The Story of Great Inventions Part 2

The imperial army under Tilly and Pappenheim laid siege to the city. On the one side there was hope that Gustavus would arrive in time to effect a rescue; on the other, a determination to conquer before such aid could arrive. While Gustavus was on his way to the rescue, Magdeburg was taken by storm, and the most horrible scene of the Thirty Years' War was enacted. Tilly gave up the city to plunder, and his soldiers without mercy killed men, women, and children. In the midst of the scene of carnage the city was set on fire, and soon the horrors of fire were added to the horrors of the sword. In less than twelve hours twenty thousand people perished.

Guericke's house and family were saved, but the sufferings of the city were not yet ended. In five years the enemy was again before the walls, and Magdeburg, then in the possession of the Swedes, was compelled to yield to the combined Saxon and imperial troops. Guericke entered the service of Saxony, and was again made mayor of the city.

In the midst of these scenes of war, he found time to continue his studies. He made the first air-pump, and with it performed experiments which led to some very important results.

The experiments which Guericke made with his air-pump aroused the attention of the princes, and especially Emperor Ferdinand. Guericke was called to perform his experiments before the Emperor. The most striking of these experiments he performed with two hollow copper hemispheres about a foot in diameter, fitted closely together. When the air was pumped out, sixteen horses were barely able to pull the hemispheres apart, though, when air was admitted, they fell apart of their own weight.

Another experiment which astonished his audience was performed with the cylinder of a large pump (Fig. 5). A rope was tied to the piston. This rope was pa.s.sed over a pulley, and a large number of men applied their strength to the rope to hold the piston in place. When the air was taken out of the cylinder, the piston was forced down by air-pressure, and the men were lifted violently from the ground. This experiment, as we shall see, was of great importance in the invention of the steam-engine.

[Ill.u.s.tration: FIG. 5--GUERICKE'S AIR-PUMP Men lifted from the ground by air-pressure.]

Guericke's study of air-pressure led him to make a water barometer (Fig.

6). This consisted of a gla.s.s tube about thirty feet long dipping into a dish of water. The tube was filled with water, and the top projected above the roof of the house. On the water in the tube he placed a wooden image of a man. In fair weather the image would be seen above the housetop. On the approach of a storm the image would drop out of sight.

This led his superst.i.tious neighbors to accuse him of being in league with Satan.

[Ill.u.s.tration: FIG. 6--GUERICKE'S WATER BAROMETER In fair weather the image appeared above the housetop. When a storm was approaching the image dropped below the roof into the house.]

The first electrical machine was made by Guericke. This was simply a globe of sulphur turning on a wooden axle. He observed that when the dry hand was held against the revolving globe, the globe would attract bits of paper and other light objects.

Robert Boyle and the Pressure of Air and Steam

Robert Boyle, in England, improved the air-pump and performed many new and interesting experiments with it. One of his experiments was to make water boil by means of an air-pump without applying heat. It is now well known that water when boiling on a high mountain is not so hot as when boiling down in the valley. This is because the air-pressure is less on the mountain top than in the valley. By using an air-pump to remove the air-pressure, water may be made to boil when it is still quite cold to the hand.

Boyle compared the action of air under pressure to a steel spring. The "spring" of the air is evident to us in the pneumatic tire of the bicycle or automobile. Boyle found that the more air is compressed the greater is its pressure or "spring," and that steam as it expands exerts less and less pressure. This is important in the steam-engine.

Pascal and the Hydraulic Press

It was Blaise Pascal, a Frenchman, who proved beyond the possibility of a doubt that air-pressure supports the mercury in a barometer, and lifts the water in a pump (Fig. 7). He had two mercury barometers exactly alike set up at the foot of a mountain. The mercury stood at the same height in each. Then one barometer was left at the foot of the mountain, and the other was carried to the summit, about three thousand feet high.

The mercury in the second barometer then stood more than three inches lower than at first. As the barometer was carried down the mountain the mercury slowly rose until, at the foot, it stood at the same height as at first. The party stopped about half-way down the mountain, allowing the barometer to rest there for some time, and observing it carefully.

They found that the mercury stood about an inch and a half higher than at the foot of the mountain. During all this time the height of the mercury in the barometer which had been left at the foot of the mountain did not change.

