the top of the table. In the left-hand column of the table find the number that corresponds
with the temperature recorded by the dry bulb thermometer, which we will assume to be 78°. Now follow
this to the right until you come to the number in the column under the 3. That number is 87, and this is the
relative humidity. That is, the relative humidity is 87 %.



279



Below is a table showing observations made, and the relative humidity indicated by them, as deduced
from the table.



Date


Dry Bulb


Wet Bulb


Difference in Reading


Relative Humidity


Jan. 1


80°


78°





92%


Jan. 2


82°


78°





84%


Jan. 3 74°


67°





70%



Verify these data by use of the table for determining relative humidity. Make observations with the
dry and wet bulb thermometers, both in the schoolroom and out of doors, and, by reference to the table, find
the relative humidity. Set down the results, below, in a table similar to that just given.



280



Table for determining Relative Humidity



#



Tempera-




















































ture of I)r
Bulb Tiiek


5 i


2


3


4


5


6


7


8


9


10


n


12


13


14


15


16


17


18


19


20


21


22


23


24


25


MOMETER




















































20° . . .


85


70


56


41


27


13








































22° . . .


86


72


58


45


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Online LibraryRalph S. (Ralph Stockman) TarrA laboratory manual for physical and commercial geography → online text (page 12 of 16)