Our Debt to the Sun
Someday there no longer will be any coal or oil for man to use. How soon can not be predicted exactly; there are differences of opinion among scientists. Yet that time will surely come—one thousand, ten thousand, or perhaps one hundred thousand years from now—if we continue using fuel at the present rate. How, then, will man do the world’s work? Trains and steamships would stop, since they require coal or oil. A great many of the machines operated by electricity would cease to turn because most electric generators are driven by engines requiring steam or oil. The few that are driven by water turbines would be hardly sufficient for modern purposes. Electric cells and batteries can not do the work. The automobile would be motionless. No airplane could leave the ground.
Many homes would be cold, and most factories would be silent. Of course, we should still have the wind and flowing water, such wood as could be had from forests and the fuel that can be manufactured from plants. Yet modern civilization could not get along on these sources of power alone.
Few of us realize how much we depend upon coal and oil. What are these substances and how did they accumulate on and in the earth? For the present it is sufficient to say that coal and oil are the remains of certain plants and tiny animals which lived millions of years ago. These ancient living things used sunshine, just as plants and animals do today. Each time we burn a lump of coal, and each time we “step on the gas,” we are using up the energy of ancient sunshine.
The sun is still shining and its energy is being used by living things that could some day form great deposits of coal and oil. But we can not afford to wait for that slow process. A way must somehow be found for putting to use more of the present-day sunshine; or else we must find sources of energy that do not depend upon the sun. Scientists are beginning to make progress in both directions. Let us consider first what might be done to harness the sun for doing some of the work of the world.
Day after day, the sun pours out vast amounts of energy. It is estimated that the earth’s surface receives from the sun each year the equivalent of many thousand horsepower for every square mile. If we could make good use of the energy absorbed by even a dozen square miles the threat of a coal-and-oil famine would be banished forever. In the last one hundred years, the minds of many men have been busy trying to solve this problem.
In the year 1866, Emperor Napoleon III of France visited the shop of a French inventor named August Mouchot. In the yard of the shop stood a large, cone-shaped object resembling a huge lampshade. The opening of the cone was directed toward the sun; its inside was lined with a thin film of silver. At the small end of the cone lay a small copper box, blackened on the inside. The Emperor was told that this curious device was a solar engine, that is, a sun engine. The rays of the sun were gathered by the cone and reflected by the silver lining down upon the small copper box which contained water. The heat caused the water to boil. So impressed was the Emperor that he urged his government to support and finance the building of many of these solar engines. Yet, the scheme was not very successful.
After Mouchot came several other inventors of sun engines. All of them used one or more of three important arrangements for collecting the sun’s rays—the conical mirror; the cylindrical reflector, and the hot-box - an airtight box, black inside, and covered with two layers of glass. Heat waves pass through glass; and black absorbs heat.
A solar engine was set up in the Arizona desert in 1904. It used a cone-shaped reflector and weighed about 8,300 pounds. Seven hundred square feet of sunshine was collected, which boiled water into steam, which, in turn, operated an engine. In 1913 a solar engine erected in Egypt gathered sunshine falling on an area of 13,000 square feet. This engine developed about 55 horsepower every hour. However, the machine proved to be too costly and could not be kept running easily.
One of the most workable solar engines ever built stands atop Mount Wilson in California. It consists of a large cylindrical aluminum mirror that is free to rotate about an axis parallel to that of the earth’s. A clock mechanism causes the mirror to follow the apparent motion of the sun. The rays of the sun are focused on three continuously connected oil-filled glass tubes about six feet long. Each of these tubes is covered with two other tubes which enclose a vacuum, so that very little heat is lost by the oil. As the oil gets warm it rises and soon a circulation is set up from the oil tubes to a storage tank and from the tank to the tubes. As this continues in the sunshine, the oil gets warmer and warmer, sometimes reaching a temperature of about 390 degrees Fahrenheit—which is hot enough to bake bread, cook food or boil water into steam for power purposes.
Seven hours of sunshine a day are enough to keep the machine going day and night at a temperature near that of boiling water. This machine is sometimes called a sun cooker.
There have been other efforts to make use of direct sunshine. One of the most interesting is to use the sun’s heat to produce cold. You are familiar with the type of kitchen refrigerator which is operated by a gas flame. The heat of this flame evaporates a specIal liquid called a refrigerant. The evaporated refrigerant (now a gas) is then compressed. When the gas is allowed to expand again rapidly, it produces a cooling effect which freezes the ice cubes and keeps the food cold. Similarly, the sun’s heat pouring down upon the roof of a tropical bungalow can be made to evaporate a refrigerant which can then keep the air inside the bungalow cool.
Another scheme for making direct use of the sun’s energy is to allow it to heat the junction of two pieces of different metals. When this is done an electric current begins to flow in the metals. The current, though small in amount, can ring a bell, light a lamp, or run a motor. The metal junctions are called thermocouples. Some years ago a German scientist, by using several thermocouples, succeeded in keeping an electric lamp lit by sunshine for several months. A French scientist has proposed a plant for connecting together half a million thermocouples.
