As you know, gasoline is a very inflammable fluid, and will explode if placed too close to fire.

This explosive quality is the basic principle of the gasoline engine. By admitting a small quantity of gasoline vapor into an enclosed cylinder, and exploding it by means of an electric spark, repeating this operation continuously, the engine is given a regular rotary motion.

Look at Fig. 1. Starting from the gasoline tank, the fluid is fed into the ‘carburetor’, which is a sort of atomizer. Here the gasoline is mixed with air, and broken up into a very fine spray, in which condition it will explode readily.

The engine will not start of itself. Its fly-wheel must first be turned by hand, or by some other outside force, until the first explosion takes place. After this its action is automatic.

As shown in Fig. 1, the fly-wheel is being turned, and is drawing the piston down the cylinder, which in turn sucks gasoline vapor, (shown by little arrows) through the ‘intake valve’. This ‘intake valve’, and the ‘exhaust valve’ on the opposite side of the cylinder, are opened and closed at the proper time through the action of the gears shown in the illustration.

Passing to Fig. 2, the fly-wheel in turning has drawn the piston to its lowest point, and is now shown forcing it up the cylinder. This compresses the gasoline vapor in the cylinder to a density at which its explosion produces the greatest amount of power. The intake and exhaust valves are both closed.

Fig. 3 shows the explosion. The cylinder has been filled with compressed gas, and the piston has again started on its downward travel. The spark plug, set in the top of the cylinder, makes a spark every time an electrical current passes through it. A switch on the engine permits the current to pass to the spark plug only when the engine is at this position in its action. (Fig. 3.) The consequent explosion drives the piston downward with great force, turning the fly-wheel, which by its weight continues the rotary motion after the downward impulse of the piston has been expended.

Fig. 4 shows the fly-wheel, still turning, forcing the piston up and thus expelling the burned gases from the cylinder through the exhaust valve, held open for this purpose. From this position the engine goes again to that of Fig. 1, and through 2, 3, and 4, continuously, exploding every second revolution, and giving a regular rotary motion to the fly-wheel.

The illustrations show a one-cylinder motor, but these engines can be built with two or more cylinders, arranged to explode at different times, thus giving very smooth action to the fly-wheel and main shaft.

Aeroplanes, almost all automobiles, various pumps and other machinery are driven by gasoline engines. The rotary motion can readily be transmitted by chains or gears to the propellor of an aeroplane or motor boat, or the wheels of an automobile. It is only in the past few years that the gasoline engine has reached its present high state of perfection.

Why Does the Heart Beat When the Brain Is Asleep?

Under ordinary conditions the heart beats are controlled by certain nerve cells which are located within the heart itself, and these cause the heart to beat even while the brain is asleep. This explains why the heart beats when the brain is asleep, and the fact that the brain when asleep does not exercise its functions, shows how necessary this arrangement and the control of ordinary heart beats is. If this were not so, we should not be able to live while asleep. It is just like the management of a great business in this sense. The general manager of a great business has control of the entire works, but there are occasions when he must be thinking of only one thing in connection with the business, and so he must have his organization so complete, that the parts which he cannot be thinking about at the time will do their work just the same. So he surrounds himself with competent assistants, who look after certain departments while he is busy or away or asleep, and if anything goes wrong while he is away, he calls on special forces to set things right. Now, the brain is the general manager of the whole body and has these nerve cells in the heart as a sort of assistant manager to look after the heart beats in ordinary conditions, and to keep the heart going while he is asleep. But, by reason of his office as general manager, the brain has a special way of sending orders to the heart through special nerves which run from the brain down each side of the neck to the heart. There are two pairs of these special nerves. One pair, if set in motion, will make the heart beat faster, and the other pair will make the heart beat more slowly.

Why Do Our Hearts Beat Faster When We Are Running?

When you start running, the brain knows at once that your legs and other parts of the body will need more blood to keep them going, and so the brain sends down orders through his special nerves which make the heart beat faster, to get busy, and they do. Then when you stop running, your heart is beating faster than necessary—there is really an oversupply of blood being pumped through your system for the time being, and that makes you uncomfortable, until the brain sends word through the other set of nerves to the heart to slow down the heart beat. It is better to stop running gradually, to give the heart a chance to get back to its normal beat gradually also.

