Galileo and the Battle for TruthFor eighteen centuries after the time of Archimedes no inventions of importance were made. Men sought for truth where truth could not be found. They looked within their mouldy manuscripts and asked, "What do the great philosophers say ought to happen?" instead of looking at nature and asking, "What does happen?" And when a man arose who dared to doubt the authority of the old masters and turn to nature to find out the truth, all the weapons at the command of the old school were hurled against him.Let us, at this distance, blame neither the one side nor the other. The conflict was inevitable. It was an accident of history that the brunt of the attack fell upon a man born in Italy in 1564, and that the battle was fought chiefly in the "Eternal City," from which centuries before had marched the legions that conquered the world.The boy, Galileo, who was to become the central figure of the great conflict, was talented in many ways. In lute-playing his skill excelled that of his father, who was one of the noted musicians of his day. His skill in drawing wassuch that noted artists submitted their work to him for criticism. He wrote essays on the works of Dante and other classical writers. He amused his boy companions by constructing toy machines which, though ingenious, did not always work.His preference was for mechanics, but, as this subject offered little prospect of profitable work, he took up the study of medicine in accordance with his father's wishes.In his eighteenth year he entered the University of Pisa. Here he found men who refused to think for themselves, but decided every question by referring to what the ancient philosophers said. Galileo could not endure such slavish submission to authority. So strongly did he assert himself that he was nicknamed "The Wrangler," and, by his wrangling, he lost a scholarship in the university.He neglected his medical studies and secretly studied mathematics. His father, learning of this, consented to his becoming a mathematician. Thus he followed his bent, though it seemed to lead directly to poverty.The Pendulum ClockIt was while a student at the University of Pisa that he discovered a law of pendulums which makes possible our pendulum clocks. While at his devotions in the cathedral, he observed the swinging of the bronze lamp which had been drawn back for lighting. Timing its swinging by means of his pulse, the only timepiece in his possession, he found that the time of one swing remained the same, though the length of the swing grew smaller and smaller. Thisdiscovery led to his invention of an instrument for physicians' use in timing the pulse. About fifty years later he invented the pendulum clock (Fig. 2).FIG. 2–GALILEO'S PENDULUM CLOCKFIG. 2–GALILEO'S PENDULUM CLOCKIt had only one hand, which is not shown in the picture.Lack of funds compelled him to leave the university without completing his course. He returned to the parental roof and continued his scientific studies. The writings of Archimedes were his favorite study. With Archimedes' famous experiment on King Hiero's crown as a starting-point, he discovered the laws of floating bodies, which explain why a ship or other object floats on water, and invented a balance for weighing objects in water.But such employment won nothing more substantial than honor and fame. Food and clothing were needed. For two years he strove without success to secure employment. At the end of that time he was appointed professor of mathematics in the University of Pisa at the magnificent salary of sixty scudi (about sixty-three dollars) per year. "But any port in a storm; and in Galileo's needy circumstances even this wretched salary was not to be rejected." Moreover, he could add somewhat to his income by private tutoring.Galileo's Experiment with Falling ShotWhile teaching at the University of Pisa, he performed his famous experiment of dropping from the top of the leaning tower two shot, one weighing ten pounds, the other one pound. Now, according to Aristotle, the ten-pound shot should fall in one-tenth the time required by the one-pound shot. But the assembled company of professors and students saw the two shot start together, fall together, andstrike the ground at the same instant, and still refused to believe their own eyes. They continued to affirm that a weight of ten pounds would reach the ground in a tenth of the time taken by a one-pound weight, because they were able to quote chapter and verse in which Aristotle assured them that such is the fact. Thus Galileo made enemies of the other professors, but for a time they could do nothing more than annoy him.About this time Galileo incurred the wrath of the Grand Duke of Tuscany, from whom he had received his appointment. He was commissioned to examine a machine invented by a nephew of the Grand Duke for the purpose of cleaning harbors. Galileo plainly said that the machine was worthless. It was tried, and his opinion proved true. But like the kings of olden time who killed the bearer of evil tidings even though the tidings were true, his enemies made his position so unpleasant that he resigned.He had neither employment nor money. His father's death occurring about this time, threw upon him the care of a mother, a worthless brother, and two sisters. In his distress he sought help from a friend, and secured an appointment as professor of mathematics in the University of Padua. His salary was one hundred and eighty florins (about ninety-five dollars), while other professors received more than ten times as much.While at Padua, Galileo was busy inventing. He invented the sector, which is to be found in most cases of mathematical instruments and is used in certain kinds of drawing. He also invented an air thermometer (Fig. 3), the first instrument for measuring temperature.FIG. 3–AN AIR THERMOMETERFIG. 