In naming over the stars of the first magnitude—that is, the stars that shine the brightest—there is one star I did not mention and yet as we see it it is brighter than all the other stars put together.

This great star is our Sun and since we owe everything we possess on Earth to him—light, heat, power and even life itself—he should and does stand in a class by himself, though after all he is just as much of a fixed star as the North Star, the Dog Star, or any of the thousands of other stars which we see as mere points of light in the sky.

How to See the Sun.—You must never look directly at the Sun with the naked eye, for he is so powerful that his light will injure your sight for all time.

There are several ways, though, to observe the Sun without danger to your eyes and as all of these are simple and cost nothing you can easily try them. The most common way is to take a bit of window glass, say an inch square, and smoke one side of it over the flame of a candle, as shown in Fig. 28.

When this blackened glass is held closely to the eye, as shown in Fig. 29, and the latter is directed toward the Sun, a little circle of light will appear on the film of smoke and the surface of the Sun may be examined at length and without the least danger.

A decided improvement over the smoked glass idea is to use a piece of red, or a piece of yellow glass, as an eyepiece, or, better, place the red and yellow glasses together and bind the edges with paper. Another plan to see the Sun without injury to the eyes is to make a hole with the point of a needle in a visiting card and look through the hole directly at the Sun.

A still better view of the Sun can be obtained if a pinhole telescope is used. A telescope of this kind can be easily made without tools, metals or lenses. It is described and pictured in Chapter IX.

To observe the Sun hold the pinhole end of the tube closely to your eye, to cut off all the outside light, and sight the tube so that the Sun shines directly into your eye through the pinhole, and you will get a very brilliant view of the great yellow star which we call the Sun.

What the Sun is Made of.—When a candle is lit the wax of which it is made begins to melt and this is drawn up the wick where it is changed into gas and the burning gas forms the flame.

The flame of a candle is made up of four parts, which are really layers of heated gas surrounding the wick, as shown in Fig. 30. In the center of the flame is the wick; the first layer of gas is at the bottom of the flame and this gives a greenish-blue light; the second layer is the dark and cool part of the flame; the third layer is a cone of heated gas which gives out the bright light, and surrounding this cone is a faint blue light which can just be seen.

We know, of course, what the candle is made of and we also know why it burns and in a way how it gives off light and heat because we have examined it closely, but if we could get no nearer a candle flame than a quarter of a mile it is very doubtful if we could ever be able to learn anything about the real source of the flame—that is its greasy wick.

It is much the same with the Sun, for we can only examine it at a great distance and know it by its action on our senses, for the flaming layers of the Sun are so bright that no one ever saw through them, so the real source of its light and heat—the core of the Sun—remains unknown. Fig. 31 shows the Sun as seen with a field glass.

Since the Sun gives out light and heat it is easy to believe that it is a great ball of very hot gases and from what astronomers have learned of him with their wonderful instruments this idea seems to be pretty well founded.

The Sun must be a tremendously hot body—for the iron and other metals in it are not only melted but they boil away like water and are changed into gases. Under certain conditions gigantic flames, called prominences, shown in Fig. 32, can be seen to leap from the edge, or limb, as it is called, of the Sun, and finally, great spots, called sun spots, are formed on the Sun that are so large a dozen worlds the size of our Earth could be dropped into any one of them and rattled around like marbles in a cigar box. These are a few of the reasons we are led to believe that the Sun is a seething ball of fire.

The Sun’s Layers of Flame.—Just as the wick of a candle is surrounded with several kinds of flame, so the Sun has three layers of flame around a central core.

The core of the Sun is believed to be formed of liquid gases which are about as thick as New Orleans molasses.

Around this core, which is the real source of the Sun’s light and heat—and which has never been seen—is a dark layer of flame usually called the Sun’s surface; this layer, which is covered with numerous dark spots like freckles on the face of a red-headed boy, is called the photosphere, and it is this part of the Sun which gives out the most light.

The second layer, which is called the chromosphere, is about 5,000 miles thick, and if you could imagine the whole world afire you would then have but a faint idea of what a mighty seething sea of flame this layer is. It is in this layer of luminous gases that terrific explosions take place and red tongues of flame, or prominences, are shot out for upwards of 300,000 miles.

Around the chromosphere is another layer of flame which extends for hundreds of thousands of miles in all directions. This last layer is called the corona, and it is as thin as the stuff of which dreams are made. It is formed of the gas coronium and since it is so thin it can never be seen except when there is a total eclipse, that is, when the Moon passes between us and the Sun, which will be explained in Chapter VII, and so shuts out the intense light of the other two layers. A cross section of the Sun is shown in Fig. 33.