Why Do I Get Out of Breath When Running?

This is also caused by your brain in its efforts to keep up your supply of good blood. We breathe to take air into the lungs, where the blood which has once been through the arteries and comes back on its return trip to the heart, is exposed to the air in the lungs, before going back into the heart. The air which we take into our lungs purifies the once used blood and makes it into good blood again. When you run the heart pumps blood into your arteries faster to enable you to run. Thus also, the arteries send much more blood back to the heart through the veins, and this must be purified by the lungs before going back into the heart. To attend to purifying this extra amount of spoiled blood the lungs need more air, and thus you are made to breathe in more air for the purpose. Unless you are in good training—your wind in good condition as we say—it is almost impossible for you to supply the lungs with enough air for the purpose, but whether you can do it or not, the lungs call upon you for more air, and cause you to try to get it, and that is what makes you get out of breath.

Why Does My Heart Beat Faster When I Am Scared?

The natural tendency of a scared creature is to run or fly. The effect of being scared has the same effect on the brain that your starting to run has. The brain is always as quick as you are, and knowing that when you are scared your actual or natural inclination is to run, it is merely getting you in shape so that you can move or run fast.

Why Does Cold Make Our Hands Blue?

Your hands appear blue when cold because the veins which are near the surface are filled with impure blood which is purplish in color. Your hands become cold because there is not sufficient circulation of warm red blood going on to keep them warm. The blood in circulating through your body sends warm red blood through the arteries, and this is returned to the heart through the lungs by way of the veins. The veins carry only used-up blood or what is left of the good red blood when the arteries are through with it. Its color is a purplish blue.

When your hands are blue it means that circulation of good red blood has practically stopped—the red blood is not flowing from the heart through the arteries in sufficient quantity and there is no color in the arteries, as the blood from the arteries has practically all gone into the veins. The veins are full to purplish blue blood, and this makes the hands look blue, because there are a great many veins in the hands close to the surface.

Why Do I Get Red in the Face?

Now, when you rub your cold blue hands together, you start the circulation going again, and that brings the red blood into the arteries, giving you the healthy red color again. When you run hard to get red in the face because you are causing an unusual amount of red blood to flow through your whole body by your violent exercise. Some people with an extraordinary amount of circulation are red in the face all the time. This is because of the presence of a great deal of blood in the arteries, or because the walls of their arteries are so much thinner than others that the red blood shows through more easily.

Is Yawning Infectious?

Yawning is infectious to the extent that other habits are. The desire to yawn which comes to us when we see some one else does so comes under the heading of suggestion. The power of suggestion is greater than many of us realize. We are great imitators of each other. When one of us is downhearted, we are apt to become happy and glad simply by being with other people who are happy and glad. If enough people one at a time tell a perfectly well man that he looks sick, he will actually feel ill, provided he does not suspect a game is being played on him. So a good actor carries his audience with him. He can make them laugh or cry almost at will, and if he yawns, his audience will begin yawning.

Often, however, there is no acting connected with the yawning of the first person. Then the yawn is caused because the person is not sending enough good air into the lungs for purifying the blood, and the yawn is only nature’s way of making us take an exceptionally deep breath of air in at one time. This lack of sufficient good air in the lungs may not be due to the poor breathing, but to the amount of bad air in the room. In such cases it is quite likely that other people in the room yawn when one of them starts it because they all begin to feel the need of more good air at about the same time.

What Makes Me Want to Stretch?

The necessity or desire to stretch comes to us because certain parts of the body are not receiving the proper amount of blood circulation and it is these parts that we stretch at such times. If you have ever been to a ball game, you know, of course, that it has become customary for the crowd, no matter how large, to stretch its legs and arms during the last half of the seventh inning. In fact, that has come to be a fixture at ball games and is universally known as the “stretch inning.” Now, it is not so much the result of a desire to encourage the home team as the natural following out of nature’s laws that originally started this practice. The end of the seventh inning at a ball game generally means that the crowd has been sitting quite still for the greater part of an hour and a half, just long enough for the circulation to become poor in parts of the body, and the custom of stretching at a ball game thus comes from the necessity of getting a little more speed into the action of the heart to increase the blood supply.