3–AN AIR THERMOMETERWhen the air in the bulb grows cooler it contracts, and the air outside forces the Water up the tube. When the air in the bulb grows warmer it expands and forces the water down in the tube.In 1604 there appeared a new star of great brilliancy. It continued to shine with varying brightness for eighteen months, and then vanished. This was a strange event, and Galileo made use of it. He proved that the new star must lie among the most distant of the heavenly bodies, and this fact did not agree with Aristotle's view that the heavens are perfect, and therefore never change. A heated controversy followed, and Galileo came out boldly in favor of the theory that the earth revolves about the sun, the prevailing notion then being that the earth does not move, but that the sun and other heavenly bodies revolve around it.The TelescopeIn 1609 Galileo learned of a discovery that was to be of great value to the world, but a source of untold trouble to himself. An apprentice of a Dutch optician, while playing with spectacle lenses, chanced to observe that if two of the lenses were placed in a certain position objects seen through them appeared much nearer. Galileo, learning of this, set to work to construct a spy-glass, applying his knowledge of light. In one day he had constructed such an instrument, in which he used two lenses like the lenses of the modern opera-glass. Thus, while the Dutchman's discovery was by accident, Galileo's was by reasoning, and was the more fruitful, as we shall see.Galileo continued improving his telescope until he had made one which would magnify thirty times. He was the first to apply the telescope to the study of the heavenly bodies. The most startling of his discoveries was that ofthe moons of the planet Jupiter, which he called new planets.This aroused the fury of his enemies, who ridiculed the idea of there being new planets; "for," they said, "to see these planets they must first be put inside the telescope." The excitement was intense. Poets chanted the praise of Galileo. A public fête was held in his honor. One of his pupils was imprisoned in the tower of San Marco, where he had gone to make observations with his telescope, and could not escape until the crowd had satisfied their curiosity. Some of the philosophers refused to look lest they should see and be convinced.Galileo's StruggleHis enemies sought to steal from him the honor of his discoveries. Some claimed to have made the discoveries before Galileo did. Others claimed that his discoveries were false, that their only use was to gratify Galileo's vanity and thirst for gold. In these trying times the friendship of the great astronomer Kepler warded off some of the most exasperating attacks.Galileo's fame spread throughout Europe. Students came in great numbers, so that he had little leisure left for his own studies. He therefore decided to leave Padua, and secured an appointment as mathematician and philosopher to the Grand Duke of Tuscany. This appointment took him to Florence. It was here that an incident occurred that marked the beginning of a persecution which continued to the end of his life.As we read the story of this conflict let us remember thatit was not primarily a conflict between the Roman Catholic Church and Galileo. It was a conflict of principles. On the one side were arrayed those who said that men should always believe as the ancient writers did; on the other, those who said men should think for themselves. In the first party were most of the university professors and others who dreaded the introduction of new beliefs, whether in religion or science. In the second party were Galileo and a small band of devoted followers.At a dinner at the table of the Grand Duke in Pisa the conversation turned on the moons of Jupiter. Some praised Galileo. Others condemned him, saying that the Holy Scriptures were opposed to his theory of the motion of the earth. A friend reported the incident to Galileo, and he replied to the arguments of his opponents in a letter which was made public. No doubt the sting of his sarcasm made his enemies more bitter. He admitted that the Scriptures cannot lie or err, but this, he said, does not hold good of those who attempt to explain the Scriptures. In another letter, he quoted with approval a saying of Cardinal Baronius, "The Holy Spirit intended to teach us in the Bible how to go to Heaven, not how the heavens go."The first shot had been fired. The battle was on, and the Church, because it possessed the most powerful weapons of attack, was used by the combined forces to break the power of Galileo's reasoning. He went to Rome to make his defence, but was commanded by the Holy Office not to hold or teach that the sun is immovable, and that the earth moves about the sun.During another visit to Rome there was shown to Galileoan instrument which, it was said, would show a flea as large as a cricket. Galileo recalled that some years before he had so arranged a telescope that he had seen flies which he said looked as big as a lamb, and were covered all over with hair. This was the first microscope. Galileo quickly improved the instrument, and soon his microscopes were in great demand.In violation of the decree of the Church, to which he had submitted, he published his most famous work in which he defended the theory that the earth moves about the sun. The book was the outcome of his life-work, but the Church believed it dangerous. He was summoned to Rome. Confined to a sick-bed, he pleaded for delay, which was granted. Before he recovered, however, the summons was made imperative. He must go to Rome, or be carried in irons. He went in a litter, carried by servants of the Grand Duke. In Rome he was to appear before the Inquisition. There he was treated with a consideration never before accorded to a prisoner of the Inquisition. Nor was he subjected to torture, as has been stated by some. He was found guilty of teaching the doctrine that the sun does not move, and that the earth moves about the sun. He was compelled to recant, and sentenced to the prison of the Holy Office and, by way of penance, to repeat once a week for three years the seven penitential Psalms.He yielded without reserve to the decree of the Inquisition, renounced his "errors and heresies," and, with his hand on the Bible, took oath never again to teach the forbidden doctrine.And now, though