The Wonder Book Of Knowledge Part 27

Why are Windows Broken by Explosions?

When the large cannons in the forts on our coast are discharged during target practice, there are usually a lot of windows broken in the nearby houses. In Jersey City, N. J., several freight cars and boats loaded with dynamite and ammunition full of high explosives furnished the power for an explosion which, in July, 1916, broke considerably over a hundred thousand dollars worth of windows in the lower part of New York City.

The force of an explosion, whatever its source, throws back the air in huge waves, very much like the waves of the ocean, and whatever they come in contact with must have a sort of a tug-of-war with them, the weaker side being crumpled up and pushed back by the other. Broad expanses of gla.s.s, unprotected and without any support, except at the extreme edges, present an easy mark for air waves, therefore, and the amount of damage done to windows by explosions is usually only limited by the power of the explosives which produce the force of air waves.

The earth beneath, and the roof and walls of a building above, all receive the effects of these air waves in exactly the same way as do windows, and the resulting disaster is in direct proportion to their resisting capacity as against the pressure caused by the explosion. Many striking examples of the power of explosives have been accidentally furnished of late, in the course of making munitions for the European war.

What does the Expression "Showing the White Feather" Come From?

We say people "show the white feather" when they display cowardice, because a white feather in a bird marks a cross breed, and it is not found on a fighting game-c.o.c.k.

The Story in Elevators and Escalators[15]

Going up and down stairs is a duty every man, woman and child finds it necessary to perform daily and in many cases hourly, and some means for doing this is necessary in every modern household. Even in the old-time one-story house, steps from the outside to the inside were usually necessary, and when the two or more storied houses came into use the stairway became an indispensable feature. In modern times the art of building has had such an upward trend that edifices looming far into the air, hotels, stores, apartment houses, office buildings, etc., have come into use, one notable specimen, the Woolworth building in New York, towering upwards to fifty-four stories in height. This upward tendency has rendered the elevator, or lifting apparatus, an indispensable necessity, alike for pa.s.sengers and freight, and it has been installed abundantly in all our large cities.

[Ill.u.s.tration: IN ORDER TO ASCEND MORE EASILY, MAN DEVISED THE STAIRWAY, FROM WHICH, IN TURN, WAS DEVELOPED THE ESCALATOR, IN ORDER TO FURTHER ELIMINATE PHYSICAL EFFORT]

[Ill.u.s.tration: PRIMITIVE MAN PULLED HIMSELF UP A LADDER WHEN HE WANTED TO GO FROM ONE LEVEL TO ANOTHER]

The elevator is not exactly a new idea. Its pioneer form may be traced back to the Middle Ages, when heavy weights were lifted by aid of an apparatus worked by hand power. But it was not until well on into the nineteenth century that the steam-power elevator came into service. The first example is said to have been produced by Elisha Graves Otis, who applied steam power to an elevating machine in a little shop at Yonkers, on the banks of the Hudson, New York. A few years later, at the International Exhibition of 1853 in New York, he displayed the first elevator with a safety device to prevent the car from falling in case of a broken cable.

The elevator was then a novelty. It has long since grown into a necessity. It is to be seen in all hotels and high buildings, and the art of getting up stairs has in very many cases changed into that of being lifted up by a moving car in an enclosed shaft or cage. The steam elevator, at first used, has now in great measure been replaced by the electric elevator, the first moved by an electric motor being the Otis elevator installed in the Demarest Building, New York, in 1889. This is still in active use.

The first electric elevators were confined to the drum type of machine, these having a grooved drum around which the hoisting cables were wound, the drum being revolved through worm gearing by an electric motor. But the erection of buildings, ranging from 200 to 700 feet in height has put this type of traction out of business on account of the great size of drums required and the necessary slowness of motion. It has been replaced by the electric traction elevator. In this the hoisting cables from which the car is suspended have at the other end a counterweight and pa.s.s around driving sheaves in place of a drum. This, in its latest form known as the gearless traction elevator, does away with all intricate machinery, and yields a machine moving with equal speed whatever the height.

[Ill.u.s.tration: AN ELEVATOR OF THE MIDDLE AGES

History tells us this form of elevator was used in monasteries for hoisting pa.s.sengers and supplies.]

[Ill.u.s.tration: ELEVATOR INSTALLATION IN THE WOOLWORTH BUILDING, NEW YORK]

To obviate danger from accidents, safety devices are installed for gripping the rails in case of the car attaining excessive speed. Another feature of security is the oil cus.h.i.+on buffer. One of these is placed in the hoistway under the car and one under the counterweight, they being capable of bringing a car to rest from full speed without discomfort to those in the car. The oil in the buffer is driven by the impact of the car from one chamber of the buffer to another, but this is made to take place at a fixed rate of r.e.t.a.r.dation, the oil acting as a liquid cus.h.i.+on which stops the car gradually and without shock.

To do business in the modern lofty building without the aid of elevators (or lifts, as they are called in England) is today out of the question, while the great grain-transporting edifices in cities in which our annual crops are lifted and lowered, are known by the specific name of elevators. There is, however, another means of getting up and down stairs which is coming somewhat rapidly into use and in which the old stairway is restored. It is one in which the stair itself does the moving instead of the pa.s.sengers upon it. This new and interesting device is known as an escalator.