In other words, the stretching constitutes a mild form of exercise. You will notice the ball players themselves do not stretch themselves in the last half of the seventh inning. They are getting enough exercise without that.

It is natural, however, for us to stretch as we wake up from sleep after having lain quietly in one position for one or more hours. It is nature’s way of causing the heart to work faster.

What Happens When I Stretch?

What happens is simply this. When you stretch your arms and legs, you squeeze the arteries and veins which are a part of your arms and legs, much as happens when you pull on a piece of rubber tubing. The tubing becomes flat instead of perfectly round, and it is not so easy to send water through a flat tube as through a round one. Just so with the heart. It is the heart’s business to send blood through the arteries at all times, and when you make them flat the heart’s job becomes just a little harder, and it goes to work beating just a little faster to overcome this extra difficulty. By that time you are through stretching and the heart is busy pumping blood a little faster than ordinarily, and that is what makes you feel so good after you have stretched.

Why Can We Think of Only One Thing at a Time?

If you are asking the question intelligently, you must know that to think means to concentrate, and in that sense we can only think of one thing at a time, because it takes all of that part of the brain which is used for thinking for just one thing. To give close attention to any one subject means to turn the entire brain force practically in one direction. To let other things pass through the mind at the same time may appear not to interfere with the one thought, but they do, and our conclusions suffer accordingly.

You can be doing something with one part of your body, while engaged in thinking of one thing, but only such things as are more or less mechanical as the result of habit, such as walking, or moving the arms—things which the parts have done so often that actual attention by the brain is not absolutely essential. Take for instance, the fact that a man in deep thought on one subject will sometimes walk up and down the room or along the sidewalk. He can do this walking and still think concentratedly, but if he stubs his toe on the leg of a chair or on a rough place in the walk, his thought is broken, because the brain immediately takes itself out of the thought and pays its attention to the toe that was stubbed.

Why Do I Turn White When Scared?

Simply because, when you are scared or frightened, the blood almost leaves your face entirely. Under normal conditions, the red blood which is flowing through the arteries of your face, gives the face a reddish tinge, and your face becomes white when you are frightened, because then the blood leaves the face. It is quite singular, but when you are really frightened, whatever the cause may be, the human system receives such a shock that the heart just about stops beating all together. When your heart stops beating of course the flow of the blood from the heart stops and then there is no supply of fresh red blood coming through the arteries under the skin of your face. Therefore you look white—the color your face would be if no blood ever flowed through your arteries and veins. Some people have faces so white they look as though they were scared all the time. This is not because they have no blood flowing through the veins and arteries in their faces, but because their supply of blood is less than other peoples, and sometimes because the walls of their arteries and veins are much thicker than the average that the color of the blood does not show through. There are also many people who have so much blood in their systems all the time, and the walls of whose arteries are so thin, that they look at all times as though they might be blushing.

What Makes Me Blush?

Anything that will make your heart send an extra supply of blood into the arteries and veins which supply your face with blood, will make you blush. Embarrassment will do this. So will anger generally, although sometimes people get so angry that the blood is driven out of their faces. In this case they are so angry that their heart has stopped beating, practically.

What Occurs When We Think?

When we think the mind is acting on sensations; it is receiving, in conjunction with memories of sensations it has previously received. Sensations as they reach the mind arouse the mind to activity and, as soon as the sensation is received, the mind begins to compare the new sensation with sensations received at previous times, and by putting things together reaches a conclusion.

When you are thinking you are really trying to call upon memory to help you. You know the thought of one thing calls up another, and this leads to something else. This association of ideas is the faculty which enables us to think consecutively and accurately. It is the business of the mind to receive the sensations that enter it and arrange them in their proper places. That memory of past sensations is the important part of thinking, is proven by the fact that when we have forgotten a thing we are unable to think what it was.

Can Animals Think?

For this reason if animals have memory they should be able to think. It is now believed that many animals have to a certain extent the power to remember.

