The general circulation of the atmosphere may be best studied by

disregarding those smaller differences of temperature and pressure

that result from local causes and by viewing the earth and its

atmosphere as a whole, considering only those larger differences

which are in constant operation. In the great oceans of the world we

find the water constantly moving in a very systematic manner, and we

call this system of movements ocean currents. The Gulf Stream, the

Equatorial Current, the Japan Current and others may be likened to

great rivers of water moving systematically on their courses in the

ocean.

There are greater rivers of air in the atmosphere than any in the

oceans, and they move on their courses with equally systematic

precision and in obedience to fixed laws, which we may in a measure

understand.

The river, at the bottom of which we live, is broad and deep,

extending in width from Florida northward nearly to the north pole.

It flows from west to east circling the globe and its name is The

Prevailing Westerlies. The other river in this hemisphere extends

southward from latitude about 35° nearly to the equator. Its name is

The Northeast Trade Winds.

In the southern hemisphere are two similar rivers, one extending

southward from latitude about 30° nearly to the south pole with its

current, like its counterpart in the northern hemisphere, flowing

from west to east, circling the globe. It is also called The

Prevailing Westerlies. The other river in the southern hemisphere

extends from about latitude 30° northward nearly to the equator

and flows from the southeast toward the northwest, hence the name

Southeast Trade Winds. The dividing line, or bank, between the rivers

in each hemisphere belts the earth at about 35° north and 30° south

of the equator. Why does the air move and why does it move in such a

regular, systematic manner? To answer these questions we will rely

upon gravity, the heat from the sun and the effect of the rotation of

the earth on moving wind currents.

[Illustration: WINDS OF THE WORLD]

Everyone knows that water flows down hill because of the force of

gravity. Gravity is nature’s great peacemaker. It is always trying to

settle disturbances, even things up, smooth them over. If there were

no winds to bring rain to the land or to stir up the ocean, gravity

would soon run all the water into the lakes and the seas, and then

smooth them out like sheets of glass; and if there were nothing to

stir up the winds, gravity would soon settle all differences in the

atmosphere and the air would become perfectly quiet. So gravity is

kept busy trying to smooth out the water which the wind stirs up, at

the same time trying to quiet the winds which are stirred up by the

heat of the sun.

Tyndall says that heat is a mode of motion, that when heat is

imparted to a substance the molecules of which it is composed are

set into very rapid vibration. They are continually trying to get

away from each other and usually succeed in getting more space,

and thus increase the size or volume of the substance, or, in

other words, expand it. Iron, brass, copper, water and many other

substances expand under heat. Air is a gas and expands very rapidly

when heated. One cubic foot of cold air becomes two cubic feet when

heated. Now gravity pulls things down toward the center of the earth

in accordance with their weight-density, and a cubic foot of cold

air, being more dense and thus heavier than an equal volume of warm

air, is pulled down with greater force. We, therefore, say that warm

air is lighter than cold air, and if lighter it will rise. What it

actually does is to press equally in all directions and when a place

is found where there is less resistance than elsewhere it moves in

that direction. So when heat causes air to expand and become lighter

than the surrounding cool air, it moves, and air in motion is _wind_.

[Illustration: _Fig. 1. Diagram showing air currents set up by sun’s

heat._]

This diagram represents a section of the atmosphere over a broad,

level plain with the air at rest and pressing down equally on every

part of the surface. The dotted line H represents the top of the

quiet atmosphere. Such a condition occurs frequently at night after

the heat from the sun is withdrawn and gravity has settled the

atmosphere. When the rays of the sun fall upon the earth upon which

this quiet air rests they warm the earth first, then the layer of

air immediately in contact with the surface, so the atmosphere is

heated from the bottom upward. We will assume that the layer of air

between the earth and the dotted line, G, is thus heated to a higher

temperature than the air above it. It will, therefore, expand. It

cannot expand downward because of the earth. It cannot expand much

laterally because it is pressed upon by air that is also seeking more

space. It, therefore, expands upward as represented by the line A B

C. Now in expanding upward it lifts all the air above it and the line

H, representing the top of the atmosphere, will become bowed upward

also as indicated by the line A′ B′ C′. As a result, the air at the

top of the atmosphere over the warm center slides down the slopes

on either side toward the cool margins. As soon as the flow of air

away from the warm center begins, just that instant the pressure upon

the heated layer at the surface is relieved and the warm air rushes

upward (is pushed upward) and the whole circulation, as indicated by

the arrows, begins. It must be remembered that gravity is the really

active force in maintaining this movement, because it pulls down the

denser, heavier air at the cool margins with greater force than the

warm, expanded, light air at the warm center. The descent of the cool

air actually lifts the warm air.

The normal pressure, or weight, of the atmosphere at sea level is

about 14.7 pounds on each square inch of surface. It is customary,

however, to express the weight of the atmosphere in terms of inches

of mercury instead of in pounds and ounces. A column of air one

inch square from sea level to the top of the atmosphere will just

counterbalance a column of mercury 30.00 inches high in a barometer

tube of the same size. We, therefore, say that the normal pressure

of the atmosphere at sea level is about 30.00 inches. If, for any

reason, the atmosphere becomes heavier than normal, it will raise

the column of mercury above the 30 inch mark, and we say that the

pressure is “high.” If the atmosphere becomes lighter than normal,

we say that the pressure is “low.” So high pressure means a heavy

atmosphere and low pressure a light atmosphere.

At the beginning we assumed that the atmosphere over the broad, level

plain was quiet and that it pressed down equally on every part of

the surface. We will now assume that the pressure was normal, or

30.00 inches, and note the changes in pressure that result from the

interchange of air between the warm center and the cool margins. So

long as none of the air raised by the expanding layer at the surface,

moved away toward the cool margins, no change in pressure occurred;

but the instant the air began to glide down the slopes away from the

warm center, then the pressure at the surface decreased, because,

some air having moved away, there was less to press down than before.

The pressure at the warm center, therefore, became less than 30.00

inches, or in other words, low. Likewise, the air as it moved away

from the warm center, having lost much of its heat during its ascent,

was gradually pulled down by gravity because of its greater density,

thus increasing the pressure over the cool margins. We, therefore,

have low pressure at the warm center, 29.90 inches and high pressure,

30.10 inches, at the cool margins. From this illustration we obtain

the six principles of convectional circulation, viz.:

1. Low pressure at warm center.

2. High pressure at cool margins.

3. Ascending currents at warm center.

4. Descending currents at cool margins.

5. Surface winds from high pressure to low pressure.

6. Upper currents from low pressure to high pressure.

[Illustration: _Fig. 2. Isobars of the world._]

Now, we all know that the temperature of air is much higher at the

equator than at the poles and we may, therefore, let Fig. 1 represent

a section of the atmosphere along any meridian from the north to

the south pole. The equator would then become the warm center and

the poles the cool margins. We would then expect to find a belt

of low pressure around the world near the equator because of the

high temperature, and high pressure at the poles because of the low

temperature. We would, also, expect to find ascending currents at the

equator; upper currents flowing from the equator toward the poles;

descending currents at the poles, and surface winds blowing from the

poles toward the equator. Let us now test our theory by actual facts

and see how far they are in accord.

The chart, Fig. 2, represents the normal, or average, pressure at sea

level for the world, and if our theory is in accord with the facts,

we should find a belt of low pressure all around the world near the

equator, with areas of high pressure at the poles. Let us examine the

chart. Beginning at the equator, and bearing in mind that the normal

pressure is about 30.00 inches, we find irregular lines, representing

pressures of 29.90 inches--slightly below normal--around the world

on both sides of the equator. Between these lines we find pressure

as low as 29.80. It is, therefore, evident that there is a belt of

low pressure around the world near the equator, as anticipated. Let

us look for the high pressure at the poles. We have comparatively

few observations near the poles, but the line nearest the south pole

is marked 29.30 inches, a surprisingly low pressure, much lower even

than the low belt at the equator, and just the reverse of what we

expected to find. When we look at the north pole we find that the

pressure is not so low as at the south pole, but still below normal

and about as low as at the equator. Going north and south from the

equator we find that the pressure increases gradually up to about

latitude 35° in the northern hemisphere and to about latitude 30° in

the southern, after which it decreases toward the poles. So there

are two well marked belts of high pressure circling the globe; the

one about 35° north, and the other about 30°, south of the equator.

May it not be significant that these belts of high pressure coincide

so nearly with the margins, or banks, of the air rivers mentioned on

page 867?

Thus far our theory does not accord very well with the facts. True,

we found the low pressure at the equator as anticipated; but we also

found low pressure at the poles, where the reverse was expected;

and the high pressure that we anticipated at the poles, we found

not far north and south of the equator. We will, therefore, have to

discard our theory, or reconstruct it to accord with the facts. Let

us reconstruct Fig. 1, and mark the pressure on the line representing

the earth’s surface along any meridian to accord with the facts as

they appear on Fig. 2.

[Illustration: _Fig. 3. Diagram showing air currents along any

meridian._]

The above diagram now represents the true pressure along any

meridian, as determined by actual observations, and we cannot

escape the conviction that the requirements as to temperature and

pressure at the warm center are fulfilled by the high temperature

and low pressure found at the equator. Furthermore, the temperature

decreases north and south from the equator, and thus the belts

of high pressure near the tropics may be taken to represent the

conditions at the cool margins. The first and second principles of a

convectional circulation, viz., low pressure at the warm center and

a high pressure at the cool margins, are thus fulfilled. To satisfy

the remaining conditions, we should find ascending currents near the

equator, upper currents flowing from the equator toward the tropical

belts of high pressure, descending currents at the tropics, and

surface winds blowing from the tropics toward the equator. Let us now

examine the surface winds of the world as illustrated by the diagram

on page 867.

On either side of the equator and blowing toward it, we find the

famous trade winds--the most constant and steady winds of the world.

Their northern and southern margins coincide with the tropical belts

of high pressure. They blow from high pressure to low pressure and

we cannot doubt that they act in obedience to the fifth principle

of convectional circulation. From observation of the lofty, cirrus

clouds in the trade wind belts, we have abundant evidence of upper

currents, flowing away from the equator toward the tropical belts of

high pressure; thus the sixth principle is satisfied. The torrential

rains and violent thunderstorms, characteristic of the equatorial

regions, bear evidence to the rapid cooling of the ascending currents

near the equator; while the clear, cool weather and light winds of

the Horse Latitudes clearly indicate the presence of descending

currents at the tropics. Thus, the six principles of a convectional

circulation are satisfied, and the evidence is conclusive that the

trade winds form a part of a convectional circulation between the

tropical belts of high pressure and the equatorial belt of low

pressure.

You have doubtless observed that the trade winds do not blow directly

toward the equator but are turned to the west so that they blow from

the northeast in the northern hemisphere, and from the southeast in

the southern. This peculiarity is not in strict accord with our ideas

of a simple convectional circulation and suggests, at least, the

presence of some outside influence. If we turn to Ferre’s treatise

on the winds, we find a demonstration of the following principle:

a free moving body, such as air, in moving over the surface of a

rotating globe, such as the earth, describes a path on the surface

that turns to the right of the direction of motion in the northern

hemisphere and to the left in the southern. The curvature of the path

increases with the latitude, being zero at the equator and greatest

at the poles, and is independent of direction. With this in mind,

if we take position at the northern limit of the trade winds in the

northern hemisphere and face the equator, (see p. 867), we find that

the winds moving toward the equator turn to our right; likewise, if

we face the equator from the southern limit of the southeast trades,

we find them turning to our left. Observations of upper clouds in

the trade wind belts show that the upper currents also turn to the

right in the northern hemisphere, and to the left in the southern. It

is, therefore, clear that the systematic turning of the trade winds

from the meridian is due to the rotation of the earth. The value of

a force at various latitudes and for various velocities that would

cause a body to turn away from a straight line, is purely a problem

in mathematics, and for the benefit of those versed in the science

the formula is given. The amount of such a force is expressed by

2 MVW sin D, where M is the mass, V the velocity, W the angular

rotation of the earth, and D the latitude.

Not all of us may be able to solve the problem, but we may understand

something of the effect of the rotation of the earth on moving wind

currents. It is a well-known principle of physics that if a body

be given a motion in any direction, it will continue to move in a

straight line by reason of its inertia, without reference to north,

south, east or west. A personal experience of this principle may be

gained in a street car while it is rounding a curve.

[Illustration: _Diagram showing effect of earth’s rotation on the

atmosphere._]

In this diagram, we have a view of the northern hemisphere. The

direction of the rotation is indicated by the curved arrows outside

the circle representing the equator. Suppose that a wind starts from

the equator, moving along the meridian A directly toward the north

pole. It is clear that it cannot continue to move along the meridian,

because the direction of the meridian with reference to space, is

continually changing, and the inertia of the wind compels it to move

in a straight line without reference to the points of the compass.

So when the meridian A has been moved to B by the rotation of the

earth, the wind, although it maintains its original direction, no

longer points toward the pole but to the right of the pole. Likewise,

a wind starting from the pole toward the equator also turns to the

right of the meridians and becomes a northeast wind as it approaches

the equator. A wind moving east or west, also turns to the right of

the parallels for the same reason. So a wind starting out from the

equator with the best possible intention of hitting the pole, and all

the while continuing in the same straight line, will miss the pole by

many miles, and always on the right side in the northern and on the

left side in the southern hemisphere. Thus, the oblique movement of

both the trade winds and the prevailing westerlies is accounted for.

