Does the Air Ever Get Used Up?
We may say that, in a sense, a great deal of the air has already been used up: for we know that by far the greater part of all the surface of the earth, including all the water of the seas, is already burned, and so has used up a great deal of the oxygen of the air. That happened a long time ago, however, before there were any living creatures. on the earth.
The air is constantly being used now - or, rather, the oxygen of it is being used - in the breathing of all living creatures: while the nitrogen of the air is being used by certain microbes, and now also by men themselves, who use electricity for this purpose; and, thirdly, green plants use the carbon dioxide of the air, upon which they feed.
Yet the air does not get used up as far as any of these gases are concerned. There must be compensation of some kind going on. There is compensation in regard to the oxygen because green plants everywhere in the sunlight are giving off to the air a great deal of oxygen - perhaps enough to make up for what they take in by breathing, and possibly also enough to make up for what animals and men take in by breathing.
As for the nitrogen that is used, we can easily show that that is compensated for; for when animals and plants die, their bodies decompose, and most of the nitrogen they contain, which they originally got from the air, is given back to the air. Lastly, the carbon dioxide taken from the air by plants is compensated for by the carbon dioxide which all living creatures give out to the air when they breathe.
Are the Clouds Part of the Earth or Do They Go Around With It?
Certainly the clouds are part of the earth. We sometimes forget that we do not really live on the outside of the earth at all, but only at the bottom of its outside layer, which we call the air or, in technical language, the atmosphere. That outside layer, and all it contains, such as the clouds, is as much part of the earth as the mountains or the oceans are. It is true that, from our point of view, we may think of the air as something laid on outside us to serve as a parasol by day and a blanket by night, as it does; but then our point of view depends on where we are.
The clouds are part of the earth and go round with it, as does the atmosphere in which the clouds hang. No doubt it is true that, as the earth spins, the air rather tends to drag behind; and high clouds will do this also. But, in general, the air and the clouds certainly spin round with the earth.
Why Does Iron Bend When it is Hot?
We all know that things vary in the way they behave when something tries to alter their shape. Some things will rather break than bend; others will bend and then come back again to their old shape; yet others after bending will stay in the new shape. Various names are applied to these different properties of matter. A general rule that applies almost always is that the colder a thing is, the more rigid it is. This applies even to the three great states of matter, solid, liquid and gaseous; for it is only in the coldest of these - which is the solid state - that things can have any rigidity at all, and, as a rule, the colder a solid thing is. the more rigid (unbending) it becomes. We believe that when a thing is made hot, the molecules of it are thrown into a state of greater motion, and we know that they are farther apart, for the thing expands. But if the molecules are farther apart, and if they are moving about more violently, they can not be holding on to each other so tightly and rigidly as before, and so the thing which, when it was cold, could not be bent, can now be bent. Directly we understand the nature of heat, we see how reasonable it is that iron should behave as it does.
Why Do We Say that Sugar is Sweet?
This is a question which can be answered in a way, yet can not be really answered at all. We know that there is a certain well- marked part of the surface of the brain which is the real seat of the sense of taste. From, or to, this place there run at least four, perhaps more, sets of nerves, the ends of which are in the “taste bulbs” of the tongue and part of the throat. One set of these nerves, when it is excited, arouses in the brain the feeling which we call a sweet taste, and the thing which specially excites this particular set of nerves is sugar.
But no one has the least idea why sugar should not taste salt, or why salt should not taste sweet or bitter; nor is there any imaginable way of describing a sweet, a salt, or, bitter or acid taste to anyone who does not know these tastes. We can not even know that other people taste sugar or anything else just as we do.
Sugar is really a name for a closely related group of chemical substances all of which are sweet-tasting, though some are less so than others - for instance, milk sugar. But saccharin, which some people use instead of sugar, is utterly different from sugar chemically, yet it is sweeter than any sugar.
Why Does a Match Strike?
A match strikes because we make it warm by rubbing it on something. You know that you have to rub something rather rough, so there is a good deal of friction. The movement of the match is hindered by the rough thing you press it against, and that is what we mean by friction. This makes the match hot. Rub the tip of your finger on your coat, and you will soon make your finger hot.
Now, the whole thing about the match is that its head is made of a mixture of things to which nothing happens as long as they are kept ordinarily cool, but as soon as they are made hot enough they catch fire - that is to say, they combine with the oxygen of the air, and so burn.