A dog will recognize his master even though he has not seen him for years. We might think he does this by his highly developed power of smell, but if his master has come from a direction opposite to that from which the dog first sees him, he could not have tracked him by his smell. A dog will recognize his master from quite a distance, so he must have to a certain extent the ability to remember or the power of association of ideas, which amounts to the same thing. Again, a horse that once belonged to the fire department, even though now hitched to a milk wagon, will have the impulse to run to the fire when he hears the fire gong. And an old war horse will prick up his ears as he used to when he hears the bugle call.

Why Do I Sneeze?

You sneeze sometimes when you look up at the sun or at a bright light. There does not seem to be any real good explanation of why looking at a bright light should make you sneeze. It is due to the connection there is between the nerves of the eyes and the nose. You generally blink if you look at a bright light suddenly, and the blinking process stirs the nerves inside of the nose to make you sneeze.

You know, of course, that the start of the sneeze is inside of your nose. The nose is, besides being the organ of smell, the channel through which we take air into the lungs, when we breathe properly. The nose is lined with membranes, back of which are a net of very small nerves which are extremely sensitive. The membranes are placed there to catch and hold the impure particles of matter which come into the nose when we take in a breath of air, and sneezing is only one effective way of cleaning out the nose. It is brought on only when some particularly difficult job of nose-cleaning has to be done. Pepper up the nose will make you sneeze quickly, because pepper produces a very great irritation inside the nose, and the nose goes to work at once to get rid of it in the quickest possible manner as soon as the pepper comes in. Other things have the same effect. Sometimes a cold in the head causes you to sneeze. The sneeze in that event is merely nature’s effort to clean out the nose when other efforts have failed.

There are many suggestions for stopping a sneeze before it takes place, after you feel it coming on, such as putting the finger on each side of the nose, and many others. But a half sneeze does not remove the cause of the sneeze, so it is much better to sneeze it out, and many people enjoy the after effects of sneezing so much that they take snuff into the nose to produce it.

What Happens When I Swallow?

The muscles of your throat act in the form of a ring when food passes into your throat. The food does not drop directly into your stomach. In other words, the action is not quite the same as when you drop a stone out of the window. When you do the latter, the stone hits the sidewalk or whatever is below at the time, with a smash. It would hardly do to have our food drop into the stomach, so the muscles of the throat are arranged to contract in rings which push or squeeze the food downward, and the food is passed from one ring of muscles to the other. It is just like pushing a ball down into the foot of a stocking that is apparently too small for it to drop down. You put the ball in the top of the stocking and then by making a ring of your fingers around the stocking you can push the ball down. When you swallow, you start the muscles of your throat to making these rings. The upper ring squeezes the food on to the ring below it and so on down to the stomach.

What Makes the Lump Come In My Throat When I Cry?

The “lump” which comes up into your throat when you cry is caused by a sort of paralysis of the rings of muscles in your throat. The muscles of your throat can make these rings or waves upward also, but it is more difficult upward than downward—probably because of lack of practice, as we say. When you have put something into your stomach that makes you sick and causes you to vomit, the throat muscles take the matter from your stomach and bring it back to the mouth in the same way, except, of course, that this action begins at the bottom.

Sometimes when you cry, or lose control of yourself in some other way (you know, of course, that in crying you always lose control of yourself, don’t you) practically the same effect is produced as when you have something in your stomach that should come out. Crying, or the thing that happens sometimes when we cry, makes the throat muscles act just as if we were vomiting, and as the action is an unnatural one, when the ring or wave reaches the top of the throat, we feel the lump or ball as we call it. We feel the lump because the throat has been made to go through the motion of eliminating something in an unnatural way, just as your arm will hurt if you pretend to have a ball or a stone in it, and in throwing the imaginary ball or stone, you put the same force into your movements as you would if you had an actual ball or stone in your hand and were seeing how far you could throw it.

Why Do We Stop Growing?

We eventually stop growing because certain of the cells of the body lose their ability of increasing in size and producing other cells. It is one of the marvels of the construction of the human body that this is so and one of the wisest provisions also. At first the cells of the body crave lots of food and increase in size, divide and then the parts go on growing until they become of a certain size, when they again divide and each part goes on growing, etc., and thus we grow. A growing boy needs more fond than a mature man, because he needs some of it to grow with, while the man only has to keep what growth he has going, i. e., alive.

