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, Arpil, 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?

IO. 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?

II.

west?

At what time of the year does the sun rise due east and set due

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

A shadow-stick.

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.

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.

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.

To make the gnomon-The word gnomon is from a Greek word meaning "one who knows." It is the hand of

The gnomon.

u

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 90°, 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 onefourth 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 onefourth 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 halfcircle G, G', G" from c' as a center.

Find the points M, M' just six inches from the points F, G; line J, K through M, M' exactly at right angles to the line A, A'.

draw the This will

mark the six o'clock point so the figures VI may be placed on it in the space between the two inner circles. The noon mark XII should be placed as indicated (the "X" at D, F, the "II" at E, G). With black paint outline all the semi-circles and figures.

To set up the sundial-Fasten the base of the gnomon by screws or brads to the dial with the point s of the gnomon at F, G, and the point v of the gnomon at M, M', so that the point W is up in the air. Set the dial on some perfectly level standard with the line A, A" extending exactly north and south. If no compass is available, wait until noon and set the dial so that the shadow from W will fall exactly between the points A, B, and this will mean that the dial is set exactly right. Then with a good watch note the points on the arc E, K', on which the shadow falls at one, two, three, four, and five o'clock: and in the morning the points on the arc J'D on which the shadow falls at seven, eight, nine, ten and eleven o'clock. Draw lines from M to these points, and lines from M' to the points on the arc E K'. Then place the figures on the dial as indicated in the spaces between the two inner circles. The space between the two outer circles may be marked with lines indicating the half and quarter hours. The figures should be outlined in pencil and then painted with black paint, or carved in the wood and then painted.

Twilight, twilight of the west,
Sky-lines fading into rest,
Cloud-bars lying far and slight,
Shadows sinking into night,-
O moon, ye moon, so faint and still,
Hanging, hanging as ye will
Low along the western sky,
Far and far and yet so nigh
A finger's breadth within the sheen
And silent shoreless vasts between-
Thy aching heart is long ages lost,
And clear and calm as film of frost,
Ye know no longer strain or stress,
All passionless and passionless.

-From "The New Moon," L. H. BAILEY.

The moon is in more senses than one an illuminating object for both the earth and the skies. As a beginning for earth study it is an object lesson, illustrating what air and water do for our world and incidentally for us; while as the beginning of the study of astronomy, it is the largest and brightest object seen in the sky at night; and since it lies nearest us, it is the first natural step from our world to outer space.

The moon is a little dead world that circles around our earth with one face always towards us, just as a hat-pin thrust into an apple would keep the same side of its head always toward the apple no matter how rapidly the apple was twirled. As we study the face of the moon, thus always turned toward us, we see that it is dark in some places and shining in others, and some ignorant people have thought that the dark places are oceans and the light places, land. But the dark portions are simply areas of darker rocks, while the lighter portions are yellowish or whitish rocks. The dark portions are of such a form that people have imagined them to represent the eyes, nose and mouth of a man's face; but a far prettier picture is that of a woman's uplifted face in profile. The author has a personal feeling on this point, for as a child she saw the man's face always and thought it very ugly and, moreover, concluded that he chewed tobacco; but after she had been taught to find the face of the lady, the moon was always a beautiful object to her.

The moon is a member of our sun's family, his granddaughter we might call her if the earth be his daughter; and since the moon has no fires or light of its own, it shines by light reflected from the sun and, therefore, one-half of it is always in shadow. When we see the whole surface of the lighted half we say the moon is full; but when we see only half of the