Sun Spots and Their Effect on the Earth.—Very often great spots are seen on the Sun’s surface. These purplish black spots appear to be holes, like the craters of volcanoes, in the photosphere, or layer of flame next to the core of the Sun. The sun spots are caused by great eruptions which take place in the core of the Sun, and these sun spots are sometimes over 100,000 miles in diameter, when they can be easily seen with the naked eye; indeed if a sun spot has a diameter only as large as that of our Earth, it can be seen with the naked eye, protected, of course, with either a smoked or a colored glass, or better, with a pinhole telescope; in any case it will look like a black speck about the size of a pinhead. Fig. 34 shows a view of a sun spot made through a large telescope.

Whenever the sun changes his spots magnetic storms take place on the Earth, when compass needles, telegraph and telephone apparatus and wireless systems are disturbed. When a large number of spots appear at the same time on the Sun the Northern Lights are often very bright. Sun spots have something to do with our weather, but the effects are not yet well understood.

The Sun and the Weather.—Of course the Sun has everything to do with the weather, but to be able to predict the kind of weather we shall have even the next day is a very hard thing to do.

The changes in the weather are caused by the heat of the Sun alone. The heat of the Sun produces clouds by vaporizing the water of rivers, lakes and oceans. He causes hot and cold weather by heating some parts of the air more than other parts, and this sets the air in motion and we call this movement of the air the wind.

Changes of heat, moisture and wind are the cause of all the kinds of weather we have, and we have a good many kinds, be it hot or cold, dry or wet, calm or windy, clear or stormy, good, bad and indifferent.

To Forecast the Weather by a Barometer.—The best way to tell what the coming weather will be in the next few hours is by the rise and the fall of the pressure of the air, or barometric pressure, as it is called.

A simple barometer for showing the changes in the pressure of the air can be made of a glass tube about 3 feet long, ½ inch in diameter, and closed at one end as shown in Fig. 35. Fill the tube with mercury and, placing your finger over the mouth of the tube, turn it upside down and put the open end into a cup, or other vessel, which is half full of mercury; in placing it into the cup be careful that no air gets into the tube.

Only a small part of the mercury in the tube will run into the cup and this will leave a space in the top of the tube. Now fasten a yardstick, the purpose of which is to show the changes in the height of the mercury in the tube, with a string or wire to the tube, and your barometer will be complete, as shown in Fig. 36.

Since the air presses on the mercury in the cup but not in the tube, the pressure of the air on the mercury in the cup just balances the weight of the mercury in the tube and, hence, any increase or decrease in the pressure of the air, which ordinarily is about 15 pounds to the square inch, is shown by the rising or the falling of the mercury in the tube.

The barometer in helping to forecast the weather shows that: (1) when the mercury rises in the tube, that is when it is high, the weather will be fair; (2) when the mercury falls in the tube, that is when it is low, bad weather may be looked for; (3) when the mercury suddenly falls in the tube a storm is coming, and (4) when the mercury continues at a high point the weather will remain fair.

To remember these forecasts easily they may be briefly stated thus:

• (1) A high barometer shows fair weather.
• (2) A low barometer shows bad weather.
• (3) A sudden fall of the barometer shows a coming storm.
• (4) A constant high barometer shows continued fair weather.

To Forecast the Weather by Signs.—It will seldom happen that a boy who goes camping, or one who otherwise wants to know what the weather is likely to be on the morrow, will have a barometer to consult, so the next best thing is to know how to read the weather signs:

To Light a Fire with the Heat of the Sun.—A small magnifying glass, or burning glass, is simply a convex lens. It is a little piece of apparatus that every boy should always carry with him just as he does his pocket knife and compass. A lens 1½ inches in diameter and having a 4-inch focus may be bought for 25 or 30 cents.

A lens of this kind will be found very useful in many ways, for it will greatly magnify any object such as cloth, leaves, insects, finger-prints, in fact anything you may wish to see better than you could with your naked eye, though you cannot use a single lens for a spyglass. A magnifying glass will also frequently come in handy for lighting fires, by using the Sun’s rays when matches are scarce.

While a Boy Scout would disdain to use paper to kindle a fire, yet if a scrap of paper is at hand it will prove a good medium on which to direct the rays of the Sun with a burning glass. If you have no paper focus your glass on some punk or very dry leaves, as shown in Fig. 37.

To focus the glass means to hold it away from the paper or leaves so that the rays of the Sun are brought to a point like the sharpened end of a lead pencil; when all the rays of sunlight, each of which carries a little heat, are brought to a point, they will make enough heat to light a piece of paper or a dry leaf.

Signaling with the Sun’s Rays.—There are many ways of sending a signal or a message across space by day, as, for instance, by means of smoke, by flags and flashes of sunlight; by bonfires, pine-knot flames and burning arrows by night, and by wireless, which can be used either by day or by night.