Our business, then, is to get a kind of mixture that will stay on the end of a piece of wood, or some such thing, and will catch fire even when made only so hot as we can make it by rubbing. Over a hundred years ago the first friction match was made, and almost the best of these at first required a lot of friction, for it had to be drawn up between two pieces of sand-paper before it would catch fire. Then the curious element called phosphorus, which really means light- bearer, began to be used, and matches were made very much like those we use now. The special peculiarity of phosphorus is that it readily catches fire just as we want it to do, but a number of other things are put into the match head, and especially something which itself contains oxygen, and can supply it for purposes of burning even more readily than the oxygen of the air. That is why you get a little explosion when you strike some kinds of matches.
But of course there is a certain amount of danger in having anything about you that will catch fire readily. Thus, if you have ordinary matches (what we now call kitchen matches) loose in your pocket, they may get rubbed together accidentally and they may catch fire. Therefore, the question arose whether there could not be made some kind of match which could be struck quite readily, but of which we could be sure that it would strike only when we really meant it to strike.
This kind of match was invented more than fifty years ago. Generally they are called safety matches. The point about them is that there is no phosphorus in their heads; the phosphorus is put on the outside of the box instead, and so this kind of match is almost certain not to catch on fire except when it is purposely struck where the phosphorus is. Now, there are at least two different kinds of phosphorus, and the commonest and cheapest of these, white or yellow phosphorus, is a very deadly poison. It is, in fact, used in making a poison to kill rats and other animal and insect pests. One grain of it may easily kill a man. People have often been killed by swallowing match- heads. Further, this dangerous kind of phosphorus was used in the heads of ordinary matches, and the people who made those matches often suffered great damage from phosphorus-poisoning.
However, the Belgian Government once offered a big prize for a “strike-anywhere” match that would contain no poisonous phosphorus. Two Frenchmen succeeded in making one, and now these safe matches are commonly used. Special laws are now in force in many countries forbidding the use of the dangerous white phosphorus in the match industry.
Why is it Dark at Night?
If you take a ball and hold it near a bright light the half of the ball next to the light is shown upon, and the half of the ball away from the light is dark. If you mark a spot on the ball, and then turn the ball round and round like a top, that spot will be shone upon half the time and will be in the dark the other half of the time. We live on a big ball called the earth, which is always spinning round and round, and it is shone upon all the time, day and night, by the bright light called the sun.
The place where we live is like the spot on the ball, and, as the great earth-ball spins, part of the time we are on the side toward the sun and part of the time we are on the side away from the sun. When we are on that side it is dark at night, but while it is our night it is daytime for the people who live on the other side of the ball. However dark it is where we live, the sun is always shining somewhere. If you think of the ball and the light you will understand that, however dark it is where we are, the spinning of the earth will soon carry us round into the light again.
Why Does Smoke Sometimes Rise and Sometimes Fall?
To answer this question, we must first understand what smoke is. You know that smoke usually results when a substance such as coal, wood or tobacco burns. Smoke is a mixture of gases, mostly water vapor, in which tiny solid particles are held. It is because of these solid particles that we can see smoke. As it leaves a burning log or a cigarette, it is of course quite hot, and this makes it lighter than the surrounding air. So it drifts up, as warm air will rise above cool air.
Eventually the gases become mixed with the air and the solid particles fall as dust or soot. On a damp day, however, when the air already contains as much water vapor as it can hold, the water vapor in the smoke is precipitated, that is, it forms into tiny drops of water and falls just as rain does. As it falls it carries with it the solid particles, and so we see the smoke fall though the amount of water present is too small for us to notice it. We see only the dark particles.
What is Chewing Gum Made of?
If you live in the country, you may have chewed on the little balls of spruce gum which drop off the white or black spruce or balsam fir trees. The gum which comes in packages, however, is really a substance called chicle. This is the milky juice (latex) of a hardwood tree called zapota which grows in the American tropics, especially in Mexico, British Honduras and Guatemala.
The latex is collected by tapping the trunk, very much as rubber is collected. Deep zigzag cuts are made in the trunk up to a height of thirty feet, and the thick latex oozes out and runs slowly down into a pan placed at the foot of the tree. The flow lasts about two hours and many quarts may be collected at one time. After the raw gum has been boiled in large kettles, it is poured out on greased canvas and molded into inarquettas or blocks weighing about twenty-five pounds. The gum is packed into bales of four blocks each for shipping.