[Ill.u.s.tration: FIG. 7--A LIFT-PUMP Air pressing down on the water in the well causes the water to rise in the pump. The air can do this only when the plunger is at work removing air or water and reducing the pressure inside the pump.]

It is now known that when a barometer is carried up to a height of nine hundred feet, the mercury stands an inch lower than at the earth's surface. For every nine hundred feet of elevation the mercury is lowered about one inch. In this way the height of a mountain can be measured, and a man in a balloon or an air-s.h.i.+p can tell at what height he is sailing. For this purpose, however, a barometer is used that is more easily carried than a mercury barometer.

Pascal invented the hydraulic press, a machine with which he said he could multiply pressure to any extent, which reminds us of Archimedes'

saying that, with his own hand, he could move the earth if only he had a place to stand. Pascal could so arrange his machine that a man pressing with a force of a hundred pounds on the handle could produce a pressure of many tons. In fact, a man can so arrange this machine that he can lift any weight whatever (Fig. 8).

[Ill.u.s.tration: FIG. 8--A SIMPLE HYDRAULIC PRESS A one-pound weight holds up a hundred pounds.]

The hydraulic press has two cylinders. One cylinder must be larger than the other. The two cylinders are filled with a liquid, as water or oil, and are connected by a tube so that the liquid can flow from one cylinder into the other. There is a tightly fitting piston in each cylinder. If one piston has an area of one square inch, and the other has an area of one hundred square inches, then every pound of pressure on the small piston causes a hundred pounds of pressure on the large piston. A hundred pounds on the small piston would lift a weight of ten thousand pounds on the large piston. But we can see that the large piston cannot move as fast as the small one does. Though we can lift a very heavy weight with this machine, we must expect this heavy weight to move slowly. There must be a loss in speed to make up for the gain in the weight lifted (Fig. 9). An hydraulic press with belt-driven pump is ill.u.s.trated in Fig. 10.

[Ill.u.s.tration: FIG. 9--HOW AN HYDRAULIC PRESS WORKS One man with the machine can exert as much pressure as a hundred men could without the machine. The arrows show the direction in which the liquid is forced by the action of the plunger _p_. The large piston _P_ is forced up, thus compressing the paper.]

[Ill.u.s.tration: FIG. 10--AN HYDRAULIC PRESS WITH BELT-DRIVEN PUMP]

Newton

Sir Isaac Newton as a boy did not show any unusual talent. In school he was backward and inattentive for a number of years, until one day the boy above him in cla.s.s gave him a kick in the stomach. This roused him and, to avenge the insult, he applied himself to study and quickly pa.s.sed above his offending cla.s.smate. His strong spirit was aroused, and he soon took up his position at the head of his cla.s.s.

It was his delight to invent amus.e.m.e.nts for his cla.s.smates. He made paper kites, and carefully thought out the best shape for a kite and the number of points to which to attach the string. He would attach paper lanterns to these kites and fly them on dark nights, to the delight of his companions and the dismay of the superst.i.tious country people, who mistook them for comets portending some great calamity. He made a toy mill to be run by a mouse, which he called the miller; a mechanical carriage, run by a handle worked by the person inside, a water-clock, the hand of which was turned by a piece of wood which fell or rose by the action of dropping water.

At the age of fifteen, his mother, then a widow, removed him from school to take charge of the family estate. But the farm was not to his liking.

The sheep went astray, and the cattle trod down the corn while he was perusing a book or working with some machine of his own construction.

His mother wisely permitted him to return to school. After completing the course in the village school he entered Trinity College, Cambridge.

Gravitation

It was in the year following his graduation from Cambridge that he made his greatest discovery--that of the law of gravitation. A plague had broken out in Cambridge, to escape which Newton had retired to his estate at Woolsthorpe. Here he was sitting one day alone in the garden thinking of the wonderful power which causes all bodies to fall toward the earth. The same power, he thought, which causes an apple to fall to the ground causes bodies to fall on the tops of the highest mountains and in the deepest mines. May it not extend farther than the tops of the mountains? May it not extend even as far as the moon? And, if it does, is not this power alone able to hold the moon in its...o...b..t, as it bends into a curve a stone thrown from the hand?