A simple and effective way to signal in the daytime when the Sun is shining is by using a mirror, that is, a looking-glass, as it is commonly called. Every boy knows how to make flashes with a mirror, so it will be enough to say here that the glass is held in the hand in such a position that the sunlight falling upon it will be reflected in the direction you wish to send the signals. Fig. 38 shows how it is done.

Any sort of a code can be used, but it is far more interesting and will prove very useful if you are able to send and receive messages in the dot and dash alphabet, or Morse telegraph code, which is given in Fig. 39. A short flash represents a dot, a long flash a dash and short and long flashes represent letters. This is the same code that is used for wireless telegraphy.

How to Make a Simple Heliograph.—A heliograph is merely a mirror mounted on a baseboard, but this is a big improvement over holding the mirror in the hand, for to send and receive flashes over long distances the mirror must be carefully aimed and kept in position.

To make a heliograph, get a board 12 inches long, 4 inches wide and 1 inch thick and cut a piece out of one end 4 inches long and 1 inch wide, as shown in Fig. 40. Bore a ¼inch hole through the slotted end and another ¼ inch hole 4½ inches from the slotted end, as shown in the cut.

Make a block of wood 4 inches long, 1 inch wide and 1 inch thick and bore a ¼ inch hole through it near one end. To the other end of this stick fasten a mirror about 4 inches square. This mirror should be perfectly smooth—a plate glass mirror is the best—and have a hole ¹/₁₆ inch in diameter drilled through the center of the mirror for sighting the heliograph, as shown in Fig. 41. Any optician will drill the hole for you for a quarter or less. Fig. 42 shows a top view of the heliograph and Fig. 43 shows a side view of it.

Make a wood frame so that the mirror can be fastened in it and screw the frame to a stick of wood. Get a bolt 5 inches long and ¼ inch in diameter and have a thumb screw fitted to it. Set the end of the stick which has the mirror fastened to it into the slotted end of the baseboard, push the bolt through the holes and after slipping on the washer put on the thumb screw. The mirror can now be moved to and fro.

Into the hole in the front part of the base put a wire or a thin round stick to sight the mirror by. The heliograph is now ready for use.

After sighting the mirror at the place where the signals are to be received, set the mirror so that the reflected beam of sunlight shines directly on the place. To send signals in the Morse code all you need to do to make dots and dashes is to place a sheet of cardboard before the mirror and take it away; the length of time the mirror remains uncovered determines whether it is a dot or a dash. The heliograph complete is shown in Fig. 44.

How to Make a Simple Sundial.—To make a sundial of the usual kind that will give the correct Sun time is not an easy matter, for the spaces marking the hours on the dial are not equal as they are on the face of the clock and this will make it hard to figure out.

A kind of sundial that will give the correct Sun time though, can be easily made and at little cost. Get a strip of tin 2 inches wide and 24 inches long; mark it off into 24 equal spaces like those on a two-foot rule, and beginning at one end with the number 1, number each space to 24, as shown in Fig. 45. This done, bend the strip of tin into a perfect ring with the numbers inside and solder the joint, as shown in Fig. 46.

Next get a strip of iron or brass ¼ inch wide, ¹/₁₆ inch thick and 13 inches long; drill a ¹/₁₆ inch hole through each end and a ⅛ inch hole 4 inches from one end; bend this strip into an exact semi-circle, as shown in Fig. 47 and solder the tin ring, at the point where numbers 1 and 24 meet, to the middle of the brass semi-circle. Through the holes in the ends of the brass semi-circle fasten a wire, and this wire must run exactly through the center of the tin ring. Now screw the brass semi-circle to a baseboard (see Fig. 48), so that the angle made by the wire and the surface of the board will be equal to the latitude of the place where it is to be used; in other words, when the board is level the wire should point directly to the North Star and when this is done it will be adjusted to the proper angle. The board should be about 12 inches square and 1 inch thick.

Since the shadow of the wire made by the sunlight will fall on XII at noon, it will be plain that the shadow of the wire falling on the numbers on one side or the other of the ring will mark the Sun time. To change Sun time to mean solar time, or ordinary time, see Equation of Time, Appendix M.

To Find the North by a Watch.—To use a watch as a compass, that is to find the north by means of a watch, is easy if the Sun is shining. The watch should be held face upward; then turn the watch around until the hour hand points in the direction of the Sun. Draw an imaginary line from the hour XII to the center of your watch.

If, now, in the middle between this line and the hour hand you draw another line from the center of the watch and produce, or extend it, the middle line will point just about north, all of which is clearly shown in Fig. 49.