The junctions would all be exposed to the sun and the ends would be embedded in concrete, so as to keep them at a lower temperature. In this way, huge amounts of electricity would be obtained. Unfortunately, the cost of building the arrangement would be too great as long as there is still enough cheap coal and oil available for generating electricity.
The most likely use of direct sunshine in the near future is the opening up of desert areas. These regions have plenty of steady sunshine. If this almost boundless energy can be caught by some form of solar engine, it can be changed either into the heat energy of steam or into electrical energy. With energy available, many such deserts can be irrigated and transformed into fertile farms and gardens. Excess electrical energy can be sent out to other regions which do not enjoy such intense and steady sunshine.
We spoke of finding sources of energy that do not depend on the sun. Men have dreamed for years of using the power of the tides; and successful experiments have been made. The greatest field for power research today is within the atom. Ceaseless activity goes on inside the atom, and an enormous amount of energy is occasionally developed accidentally when atomic particles collide. Some atoms, as you know, are breaking up and giving off (radiating) energy. Radium is one of these elements whose atoms are breaking up. Other atoms can be made to break up. We call the process atom-smashing. For some years atom-smashing has been going on in laboratories all over the world. Not until 1945 was a way found to employ the energy thus created. This use, as you know, was in the terrible atomic bomb. When we can learn how to harness the enormous energy that is now locked within the atom, we can have all the heat and mechanical power, all the electric power and light that we need. But even then we shall be dependent upon the sun for other things.
The Enormous Heat of the Sun, Our Source of Energy
The sun is a star some 93,000,000 miles away. It consists of many different layers of gases at a very high temperature. The temperature of the surface of the sun is estimated at about i r,ooo degrees Fahrenheit. This is twice as hot as anything man has been able to devise. The sun’s interior may be ten times hotter. At these temperatures, the molecules in matter break down into the smaller particles called atoms. The atoms themselves undergo change, sending out rays of light and heat. Though these rays travel for 93,000,000 miles before they reach the earth, they can cause a pretty severe sunburn in less than fifteen minutes.
The sun is the basis of our existence and the source of all our usable energy. There are several forms of energy: light, heat, mechanical, electrical and chemical. Each form can be changed into another. The starting point for most of these changes, however, is the light energy which pours down from the sun. You have probably tried to concentrate the light rays of the sun with a magnifying glass or a mirror. The light changes into heat, which can boil water into steam. The steam can turn a small dynamo.
Thus the heat energy is changed into mechanical energy. The dynamo generates electricity, showing how mechanical energy can be changed into electrical energy. Electricity can decompose water into hydrogen and oxygen. This is a change from electrical to chemical energy. Aside from certain kinds of chemical energy and the energy within the atoms of matter, all means for carrying on life activities come to us from the sun.
How We Use Heat Energy to Get Electrical Energy
The rays of the sun cause the water of lakes, rivers and oceans to evaporate into the air. Later the air moisture condenses and falls as rain, snow or hail. This fills the rivers, which can be dammed so as to store water at a height. When allowed to fall and press against the blades of a turbine or water-wheel, the mechanical energy is changed to electrical energy.
The sun warms the land and the water; but water heats up more slowly than land, and then holds the heat for a longer time. When the land is warmer (during the day) the air over it rises, letting in the cooler sea breezes. When the sea is warmer (during the night) the air over it rises, letting the cooler land air blow toward the sea.
You know that the earth is tilted with respect to its path around the sun. You know that because of this tilt certain regions of the earth receive the direct and concentrated rays of the sun, while other regions receive rays that are slanting and spread thinly over the area. The summer season comes to those parts of the earth which are bathed by direct sunshine, and the winter season arrives where a section of the earth receives the rays slantwise. Regions near the earth’s Equator receive rays that are close to perpendicular during the entire trip. Hence such regions enjoy hot summer weather all the time.
Areas near the Poles never receive direct rays, and have periods when they receive no sunshine. So polar regions are always cold.
The fact that certain areas are always warm and others always cold, sets up huge movements of the air. As the earth spins, these air movements are caused to swerve and give rise to the well-known wind belts. It is in these moving air masses that weather conditions start. In a sense, then, the sun is responsible for our weather. It is the sun’s energy which heats the land, heats the air, causes the air to rise and evaporates the water into the air. Even the electric storms are due to the sun, because evaporation produces electrical charges on the moisture particles and some of the sun’s rays help to increase these charges. We owe to the sun our seasons, our climate and our weather.
Light can stimulate the retina of the eye. The eye lens forms an image on the retina and the brain interprets the stimulus as the picture which we see. Certain chemicals are also affected by light. A piece of photographic film contains small grains of a chemical called silver bromide. This silver bromide is colorless and opaque. (Light can not pass through it.) When light strikes the film, the molecules of silver bromide are changed so as to leave a black silver deposit. This is what happens when a camera lens forms an image n the film. Even when you take a snapshot, the momentary flash of light produces an effect on the silver bromide. The effect is later continued when the film is developed and the picture printed.