We say this limit of growth is a wise provision of nature because if there were no limit to the size we might become, we would not know how large to build houses, barns, etc., or else we would have to build them so large to start with that we would be lost in them for a long time. We would constantly be forced to change these things and there would be no basis to reckon from. Dogs might be as big as elephants and then they would be of no use to us, or of what use would a dog as big as an elephant be to a boy of five years. You see it would not do at all to have this rule changed.

Why Do We Grow Aged?

We age directly in accordance with the lives we lead. You can bend a wire back and forth a number of times at the same point without breaking it, but eventually it will break. Just so with the human body. You can use each part of it for its own purposes a number of times, but eventually the break will come. Or, you can fail to make a part of it perform its regular functions, and it will die—the break will come. The human body is the most wonderful machine in the world, but even it will eventually wear out. Every time you move your arm, leg or some other part of your body, you destroy some tissues. The body replenishes and builds up those tissues again for a certain time. When you bend a joint in your body, the body oils the joint naturally, but as you grow older, or rather, as you use the different parts of your body more and more, it brings nearer always the time, when the body cannot, of its own accord, build up again the tissues you have destroyed. That is why some people become very old at forty and others are still comparatively young at seventy. It requires a great deal of care and attention and the elimination of all abuse of the body to keep us young when we are old. The use of drink, lack of sufficient sleep and other abuses prevent the body from restoring the tissues which have been destroyed. Worry and sorrow age us very rapidly, because these things affect the nerves. If the nerves are not quiet we cannot get any rest and without rest we grow old very rapidly.

What Causes Wrinkles?

Wrinkles come to us in several ways. An easy way to cause wrinkles is to scowl and frown and get into the habit of doing this. When you scowl or frown you pucker up the skin on your forehead into wrinkles and if you continue the habit the skin on your forehead makes the wrinkles permanent. You have given your skin the wrinkle habit. This acts just the same way as your arm would, if you tied it up in a sling and held it close to your side for a very long time—a number of weeks. When you took the sling off you would find your arm useless—a dead arm. It had developed the habit of doing nothing.

In old people, however, wrinkles come more naturally. There it is the case of the skin not receiving the proper nourishment and attention to keep the circulation of the blood right. When people become old they are apt to lose the fat which has accumulated under their skins. If they had taken just the right amount of exercise all of their lives and kept their circulation perfect in all parts of the body, there would have been no fat there. But when the fat accumulates, it makes the skin grow larger, and then when the fat disappears and people get thin again, the skin is too large and makes the wrinkles.

Does Thunder Sour Milk?

Milk will sour in any kind of warm and moist temperature and, because just before and during a thunderstorm the air is generally quite warm and moist, it is only natural that it should turn sour. It is wrong, however, to say or think that thunder makes milk sour. Thunder is only a noise and noise cannot do anything but make itself heard. The fact that it is generally warm and moist, however, when it thunders, coupled with the fact that these conditions of the air sour milk very rapidly, have led people to connect the two in their minds and caused them to fall into the error of believing that the thunder is responsible for the change in the milk.

What Makes the Rings in the Water When I Throw a Stone Into It?

Every movement has a beginning. When a movement on the earth is once started it keeps on going until something stops it. If nothing stops it it will go on forever.

When you shout you start air waves going in every direction, which keeps on going until stopped by something which has the power to break up their waves.

When you throw a stone into the ocean you start a series of ripples or waves which spread out in every direction and if you dropped your stone into the exact middle of the ocean—half way from each side—in a perfectly calm sea undisturbed by other forces, your ring of ripples would go on getting larger until it landed on the beach or shore on each side of the ocean at the exactly the same time and there the beach or shore would stop it.

The original ring of ripples is caused by the fact that when you drop a stone into the water it disturbs the water where it goes in and the water moves away from the stone to the sides, and as the stone goes down, over and up above it, and the whole body of the water is disturbed in such a way that makes the ripple appear on the surface and spread out in every direction. As the stone goes down into the water further and further the disturbance is repeated and ring after ring appears on the surface.