There followed a long calculation requiring years to complete. Seeing that the results were likely to prove his theory of gravitation, he was so overcome that he could not finish the work. When this was done by one of his friends, it was found that Newton's thought was correct--that the force of gravitation which causes bodies to fall at the earth's surface is the same as the force which holds the moon in its...o...b..t. As the earth and moon attract each other, so every star and planet attracts every other star and planet, and this attraction is gravitation.

Colors in Sunlight

About the same time that he made his first discoveries regarding gravitation, he took up the study of light with a view to improving the construction of telescopes. His first experiment was to admit sunlight into a darkened room through a circular hole in the shutter, and allow this beam of light to pa.s.s through a gla.s.s prism to a white screen beyond. He expected to see a round spot of light, but to his surprise the light was drawn out into a band of brilliant colors.

He found that the light which comes from the sun is not a simple thing, but is composed of colors, and these colors were separated by the gla.s.s prism. In the same way the colors of sunlight are separated by raindrops to form a rainbow. The colors may be again mingled together by pa.s.sing them through a second prism. They will then form a white light.

Suppose that the light of the sun were not composed of different colors, that all parts of white light were alike, then there would be no colors in nature. All the trees and flowers would have a dull, leaden hue, and the human countenance would have the appearance of a pencil-sketch or a photographic picture. The rainbow itself would dwindle into a narrow arch of white light; the sun would s.h.i.+ne through a gray sky, and the beauty of the setting sun would be replaced by the gray of twilight (Fig. 11).

[Ill.u.s.tration: FIG. 11--NEWTON'S EXPERIMENT WITH THE PRISM Sunlight separated into the colors of the rainbow. The seven colors are: violet, indigo, blue, green, yellow, orange, red.]

One of Newton's inventions was a reflecting telescope--that is, a telescope in which a curved mirror was used in place of a lens. He made such a telescope only six inches long, which would magnify forty times.

Newton was a member of the Convention Parliament, which declared James II. to be no longer King of England and tendered the crown to William and Mary. He was made a knight by Queen Anne in 1705.

His knowledge of chemistry was used in the service of his country when he was Master of the Mint. It was his duty to superintend the recoining of the money of England, which had been debased by dishonest officials at the mint. He did his work without fear or favor.

Once a bribe of 6000 ($30,000) was offered him. He refused it, whereupon the agent who made the offer said to him that it came from a great d.u.c.h.ess. Newton replied: "Tell the lady that if she were here herself, and had made me this offer, I would have desired her to go out of my house; and so I desire you, or you shall be turned out."

Although Newton's discoveries in the world of thought were among the greatest ever made by man, he regarded them as insignificant compared with the truth yet undiscovered. He said of himself: "I do not know what I may appear to the world, but to myself I seem to have been only like a boy playing on the sea-sh.o.r.e and diverting myself in now and then finding a smoother pebble or a prettier sh.e.l.l than the ordinary, whilst the great ocean of truth lay all undiscovered before me."

Chapter III

THE EIGHTEENTH CENTURY

James Watt and the Steam-Engine

If you had visited the coal-mines of England and Scotland three hundred years ago, you might have seen women bending under baskets of coal toiling up spiral stairways leading from the depths of the mines. At some of the mines horses were used. A combination of windla.s.s and pulleys made it possible for a horse to lift a heavy bucket of coal.

There came a time, however, when slow and crude methods such as these could not supply the coal as fast as it was needed. The shallower mines were being exhausted. The mines must be dug deeper. The demand for coal was increasing. The supply of coal, it was thought, would not last until the end of the century. The wood supply was already exhausted. It seemed that England was facing a fuel famine.

There was only one way out of the difficulty. A machine must be invented that would do the work of the women and horses, a machine strong enough to raise coal with speed from the deepest mines. Then it happened that two great inventors, Newcomen and Watt, arose to produce the machine that was needed. When the world needs an invention it seldom fails to appear. It is true of the world, as of an individual, that "Necessity is the mother of invention."

In the mean time Torricelli had performed his famous barometer experiment, and Otto von Guericke had astonished princes with proofs of the pressure of the air. There was no apparent connection between these experiments and the art of coal-mining, yet these discoveries made possible the steam-engine which was to revolutionize first the coal-mining industry and, later, the entire industrial world.