It now remains to consider the cause of the unexpected low pressure

found at the poles, and the reason for the belts of high pressure

at the tropics. If we refer to Fig. 2, it is evident that not all

the air that ascends at the equator descends at the tropics, else

there would be an absence of air at the higher latitudes, which is

manifestly not the case. On the other hand, it is equally impossible

that all the air ascending at the equator should move to the poles,

because the space it could occupy decreases rapidly from a maximum at

the equator to zero at the poles. Only a part of the air that ascends

at the equator is, therefore, involved in the trade wind circulation

and a part passes over the tropics and moves on toward the low

pressure at the poles. Furthermore, some of the air that descends at

the tropics moves along the surface toward the poles, obeying the law

that impels air to move from high pressure to low pressure. Now every

particle of air that passes over the tropics, every particle that

moves northward along the surface, turns to the right in the northern

and to the left in the southern hemisphere. All, therefore, miss the

poles--on the right side in the northern and on the left side in

the southern hemisphere. The result is that two great whirlpools

develop in the atmosphere; one whirling about the north and the other

whirling about the south pole. The outer margins of these whirlpools

coincide with the tropical belts of high pressure.

[Illustration: CIRCUMPOLAR WHIRL]

As an example of a whirlpool we may take a basin having a vent at the

center of the bottom. If the basin is filled with water, the plug

withdrawn and the water given a slight rotary motion, its velocity

will increase as it approaches the center and the rapid whirling will

develop sufficient centrifugal force to open an empty core. Those

who have visited the great whirlpool at Niagara, undoubtedly noticed

that the whirling waters are held away from the center and piled up

around the margins by the centrifugal force developed. Let us suppose

that air starting from the equator, moves without friction or other

resistances toward the pole. Its velocity must increase as its radius

shortens, because the law of the conservation of areas requires that

the radius must always sweep over equal areas in a given unit of

time. (See law of conservation of areas.) At the equator, the air

has an easterly motion equal to the eastward motion of the earth,

which is 1,000 miles per hour. At latitude 60° the radius will have

decreased one-half and the velocity, therefore, doubled; but at

latitude 60° the eastward motion of the earth is only 500 miles per

hour, so the air would be moving 1,500 miles per hour faster than the

earth. At a distance of 40 miles from the pole the wind would attain

an easterly velocity of 100,000 miles per hour, and moving on so

short a radius would develop sufficient centrifugal force to hold all

the air away from the pole and thus form a vacuum. That the supposed

case of no friction is far from the truth is evidenced by the fact

that the pressure at the north pole is but little less than at the

equator, but the centrifugal force developed by the gyration winds,

in thus withdrawing the air from the poles and piling it up at the

tropics, may be fairly taken as sufficient cause for the low pressure

found at the poles and the belts of high pressure at the tropics.

The questions that remain to be considered are: (1) the low pressure

at the south pole as compared with the pressure at the north pole and

(2) the unequal distance of the tropical belts of high pressure from

the equator. These questions may be considered together.

It is to be remembered that the southern hemisphere is the water

hemisphere, and that the prevailing westerlies, in gliding over

the smooth water surface, are but little retarded by friction and,

therefore, attain a higher velocity than the corresponding winds of

the northern hemisphere, where the rougher surface materially retards

their movement. As a consequence, the circumpolar whirl of the

southern hemisphere is stronger, and develops a greater centrifugal

force, thus holding a larger quantity of air away from the south pole

and reducing the pressure to a greater degree than is brought about

by the weaker winds of the northern hemisphere.

Since the circumpolar whirl of the southern hemisphere is the

stronger of the two, it withdraws the air to a greater distance from

the pole than does its weaker counterpart of the northern hemisphere,

and piles it up in the tropical belt of high pressure about five

degrees nearer the equator than does the weaker forces of the

northern hemisphere.

STORMS

[Illustration: _Snow crystal._

Photomicrograph by W. A. Bentley.]

Having gained a comprehensive view of the general, planetary wind

system, we may now undertake the study of local disturbances that

arise within the general circulation and are known as “storms.”

Storms are simply eddies in the atmosphere. They may be compared to

the eddies that are often seen floating along with the current of a

river or creek. In these eddies the water is seen to move rapidly

around a central vertex, developing sufficient centrifugal force to

hold some of the water away from the center, thus forming a well

marked depression, frequently of considerable depth. The whole

circulation of the eddy is quite independent of the current of the

stream which carries it along its course, and while its general

direction and velocity of movement coincide with that of the current,

there are times when it will be seen to move quickly from side to

side and again when it will remain nearly stationary for a time or

take on a rapid movement.

The eddies or storms in the atmosphere act in much the same way.

They are carried along by the general currents of the river of air

in which they exist. Their general direction coincides with the

direction of the current in which they are floating, and their rate

of movement conforms in a general way to its velocity; but like the

eddies in the river, they do not always move in straight lines nor at

a uniform rate of speed.

There is one important respect in which the eddies in the air

differ from eddies in water. The water eddy may revolve in either

direction, depending upon the direction in which the initial force

was applied, but the storm eddies in the atmosphere always revolve

counter-clockwise in the northern hemisphere, and clockwise in the

southern.

This is due to the deflecting force of the earth’s rotation, which is

fully explained on page 872.

WEATHER MAPS

[Illustration: _Snow crystal._

Photomicrograph by W. A. Bentley.]

A weather map is a sort of flashlight photograph of a section of the

bottom of one or more of these great rivers of air. It brings into

view the whole meteorological situation over a large territory at a

given instant of time; and, while a single map conveys no indication

of the movements continually taking place in the atmosphere, a series

of maps, like a moving picture, shows not only the whirling eddies,

the hurrying clouds and the fast-moving winds, but the ceaseless

on-flow of the great river of air in which they float. Our present

knowledge of the movements of the atmosphere has been gained chiefly

from a study of weather maps; they form the basis of the modern

system of weather forecasting, and their careful study is essential

to any adequate understanding of the problems presented by the

atmosphere. (See pages 884–885.)

_The Principles of Weather Forecasting_

[Illustration: _Snow crystal._

Photomicrograph by W. A. Bentley.]

The forecasting of the weather has been made possible by the electric

telegraph. It is based upon a perfectly simple, rational process

constantly employed in everyday affairs. We go to a railway station

and ask the operator about a certain train. He tells us that it

will arrive in an hour. We accept his statement without question,

because we are confident that he knows the speed at which the train

is approaching, a few clicks of his telegraph instrument has told

him just where it is and the time it will arrive, barring accidents,

is a simple calculation. Information of coming weather changes are

obtained in a similar manner. Although storms do not run on steel

rails like a train, nevertheless their movements may be foreseen with

a reasonable degree of accuracy, depending chiefly upon the size of

the territory from which telegraphic reports are received and the

experience and skill of the forecaster. As a rule, the larger the

territory brought under observation, especially in its longitudinal

extent (the general currents carry storms of the middle latitudes

eastward around the world and those or the tropics westward), the

earlier advancing changes may be recognized and the more accurately

their movements foreseen.

_Forecasts Based on Weather Maps_

The forecasts issued by the United States Weather Bureau are based on

weather maps, prepared from observations taken at 8 a. m. and 8 p.

m. at about 200 observatories. In addition to the reports received

by telegraph by the Central Office at Washington, the several

forecast centers and other designated stations from observatories or

stations in the United States, a system of interchange with Canada,

Mexico, the West Indies and other island outposts in the Atlantic

and Pacific gives to the forecaster two daily photographs of the

weather conditions over a territory embracing nearly the whole of

the inhabited part of the western hemisphere north of the equator.

Any sort of disturbance within this vast region is photographed at

once upon the weather map. If it be a West Indies hurricane or other

destructive storm, its character is recognized instantly, its rate

and direction determined and information of the probable time of its

arrival sent to those places that lie in its path. The method is

perfectly simple. Anyone with a weather map and a little experience

can forecast the weather with some degree of accuracy, or, at least,

gain an intelligent understanding of the conditions upon which the

forecasts that accompany the map are based.

_Maps, Where Published and How Obtained_

Weather maps are published in many daily papers, and in somewhat

larger form and more in detail, at many Weather Bureau stations. They

may usually be obtained for school use by applying to the nearest

Weather Bureau station or to the Chief of the Weather Bureau at

Washington, D. C.

The forecasts that accompany the maps are simply an expression on the

part of the official forecaster as to the weather changes he expects

to occur in various parts of the country within the time specified,

usually within 36 to 48 hours. His opinion is based upon the

conditions shown by the map. He has no secret source of information.

You may accept his conclusions, or, if in your opinion they are not

justified, you have all the information necessary to make a forecast

for yourself. Weather maps are published so extensively with a

view to thus stimulating an intelligent interest in the problem of

weather forecasting, and also that one may see at a glance what the

temperature, rainfall, wind and weather is in any part of the country

in which he may be interested. The friends of the weather service are

those who best understand its work.

THE VALUE OF THE WEATHER SERVICE

[Illustration: _Snow crystal._

Photomicrograph by W. A. Bentley.]

No one knows so well as the forecaster that the changes that appear

most certain to come sometimes fail, or come too late; but taking

all in all, about 85 out of 100 forecasts are correct. Of those that

fail, probably not more than three or four per cent. fail because

the changes come unannounced. Most forecasters predict too much, and

their forecasts fail because the expected changes come after the time

specified or not at all. It is fortunate that this is so; for it is

better to be prepared for the change though it be late in coming than

to have it come without warning.

The value of the weather service to the agriculture and commerce

of the United States cannot be questioned seriously. That the

appropriations for its support have been increased year by year from

$1,500 in 1871 to nearly $1,500,000 in 1910 is evidence of its value

and efficiency. A conservative estimate places the value of property

saved by the warnings issued by the Weather Bureau at $30,000,000

annually.

LESSON CCXXII

EXPERIMENTS TO SHOW AIR PRESSURE

_Leading thought_--The air presses equally in all directions.

_Experiment 1--To show that air presses upward_--Fill a tumbler which

has an unbroken edge as full of water as possible. Take a piece of

writing paper and cover the tumbler, pressing the paper down firmly

upon the edge of the glass. Turn the glass bottom side up and ask

why the water does not flow out. Allow a little air to enter; what

happens? Why? Turn the glass filled with water and covered with paper

sidewise; does the water flow out? If not, why?

[Illustration: _Composite crystal; high cloud at center and medium

high cloud at the border._

Photomicrograph by W. A. Bentley.]

_Experiment 2--To show that air passes downward_--Ask some of the

boys of the class to make what they call a sucker. This is a piece

of leather a few inches across. Through its center a string is drawn

which fits very closely into the leather and is held in place by a

very flat knot on the lower side. Dampen the leather and press it

against any flat surface, and try to pull it off. If possible, place

the sucker on a flat stone and see how heavy a stone can be lifted

by the sucker. Ask why a sucker clings so to the flat surface. If a

little air is allowed to get between the sucker and the stone, what

happens? Why?

_Hints to the teacher regarding the Experiments_--The water is kept

in the tumbler in Experiment 1 by the pressure of the atmosphere

against the paper. If the tumbler is tipped to one side the water

still remains in the glass, which shows that the air is pressing

against the paper from the side with sufficient force to restrain the

water, and if the tumbler is tipped bottom side up it shows the air

is pressing upward with sufficient force to keep the water within the

glass.

In the case of Experiment 2, we know that the leather pressing upon

the floor or on the stone is not in itself adhesive, but it is made

wet simply so that it shall press against the smooth surface more

closely. The reason why we cannot pull it off is that the air is

pressing down upon it with the force of about fifteen pounds to the

square inch. If the experiment is performed at sea level, we should

be able to lift by the string of the sucker a stone weighing fifteen

pounds. The reason why the water falls out of the tumbler after a

little air is let beneath the paper, is that then the air is pressing

on both sides of the paper; and the reason why the sucker will not

hold if there is any air between it and the stone, is because the air

is pressing in both directions upon it.

_Supplementary reading_--The Wonderbook of the Atmosphere, Houston,

Chapters III, IV, V.

LESSON CCXXIII

THE BAROMETER

_Leading thought_--The weight of our atmosphere balances a column

of mercury about thirty inches high, and is equal to about fifteen

pounds to the square inch. This pressure varies from day to day, and

becomes less as the height of the place increases. The barometer is

an instrument for measuring the atmospheric pressure. It is used

in finding the height of mountains, and, to a certain extent, it

indicates changes of the weather.

[Illustration: _Compound snow crystals._

Photo by W. A. Bentley.]

_Method_--A glass tube about 36 inches long, closed at one end; a

little glass funnel about an inch in diameter at the top; a small

cup--a bird’s bathtub is a good size since it allows plenty of room

for the fingers; mercury enough to fill the tube and have the mercury

an inch or more deep in the cup. Be careful not to spill the mercury

in the following process, or you will be as badly off as old Sisyphus

with his rolling stone.

[Illustration: _A barometer made by pupils._]

Set the closed end of the tube in the cup so that any spilled mercury

will not be lost; with the help of the funnel slowly and carefully

fill the tube clear to the top with the mercury; empty the rest of

the mercury into the cup; place the end of one of the fingers of the

left hand tightly over the open end of the tube and keep it there;

with the right hand invert the tube, keeping the end closed with

the finger, and place the hand, finger and all, beneath the mercury

in the cup then remove the finger, keeping the open end of the tube

all the time below the surface of the mercury. When the mercury has

ceased to fall measure the distance from the surface in the cup to

the top of the mercury in the tube.

_Observations_--1. How high is the column of mercury in the tube?

2. What keeps the mercury in the tube? Place the cup and the tube on

a table in the corner of the room, place behind the tube a yardstick,

and note whether the column of mercury is the same height day after

day. If it varies, why?

3. Would the mercury column be as high in the tube if it were placed

on top of a mountain as it would at the foot? Why?

_Supplementary reading_--Chap. II in The Wonderbook of the

Atmosphere, Houston.