[Ill.u.s.tration: A STEAM-DRIVEN ELEVATOR OF EARLY DATE]

The Escalator.

The earliest way to get upward from the ground was that adopted by climbing animals in clambering up tree trunks, and by man himself in "s.h.i.+nning" up trees by aid of his arms and legs. This was followed by the plank leading from a lower to a higher level, by the ladder, and finally by the stairway. In our days the stairway has been put on a set of revolving wheels and moves upward itself, carrying its pa.s.sengers with no need on their part to use their feet. This simple but effective device is known as the escalator.

It is a very useful contrivance for tired shoppers needing to make their way from floor to floor in the great department stores, for travelers on subway or elevated railways, for large mills, theaters, or other places where easy getting up and down stairs is necessary. The escalator is a simple device. No intricate machinery is needed. It is so arranged as to be always going, traveling upwards or downwards, and returning out of sight below. It has been called "an elevator with the doors always open." It is capable of carrying all the pa.s.sengers who can crowd upon it, stepping on or off at the bottom or top, it being estimated that more than 10,000 people an hour can be thus moved.

[Ill.u.s.tration: BATTERY OF ELEVATORS IN A DEPARTMENT STORE]

[Ill.u.s.tration: ELECTRIC DUMBWAITER INSTALLATION WITH MACHINE IN BAs.e.m.e.nT SHOWING CALL b.u.t.tONS]

[Ill.u.s.tration: A COMPLETE INSTALLATION OF A 2 : 1 ELECTRIC TRACTION Pa.s.sENGER ELEVATOR, SHOWING MACHINE AND CONTROLLER AT TOP OF HATCHWAY

This elevator is used where the slower speeds are required as in department stores.]

[Ill.u.s.tration: ESCALATOR OR MOVING STAIRWAY AT SIXTH AVENUE AND THIRTY-THIRD STREET STATION OF ELEVATED RAILWAY, NEW YORK CITY]

[Ill.u.s.tration: A DUPLEX ESCALATOR OF THE CLEAT TYPE IN A DEPARTMENT STORE

This type of escalator makes use of hard wood cleats in place of steps.]

[Ill.u.s.tration: AN ESCALATOR OR MOVING STAIRWAY FOR THE USE OF EMPLOYEES IN A LARGE WORSTED MILL]

The Cleat Escalator.

In the original type of escalator the steps flatten out into a level platform at top and bottom, easy to step on and off, and divide into regular steps as they climb upward, pa.s.sengers in a hurry being able to hasten their speed by walking at the same time that they are carried.

Another type is that known as the cleat escalator. In this there are no steps, it being composed of hardwood cleats moving in longitudinal ridges and grooves, there being a handrail on either side moving at the same speed. The platform glides through the p.r.o.ngs of a comb at the lower level and journeys upward at a moderate speed. At the upper level it disappears through a similar comb and returns out of sight. The pa.s.sengers slide off upon the p.r.o.ngs of the comb at the top and land without jar or shock. Both these types of escalators can be made to move up or down by aid of a swinging switch, or two of them can be placed side by side, one moving upward and the other downward.

[Ill.u.s.tration: A CLEAT TYPE ESCALATOR, SHOWING THE HARDWOOD CLEATS USED IN PLACE OF STEPS]

The Moving Platform.

A device acting on the same principle is the moving platform, with the difference that this may be of indefinite length and act as a sort of railway for carrying pa.s.sengers from place to place. The pa.s.senger steps from a sideway at rest to one in moderate motion, and from this to a second one moving more rapidly, and in this way can be carried horizontally at a fair rate of speed. On reaching his station he has but to step back on the slower platform and from this to the moveless sideway. The pioneer example of this contrivance was installed on a long pier leading into Lake Michigan at the Chicago Exposition of 1893, and plans for putting it into practical use in various cities have been entertained. None of these, however, have yet been put into effect.

Certain drawbacks, possibly that of cost of installation and operation, has served as a hindrance.

[Ill.u.s.tration: A GRAVITY CONVEYOR OF THE SINGLE SPIRAL OPEN TYPE

For the quick and safe conveyance of heavy goods from upper to lower levels.]

What Happens when Animals Hibernate?

We have all heard of certain animals sleeping through the long winter months and most of us have probably wondered what happens to them when they do this.

This hiding away for a long sleep, or hibernation, as it is called, commences when the food of the animal begins to get scarce, and the length and depth of the sleep depends on the habit and const.i.tution of the animal.

Bats, bears, some animals of the rodent order, such as the porcupine, the dormouse, some squirrels, etc., all the animals belonging to the cla.s.ses of _Amphibia_ and _Reptilia_, such as tortoises, lizards, snakes, frogs, etc., and many species of mollusks and insects, hibernate more or less completely, retiring to suitable places of concealment--the bat to dark caves, the hedgehog to fern-brakes, snakes to holes in trees, etc.

During hibernation there is a great decrease of heat in the bodies of the animals, the temperature sometimes sinking to 40 or even 20 F., or in general to a point a little above that of the surrounding atmosphere.

The respiration as well as the pulsation of the heart is exceedingly slow, and the irritability of the animal often so low that in some cases it can be awakened only by strong electric shocks.

With frogs and amphibious reptiles the dormant state is very common, and if the temperature is kept low by artificial means they may remain dormant for years.