Of course there are many disturbances in the water at all times. Many things may happen to break up your little ring of ripples before they touch the sides of the ocean—a ship—a fish—the wind—or one of many other things, and because this is true you would have difficulty in sending the waves made by your little pebble across the ocean, but you can take a dishpan from the kitchen and after filling it with water drop pebbles into it as nearly the middle as possible, and you will see the ripples or waves your pebble makes spread out from the point where the pebble entered the water in all directions.

Why Are There Many Languages?

Different languages developed in different parts of the world because there was no inter-communication between people in different communities, and each was really developing a language for itself. In doing so they developed their language without knowing that other communities were working out the same problems for themselves. So they first developed their own sign and gesture language and later on their word or sound language and kept on using it. While they may thus have developed the use of some of the same signs and sounds or combination of sounds to express one thing perfectly understandable to themselves, these sounds or combinations of sounds might mean something entirely different to another community, where that particular sound or combination of sounds may have been hit upon to mean something entirely different.

Of course, not all languages were developed in this way. There are, you know, a great many languages used in the world. Some of them are offshoots of others, where part of a community moved to another part of the world, taking their language with them, but developing it further along new lines, and using new combinations of sounds for new words. Then also, there are many words which mean the same thing in different languages and are spoken with practically the same sounds. This is due to the movement of people from one nation to another and bringing their own words with them, so to speak. In many instances a stranger would come to another nation, and use his own word for expressing a certain thing and that would eventually be taken up and used as a better word, and the old word dropped. It is strange that this should be true, but this accounts for the fact that many words are the same in sound and meaning in numerous languages.

What Makes a Match Light When We Strike It?

The match lights when we rub it along a rough substance, because the rubbing produces sufficient heat on the end of the match to set fire to the head, as we call it, which is made of chemicals that light more easily than the stick of wood, which is the rest of the match. The fire thus started is hot enough and burns long enough to set fire to the wooden part of the match.

To explain this more fully, let me say this. Rub your finger quickly along your coat sleeve or along the seat of your trousers, long a favorite place for men to strike matches, pretending that your finger is a match. You find the end of your finger becomes warm, don’t you? Not warm enough to set your finger on fire, of course, but if you had the same combination of chemicals on the end of your finger that there is on the match, you would set the chemicals afire and this would burn your finger, just as it sets fire to the wooden part of the match.

It took a great many years to discover the combination of chemicals of which the head of the match is made. Before that discovery was made it was far from easy to light the light in the evening as it is now. It must have been a serious thing to let the fire go out in the furnace in those days.

What Makes the Kettle Whistle?

The kettle whistles only when the water boils and the steam or gas which is the form the water turns into when boiling is trying to escape through the spout of the kettle. You see, when the water starts boiling, the inside of the kettle is at once filled with steam and more is coming out of the water all the time. This steam must get out some way, so it rushes for the spout of the kettle, and because so much of it is trying to get out of a comparatively small opening at once there is quite a pressure and this results in making the whistle out of the spout of the kettle. It is just the same process as when you whistle yourself. To whistle you fill your mouth with air and force it out through your lips, which you have closed excepting for a small opening, by the pressure you can bring to bear with the roof and sides of your mouth, and if you have learned to make your lips into the proper shape and apply the pressure steadily you can sound a very long note and make different notes by making the opening in your lips large or small. The kettle spout has only one size of opening so the sound is practically the same at all times though louder at sometimes than at others. This is caused by the varying pressure at which the steam in the kettle is being forced out.

What Makes the Water From a Fountain Shoot Into the Air?

The water from the fountain shoots into the air because water anywhere will run down if given a chance. To produce a fountain you must have a source of water supply for the fountain which is higher than the openings of the fountain out of which the water shoots. The water comes out of the holes in the fountain for the same reason that it comes out of the faucet in the kitchen or bath room. In the latter case the water comes from the waterworks reservoir in which the level of the water is much higher than the opening in the faucet in your home. Being higher the water in the reservoir is trying to get away through the pipes all the time and all the pipes leading from the reservoir are full of this water trying to get away. Just as soon as you turn the valve in the faucet the water comes out and runs down into the bowl.