HOW TO READ WEATHER MAPS

_Teacher’s Story_

Weather maps may be obtained by writing to the nearest Weather

Station, or by writing to the Chief of the Weather Bureau, Dr. Willis

L. Moore, Washington, D. C., stating that you wish to post the maps

in a public place. A supply of maps for three successive days for use

in these lessons may be obtained at 20 cents per hundred. Sometimes

they are sent free, if it is stated that they are to be used for

school purposes.

[Illustration: _Dew on clover leaf. Hoar frost on clover leaf._

Photo by W. A. Bentley.]

The words isobar and isotherm have been bogies which have frightened

many a teacher from undertaking to teach about weather maps, and yet

how simple are the meaning of these two words. Isobar is made up of

two Greek words, _isos_ meaning equal and _baros_ meaning weight.

Therefore, an isobar means equal weight, and on a map one of these

continuous lines means that, wherever it passes, the atmosphere there

has equal weight and the barometer stands at equal height. The isobar

of 30 means that the mercury in the barometer stands 30 inches in

height in all the regions where that line passes.

“Isotherm” comes from the two Greek words, _isos_ meaning equal and

_therme_ meaning heat. Therefore, on the map the dotted lines show

the region where the temperature is the same. If at the end of the

dotted line you find 60 it means that, wherever that line passes, the

thermometer stands at 60 degrees.

Many of the “highs” and “lows” enter the United States from the

Pacific Ocean about the latitude of Washington State or southwest

British Columbia. They follow one another alternately, crossing the

continent in the general direction of west to east in a path which

curves somewhat to the north, and they leave the United States in the

latitude of Maine or New Brunswick. If they enter by way of lower

California, they pass over to the Atlantic Ocean farther south. The

time for the passage of a high or low across the continent averages

about three and one-half days, sometimes a little more. These areas

are usually more marked in winter, and wind storms are more marked

and more regular.

A low area is called a cyclone and a high area an anti-cyclone. The

destructive winds, popularly called cyclones, which occur in certain

regions, should be called tornadoes instead, although in fact they

are simply small and violent cyclones. But a cyclone, when used in a

meteorological sense, extends over thousands of square miles and is

not violent; while a tornado may be only a few rods in diameter and

be very destructive. The little whirlwinds which lift the dust in the

roads are rotary winds also, but merely the eddies of a gentle wind.

In a cyclone or “low,” and also in a tornado, the air blows from

_all_ sides spirally inward _toward_ the center where there is a

column of _ascending_ air.

In an anti-cyclone or “high” the air blows outward in every direction

in curved lines _from_ a column of _descending_ air.

[Illustration: _Map of a storm._]

In the above map, the curved lines are isobars; the line of crosses

from A to B indicates the course of the storm; the arrows indicate

the direction of the wind, note that it is moving counter-clockwise

around the area of low pressure; the shaded area indicates the region

where it is raining or snowing; note that this is the area where the

warm, moist air from the Gulf and the Ocean meets the colder air of

the North.

The weather conditions during the passage of a cyclone are briefly as

follows: Small, changing wisps of cirrus clouds appear about 24 hours

before rain; these gradually become larger and cover the whole sky,

making a nimbus cloud. The wind changes from northeast to east or

southeast to south. The barometer falls; the thermometer rises, that

is, air pressure is less to the square inch, and the temperature of

the atmosphere is warmer. Rain begins and falls for a time, varying

from an hour to a day or more. After the rain there appear breaks in

the great nimbus clouds and finally the blue sky conquers until there

are only a few or no clouds. The wind changes to southwest and west;

the barometer rises, the temperature falls. The rain ceases, the sun

shines out brightly. The low has passed and the high is approaching

to last about three days.

U. S. DEPARTMENT OF AGRICULTURE, WEATHER BUREAU

EXPLANATION OF WEATHER SIGNALS

[Illustration:

No. 1

Fair Weather

No. 2

Rain or Snow

No. 3

Local Rain or Snow

No. 4

Temperature

No. 5

Cold Wave

INTERPRETATION OF DISPLAYS

No. 1, alone, indicates fair weather, stationary temperature.

No. 2, alone, indicates rain or snow, stationary temperature.

No. 3, alone, indicates local rain or snow, stationary temperature.

No. 1, with No. 4 above it, indicates fair weather, warmer.

No. 1, with No. 4 below it, indicates fair weather, colder.

No. 2, with No. 4 above it, indicates rain or snow, warmer.

No. 2, with No. 4 below it, indicates rain or snow, colder.

No. 3, with No. 4 above it, indicates local rain or snow, warmer.

No. 3, with No. 4 below it, indicates local rain or snow colder.

WILLIS L. MOORE,

_Chief U. S. Weather Bureau_.

]

EXPLANATION OF WHISTLE SIGNALS

A warning blast of fifteen to twenty seconds duration is sounded to

attract attention. After this warning the longer blasts (of four to

six seconds duration) refer to weather, and shorter blasts (of one to

three seconds duration) refer to temperature; those for weather are

sounded first.

Blasts Indicate.

One long Fair weather.

Two long Rain or snow.

Three long Local rain or snow.

One short Lower temperature.

Two short Higher temperature.

Three short Cold wave.

By repeating each combination a few times, with intervals of ten

seconds, liability to error in reading the signals may be avoided.

STORM AND HURRICANE WARNINGS

[Illustration:

Storm warnings. Hurricane

warning.

NE. winds. SE. winds. NW. winds. SW. winds.

EXPLANATION OF STORM AND HURRICANE SIGNALS

_Storm warning_--A red flag with a black center indicates that

a storm of marked violence is expected.

The pennants displayed with the flags indicate the direction

of the wind; red, easterly (from northeast to south); white

(westerly from southwest to north). The pennant above the flag

indicates that the wind is expected to blow from the northerly

quadrants; below from the southerly quadrants.

By night a red light indicates easterly winds and a white

light below a red light westerly winds.

_Hurricane warning_--Two red flags with black centers

displayed one above the other indicates the expected approach

of a tropical hurricane or one of those extremely severe and

dangerous storms which occasionally move across the Lakes and

northern Atlantic coast.

No night hurricane warnings are displayed.

]

[Illustration:]

[Illustration:]

[Illustration:]

[Illustration: _U. S. weather maps, showing the eastward progress of

an area of low pressure for four consecutive days._

Note the course of the low that was on the Pacific Coast Dec. 24;

this is indicated by the line of dots and dashes on the later maps.]

LESSON CCXXIV

HOW TO READ WEATHER MAPS

_Leading thought_--Weather maps are made with great care by the

Weather Bureau experts. Each map is the result of many telegraphic

communications from all parts of the country. Every intelligent

person should be able to understand the weather maps.

_Method_--Get several weather maps of the nearest Weather Bureau

Station. They should be maps for successive days, and there should be

enough so that each pupil can have three maps, showing the weather

conditions for three successive days.

_Observations_--1. Take the map of the earliest date of the three.

Where was your map used? What is its date? How many kinds of lines

are there on your map? Are there explanatory notes on the lower

left-hand corner of your map? Explain what the continuous lines mean.

Find an isobar of 30; to what does this figure refer? Find all the

towns on your map where the barometer stands at 30 inches. Is there

more than one isobar on your map where the barometer stands at 30?

2. Where is the greatest air pressure on your map? How high does the

barometer stand there? How are the isobars arranged with reference

to this region? What word is printed in the center of this series of

isobars?

3. What do the arrows indicate? What do the circles attached to the

arrows indicate?

4. In general, what is the direction of the winds with reference to

this high center?

5. Is the air rising or sinking at the center of this area? If the

wind is blowing in all directions from a center marked high, what

sort of weather must the places just east of the high be having? Do

the arrows with their circles indicate this?

6. Find a center marked low. How high does the barometer stand there?

Does the air pressure increase or diminish away from the center

marked low, as indicated by the isobars? Do the winds blow toward

this center or away from it?

7. What must the weather in the region just east of the low be? Why?

Do the arrows and circles indicate this?

8. Is there a shaded area on your map? If so, what does this show?

9. Compare the map of the next date with the one you have just

studied. Are the highs and lows in just the same position that they

were the day before? Where are the centers high and low now? In what

directions have they moved?

10. Look at the third map and compare the three maps. Where do the

high and low centers seem to have originated? How long does it take a

high or low to cross the United States? How far north and south does

a high or low, with all its isobars, extend?

11. What do the dotted lines on your map mean? Do they follow exactly

the isobars?

12. What is the greatest isotherm on your map? Through or near what

towns does it pass?

13. Do the regions of high air pressure have the highest temperature

or the lowest? Do high temperatures accompany low pressures? Why?

14. What is the condition of the sky just east of a low center? What

is its condition just west of low?

15. If the isobars are near together in a low, it means that the wind

is moving rather fast and that there will be a well marked storm.

Look at the column giving wind velocity. Was the wind blowing toward

the center of the low on the map? If so, does that mean it is coming

fast or slow? How does this fact correspond with the indications

shown by the distance between the isobars?

16. Describe the weather accompanying the approach and passage

of a low in the region where your town is situated? What sort of

clouds would you have, what winds, what change of the barometer and

thermometer?

_How to Find the General Direction and Average Rate of Motion of

Highs and Lows_

_Observations_--1. On the first map of the series of three given, put

an X in red pencil or crayon at the center of the high and a blue one

at the center of the low; or if you do not have the colored pencils,

use some other distinguishing marks for the two. If there are two

highs and two lows use a different mark for each one.

2. Mark the position of each center on this map for the following day

with the same mark that you first used for that area. Do this for

each of the highs and lows until it leaves the map or until your maps

have been used. All the marks of one kind can be joined by a line,

using a red line for the red marks and a blue line for the blue marks.

3. What do you find to be the general direction of the movement of

the highs and lows?

4. Examine the scale marked statute miles at the bottom of the map.

How many miles are represented by one inch on the scale?

5. With your ruler find out how many miles one area of high or low

has moved in twenty-four hours; in three days. Divide the distance

which the area has moved in three days by three and this will give

the average velocity for one day.

6. In the same way find the average velocity of each of the areas on

your map for three days and write down all your answers. From all

your results find the average weekly velocity; that is, how many

miles per hour and the general direction which has characterized the

movement of the high and low areas.

_Supplementary reading_--The Wonderbook of the Atmosphere, Houston,

Chapters XIV-XXIII.

_How to Keep a Daily Weather Map_

The pupils should keep a daily weather map record for at least six

months. The observations should be made twice each day and always

at the same hours. While it would be better if these records could

be made at 8 o’clock in the morning and again at 8 o’clock in the

evening, this is hardly practicable and they should, therefore, be

made at 9 o’clock and at 4. The accompanying chart may be drawn

enlarged. Sheets of manila paper are often used, so that one chart

may cover the observations for a month.

Few schools are able to have a working barometer, but observations of

temperature and sky should be made in every school. Almost any boy

can make a weather vane, which should be placed on a high building

or tree where the wind will not be deflected from its true direction

when striking it. A thermometer should be placed on the north side

of a post and on a level with the eyes; it should not be hung to a

building, as the temperature of the building might affect it.

The direction of the wind and the cloudiness of the day may be

indicated on the chart, as it is on the weather maps, by a circle

attached to an arrow which points in the direction in which the wind

is blowing.

_References_--Elementary Meteorology, Waldo, American Book Co.,

$1.50; Elementary Meteorology, Davis, Ginn and Co., $2.50; Bulletins

from the United States Weather Bureau, Washington, D. C.

CHART FOR SCHOOL WEATHER-RECORDS.

======+====+=====+=======+=========+===========+======+====+========

Date |Hour|Temp.|Baro- |Direction|Cloudi- | | |

ness. |Dew or|Rain or|Remarks.

| | | meter | of wind |Fogs. | Frost| Snow |

------+----+-----+-------+---------+--------+------+-------+--------

| | | | | | | |

| | | | | | | |

| | | | | | | |

------+----+-----+-------+---------+--------+------+-------+--------

| | | | | | | |

| | | | | | | |

| | | | | | | |

------+----+-----+-------+---------+--------+------+-------+--------

| | | | | | | |

| | | | | | | |

| | | | | | | |

------+----+-----+-------+---------+--------+------+-------+--------

| | | | | | | |

| | | | | | | |

| | | | | | | |

------+----+-----+-------+---------+--------+------+-------+--------

| | | | | | | |

| | | | | | | |

| | | | | | | |

------+----+-----+-------+---------+--------+------+-------+--------

| | | | | | | |

| | | | | | | |

| | | | | | | |

------+----+-----+-------+---------+--------+------+-------+--------

| | | | | | | |

| | | | | | | |

| | | | | | | |

------+----+-----+-------+---------+--------+------+-------+--------

Weekly| | | | | | | |

Sum- | | | | | | | |

mary | | | | | | | |

------+----+-----+-------+---------+--------+------+-------+--------

[Illustration: “_Though I know not what you are, twinkle, twinkle

little star._”]

THE STORY OF THE STARS

_Teacher’s Story_

“_Why did not somebody teach me the constellations and make me

at home in the starry heavens, which are always overhead,

and which I don’t half know to this day._”

--THOMAS CARLYLE.

For many reasons aside from the mere knowledge acquired, children

should be taught to know something of the stars. It is an investment

for future years; the stars are a constant reminder to us of

the thousands of worlds outside our own, and looking at them

intelligently, lifts us out of ourselves in wonder and admiration

for the infinity of the universe, and serves to make our own cares

and trials seem trivial. The author has not a wide knowledge of the

stars; a dozen constellations were taught to her as a little child

by her mother, who loved the sky as well as the earth; but perhaps

nothing she has ever learned has been to her such a constant source

of satisfaction and pleasure as this ability to call a few stars by

the names they have borne since the men of ancient times first mapped

the heavens. It has given her a sense of friendliness with the night

sky, that can only be understood by those who have had a similar

experience.