Contained in sunlight is a kind of ray called ultraviolet. This ultraviolet light is colorless and invisible to our eyes, yet it makes its presence known and felt. It is very penetrating, and is responsible for sunburn. This can be observed in the effects produced by the mercury-vapor lamp, which is a rich source of ultraviolet light. While direct sunlight can produce a burn in about fifteen minutes, a mercury lamp can cause a similar, or even more serious, burn in two or three minutes. The nature of skin burning or tanning is quite interesting. The action of sunlight on the skin, or of the ultraviolet light contained in sunlight, is to produce a substance called vitamin D on the surface of the skin. The same vitamin D can be produced in foods, such as milk or oils and fats, by exposing them to ultraviolet light. The process is called irradiation. As you know, vitamin D is necessary if our bones are to grow strong, and it is most important to general good health.
It has been shown that ordinary window glass allows most of the sun’s light to pass but blocks the rays of ultraviolet. That is why we are warmed but not burned by the sun in a glassed-in porch, or sun-room. There are special types of glass which permit the passage of the ultraviolet rays. There is room for much further study and improvement in this field.
Every leaf, every blade of grass enjoys a secret which the wisest scientist does not know. For years scientists have been trying to find out how plants make use of sunshine. We know that water and minerals come up from the soil through the roots and stems of plants to the leaves. We know, too, that there are millions of openings on the under surfaces of leaves which let in air containing carbon dioxide. Then, in the presence of a green material called chlorophyl, and while the sun sends down its rays, a chemical action takes place in the cells of the leaves. As a result of this action, carbohydrates are formed and oxygen is released to the air. Carbohydrates—starches and sugars are examples of carbohydrates—are the food which the plant makes for its own use. Then we eat the plants. Thus corn, wheat, fruits and vegetables are the products which plants manufacture with the help of sunshine. They are the food for all animal life, including man. Yet we do not know all we should like to know about the chemical process in the leaf which means so much to our lives.
The Secret of Photosynthesis
It is estimated that one hour of sunshine, falling upon a square yard of leaf surface results in the manufacture of about one gram of carbohydrates. No wonder each plant always turns its leaves so that they catch as much direct sunshine as possible! In an acre of plants there are about two acres of leaf surface. During a summer’s growth, a wheat field may take from the air about eleven tons of carbon dioxide, and with the help of sun energy it will manufacture about seven tons of wheat.
Several scientists have already been able to duplicate the process of photosynthesis on a small scale, in the laboratory. It is as yet too costly for large-scale manufacture. Many are studying the substance, chlorophyl, whose presence is essential to the process. In the Boyce Thompson Laboratory for Plant Research, at Yonkers, New York, some very interesting experiments are now in progress. While the plant’s secret is not yet discovered, some strange results have been obtained.
Marine plant life is also affected by the light and heat of the sun. In the oceans there exists a kind of one-celled plant called the diatom. Diatoms are bacteria of a sort which, with the help of sunshine, can produce the starch needed for their growth. Small marine animals feed on the diatoms. Larger fish feed on the smaller ones, and so on. Thus the sun maintains ocean life.
The heat of the sun also affects all animal life. In the winter time, in the Northern Hemisphere, the sun is closest to the earth. However, since the sun’s rays at this time reach us slantwise and not perpendicularly, little heat can be gathered. This absence of heat and the decrease in amount of sunlight (since the days are short) causes many animals to hibernate, that is, to go into a sleepy state for the winter. Snakes, lizards, frogs, most wild bears, ants and squirrels retire for the winter. If it were not necessary to come out occasionally for food, it is likely that many animals would scarcely be seen during the winter months. As the earth revolves about the sun, and spring arrives, the animals come out of their partial sleep. They become active. Everywhere on the earth animals tend to follow the sun. This is not just accidental. It is necessary for the preservation of their lives.
It is sometimes asked how long could life exist without the sun. Would life suddenly cease, or would there be a gradual decay? As you know, in the far north there is an almost total lack of sunlight for about six months. Does life cease during that time, to be revived with the coming of the sun? No, enough energy is stored away during the dark period to maintain the necessities of life. Animals hibernate and become dormant. Man needs more than just food and shelter. He can not afford to hibernate. Life must go on.
Should the sun fail to make an appearance for a single year the result would be ruinous. Plant life as we know it would vanish and animal life would soon follow.
Is there a substitute for the sun? Can an artificial sun be created? The nearest thing to an artificial sun is artificial ultraviolet light. However, it requires electricity to operate the mercury-vapor lamps, and electricity is dependent upon the sun.
Our debt to the sun is one that can not be repaid. All our lives we are indebted to the sun for food, clothing and shelter. There is only one thing we can do to repay in part this great debt. We can practice conservation. This means saving and not wasting. It is true that the sun’s energy is apparently endless, yet we must learn to take all we need and yet leave some for succeeding generations. In this sense, conservation means careful and purposeful use. Only in this way can we repay partially our debt to the sun.