If you were to turn the opening of the faucet up instead of down as it is, the water would shoot up instead of down. Not very much, it is true, but it would act much like the water from the fountain. The reason it does not shoot up high in the air like a fountain is because the opening in the faucet is the same size as the opening in the little pipe which leads the water from the street into the house. If you would turn the opening of the faucet up and attach to it a pipe which made the opening much smaller (the size of the opening in the fountains), you would see the water shoot into the air just as it does from the fountain. When you reduce the size of the opening you increase the pressure of the water coming from the pipes in proportion to the reduction you have made in the size of the opening.

Water from the fountain will not, however, shoot as high as the level of the water in the reservoir because, as soon as it leaves the pipes, it encounters the pressure of the air outside the pipes and the law of gravitation which pulls all things toward the center of the earth.

It is not natural for water to shoot into the air as it does in a fountain. The only way water can go naturally is down, and it only goes up a little way from a fountain because of the pressure of the water in the pipes behind the openings in the pipes in the fountain.

What Keeps a Balloon Up?

A balloon stays up in the air, because of the air in it, together with the weight of the balloon, is less than an equal bulk of the air in which it floats.

In former days of ballooning the balloons were filled with hot air and were then found to rise and stay up until the air inside of the balloon became of the same temperature as that in which it floated. When this stage was reached, the balloon itself would fall because the material of which it was made was denser than air.

Today balloonists fill their balloons with gas which is lighter than air, even when as cool as the air in which they rise and are thus able to stay up a long time.

You, of course, have seen many of the red, white and blue paper balloons which are sent up on the Fourth of July. You will remember that father, or whoever it is that is sending them up, lights the oil-soaked knot of cloth that is attached to the balloon immediately below the opening at the bottom. He first lights this and then holds the balloon for a time with his hands.

Soon, however, you will remember that the balloon starts upward with father still holding it. This is because the air inside the balloon is becoming heated. You will notice also that at first he has to hold out the sides of the top of the balloon with his hands or has some one help him do this, but that even so the balloon does not stand out round and full as it should. When the balloon starts to rise, however, you will notice that it is round and full. This is because the air in the balloon has become heated and is expanding. Soon the balloon is tugging to get away and father lets go and it rises and sails away with the wind. As long as the fire below it burns, and if the wind does not upset it so as to make the paper part catch fire, the balloon will stay up; but, when the fire burns out, the balloon will come down.

The balloon merely rises because the air inside, and held there by the covering of the balloon, is warmer air and lighter than the air on the outside.

Why Did People of Long Ago Live Longer Than We Do Now?

When reading of people who lived long years ago and especially when reading about the length of their lives, we are told that in the old days people lived longer than they do now. Some of the early historical records speak of single individuals who lived hundreds of years. There is great doubt as to whether these statements are founded on fact. In thinking about this we must first take into consideration that these records of long ages were recorded at a time when man had no accurate ideas of the actual passage of long periods of time such as a year. They did not have our calendar as a basis for figuring at all. Learned men now tell us that the actual age of men who lived at the time these records of great ages were recorded probably lived shorter lives than we do now, and that what they record as a period of one year was probably a much shorter period than one year.

It is true beyond the question of a doubt that the people of today live longer on the average than people who lived ten, twenty or more years ago.

In other words, the average period of life has increased steadily. This is due to the fact that we have taken great care of our bodies; have improved the conditions in which we live, and made them more sanitary; have learned to fight and check and eradicate diseases, which only a few years ago we could not prevent people dying of when they once contracted them, and we know from the records which we keep that actually people live longer on the average today than only a few years ago, and it is safe to say that they live longer now on the average than at any time in the world’s history.

Is There a Reason for Everything?

The world is so constructed that there must be a reason or cause for everything. There are so many forces in the world that man has not yet been able to locate the original cause of every one of them. Concerning other things, he sees the effects without having any knowledge of the forces which are their cause. Other things he has never even bothered to inquire about, but simply takes them for granted. But every force, which means, of course, everything in the world, must have had a beginning and therefore something or a combination of things must have caused it to begin, and the thing or things that caused it to be is the reason for its being. Every little while someone makes a discovery of some new force, and then we suddenly realize that this force has been in existence all the time although not known to man, and we discover through this the reason for many other things being as they are.