There are three ways in which the mysteries of the skies are

made plain to us: First, by the telescope; second, by geometry,

trigonometry and calculations--a proof that mathematics is even more

of a heavenly than an earthly science; and third, by the use of the

spectroscope, which can only be understood after we study physics. It

is an instrument which tells us, by analyzing the light of the stars,

what chemical elements compose them; and also, by the means of the

light, it estimates the rate at which the stars are moving and the

direction of their motion.

Thus, we have learned many things about the stars; we know that

every shining star is a great blazing sun, and there is no reason to

doubt that many of these suns have worlds, like the earth, spinning

around them although, of course, so far away as to be invisible to

us; for our world could not be seen at all from even the nearest

star. We also know that many of the stars which seem single to us

are really double--made up of two vast suns swinging around a common

center; and although they may be millions of miles apart, they are

so far away that they seem to us as one star. The telescope reveals

many of these double stars and shows that they circle around their

orbits in various periods of time, the most rapid making the circle

in five years, another in sixteen years, another in forty-six years;

while there is at least one lazy pair which seems to require fully

sixteen hundred years to complete their circle. And the spectroscope

has revealed to us that many of the stars which seem single through

the largest telescope are really double, and some of these great suns

race around each other in the period of a few hours, which is a rate

of speed we could hardly imagine.

Astronomers have been able to measure the distance from us to many

of the stars, but when this distance is expressed in miles it is

too much for us to grasp. Thus, they have come to measure heavenly

distance in terms of the rate at which light travels, which is

186,400 miles per second or about six trillions of miles per year;

this distance is called a light-year. Light reaches us from the

sun in about eight minutes, but it takes more than four years for

a ray to reach us from the nearest star. It adds new interest to

the Pole-star to know that the light which reaches our eyes left

that star almost half a century ago, and that the light we get from

the Pleiades may have started on its journey before America was

discovered. Most of the stars are so far away that we cannot measure

the distance.

Although the stars seem always to be in the same places, they are

all moving through space just as our sun and its family are doing;

but the stars are so far away that, although one may move a million

miles a day, it would require many years of observation for us to

detect that it moved at all. We know the rate at which some of the

stars are moving but have no idea of their goal; nor do we have any

idea where our sun is dragging us at the rate of nearly 800 miles per

minute. It is thought that our sun and the other suns are whirling

around some greater center or centers; but if so, the orbits are so

many trillions of miles across that the suns all seem to be going

somewhere in a straight line, each attending strictly to its own

business.

Through the spectroscope we know something of the life of stars; we

know that when they are young they are composed of thin gases and

shine white or blue; and as they grow older, they become more solid

and shine yellow, like our sun; and when older still, they grow red

and are yet more condensed, like Bethelguese in Orion, which is an

aged sun and which will, in time, grow cold and dark and invisible

to us. The spectroscope reveals many dark stars whirling through

space--vast, dead suns with their fires extinguished, never to be

lighted again unless, in its swift course, one of them should hurl

itself against another star with a fearful force which shall shatter

it into gaseous atoms, and these be thrown into fierce spiral

whirlpools, from which it shall again be fashioned into a white-hot

sun and become a star in our sky.

The scientists are coming to understand a little of how the stars

are made; for scattered through the skies are masses of misty light,

called nebulæ, which means clouds; nebulæ are vast gaseous bodies

composed of the stuff of which stars are made. Each nebula keeps its

own special place in the heavens--just like a star, and is moving

through space--like a star. The spectroscope shows that many of these

shining, misty masses are made up of glowing gases, largely hydrogen;

and many are disk-shaped, twisted into a spiral. There are grounds

for believing that these spiral nebulæ are stars in the process of

forming. Nebulæ are mostly telescopic, although two or three may be

detected by the keen, unaided eye as a little blur of light, like

that surrounding the third star of Orion’s sword. There are eight

thousand or more nebulæ which have been discovered and mapped. Some

idea of their tremendous size is given by Ball when speaking of the

ring nebula of Lyra, which we cannot see with the naked eye, and yet

if a railroad train started to cross its diameter at the middle, and

went at the rate of a mile a minute, one thousand years would not

complete the journey.

The number of stars that may be seen with the unaided eye, if one

were to travel from the southern to the northern polar region, would

be between six and seven thousand; but it would require very keen

eyes to see two thousand at one time. With the help of the telescope,

about eight hundred thousand stars have been discovered, classified

and catalogued, while photography of the skies reveals millions. It

is thought that the new international photographic chart, which shall

cover all the space seen from our globe may show thirty millions of

stars. The Milky Way or Galaxy, that great, white band across the

heavens, is made up of stars which are so far away that we cannot see

them, but see only their diffused light. It is well called a “River

of Stars” flowing in a circle around our whole solar system; and,

except during the spring months, one-half of it may be seen directly

above us while the other half is hidden below us. The place of the

Milky Way in the heavens seems fixed and eternal; any star within its

borders is always seen at the same point. When the Northern Cross

lifts itself toward the zenith we are able to see that, near that

constellation, the star river divides into three streams with long,

blue islands between.

_Reference books_--There are a large number of excellent text-books

and popular books on astronomy. The following are a few which I

have used most often: Astronomy for Everybody, Newcomb; Todd’s New

Astronomy; The Friendly Stars, Martin; Starland, Ball; The Stars

Through an Opera Glass, Serviss; Other Suns than Ours, Proctor; Other

Worlds than Ours, Proctor.

_For children_--Earth and Sky, Holden; Stories of Starland, Proctor;

The Children’s Book of Stars, G. E. Mitton; Story land of the Stars,

Pratt; Stars in Song and Legend, Porter; The Planisphere, Thos.

Whittaker.

HOW TO BEGIN STAR STUDY

THE POLE-STAR AND THE DIPPERS

_Teacher’s Story_

The way to begin star study is to learn to know the Big Dipper, and

through its pointers to distinguish the Pole-star; for whenever we

try to find any star we have to find the Big Dipper and Pole-star

first so as to have some fixed point to start from. There are four

stars in the bowl of the Big Dipper and three in the curved handle.

A line drawn through the outer two stars of the bowl, if extended,

will touch the North Star, or Pole-star. It is very important for us

to know the Pole-star, because the northern end of the earth’s axis

is directed toward it, and it is therefore situated in the heavens

almost directly above our North Pole. For those of us who live in the

northern Hemisphere, the North Star never sets, but is always in our

sky. Of course, the North Star has nothing to do with the axis of our

earth any more than the figure on the blackboard has to do with the

pointer; it simply happens to lie in the direction toward which the

northern end of the earth’s axis points. In the southern skies, there

is no convenient star which lies directly above the South Pole, so

there is no South Pole-star. It is also a coincidence that the needle

of the mariner’s compass points toward the North Star; the earth

being a large magnet exercises its influence on all substances which

can be magnetized, and since the poles of our great earth-magnet

are nearly in line with the poles of the earth’s axis, the magnetic

needle naturally points north and south, and the North Star chances

to be nearly in the direction toward which the northern end of the

compass needle points.

The Pole-star cannot be seen from the southern hemisphere; but if

we should start from Florida, on a journey toward Baffin’s Bay, we

should discover that each night this star would seem higher in the

sky. And if we should succeed in reaching the North Pole, we would

find the Pole-star directly over our heads, and what a wonderful

sight the stars would be from this point! For none of the stars which

we could see would rise or set, but would move around us in circles

parallel to the horizon.

The Big Dipper points towards the Pole-star, and to us seems to

revolve around it every twenty-four hours but, of course, this

appearance is caused by the fact that we ourselves are revolving

from west to east. Therefore, the stars seems to revolve from west

to east under the Pole-star and from east to west above it, or in

exactly the opposite direction in which the hands of a clock turn.

Owing to the movement of the earth in its orbit, the Big Dipper and

all the other stars arrive at a certain point in our sky four minutes

earlier each day or about two hours earlier each month; thus, the Big

Dipper is east of the Pole-star with handle down in the evenings of

January, while at the same time of night in July, it is west of the

Pole-star with the handle up. But the time of year that a certain

star reaches a certain point is so invariable, that if we know star

time, or sidereal time as it is called, we can tell just what hour of

the night it is when a star passes this point. Thus, the Big Dipper

and the other polar constellations are the night clock of the sailors

of the northern hemisphere; for though this great polar clock has its

hands moving around the wrong way, it gains time with such regularity

that anyone who understands is able to compute exact time by it.

[Illustration: _The Pole-star and the Big and Little Dippers._]

The Little Dipper lies much nearer the Pole-star than does the Big

Dipper; in fact, the Pole-star itself is the end of the handle of

the Little Dipper. Besides the Pole-star, there are two more stars

in the handle of the Little Dipper, and of the four stars which make

the bowl, the two that form the outer edge are much the brighter. The

bowl of the Little Dipper is above or below the Pole-star according

to the hour of the evening, or the night of the year, for it

apparently revolves about the Pole-star as does the Big Dipper. The

two Dippers open toward each other, and some one said “they pour into

each other.”

The Big Dipper is a part of a constellation called _Ursa Major_, the

Great Bear; and the Little Dipper is the Little Bear, the handle of

the dipper being the bear’s tail.

There is an ancient myth telling the story of the Big and Little

Bears: A beautiful mother called Callisto had a little son whom she

named Arcas. Callisto was so beautiful that she awakened the anger of

Juno, who changed her to a bear; and when her son grew up he became

a hunter, and one day would have killed his transformed mother; but

Jupiter seeing the danger of this crime caught the two up into the

heavens, and set them there as shining stars. But Juno was still

vindictive, so she wrought a spell which never allowed these stars to

rise and set like other stars, but kept them always moving around and

around.

_References_--The Friendly Stars by Martin is a most delightful book

and at the same time gives explicit directions for finding the stars

and much interesting information concerning them. The planisphere is

a little chart with a mechanical device which enables us to find what

stars are in sight every night of the year, or at any time of night.

It is published by Thos. Whittaker, Bible House, New York, and costs

seventy-five cents.

LESSON CCXXV

THE TWO DIPPERS

_Leading thought_--The North Star or Pole-star may always be found by

the stars known as the pointers in the Big Dipper; the stars of the

Big Dipper seem to revolve around the Pole-star once in twenty-four

hours.

_Method_--The time to begin these observations is when the moon is in

its last quarter, so that the moonlight will not make pale the stars

in early evening. Draw upon the blackboard, from the chart shown on

page 890, the Big Dipper and the Pole-star, with a line extending

through the pointers. Say to the pupils that this Big Dipper is

above or below or at one side of the Pole-star, and that you wish

them to observe for themselves where it is and tell you about it the

next day. After they surely know the Big Dipper, ask the following

questions:

_Observations_--1. Can you find the Big Dipper among the stars?

2. Is it in the north, south, east or west?

3. Which stars are the “pointers” in the dipper, and why are they

called so?

4. Make a drawing showing how you can always find the Pole-star, if

you can see the Big Dipper.

5. How many stars make the bowl of the Dipper?

6. How many stars in the handle?

7. Is the handle straight or is it curved?

8. Does the Big Dipper open toward the Pole-star, or away from it?

9. Is it above or below the Pole-star at eight o’clock in the

evening, or at the right or the left of it?

10. Does the Big Dipper remain in the same direction from the

Pole-star all night? Look at it at seven o’clock and again at nine

o’clock and see if it has changed position?

11. Do you think it moves around the Pole-star once every twenty-four

hours? In which direction? How could you tell the time of night by

the Big Dipper and the Pole-star?

12. Does the Big Dipper ever rise and set?

13. The Big Dipper is also called the Great Bear. Can you find the

stars which make the bear’s head and front legs?

After the pupils surely know the Big Dipper and Pole-star draw the

complete diagram upon the board to show the Little Dipper and where

it may be found, and call attention to the fact that the end of the

Little Dipper’s handle is the Pole-star itself and that its bowl is

not flaring, like that of the Big Dipper and that the two pour into

each other. Let the pupils find the Little Dipper in the sky for

themselves and ask the following questions:

_Observations_--14. Is the Little Dipper nearer or farther from the

Pole-star than the Big Dipper?

15. How many stars in the handle of the Little Dipper?

16. How many stars make the bowl of the Little Dipper? Which of these

stars are the brightest? Is the bowl of the Little Dipper above or

below the Pole-star?

17. Does the Little Dipper extend in the same direction in relation

to the Pole-star all night?

18. Make observations on the relation to each other of the two

dippers at eight o’clock in the evening of January, February, March

and April.

After the above lessons are well learned, give the following

questions, and try to have the pupils answer by thinking:

_Questions about Polaris_ (_the North Star_) _for the pupils to think

about and answer_:

19. How many names has the Pole-star? Can the Pole-star be seen from

the southern hemisphere? If not, why not?

20. If you should start from southern Florida and travel straight

north, how would the Pole-star seem to change position each

succeeding night?

21. If you could stand at the North Pole, where would the Pole-star

seem to be?

22. If you were at the North Pole, would any of the stars rise and

set? In what direction would the stars seem to move and why?

23. How does the North Star help the sailors to navigate the seas and

why?

24. How do astronomers reckon distances between us and the stars?

What is a light-year?

_Topics for English lesson_--(_a_) What a star is. (_b_) What a

constellation is. (_c_) How the stars and constellations received

their names in ancient times. In ancient times the Big and Little

Dippers were named the Big and Little Bears, and that is their Latin

name to this day. Write a story about what the ancient Greeks told

about these Bears and how they came to be in the sky.

_Supplementary reading_--Stories of Starland, Proctor, pp. 117–121;

Storyland of the Stars, Pratt, p. 75; Child’s Study of the Classics,

p. 33.