To be manufactured into chewing gum, the grayish-brown blocks are re-melted, impurities are removed and sugar and flavoring are added. The finished product is then molded and wrapped into the familiar packages. Millions of people in the United States have the habit of chewing gum - far more than in any other country. Almost $70,000,000 worth of gum is made each year.
What Makes Me Wake Up in the Morning?
In order to understand this we must realize that we do not sleep in just the same way all through the night. At first we sleep deeply. Now, it is good to sleep deeply. It makes us look well and beautiful, and people seem to have noticed this, for they call the first hours of sleep the “beauty sleep.”
But for some hours after this we sleep less and less deeply. We can easily find this out by noticing exactly how loud a noise is required to wake one up at various times in his sleep. And we find that when a person has had nearly enough sleep he will be wakened by a noise which, a few hours before he would not have noticed.
That is the sort of thing that happens when we wake. We have been sleeping less and less deeply for some time, and our brain has almost awakened of itself. Then there comes a sound or a light, or perhaps we move in bed and feel ourselves moving, and since we are already very nearly awake, the sound or the light or the feeling wakes us up. Of course if we lived out-of-doors, as men did long ago, and as birds do still, light would wake us up. That is what wakes the birds now.
How Does the Speedometer of a Motorcar Work?
We can get an idea of how a speedometer works if we imagine that we hold in our hand a small wheel with a spindle through it, and a fine coil spring attached to the spindle. If we keep tapping the edge of the wheel, it will go round and gradually wind the spring up, but as soon as we stop tapping, the pull of the spring will send the wheel back to its original position. If a hand were fitted to the spindle so as to move over a properly numbered disc, a measure of speed would be obtained. Thinking of this, we can look at two popular types of the speedometer, the rotary and the dial types.
From the driving shaft of an automobile a flexible tube runs to the dial box. When the car is moving a flexible cable within the tube is revolved by means of worm gears attached to the driving shaft. At the top of the flexible cable is a circular magnet, and this therefore revolves. Fitting over the magnet, but not touching it, is (in the rotary type) an inverted drum on which are printed figures to show the car’s speed. The rotating magnet acts with magnetic force on the drum, and this magnetic influence has the same effect as the finger tapping on the wheel: it causes the drum to revolve. The faster the magnet revolves—that is, the faster the car is moving - the greater the magnetic pull on the drum, and a number is brought to the opening showing the speed of the car.
In the dial type the magnet fits into the centre of the indicator body, but is not in contact with it. As the magnet revolves, a current moves a pointer round a fixed dial. Movement of the drum or pointer is restrained by the counter-tension of a coiled spring. As the magnetic attraction increases with the speed, the resistance of the spring is gradually overcome, and the hand or drum moves round. As the car slows and stops, the magnetic force declines too, and the hand or drum goes back to zero.
The same driving power carried up the flexible tube actuates gears which turn the mileage recorder. This part of the speedometer which registers mileage has its own special name. It is called the odometer (from two Greek words meaning way and measure). One type measures separately the total mileage and the trip mileage. The trip mileage is registered up to ioo or iooo miles. In this recorder the extreme right-hand figure indicates a fraction of a mile. When the right - hand figure has recorded 9, and o is appearing, the disc on which the o is engages the disc immediately to the left which thus advances one figure higher, and so on right across. When 99.9 or 999.9 miles are recorded and the final one-tenth of a mile is just completed, the recorder shows zero in all places. At the start of a day’s run the trip recorder can be set at zero by turning a knob which advances the figures.
The sum of all these trip mileages is shown on the total mileage recorder. When the total mileage has reached 99,999 miles the addition of another mile sets all these numbers back to zero again.
Why Does a Tree Grow Upward?
The first thing to say in answering this question is that the whole tree does not grow up. Part of the tree grows downward, and that is the root. Each grows to the place where it can do the work for which it was made. In the seed from which the tree grows there are certain cells which are meant to form the part of the tree that is to live in the air and the light. Wherever the light is, they grow toward it. On the other hand, there are other cells which grow best in the dark, and which even seem to be affected by the gravitation of the earth, so that they grow best toward the centre of the earth.
So the tree - and this is true of nearly all plants - has two parts: one that lives in the air, and one that lives in the soil. Neither part could live without the other, and the tree is so made from the first that the right part of it, that which is capable of making leaves, must grow upward into the light and air; while that part of it which can suck up water and salts, and also can hold firm, must grow downward into the earth. So, in whatever position you plant a seed, when it sprouts the young shoot will grow upward and the young root downward.
