Part 89

There are two principal types of elevators used to-day; the hydraulic, which is worked by water under pressure, and the electric, which is worked by electricity through an electric motor. The latter type, because of the tendency towards the general use of electricity in recent years, has largely superseded the hydraulic, and, as when you think of elevators you probably have in mind those you have seen in some huge skyscraper, we shall look at one of these.

What are the Principal Parts of an Elevator?

The most advanced type of elevator to-day is called a Gearless Traction Elevator. In this elevator the principal parts are a motor, a grooved wheel on the motor shaft called a driving sheave and a brake, all mounted on one cast-iron bed-plate; a number of cables of equal length which pass over the driving sheave and thence around another grooved wheel called an idler sheave, located just below the driving sheave, and to one end of which is attached the car or cage, and to the other end a weight called a counterweight; also a controller which governs the flow of electric current into the motor and thereby the speed, starts and stops of the elevator car. Although the controller, motor, brake and sheaves are usually placed way at the top of the building out of our sight, they are really very important parts of the elevator.

The cage or car in which we ride is held in place by tracks built upright in the elevator shaft, and the counterweight at one side of the shaft travels up and down along two separate upright tracks. When the car goes up the counterweight on the other end of the cables goes down an equal distance. The counterweight is used to balance the load of the car and to make it easier for the motor to move the car.

Electricity is the power that makes the car go up or down. The operator in the car moves a master switch--in one direction if he wishes to go up, in the other direction if he wishes to go down. This master switch sets the electro-magnetic switches of the controller at the top of the hatchway into action, electrically, and the controller in turn allows the electric current to flow into the motor. The motor then begins to revolve, gradually at first, and then faster, turning the driving sheave with which it is directly connected. As this driving sheave revolves, the cables passing over it are set in motion, and the car and counterweight to which they are attached begin to move.

Why Does Not the Car Fall?

Of course, the question of safety is a very important one in any elevator, and you wonder what would happen if the cables broke. You think of this especially when you are going up in one of the big skyscrapers--where the elevators sometimes travel to a height of 700 feet. It can be truthfully said that on every modern elevator there are safety devices which should make it practically impossible to have a serious accident, due to the fall of the car. Every elevator is equipped with wedging or clamping devices which automatically grip the rails in case the car goes too fast either up or down. These gripping devices can be adjusted to work at any speed that is desired above the regular speed. It is not at all probable that all the cables will break at once, because there are usually six of these, and any one of them is strong enough to hold the car if the others break; but even if they all should break the gripping devices on the rails will operate and hold the car safely, just as soon as it starts down at great speed.

Suppose that the car should descend at full speed, but not sufficiently fast to work the rail-gripping devices, it would be brought to a gradual rest at the bottom of the hatchway, because of the oil-cushion buffer against which it would strike. This is a remarkable invention, with a plunger working in oil in such a way that a car striking it at full speed will come to rest so gradually that there is scarcely any shock. You have perhaps seen a clever juggler on the stage throw an ordinary hen’s egg high into the air and catch it in a china dish without cracking it He does it by putting the dish under the falling egg just at the right moment, and bringing the dish down with the egg at just the right speed, so that eventually he has the egg in the dish without cracking it. The trick is in calculating the rate of speed of the falling egg accurately and adjusting the insertion of the dish under the falling egg to a nicety. The oil-cushion buffer in the modern elevator works in very much the same way.

If it were not for the genius which has made possible these new types of elevators we could not have the high buildings. The elevators in the Woolworth Building are the latest type in modern elevator construction. In this one building alone there are 29 elevators, and when you are told that the electric elevators in the United States installed by a single company represent a total of 525,000 horse-power, you will have some idea of the power required to operate elevators all over the country.

Does Air Weigh Anything?

Air is very light, so light that it seems to have no weight at all; but, if you will think a minute you will see that it must have some weight, because birds fly in it and balloons can be made to float through it. It has been found that one hundred cubic inches of air at the sea level weighs, under ordinary conditions, about thirty-one grains. This seems a very small weight, but when we remember the thickness of the atmospheric envelope over the earth we see that it must press quite heavily upon the earth’s surface. There is a very simple instrument called a barometer, which is used for measuring the amount of this pressure. The name means pressure-measure.

Another striking feature of air is its elasticity, and this explains something that is noticed by all mountain climbers. On a high mountain, it is difficult to get enough air to the lungs, though one breathes rapidly and deeply. The reason is, that the air at the foot of the mountain is compressed by the weight of that above it, and consequently the lungs can hold more of it than of the air on the mountain top, which has less weight resting upon it and is, therefore, not so much compressed. On account of the ease with which it is compressed, we find that more than half of all the envelope of air that surrounds the earth is within three miles of the surface.

When air is chemically analyzed it is found to consist of a number of substances mingled together, but not chemically united. These include nitrogen, oxygen, argon, carbonic acid gas, water vapor, ozone, nitric acid, ammonia, and dust.

Oxygen is the most important of these constituents, for it is the part that is necessary to support life. Yet, notwithstanding its importance, it forms only about one-fifth of the entire bulk of the atmosphere.

Oxygen is a very interesting substance and many striking experiments may be performed with it. If a lighted candle is thrust into a vessel filled with oxygen, it burns very much more rapidly and brilliantly than in air. A piece of wood with a mere spark on it bursts into flame and burns brightly when thrust into oxygen, and some things that will not burn at all in air, can be made to burn very rapidly in oxygen. For example, if a piece of clock spring be dipped in melted sulphur and then put into a jar of oxygen, after the sulphur has been set on fire, the steel spring will take fire and burn fiercely. The heat produced is so great that drops of molten steel form at the end of the spring, and falling on the bottom of the jar, melt the surface of the glass where they strike.