CASSIOPEIA’S CHAIR, CEPHEUS, AND THE DRAGON

_Teacher’s Story_

There are other constellations besides the two Dippers, which never

rise and set in this latitude, because they are so near to the

Pole-star that, when revolving around it, they do not fall below the

horizon. There is one very brilliant star, called Capella, which

almost belongs to the polar constellations but not quite, for it is

far enough away from Polaris to dip below the horizon for four hours

of the twenty-four.

[Illustration: _The polar constellations as they appear at about

8 o’clock January 20, the Dragon being south of the Pole-star. By

revolving this chart as indicated, the positions of the stars is

shown for 6 p. m., midnight, 6 a. m. and noon of January 20th._]

Queen Cassiopeia’s Chair is on the opposite side of the Pole-star

from the Big Dipper and at about equal distance from it. It consists

of five brilliant stars that form a W with the top toward Polaris,

one-half of the W being wider than the other. There is a less

brilliant sixth star which finishes out half of the W into a chair

seat, making of the figure a very uneasy looking throne for a poor

queen to sit upon.

King Cepheus is Queen Cassiopeia’s husband, and he sits with one foot

on the Pole-star quite near to his royal spouse. His constellation

is marked by five stars, four of which form a lozenge, and a line

connecting the two stars on the side of the lozenge farthest from

Cassiopeia, if extended, will reach the Pole-star as surely as a line

from the Big Dipper pointers. Cepheus is not such a shining light

in the heavens as is his wife, for his stars are not so brilliant.

Perhaps this is because he was only incidentally put in the skies.

He was merely the consort of Queen Cassiopeia, who being a vain and

jealous lady boasted that she and her daughter, Andromeda, were far

more beautiful than any other goddesses that ever were, and thus

incurred the wrath of Juno and Jupiter who set the whole family “sky

high” and quite out of the way, a punishment which must have had its

compensations since they are where the world of men may look at and

admire them for all ages.

Lying between the Big and Little Dippers and extending beyond the

latter is a straggling line of stars, which, if connected by a line,

make a very satisfactory dragon. Nine stars form his body, three his

head, the two brighter ones being the eyes.

LESSON CCXXVI

CASSIOPEIA’S CHAIR, CEPHEUS, AND THE DRAGON

_Leading thought_--To learn to know and to map the constellations

which are so near the Pole-star that they never rise or set in our

latitude, but seem to swing around the North Star once in twenty-four

hours.

_Method_--Place on the blackboard the diagram given showing the

Pole-star, Big and Little Dippers and Cassiopeia’s Chair, and ask for

observations and sketches showing their position in the skies the

following evening. After the pupils have observed the Chair and know

it, add to your diagram, first Cepheus and then the Dragon. After you

are sure the pupils know these constellations, give the following

lesson. The observations should be made early and late in the same

evening and at different times of the month, so that pupils will in

every case note the apparent movement of these stars around Polaris.

_Observations_--1. How many stars form Cassiopeia’s Chair? Make a

drawing showing them and their relation to the Pole-star.

2. Is the Queen’s Chair on the same side of the Pole-star as the Big

Dipper? Is the top or the bottom of the “W” which forms Cassiopeia’s

Chair turned toward the Pole-star?

3. Does Cassiopeia’s Chair move around the Pole-star, like the Big

Dipper?

4. How many stars mark the constellation of Cepheus?

5. Make a sketch of these stars and show the two which are pointers

toward the North Star.

6. Does Cepheus also move around the Pole-star, and in which

direction?

7. Describe where the Dragon lies, and where are his tail and his

head in relation to the two Dippers. Make a sketch of the Dragon.

8. Why do all the polar constellations seem to move around the

Pole-star every twenty-four hours, and why do they seem to go in a

direction opposite the movement of the hands of a clock? What do we

mean by “Polar constellations”?

_Topics for English Themes_--The Story of Queen Cassiopeia, King

Cepheus and their daughter, Andromeda; the story of the Dragon.

_Supplementary reading_--Storyland of the Stars, Pratt.

[Illustration: _A diagram of the principal stars of winter as seen in

early evening late in February._

To use the chart take it in the hands, face the Pole-star and hold

the chart above the head so that the side marked east will extend

eastward.]

THE WINTER STARS

_Teacher’s Story_

The natural time for beginning star study is in the autumn when the

days are shortening and the early evenings give us opportunity for

observation. After the polar constellations are learned, we are then

ready for further study in the still earlier evenings of winter, when

the clear atmosphere and beautiful blue of the heavens make the stars

seem more alive, more sparkling, and more beautiful than at any other

period of the year. One of the first lessons should be to instruct

the pupils how to draw an imaginary straight line from one star to

another, and to perceive the angles which such lines make when they

meet at a given star. A rule, or what is just as effective, a postal

card or some other piece of stiff paper which shows right-angled

corners, is very useful in this work. It should be held between the

eyes and the stars which we wish to connect, and thus make us certain

of a straight line and a right angle.

ORION (_o-ri´on_)

During the evenings of January, February and March the splendid

constellation of Orion takes possession of the southern half of the

heavens; and so striking is it that we find other stars by referring

to it instead of to the Pole-star. Orion is a constellation which

almost everyone knows; three stars in a row outline his belt, and

a curving line of stars, set obliquely below the belt, outline the

sword. Above the belt in the evening sky we can see the splendid

red star Betelgeuse (_bet-el-gerz_), and below the belt, at about

an equal distance, is the white star Rigel (_re-jel_). West of the

red star above, and east of the white star below, are two fainter

stars, and if these four stars are connected by lines, an irregular

four-sided figure results, which includes the belt and the sword.

In this constellation the ancients saw Orion, the great hunter,

with his belt and his sword; Betelgeuse was set like a glowing ruby

on his shoulder, and the white star Rigel was set like a spur on

his heel. Thus, stood the great hunter in the sky, with his club

raised to keep oft the plunging bull whose eye is the red Aldebaran

(_al-deb´a-ran_). And beyond him follows the Great Dog with the

bright blue star Sirius (_sir´i-us_) in his mouth, and the Little

Dog branded by the white star Procyon (_pro´si-on_). However, our

New England ancestors did not see this grand figure in the sky; they

called the constellation the Yard-ell or the Ell-yard.

[Illustration:

_Orion, the three large stars in a line forming the belt,

the curved line of smaller stars below forming the sword,

Betelgeuse above, Rigel below._

]

The three beautiful stars which make Orion’s belt are all double

stars; the belt is just three degrees long and is a good unit for

sky measurement. The sword is not merely the three stars which we

ordinarily see, but is really a curved line of five stars; and what

seems to be the third star from the tip of the sword and which

looks hazy, is in fact a great nebula. Through the telescope this

nebula seems a splash of light with six beautiful stars within it.

Betelgeuse is a brilliant red star, and is the first star in the

constellation to appear above the horizon. It is an old, old star

and is growing cold, as is shown by its red glow. It glows redder

sometimes than at others; it is so far away that we have not been

able to measure its distance from us surely, and it is receding from

us all the time. About fifteen minutes after Betelgeuse rises, and

after the belt and sword are in sight, a white sparkling star appears

at the southwest of the belt. This is Rigel, and this star, too,

is so far from us that we do not know the distance, and it is also

receding.

LESSON CCXXVII

ORION

_Leading thought_--Orion is one of the most beautiful constellations

in the heavens. It is especially marked by the three stars which form

Orion’s belt, and the line of stars below the belt which form the

sword.

_Method_--Place on the blackboard the outline of Orion as given in

the diagram. Ask the pupils to make the following observations in the

evening and give their report the next day.

_Observations_--1. Where is Orion in relation to the Pole-star?

2. How many stars in the belt of Orion? How many stars in the sword?

Can you see plainly the third star from the bottom of the sword?

3. Notice above the belt, about three times its length, a bright

star; this is Betelgeuse. What is the color of this star? What do we

know about the age of a star if it is red?

4. Look below the belt and observe another bright star at about the

same distance below that Betelgeuse is above. What is the color of

this star? What does its color signify? The name of this star is

Rigel.

5. Note that west of the red star above and east of the white star

below are two fainter stars. If we connect these four stars by lines

we shall make an irregular four-sided figure, fencing in the belt and

sword. Sketch this figure with the belt and sword, and write on your

diagram the name of the red star above and the white star below and

also the name of the constellation.

6. Which star of the constellation rises first in the evening? Which

last?

7. Write an English theme on the story of Orion, the great hunter.

_Supplementary reading_--Stories of Starland, Proctor; The Stars in

Song and Legend, Porter; Storyland of the Stars, Pratt.

ALDEBARAN AND THE PLEIADES

_Teacher’s Story_

[Illustration:

_Aldebaran in the V-shaped constellation called the Hyades.

This is a part of the constellation, Taurus._

]

Almost in a line with the belt of Orion, up in the skies northwest

from it, is the rosy star Aldebaran. This ruddy star, which is

not so red as Betelgeuse, marks the end of the lower arm of a

V-shaped constellation composed of this and four other stars. This

constellation is the Hyades (_hi´a-dez_). The Hyades is a part of

the constellation called by the ancients Taurus, the bull, and is

the head of the infuriated animal. Aldebaran is a comparatively near

neighbor of ours, since it takes light only thirty-two years to pass

from it to us. It gives off about forty-five times as much light as

does our sun; it lies in the path traversed by the moon as it crosses

the sky, and is often thus hidden from our view.

[Illustration:

_The Pleiades, a group of six small stars surrounded by a

misty light._

]

Although we are attracted by many bright stars in the winter sky, yet

there is a little misty group of stars, which has ever held the human

attention enthralled, and of which the poets of all the ages have

sung. These stars are called the Pleiades (_ple´ya-dees_); most eyes

can count only six stars in the constellation. There are nine stars

large enough to be seen through the telescope, and which have been

given names; but sky photography has revealed to us that there are

more than three thousand stars in this little group. Perhaps no stars

in the heavens give us such a feeling of the infinity of the universe

as do the Pleiades; for astronomers believe that they form a great

star system which is now being evolved from a nebula. The reason for

this belief is that these stars seem to be surrounded by a brilliant

mist which sometimes seems to be looped from one to another; and,

too, the stars are all in the same stage of development and have the

same chemical composition, and they are all moving together in the

same direction. These stars which look so close together to us are so

far apart really that our own sun and all its planets could roll in

between them and never be noticed. It would require several years for

light to travel from one of these stars in the Pleiades to another.

The Pleiades are so far from us that we cannot estimate the distance,

but we know that it takes light several hundred years to reach us

from them. There is a mythical story found in literature, that once

the unaided eye could see seven instead of six stars in the Pleiades,

and much poetic imagining has been developed to account for the “lost

Pleiad.”

LESSON CCXXVIII

ALDEBARAN AND THE PLEIADES

_Leading thought_--The Pleiades seem to be a little misty group of

six stars, but instead there are in it three thousand stars. Half way

between the Pleiades and Orion’s belt is Aldebaran, an ageing ruddy

star.

_Method_--Draw the diagram (p. 895) on the blackboard showing Orion,

Aldebaran and the Pleiades, and the lines B, C, D. Give an outline of

the observations to be made by the pupils, and let them work out the

answers when they have opportunity. Each pupil should prepare a chart

of these constellations.

_Observations_--1. Imagine a line drawn from Rigel to Betelgeuse and

then another line just as long extending to the west of the latter at

a little less than a right angle, and it will end in a bright, rosy

star, not so red as Betelgeuse.

2. What is the name of this star? Write it on your chart.

3. Can you see the figure V formed by Aldebaran and four fainter

stars? Sketch the V and show where in it Aldebaran belongs. This

V-shaped constellation is called the Hyades.

4. Imagine a line drawn from Orion’s belt to Aldebaran and extend it

to not quite an equal length beyond it, and it will end near a “fuzzy

little bunch” of stars which are called the Pleiades. Place the

Pleiades on your chart.

5. How many stars can you see in the Pleiades?

6. Why are they called the seven sisters?

7. How many stars in the Pleiades which are named, and how many does

photography show that there really are in the group?

8. How far apart from each other are the nearest neighbors of the

Pleiades?

9. What do the astronomers think about the Pleiades and why do they

think this?

THE TWO DOG STARS, SIRIUS AND PROCYON

_Teacher’s Story_

If a line from Aldebaran pass through the belt of Orion and is

extended about as far on the other side, it will reach the Great Dog

Star, following at Orion’s heels. This is Sirius, (_Sir´-e-us_) the

most brilliant of all the stars in our skies, glinting with ever

changing colors, sometimes blue, at others rosy or white. It must

have been of this star that Browning wrote:

“All that I know

Of, a certain star

Is, it can throw

(Like the angled spar)

Now a dart of red,

Now a dart of blue.”

[Illustration: _Orion and the Dog Stars._

B, Betelgeuse; R, Rigel; S, Sirius, the Great Dog Star; P, Procyon,

the Little Dog Star.]

Sirius is a comparatively young star, and is estimated by Proctor to

have a diameter of about twelve million miles or fourteen times that

of our own sun; it is only eight and one-half light-years away from

us and is the most celebrated star in literature. The ancients knew

it, the Egyptians worshipped it, Homer sang of it, and it has had its

place in the poetry of all ages.

Procyon, (_pro´-se-on_) the Little Dog Star, was so-called perhaps

because it trots up the eastern skies a little ahead of the

magnificent Great Dog Star; it gives out eight times as much light as

our sun, and is only ten light-years away from us. It has a fainter

companion about three or four degrees to the northwest of it.

LESSON CCXXIX

THE TWO DOG STARS

_Leading thought_--The Great Dog Star, Sirius, is the most famous

of all stars in the literature of the ages. The Two Dog Stars were

supposed by the ancients to be following the great hunter, Orion.