The other thing or side of the question is also true. We cannot have a cause without an effect. You cannot do anything without causing something to happen and producing an effect on one or more other objects either animate or inanimate. You cannot move your hand without creating some disturbance in the air. When you make a noise, low or loud, you produce sound waves. When you burn a stick of wood, you create smoke, ashes and gases of various kinds. You change the whole nature of what was the piece of wood, and yet no particle of what made the stick of wood is ever destroyed or lost, but appears in some other thing in the air or on or in the earth.

What Makes an Echo?

An echo is caused when the waves of air which you create when you shout are thrown back again when they are stopped by something they encounter and are turned back without changing their shape. Any kind of a sound wave will make an echo in this way.

You see, you can have no sound of any kind without sound waves. You could not make a sound if there were no air. Now, when you shout, you start a series of sound waves that go out from you in every direction and they spread away from you in circles just like the rings of ripples that are caused when you drop a stone into a pool of water. You can prove this to yourself easily by having one, two, three or more of your friends stand around you in a large circle. You can place them as far away from you as your shout can be heard if you wish. When you shout, each of your friends will hear the shout at the same time, provided, of course, they are at equal distances from you.

Sometimes these sound waves as they go away from you in circles strike objects that turn the waves back unbroken just as they came to them. The waves will bounce back just like a rubber ball from a wall against which it has been thrown and this is the echo. However, some things that the sound waves strike break up these waves entirely and others partially.

No doubt you have sometimes noticed when you shout you hear a distinct echo and that at other times, standing in the same place, you cannot hear any echo, although you shout in the same way. This is explained by the fact that at times conditions of the air are such that no echo is produced while at other times a perfect echo results.

What is a Whispering Gallery?

The possibilities of an echo have to be taken into account by the architects and builders of all public buildings, such as theaters, halls and churches, where anyone is to speak or entertain others. Unless they are very careful the walls and ceilings may be so arranged that when any one sings or speaks in the room, there is such an echo that it interferes with the music or speaking. It sometimes happens also that through some peculiarity in which the walls and ceiling of a building are constructed there will be certain places in the room where an echo can be heard, even a whisper, and which cannot be heard in other parts of the room at all. This is likely to occur in rooms where there is a dome-shaped ceiling. There will be certain spots in the room hundreds of feet apart, where if you stand on one spot and another person is on another definite spot clear across the room, the tiniest whisper can be heard, while the people in between cannot hear at all. This is called a whispering gallery. Of course, loud talking would produce the same effect. A whispering gallery is a gallery with an echo which can be heard from certain positions. There are a number of famous whispering galleries of the world. In the room beneath the great dome of our Capitol at Washington is an almost perfect whispering gallery. There are quite a number of points at which you can stand and hear the whispers across the room which is more than a hundred feet. These whispering galleries come accidentally, of course. It would be difficult to deliberately construct a building in such a way as to produce a whispering gallery.

Why Do We Get a Bump Instead of a Dent When We Knock Our Heads?

When you knock your head against a sharp corner, or if some one hits you on the head with anything with a sharp edge, you do receive a dent in your head, but it does not last. In other words, the head has one of the qualities of a rubber ball. You can press your finger against the sides of the rubber ball and push it in, but when you take your finger off the ball resumes its shape. Just so with your head—it resumes its shape after a blow.

After doing this, however, a bump or lump is formed. I will endeavor to tell you how the bump is formed or rather what causes it to form. You cannot knock your head against anything that is harder than your head without causing some injury to the parts which received the bump. Now, what happens then is just what happens to any other part of your body when it is injured whether as a result of a bump, a cut or a bee or mosquito sting.

As soon as the injury occurs the brain starts the “repair crew” to work. The result is that first a great supply of blood is rushed to the injured part with the result that the blood vessels are filled up and extended with blood. Certain parts of the blood cells find their way through the walls of the blood vessels at the part of the injury and other fluids from the body are piled up there, so to speak, to form a congestion. This “piling up or congestion” distends the skin and raises the bump. On the head where the layer of muscular structure is thinner and where there is less space between the bones of the skull and the outside skin, the bump will be larger and more noticeable, because a good deal of blood and other fluids are piled up in a comparatively small space, and so the skin gets pushed out further to accommodate this great congestion, whereas in other parts of the body the bump may be quite as large but not so noticeable.