The other two substances found in pure air, nitrogen and argon, are very much alike. They make up the remaining four-fifths of the air, and are very different from oxygen in nearly every respect.

Nitrogen and argon resemble oxygen in being colorless, odorless, and tasteless gases; and they are of nearly the same weight as oxygen, argon being a little heavier and nitrogen a little lighter; but here the similarity ends. Oxygen is what we call a very active substance. As we have seen, it causes things to burn very much more rapidly in it than in air. Nitrogen and argon, on the contrary, put out fire. If a lighted candle is put into a jar of nitrogen or argon its flame will be extinguished as quickly as if put into water.

We must now consider the impurities found in air. Of these the most important is carbonic acid gas, or, as it is frequently called, carbon dioxide. It is always produced when wood or coal is burned, and is, of course, constantly being poured out of chimneys. It is also produced in our lungs and we give off some of it when we breathe. It is colorless, like the gases found in pure air, has no odor or taste, and is considerably heavier than oxygen or nitrogen. In its other properties it is much more like nitrogen than oxygen, for when a candle is put into it the flame is extinguished at once. To find out whether air contains carbonic acid gas, it is only necessary to force it through a little lime water, in a glass vessel, and watch what change takes place in the water. Fresh lime water is as clear as pure water; but after forcing air containing carbonic acid through it, it becomes turbid and milky. If the turbid water is allowed to stand for a time, a white powder will settle to the bottom, and if we examine this powder, we find it to be very much the same thing as chalk. While it is true that air generally contains only a very small portion of carbonic acid gas, there are some places in which it is present in such large quantities as to render the air unfit for breathing. The air at the bottom of deep mines and old wells often has an unusually large proportion of this gas, which, because of its great weight, accumulates at the bottom, and remains confined there. The presence of a dangerous quantity of the gas in such places may be detected by lowering a candle into it.

Why Does the Scenery Appear to Move When We Are Riding in a Train?

When you sit in a moving train looking out of the window it appears as though the fields, the telegraph poles and everything else outside were moving, instead of you. This is because our only ideas of motion are arrived at by comparison, and the fact that neither you nor the seats of the car or any other part of the inside of the car is changing its position, leads you to the delusion that the things outside the car are moving and not you. If you were to pull down all the curtains and the train were making no noise at all, you would not think that anything was moving. It would appear as though you were motionless just as everything in the car appears so. When you turn then to the window, and lift the curtain you carry in the back of your mind the idea of being at rest and that is what makes it appear as though the fields and everything outside were moving in an opposite direction.

This is particularly noticeable when you are in a train in a station with another train on the next track. There is a sense of motion if one of the trains only is moving and you feel that it is the other train, because you are surrounded by objects in the car which are at rest, and when you look out at the other train with this half consciousness of rest in your mind, it appears as though the other train were moving when as a matter of fact it is your train. If the delusion happens to be turned the other way, it will appear as though you are moving and the other is still. It depends upon what cause the impression starts with.

Why Don’t the Scenery Appear to Move When I am in a Street Car?

If you are in a street car in the country and moving along fast you will receive the same impression, especially in a closed car, because you are looking out of one hole or one window. In an open car you do not receive the same impression because your range of vision is broader. You can and do, although perhaps unconsciously, look out on both sides and the impression your mind gets through the eyes is not the same. If you were to pull down all the storm curtains in a moving open street car, and then look out of one little crack, you would think the outside was moving. But if you stop to remember that you are moving and not the things outside the car, then the impression vanishes. In the city, of course, your brain is so thoroughly impressed with the fact that houses and pavements do not move, and the cars move so much more slowly, that it is difficult to make yourself believe otherwise. The impression is more difficult always when you are moving through or past objects with which you are perfectly familiar. It is all, of course, a question of impressions.

Why Does the Moon Travel With Us When We Walk or Ride?

The moon does not really travel with us. It only seems to do so. The moon is so far away that when we walk a block or two or a hundred, we cannot notice any relative difference in the relative positions of the moon and ourselves. When a thing is close at hand we can notice every change in our position toward it, but when it is far away the change of our position toward it is so slight that it is hardly perceptible. A very good way to illustrate this is to ask you to recall the last time you were in a railroad train looking out at the scenery in the country. The telegraph poles rush past you so fast you cannot count them. The cows in the pasture beside the railroad do not seem to go by so fast. You can count them easily. The tree farther over in the next field does not appear to be moving but slightly, while the church steeple which you can see far in the distance, does not go out of sight for a long time--in fact, seems almost to be moving along with you. The moon is just like the church steeple in this case, except that it is so much farther away that it seems to travel right with you. It is all due to the fact as stated at the beginning of this answer, that the relative positions of yourself and the moon are only slightly changed as you move from place to place, so slight in fact as to appear imperceptible.

Is There a Man in the Moon?

The markings which we see on the face of the moon when it is full can by a stretch of the imagination be said to form the face of a man. On some nights this face appears to be quite distinct. If, however, we look at the moon through a telescope, we see distinctly that it is not the face of a man. Through a very large telescope we can see very plainly that the marks are mountains and craters of extinct volcanoes. It just happens that these marks on the moon, aided by the reflections of the light from the sun, which gives the moon all the light it has, make a combination that looks like a face.

Does the Air Surrounding the Earth Move With It?