_Method_--Draw upon the board from the chart shown on this page, the

constellation of Orion with Sirius and Procyon. Ask the pupils to

note that after Orion is well up in the sky a straight line drawn

through Orion’s belt and dropping down toward the eastern horizon

ends in a beautiful white star, which is Sirius. And that if we draw

a line from Betelgeuse to Rigel from Rigel to Sirius and then draw

lines to complete a quadrangle, we shall find our lines meet at a

bright star just a little too far away to make the figure a square,

but making it somewhat kite-shaped instead. This is the Little Dog

Star, Procyon, and it has a twin star near it. After giving these

directions let the children make the following observations:

1. How do you find Sirius? Which rises first, Orion or Sirius?

2. What color is Sirius? Judging from its color what stage of

development do you think it is in?

3. Try and find out how large Sirius is compared with our sun and how

near it is to us.

4. Why is Sirius called the Great Dog Star? Is the Little Dog Star

nearer to the North Star than Sirius? Which is the brighter, the

Great Dog Star or the Little Dog Star? Can you see any fainter star

near Procyon?

5. Why is Procyon called the Little Dog Star?

6. Make a chart showing Orion and the two Dog Stars.

CAPELLA AND THE HEAVENLY TWINS

_Teacher’s Story_

[Illustration: _Capella in the constellation Auriga._]

Capella is nearer to the North Star than any other of the bright

stars and it comes very near belonging to the strictly polar

constellations, since it falls below the horizon only four hours

out of twenty-four. In composition it much resembles our sun, as

do all the bright yellow stars; but it is much larger; it gives

off one hundred and twenty times as much light as our sun, and it

is forty light-years away from us. Capella is always a beautiful

feature of the northern skies, being almost in the zenith during the

evenings of January and February. It is in a brilliant shield-shaped

constellation known as Auriga.

[Illustration:

_Gemini, the heavenly twins, the larger one is Pollux and the

other is Castor._

]

During the winter evenings we see two stars set like glowing eyes

almost in the zenith, and in a region of the sky where there are no

other bright stars. These twin stars are set just a little closer

together than are the pointers of the Big Dipper. To this brilliant

pair the ancients gave the names of Castor and Pollux. Pollux is the

brighter of the two and is the more southward in situation. Pollux

and Castor were two beautiful twin boys who loved each other so much

that, after they were dead, they were placed in the skies where they

could always be near each other. The twin stars are supposed to exert

a benign influence on oceans and seas and are, therefore, beloved

by sailors. Although they seem to us so near together, they are

separated by a space so great that we cannot conceive of it and they

are going in opposite directions.

Pollux is a yellow star, and supposed to be in the same stage of

development as our sun, while Castor is white and according to star

ages is young. When a boy says “By Jimminy,” he does not realize that

he is using an ancient expletive “By Gemini,” which is the Latin name

of these twin stars and was a favorite ancient oath, especially of

sailors.

LESSON CCXXX

CAPELLA AND THE HEAVENLY TWINS

_Leading thought_--There are, during the evenings of January and

February, three brilliant stars almost directly overhead. One of

these is Capella, the other two are the Heavenly Twins.

_Method_--Place on the board the part of the chart (p. 895) showing

the Big Dipper, Pole-star, Capella and the Twins. Draw a line, L,

from the pointers of the Big Dipper, and extend it to the Pole-star.

Draw another line, K, from the Pole-star at right angles to the line

L, and on the side away from the Big Dipper’s handle, and it will

pass through a large, brilliant, yellow star which is Capella. Ask

the pupils to imagine similar lines drawn across the sky, when they

are making their observations and thus find these stars, and to place

them on their charts, making the following observations:

1. What color is Capella, and how does its color compare with that of

our sun?

2. Is Capella as near to the Pole-star as the Big Dipper? Is it near

enough so that it never sets?

3. Can you see the shield-like constellation of which Capella is a

part? Do you know the name of this constellation?

4. How do you find the Heavenly Twins after you have found Capella?

5. Why are these stars called the Heavenly Twins? What is their Latin

name? What are the names of the two stars? Are these twins set nearer

together than the pointers of the Big Dipper?

6. How can you tell the Heavenly Twins from the Little Dog Star and

its companion?

7. Read in the books all that you can find about the Heavenly Twins.

Try and find if they are the same age, if they are as near together

as they seem, and if they are going in the same direction. What did

the ancient sailors think of these twin stars?

THE STARS OF SUMMER

To us, who dwell in a world of change, the stars give the comfort of

abidingness; they remain ever the same to our eyes and the teacher

should make much of this. When we once come to know a star, we know

exactly where to find it in the heavens, wherever we may be. A star

which a person knows during childhood will, in later life and in

other lands, seem a staunch friend and a bond, drawing him back to

his early home and associations.

[Illustration: _A chart of the brightest stars of summer, showing

their positions in early evenings of June. To find the stars hold the

chart above the head and face the north._]

The summer is an enticing season for making the acquaintance of eight

of the fifteen brightest stars visible in northern latitudes. Few

midsummer entertainments rival that of lying on one’s back on the

grass of some open space which commands a wide view of the heavens,

and there with a planisphere and an intermittently lighted candle

with which to consult it, learn by sight, by name and by heart those

brilliant stars which will ever after meet with friendly greeting our

uplifted eyes. To teach the children in a true informing way about

the stars, the teacher should know them, and nowhere in nature’s

realm is there a more thought-awakening lesson.

LESSON CCXXXI

THE BRIGHT STARS OF SUMMER

_Leading thought_--The stars which we see shining during summer

evenings are not the same ones that we see during the winter

evenings, except those in the polar constellations. There are eight

of the brilliant summer stars, which we should be able to distinguish

and call by name.

_Method_--Begin by the middle of May when the Big Dipper is well

above the Pole-star in the early evening, and when, therefore,

Regulus, Spica, Arcturus and the Crown are high in the sky. The

others may be learned in June, although July is the best month for

observing them. In teaching the pupils how to find the stars, again

instruct them how to draw an imaginary straight line from one star to

another and to observe the angles made by such lines connecting three

or four stars.

Place upon the blackboard the figures from the chart (page 901), as

indicated, leaving each one there until the pupils have observed and

learned it. Then erase and place another figure. In each case try to

get the pupils interested in what we know about each star, a brief

summary of which is given. Note that the observations given in the

lessons are for early in the evenings of the last of May, of June,

and of early July.

_Regulus_ (_reg´-u-lus_)

[Illustration:

_Regulus, the large star in the handle of the sickle._

]

Draw upon the blackboard from the chart (p. 901) the Pole-star, the

Big Dipper, the line G and the Sickle shown just below the outer end

of the line. Extend the line that passes through the pointers of the

Big Dipper to the North Star backward into the western skies; just

west of this line lies a constellation called the Sickle, and the

stars that form it outline this implement. The Sickle has a jewel at

the end of the handle, which is a white and diamond-glittering star

called Regulus. It is a great sun giving out one thousand times as

much light as our own sun, and this light reaches us in about one

hundred and sixty years. The Sickle is part of a constellation called

the Lion, and from which comes the shower of meteors which we see on

the evening of November 13th. Regulus is seen best in Spring.

_Arcturus_ (_ark-tu´rus_)

[Illustration: _Arcturus and the Big Dipper._]

Place on the blackboard the Big Dipper, the Pole-star and the line

E, Arcturus and the Crown. Extend the handle of the Big Dipper

following its own curve for about twice its length and it will end

in a beautiful, yellow star, the only very bright one in that region.

It is a thousand times brighter than our own sun, but its light does

not reach us for a hundred years after it is given off. Arcturus is

supposed to be one of the largest of all the suns, having a diameter

of several millions of miles. During the latter part of June and July

it is almost overhead in the early evening.

_The Crown_

[Illustration: _The Northern Crown._]

Between Arcturus and Vega, but much nearer the former, is a circle of

smaller stars that is called the Northern Crown, and which because of

its form is quite noticeable.

_Spica_ (_spi´-ka_)

Place on the blackboard the Big Dipper, the Pole-star, the line F and

Spica. To find Spica draw a line through the star on the outer edge

of the top of the bowl of the Big Dipper, through the star at the

bottom of the bowl next the handle, and extend this line far over to

the southwest, during the evenings of June and July. (See page 901)

In August, this star sets at ten o’clock. Spica is a white star, and

is the only bright one in that part of the sky. It is so far away

from us that the distance has never been measured. Spica is in the

constellation called the Virgin.

_Vega_ (_vee´-ga_)

[Illustration: _Vega and her train of five stars._]

Place on the blackboard the Pole-star, the Big Dipper, the lines H

and I and Vega with her five attendant stars, as shown in the chart.

Teach that these stars are the chief ones in the constellation called

_The Lyre_. To find Vega, draw a line from the Pole-star to the star

in the Big Dipper which joins the bowl to the handle. Then draw a

line at right angles to this (see chart lines H, I) and extend the

line I a little farther from the North-star than is the end star of

the Dipper handle; this line will reach a bright star, bluish in

color, which can always be identified by four smaller attendant stars

which lie near it and outline a parallelogram with slanting ends.

Vega is the most brilliant summer star that we see in the northern

hemisphere. It is a very large sun, giving out ninety times as much

light as our sun; it is so far away that it requires twenty-nine

years for a ray of light to reach us from it. Vega’s chief interest

for us, aside from its beauty, is that toward it our sun and all its

planets, including our earth, are moving at the rate of thirteen

miles per second.

_Antares_ (_an-ta´-rees_)

[Illustration: _Antares, a brilliant star in the southern skies._]

Add to the last diagram on the blackboard the line E, Arcturus, the

line B and Antares. To find this star, draw a line half way between

Arcturus and Vega from the Pole-star straight across the sky to the

south, and just above the southern horizon it will point to the

glowing star, Antares, in the constellation of the Scorpion. Also

a line drawn at right angles to the line connecting Altair with

its companions and extending toward the south will reach Antares.

Late June and July about ten o’clock in the evening is the best for

viewing this beautiful star. An interesting thing about Antares is

that, although it is red, it has, whirling around it, a companion

star which is bright green.

_Deneb, or Arided_ (_den´-eb_; _a´-ri-ded_)

[Illustration: _The Northern Cross, in the constellation of the

Swan._]

Erase from the last diagram Antares and the line B. Add to it the

lines C and D making a right angle at Deneb; and the Cross--the head

of which is Deneb, the foot ending near the letter on line L. This

star is at the head of the Northern Cross, which is a very shaky

looking cross and appears upside down in the eastern skies during

the evenings of June and July. Deneb is white in color and is a very

large sun, because it seems to us a bright star although it is so far

away from us that the distance has never been surely measured; but

it has been estimated that a ray of light would need at least three

hundred and twenty-five years to reach us from Deneb. It and the

cross are a part of the constellation of Cygnus, or the Swan.

_Altair_

[Illustration: _Altair in the constellation of the Eagle._]

Add to the last diagram on the board the lines L, K, Altair and its

two attendant stars and the Dolphin. Emphasize the fact that Altair

marks the constellation of Aquila, or the Eagle. This beautiful star

is easily distinguished because of its small companions, one on each

side, all three in a line. The three belong to a constellation called

the Eagle, and may be seen in early evening from June to December.

Altair, Deneb and Vega form a triangle with the most acute angle

at Altair. (See chart L, K.) Just northeast of Altair is a little

diamond-shaped cluster of stars called the Dolphin, which is a good

name for it, since it looks like a Dolphin, the fifth star forming

the tail. It is also called Job’s Coffin, but the reason for this is

uncertain, unless Job’s trials extended to a coffin which could not

possibly fit him. If the line C on the chart drawn from the Pole-star

to Deneb be extended, it will touch the Dolphin. Altair is always low

in the sky; it is a great sun giving off nearly ten times as much

light as our own sun; light reaches us from it in fifteen years.

[Illustration: _The Dolphin or Job’s Coffin._]

THE SUN

_Teacher’s Story_

To be retold to pupils.

If, only once in a century, there came to us from our great sun,

light and heat, bringing the power to awaken dormant life, to lift

the plant from the seed and clothe the earth with verdure, then it

would indeed be a miracle. But the sun by shining every day cheapens

its miracles in the eyes of the thoughtless. While it hardly comes

within the province of the nature-study teacher to make a careful

study of the sun, yet she may surely stimulate in her pupils a desire

to know something of this great luminous center of our system.

Our sun is a great shining globe about one hundred and ten times as

thick through as the earth, and more than a million times as large.

If we look at the sun in a clear sky, it is so brilliant that it

hurts our eyes. Thus, it is better to look at it through a smoked

glass, or when the atmosphere is very hazy. If we should see the sun

through a telescope, we should find that its surface is not one great

glare of light but is mottled, looking like a plate of rice soup, and

at times there are dark spots to be seen upon its surface. Some of

these spots are so large that during very “smoky weather” we can see

them with the naked eye. In September, 1908, a sun-spot was plainly

visible; it was ten thousand miles across, and our whole world could

have been dropped into it with a thousand miles to spare all around

it. We do not know the cause of these sun-spots, but we know they

appear in greater numbers in certain regions of the sun, above and

below the equator. And since each sun-spot retains its place on the

surface of the sun, just as a hole dug in the surface of our earth

would retain its place, we have been able to tell by the apparent

movement of these spots how rapidly and in which direction the sun

is turning on its axis; it revolves once in about twenty-six days

and, since the sun is so much larger than our earth, a spot on the

equator travels at a rate of more than a mile a second. There is a

queer thing about the outside surface of the sun--the equator rotates

more rapidly than the parts lying nearer the poles; this shows that

the sun is a gaseous or liquid body, for if it were solid, like

our earth, all its parts would have to rotate at the same rate. At

periods of eleven years the greatest number of spots appear upon the

sun.

Another interesting feature of the sun is the tremendous explosion of

hydrogen gas mixed with the vapors of calcium and magnesium, which

shoot out flames from twenty-five thousand to three hundred thousand

miles high, at a rate of speed two hundred times as swift as a rifle

bullet travels. Think what fireworks one might see from the sun’s

surface all the time! One would not need to wait until the Fourth of

July for fireworks there. These great, explosive flames can be seen

by the telescope when the moon eclipses the sun, and they have been

analyzed by means of the spectroscope. Besides these magnificent

explosions, there is surrounding the sun a glow which is brighter

near the sun’s surface and paler at the edges; it is a magnificent

solar halo, some of its streamers being millions of miles long. This

halo is called the Corona, and is visible during total eclipses. By

means of the spectroscope we know that there are about forty chemical

elements in the sun, which are the same as those we find upon our

earth.

As the sun weighs 330,000 times as much as the earth, the force of

gravity upon its surface is twenty-seven and two-thirds times as

much as it is here. A letter which weighs an ounce here would weigh

almost a pound and three quarters on the sun; and a man of ordinary

size in this world would weigh more than two tons there, and would be

crushed to death by his own weight. Find how much your watch, your

book, your pencil, your baseball, your football would weigh on the

sun.

OUR SUN AND ITS FAMILY

First of all we shall have to acknowledge that our great, blazing sun

is simply a medium-sized star, not nearly so large as Vega, nor even

as large as the Pole-star; but it happens to be our own particular

star and so is of the greatest importance to us. The sun has several

other worlds, more or less like our own, revolving around it on

almost the same level or plane in which our world revolves, but some

of these worlds are much nearer the sun and others much farther away

than ours. Nearest of all is Mercury, but it is not half so thick

through as our earth, and it is so close to the sun that it circles

around in 88 days; that is, its year is only 88 days long. Next comes

Venus, almost as large as the earth, with a year 225 days long; next

comes our earth, which completes its year in 365 days; next beyond

us is Mars, a little more than half as thick as the earth and with a

year 687 days long; beyond Mars is a group of small planets which are

not large enough to be seen with the telescope, but we know that one

of the largest of the group is only 490 miles through; beyond this

mysterious swarm of little worlds is great Jupiter almost ten times

as thick through as the earth, and it is so far away that it does not

circle about the sun but once in 11 years; beyond great Jupiter comes

Saturn, not quite ten times the diameter of the earth and so far from

the sun that it takes 29½ years for it to move around its orbit;

beyond Saturn is Uranus, only about four times as thick through as

our world, and it has a year 84 years long; but the outermost of

all our sun’s planets is Neptune, a little larger than Mars, but

so far from the sun that 165 years are required for it to complete

its circle. Just think of a spring or a winter 41 years long! If

Methuselah had lived on Neptune, he would have died before he was

five and one-half years old.

Almost all of the Earth’s sister planets are better off for moons

than she; neither Venus nor Mercury has any moons. Mars has two

moons, Jupiter five and Saturn has nine besides some splendid rings;

and a queer thing about one of Saturn’s moons is that it revolves in

an opposite direction from the others. Uranus has four moons, while

Neptune is not any better off than we are, unless, there are some we

have not been able to discover because they are so far away.

One peculiar thing about all of the planets of the sun’s family

and all of their moons is that they all shine by reflecting the

light of the sun, and none of them are hot enough to give off light

independently; but these sister worlds of ours are so near us that

they often seem larger and brighter than the stars, which are true

suns and give off much more light than our own sun. After a little

experience the young astronomer learns to distinguish the planets

from the true stars; the planets always follow closely the path of

the sun and moon through the sky; they often seem larger and brighter

than the true stars and do not twinkle so much. The so-called morning

and evening stars are other planets of our sun’s family and are not

stars at all.

Dr. Simon Newcomb in his delightful book, “Astronomy for Everybody,”

gives the best illustration to make us understand the place of our

sun and its planets and its relation to the stars in space. He

explains that if here in the Atlantic States we should make a model

of our solar system by putting an apple down in a field to represent

the sun; then our earth could be represented by a mustard seed forty

feet away revolving around the apple; and Neptune, our outermost

planet, could be represented as a small pea circling around the apple

at the distance of a quarter of a mile. Thus, our whole solar system

could be modeled in a field one-half mile square, except for comets

which might extend out in their long orbits for several miles. But to

find the star nearest to our earth, the star that is only four and

one-half light-years away from us, we should have to travel from this

field across the whole of North America to California, and then take

a steamer and go out into the Pacific Ocean before we should reach

our nearest star neighbor, which would be another sun like our own

and be represented by another apple.

COMETS

Besides planets and stars there are in space other bodies spinning

around our great sun, and following paths shaped quite differently

than those followed by our earth and its sister planets. We move

around the sun nearly in a circle with the sun at the center, but

these other heavenly bodies swing around in great ellipses, the sun

being near one end of the ellipse and the other end being out in

space beyond our farthest planet. These bodies do not revolve around

the sun in the same plane as our world and the other planets, and

indeed they often move in quite the opposite direction. The most

noticeable of these bodies whose race-track around the sun is long

instead of circular are the comets, and we know that some of these

almost brush the sun when turning at the end of their course. The

astronomers have been able to measure the length of the race-tracks

of some of the comets and thus tell when they will come back. Encke’s

comet, named after the German astronomer, makes its course in three

and one-half years and this is the shortest period of any we know.

There are about thirty comets whose courses have been thus measured;

the longest period belongs to Halley’s comet, which makes such a long

trip that it comes back only once in seventy-six years; but there

are other comets which astronomers are sure travel such long routes

that they come back only once in hundreds or even thousands of years.

About nine hundred comets have been discovered, many of them so small

that they can only be seen through the aid of the telescope; and

it has been found that in one instance, at least, three comets are

racing around the sun on the same track.

A comet is a beautiful object, usually having a head which is a point

of brilliant light and a long, flaring tail of fainter light, which

always extends out from it on the side opposite the sun. The head of

a comet must be nearly twice as thick through as the earth in order

to be large enough for our telescopes to discover it. Some of the

comet heads have been measured, and one was thirty-one times, and

another one hundred and fifty times, as wide as our earth. If the

heads are this large, imagine how long the tails must be! Some of

them are far longer than the distance from our earth to the sun.

The head of a comet is supposed to be a mass of gas which is made to

glow by the sun’s heat, and is so volatile and thin that the heat

evaporates it. In fact, this gas has so little weight that light

can push it; one would never believe that light could push anything

because we cannot feel it strike against us; but the physicists have

found that it does push, and by pushing against the particles of the

gas of comets it sends them out into a streamer away from the sun,

just as the heat pushes out a flaring cloud of steam from the spout

of a teakettle.

Another thing we know about comets is that they are not able to hold

together, but break into pieces; and these pieces become cold out

in space and condense and harden into lumps of metallic stone; and

these lumps, each one whirling, follows the same track that the comet

followed. If a comet should break into many pieces it would make a

whole flock of these lumps all going in the same direction and in the

same path about the sun.

Since comets are moving around the sun in every direction, it is

possible that the earth may sometime meet one; and if this proves to

be a “head on collision” there are those who prophesy that there will

be no people left to tell the story; but the tails of comets are so

thin and ethereal that our earth actually passed through one once,

and no one but the astronomers knew anything about it.

SHOOTING STARS

When we look up during an evening walk and see a star falling through

space, sometimes leaving a track of light behind it, we wonder which

of the beautiful stars of the heavens has fallen. But astronomers

tell us that no real star ever fell, but that what we saw was a

lump of the matter of which worlds and comets are made; and it was

following its own swift path around the sun, when by chance it

crossed our earth’s path, and was drawn toward us by that mysterious

power called gravitation, which makes us fall down if we lose our

balance, and which also made this bit of world-stuff fall to earth

when it came so near us that its balance was disturbed. Although

this shooting star was just a dark, cold lump of metal, too small

for us to see, yet it was moving so swiftly along its path around

the sun that the friction caused by its passing through our air,

lighted it and burned it up, just as a match scratched on sandpaper

lights and burns; as soon as it blazed we saw it and said, “There

is a shooting star!” Sometimes the lump is so big that it does not

have time to burn up while passing through the hundred miles or more

of our atmosphere, and what is left of it strikes the earth usually

with such force as to bury itself deep in the soil. Such lumps are

called “meteoroids” before they fall and “meteors” while plunging

white-hot through the air, but when they reach our earth we call what

is left of them “meteorites.” There are, in museums, many meteorites

of this so-called stone, which is largely iron. Chemists find no new

metals or elements in these strangers from space, but they do find

new kinds of chemical partnerships and combinations. Some of these

meteorites weigh hundreds of pounds, one in the Yale Museum weighing

1635 pounds. It surely would not be safe for a person to be on the

spot where and when one of these meteorites strikes the earth; but

there are so few of the meteors large enough to last until they

become meteorites, that we may safely continue to enjoy the sight

of shooting stars. If it were not for the air that wraps our globe,

like a great, kindly blanket, and by its friction sets fire to the

meteors and destroys them, no one could live on this earth because

we all should be pelted to death. Prof. Newton estimated that every

twenty-four hours our world meets seven millions of these shooting

stars, some of them no larger than shot and others weighing tons.

THE RELATION BETWEEN COMETS AND METEORS

It has been discovered that many of the shooting stars are gathered

in great flocks and move about the sun in elongated paths, like the

comets. We have learned the times of year when the path our earth

follows comes close to these flocks of meteors which are flying

around the sun like birds. One of these flocks is straggling, and

we begin to meet it about the end of July and reach the center of

the crowd on August 10th, and then continue to take stragglers until

the last of August. We can see the point where we meet this flock

of meteors, if we look for it in the direction of the constellation

Perseus (see planisphere). On November 13th, we meet another flock

which we find in the direction of the constellation Leo, of which

the great star Regulus is the heart (see chart); but this flock is

usually all in a bunch and we pass it in two days. Once there was

a splendid flock which our world met every thirty-three years, and

we took so many stragglers from it that our skies were filled with

shooting stars, and ignorant people were greatly frightened; but for

some reason, this flock has changed its path and we looked in vain

for the great display of fireworks which was due to occur in 1899.

While we know from observation that the flocks of shooting stars,

which make our star showers, are just broken pieces of comets

which once traveled the same path, yet it does not follow that all

our shooting stars are comet fragments. Prof. Elkins has shown by

photographing meteors that some of them must be wanderers in the vast

spaces which lie between the stars.

[A]THE RELATION BETWEEN THE TROPIC OF CANCER AND

THE PLANTING OF THE GARDEN

By JOHN W. SPENCER

_A story to be read to the pupils_

In years gone by, many farmers had a favorite phase of the moon when

they planted certain crops, usually spoken of as the “dark” or the

“light” of the moon. I once knew a woman who picked her geese by the

“sign of the moon.” Hogs were butchered in the “light” of the moon,

and then the pork would not “fry away” so much in the skillet. It

is true some pork from some hogs wastes faster than that of others,

but the difference is due to the kind of food given the hogs. Many

farmers hold to those old superstitions yet, but the number is much

less now than twenty-five years ago. I wish I might impress on you

young agriculturists that the moon has no influence on plant life, or

pork, or geese, but the position of the sun most decidedly has. We

have some plants that had best be planted when the sun’s rays strike

the state of New York slantingly, which means in early spring or

late fall. We have other plants that should not be put in the open

ground until the rays of the sun strike the state more direct blows,

which means the hotter weather of summer. If I were in close touch

with you pupils, I should be glad to tell some things that happen to

three young friends of mine, hoping that thereby my statement might

give the boys and girls an interest in three geographical lines

concerning the tropics, and lead them to find their location on the

map, particularly when later they learn what happens to my three

young friends, whom we will call by the following names: There is one

in Quito, Ecuador, of whom we will speak as Equator Shem; the one on

the Island of Cuba is named Tropic of Cancer Ham; and the other in

San Paulo, Brazil, answers to the name of Tropic of Capricorn Japhet.

What happens to these three boys, Shem, Ham and Japhet, is this.

At certain times of the year they have no shadow when they go home

for dinner at noon. This state of affairs is no fault of theirs. It

is not because they are too thin to make shadows. It is due to the

position of the sun. If the boys should look for that luminary at

noon, they would find it as directly over their heads as a plumb

line. It is a case of direct or straight blows from rays of the

sun, and, oh, how hot--hotter than any Fourth of July the oldest

inhabitant can remember! These three boys are not hit squarely on

the head on one and the same day. Each is hit three months after the

other. The first boy to be hit this year in the above manner will be

the Equator Shem. The time will be during the last half of March. Can

any of my young friends in this grade tell me the exact day of March

that Equator Shem has no shadow? If no one of you can answer that

question at this time, you had best talk it over with your friends,

and bring your answers tomorrow. It happens at a time when our days

are of about equal length.

Another thing about this particular day is that our almanacs call it

the first day of spring. All because no boy or anything else has a

shadow on the equator at noon time. People and bluebirds and robins

in the state of New York will see squalls of snow about that time,

and there will be some freezing nights. But after the first day of

spring the cold storms do not last so long, as was the case during

December, January, and early February, when the sun’s rays hit us

with very glancing blows. Watch to see how much faster the sun melts

the snow on the last days of March than it did at Christmas time.

The light is also stronger and brighter, and plants in greenhouses

and our homes have more life, and are not so shiftless, so to speak.

Even the hens feel the influence, for they begin to lay more eggs

and cackle, and down goes the price of eggs. Do not forget to learn

what day in March spring begins, when the Equator boy finds it so hot

that he would like to take off his flesh, and sit in his bones. After

a few days, Equator Shem will find he again has a shadow at noon. A

short one it is true, but it will get longer and longer each day. Now

his shadow will be on the south side of him. Is this a queer thing to

happen? On which side of you is your noon-time shadow? I will give

every one of you a red apple that finds it anywhere but on the north

side of him at twelve o’clock. Every time the sun shines at noon,

watch to find your old uncle in the wrong, and thereby get the apple.

Each day that the shadow of Equator Shem becomes longer and longer,

the noon-day shadow of Tropic of Cancer Ham, living on the Island of

Cuba, will be getting shorter and shorter, until at last there comes

a day during the last of June that he, too, will have no shadow, and

the almanac says that that day is the beginning of summer.

Now it will be the turn of the Tropic of Cancer Ham, on the Island of

Cuba, to say the weather is hotter than two Fourths of July beat into

one, and he too will wish that he could take off his flesh, and sit

in his bones. Everybody in the state of New York will say that the

first summer day is the longest day of the year. It is on this day

that Equator Shem will have as long a shadow as _he_ ever had in his

life. No United States boy will ever be without a shadow at noon so

long as he remains in his own country. When the eight o’clock curfew

bell says it is time for boys and girls to go to bed, it will yet be

light enough to read the papers. The sun not only sets late on that

first summer day, but it appears early next morning. What a beautiful

spectacle a sunrise in June is! Men of wealth will pay thousands of

dollars for pictures showing its glory, yet I suppose that not one

boy in five hundred ever saw the beauty of the birth of a new day in

the sixth month of the year, and with no price of admission at that.

For only one day do the sun’s rays fall directly on top of the head

of Tropic of Cancer Ham, who lives on the Island of Cuba--just for

one day, after which the up and down rays travel back towards the

Equator Shem. On the twenty-first of September Shem again has no

shadow at noon, and the almanac makers say that is the last day of

summer, and tomorrow will be the first day of autumn. Again it is

very hot where Shem lives, but the alligators and monkeys and the

parrots do not seem to mind it. Where do the up and down rays of

the sun go next? They keep going south, hunting for the boy named

Tropic of Capricorn Japhet, to warm _him_ up, as was the case with

the boys in Cuba and at the Equator. The up and down rays do not

find the top of the head of the lad in the City of San Paulo, Brazil

until the last part of December, just four days before Christmas,

and then the almanac says this is the beginning of winter, and the

shorter days of the year, when we in the state of New York light the

lamp at five o’clock in the afternoon. Now, my boys and girls, do

you understand why we have a change of seasons? Do you understand

that the sun changes his manner of pitching his rays at us? That in

winter, when he is over the head of the Tropic of Capricorn Japhet in

San Paulo, and making summer on that part of the earth, to us people

in the north, in the State of New York, he pitches only slanting rays

that do not hit us hard, and have but little power? Thus you will

see that the rays of the sun that strike the earth direct blows,

swing back and forth like a pendulum, year after year, and century

after century, coming north as far as Tropic of Cancer Shem, but no

farther, and then swinging south as far as the boy named Tropic of

Capricorn Japhet, and no farther, just stopping and swinging back

again towards the north.

FOOTNOTE:

[A] A portion of a letter to apprentice gardeners from Uncle John,

published as a supplement to the Home Nature-Study Course Leaflet,

for April-May, 1907.

THE ZODIAC AND ITS SIGNS

_Teacher’s Story_

To be retold to pupils.

The mysterious symbols of the Zodiac on the first pages of almanacs

are always a source of wonder and awe to children, and remain a

life-long mystery to most people except fortune tellers; and yet the

Zodiac is the simplest thing in the world to understand. However, the

lesson should not be given until after the children have had their

lessons on the sun and the shadow-stick, and also the lessons on the

stars.

The ancients who believed the earth stood still and the sun moved

around it, noticed inevitably that the path through the heavens

pursued by the sun reached in summer a point farther north and

higher up than in the winter, and they naturally wished to map this

path, so as to fix it in their minds and writings. Nothing could

be easier, for there in the skies were the eternal stars always

following the same fixed path through the heavens and never wobbling

up and down like the sun. So they chose the constellation which

marked the highest point in the sun’s path for each month, and these

constellations might be likened to a stairway with six steps down

toward the south and six steps up toward the north, the highest

stair being reached by the sun in June, for then the sun is highest

in the heavens and the farthest north. So beginning in June with

Cancer, (the Crab), which is high in the heavens, it steps down to

Leo, (the Lion) in July, takes another step lower to the Virgin in

August, another down to the Scorpion in September, and comes to the

lowest step of all, Sagittarius, (the Archer), in November; for

at the last of November, the sun’s path reaches its lowest point

farthest south in the heavens and then the days are shortest. But in

December it begins to climb and takes a short step up to Capricornus,

(the Goat), in January it rises to Aquarius, (the Water Carrier), and

in February rises another step to Pisces, (the Fishes). In March it

reaches up to Aries, (the Ram), in April attains Taurus, (the Bull),

and in May reaches Gemini, (the Twins), which step is almost as high

and as near to the North Star as was the Cancer, where the journey

began the June before.

It may be difficult for the pupils to learn to know all these

constellations, as some of them are not very well marked; however, if

they wish to learn them they can do so by the use of the planisphere.

Some of the Zodiac constellations are marked by brilliant stars which

have already been learned. Regulus is the heart of Leo, the Lion;

Spica which means “ear” is the ear of wheat which the Virgin is

holding in the constellation Virgo. Red Antares lies in the Scorpion;

and the Milk Dipper, which is shaped like the Big Dipper, but

smaller, marks Sagittarius. Red Aldebaran is the fiery eye of Taurus,

the Bull, while the Gemini, or Twins, are the most conspicuous of

the stars in the evening skies of February and March. It should

be noted, however, that at the present day, owing to the peculiar

movement of our earth, the path of the sun in climbing up and down

these constellation steps is not quite the same as it seemed to the

ancients.

[Illustration: _From Todd’s New Astronomy._]

THE RELATIONS OF THE SUN TO THE EARTH

_Teacher’s Story_

“_Whether we look or whether we listen,

We hear life murmur or see it glisten._”

--LOWELL.

All this murmuring and glistening life on our earth planet has

its source in the great sun which swings through our skies daily,

sending to us through the friendly ether his messages of light

and warmth--messages that kindle life in the seed and perfect the

existence of every living organism, whether it be the weed in the

field or the king on his throne.

At sunrise this heat which the sun sends out equally at all times

of day and night, is tempered when it reaches us because it passes

obliquely through our atmosphere-blanket, and thus traverses a

greater distance in the cooling air. The same is true at sunset; but

at noon, when the sun is most directly over our heads its rays pass

through the least possible distance of the atmosphere-blanket and,

therefore, lose less heat on the way. It is true that often about

three o’clock in the afternoon is the hottest period of the day, but

this is because the air-blanket has become thoroughly heated; but we

receive the most heat directly from the sun at noon.

The variations in the time of the rising and the setting of the sun

may be made a most interesting investigation on the part of the

pupils. They should keep a record for a month in the winter; and with

this as a basis, use the almanac to complete the lesson. Thus, each

one may learn for himself which is the shortest and which the longest

day of the year. There is a slight variation in different years; the

shortest day of the year when this lesson was written, as computed

from a current almanac, was the 22d of December; it was nine hours

and fourteen minutes long. The longest day of the year was the 22d

of June, and it was fifteen hours and six minutes in duration. On

the longest day of the year the sun reaches its farthest point north

and is, therefore, most nearly above us at mid-day. On the shortest

day of the year, the sun reaches its farthest point south and is,

therefore, farther from the point directly above us at mid-day than

during any other day of the year.

Also the movement of the sun north and south is an interesting

subject for personal investigation, as suggested in the lesson.

Through quite involuntary observation, I have become so accustomed

to the arc traversed by the points of sunrise as seen from my home,

that I can tell what month of the year it is, by simply noting the

place where the sun rises. When it first peeps at us over a certain

pine tree far to the south, it is December; when it rises over the

reservoir it is February or October; and when it rises over Beebe

pond it is July. Only at the equinox of spring and fall does it rise

exactly in the east and set directly in the west. Equinox means equal

nights, that is, the length of the night is equal to that of the day.

So vast is the weight of the sun that the force of gravity upon

its surface is so great that even if it were not for the white-hot

fireworks there so constantly active, we could not live upon it, for

our own weight would crush us to death. But this multiplying the

weight of common objects by twenty-seven and two-thirds to find how

much they would weigh on the sun is an interesting diversion for

the pupils, and incidentally teaches them how to weigh objects, and

something about that mysterious force called gravity; and it is also

an excellent lesson in fractions.

LESSON CCXXXII

THE RELATION OF THE SUN TO THE EARTH.

_Leading thought_--The sun which is the source of all our light and

heat and, therefore, of all life on our globe travels a path that

is higher across the sky in June than the path which it follows in

December, and hence we experience changes of seasons. The lesson

should be given to the pupils of the upper grades and should be

correlated with reading, arithmetic and thinking.

_Observations_--1. What does the sun do for us?

2. At what time of the day after the sun rises do we get the least

heat from it? What hour of the day do we get the most heat from it?

3. Is the sun equally hot all day? Why does it seem hotter to us at

one time of the day than at another?

4. At what hour does the sun rise and set on the first of the

following months; February, March, April, May and June?

5. Which is the shortest day of the year, and how long is it?

6. Which is the longest day of the year, and how many hours and

minutes are there in it?

7. What day of the year is the sun nearest a point directly over our

heads at mid-day?

8. Which day of the year is the sun at mid-day farthest from the

point directly above our heads? Explain why this is so.

9. Standing in a certain place, mark by some building, tree or other

object just where the sun rises in the east and sets in the west on

the first of February. Observe the rising and setting of the sun from

the same place on the first day of March and again on the first of

April. Does it rise and set in the same place always or does it move

northward or southward?

10. Is the sun farthest south on the shortest day of the year? If so,

is it farthest north on the longest day of the year?

11. At what time of the year does the sun rise due east and set due

west?

12. The sun is so much larger than the earth that its force of

gravity is twenty-seven and two-thirds times that of the earth. How

much would your watch weigh if you were living on the sun? How much

would you yourself weigh if you were there?

13. _Experiment. A shadow stick_--Place a peg two or three inches

high upright in a board and place the board lengthwise on the sill of

a south window or where it will get the south light. Note the length

cast by the shadow of the peg during a sunny day and draw a line with

pencil or chalk outlining the tip of the shadow of the stick from 9

a. m. to 4 p. m. Make a similar outline a month later and again a

month later and note whether the shadow traces the same line during

each of these days of observation. Note especially the length of the

shadow at noon.

[Illustration: _A shadow-stick._]

Another excellent observation lesson for teaching the fact that the

sun travels farther south in the winter, is to measure the shadow

of a tree on the school grounds at noonday once a month during the

school year. The length of the tree shadow can be measured from the

base of the tree trunk, a memorandum being made of it.

14. When does the stick or tree cast its longest shadow at noon--in

December or February? February or April? April or June? Why?

_Topics for English themes_--The size and distance of the sun. The

heat of the sun and its effect upon the earth. What we know about the

sun spots. Our path around the sun.

_Supplementary reading_--Starland, Ball; The Earth and Sky, Holden.

LESSON CCXXXIII

HOW TO MAKE A SUNDIAL

_Method_--The diagram for the dial is a lesson in mechanical drawing.

Each pupil should construct a gnomon (_no-mon_) of cardboard, and

should make a drawing of the face of the dial upon paper. Then the

sundial may be constructed by the help of the more skillful in the

class. It should be made and set up by the pupils. A sundial in the

school grounds may be made a center of interest and an object of

beauty as well.

[Illustration: _A sundial made by pupils._]

_Materials_--For the gnomon a piece of board a half inch thick and

six inches square is required. It should be given several coats of

white paint so that it will not warp. For the dial, take a board

about 14 inches square and an inch or more thick. The lower edge may

be bevelled if desired. This should be given three coats of white

paint, so that it will not warp and check.

[Illustration: _The gnomon._]

_To make the gnomon_--The word gnomon is from a Greek word meaning

“one who knows.” It is the hand of the sundial, which throws its

shadow on the face of the dial, indicating the hour. Take a piece

of board six inches square, and be very sure its angles are right

angles. Let s, t, u, v represent the four angles; draw on it a

quarter of a circle from s to u with a radius equal to the line

vs. Then with a cardboard protractor, costing fifteen cents, or by

working it out without any help except knowing that a right angle is

900, draw the line vw making the angle at x the same as the degree of

latitude where the sundial is to be placed. At Ithaca the latitude is

42°, 27′ and the angle at x measures 42° 27′. Then the board should

be cut off at the line vw, and later the edge sw may be cut in some

ornamental pattern.

_To make the dial_--Take the painted board 14 inches square and find

its exact center, y. Draw on it with a pencil the line A A″ a foot

long and one-fourth inch at the left of the center. Then draw the

line B B″ exactly parallel to the line A A″ and a half inch to the

right of it. These lines should be one-half inch apart--which is just

the thickness of the gnomon. If the gnomon were only one-fourth inch

thick, then these lines should be one-fourth inch apart, etc.

With a compass, or a pencil fastened to a string, draw the

half-circle A A′ A″ with a radius of six inches with the point C for

its center. Draw a similar half-circle B B′ B″ opposite with c′ for

its center. Then draw the half-circle from D, D′, D″, from c with a

radius of five and three-quarter inches. Then draw similarly from c′

the half-circle E, E′, E″. Then draw from c the half-circle F, F′, F″

with a radius of five inches and a similar half-circle G, G′, G″ from

c′ as a center.