a shattered old man of seventy-four,enjoined to silence on the chief results of his life-work, nothing could quench his devotion to science. In these last years, he published a new book which, with his earlier work, entitles him to be regarded as the founder of the science of mechanics.In his study of machines Galileo found that no machine will do work of itself. Whenever a machine is at work, a man or a horse, or some other power, is at work upon the machine. In no case will a machine do work without receiving an equal amount of work.Torricelli and the BarometerGalileo had a pump which he found would not work when the water was thirty-five feet below the valve. He thought the pump was injured, and sent for the maker. The maker assured him that no pump would do better. This led Torricelli, one of Galileo's pupils, to the discovery of the barometer. Men had said that water rises in a pump because nature abhors a vacuum. Torricelli believed that air-pressure and not nature's "horror of a vacuum" is the cause of water rising in a pump. He invented the barometer to measure air-pressure.The first barometer was a glass tube filled with quick-silver or mercury (Fig. 4). The tube was closed at theupper end, and the lower end, which was open, dipped in a dish of mercury. He allowed the tube to stand, and saw that the height of the mercury changed. This he believed was because the air-pressure changed. Wind, Torricelli said, is caused by a difference of air-pressure, which is due to unequal heating of the air. For this reason a cool breeze blows from the mountain top to the heated valley, or from sea to land on a summer day.FIG. 4–TORRICELLI'S EXPERIMENTFIG. 4–TORRICELLI'S EXPERIMENTOtto Von Guericke and the Air-PumpAbout this time a German burgomaster, Otto von Guericke, of Magdeburg, was performing experiments on air-pressure. The Thirty Years' War had been raging for thirteen years. The Swedish King, Gustavus Adolphus, had landed in Germany, and was winning victory after victory over the imperial troops. Magdeburg had entered into an alliance with the Swedish King, by which he was granted free passage through the city, while, on the other hand, he promised protection to the city.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 thehorrors 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 passed 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.FIG. 5–GUERICKE'S AIR-PUMPFIG. 5–GUERICKE'S AIR-PUMPMen 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 glass 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 superstitious neighbors to accuse him of being in league with Satan.FIG. 6–GUERICKE'S WATER BAROMETERFIG. 6–GUERICKE'S WATER BAROMETERIn 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 SteamRobert 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 exertsless and less pressure. This is important in the steam-engine.Pascal and the Hydraulic PressIt 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, andobserving 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.FIG. 7–A LIFT-PUMPFIG. 7–A LIFT-PUMPAir 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-ship 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).FIG. 8–A SIMPLE HYDRAULIC PRESSFIG. 8–A SIMPLE HYDRAULIC PRESSA one-pound weight holds up a hundred pounds.The hydraulic press has two cylinders. One cylindermust 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 illustrated in Fig. 10.FIG. 9–HOW AN HYDRAULIC PRESS WORKSFIG. 9–HOW AN HYDRAULIC PRESS WORKSOne 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 plungerp. The large pistonPis forced up, thus compressing the paper.FIG. 10–AN HYDRAULIC PRESS WITH BELT-DRIVEN PUMPFIG. 10–AN HYDRAULIC PRESS WITH BELT-DRIVEN PUMPNewtonSir 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 class gave him a kick in the stomach. This roused him and, to avenge the insult, he applied himself to study and quickly passed above his offending classmate. His strong spirit was aroused, and he soon took up his position at the head of his class.It was his delight to invent amusements for his classmates. 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 tothese kites and fly them on dark nights, to the delight of his companions and the dismay of the superstitious 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 handleworked 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.GravitationIt 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 orbit, 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 orbit. As the earth and moon attract eachother, so every star and planet attracts every other star and planet, and this attraction is gravitation.Colors in SunlightAbout 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 pass through a glass 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 glass 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 passing 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 shine through a gray sky, and the beauty of the setting sun would be replaced by the gray of twilight (Fig. 11).FIG. 11–NEWTON'S EXPERIMENT WITH THE PRISMFIG. 11–NEWTON'S EXPERIMENT WITH THE PRISMSunlight 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. Herefused it, whereupon the agent who made the offer said to him that it came from a great duchess. 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-shore and diverting myself in now and then finding a smoother pebble or a prettier shell than the ordinary, whilst the great ocean of truth lay all undiscovered before me."Chapter IIITHE EIGHTEENTH CENTURYJames Watt and the Steam-EngineIf 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 windlass 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 inventionit 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.The First Steam-Engine with a PistonThe first steam-engine with a piston was made by Denys Papin, a Frenchman. Papin had observed that, in Guericke's experiment, air-pressure lifted several men off their feet. So he thought the air could be made to lift heavy weights and do useful work. But how should he produce the vacuum? His first thought was to explode gunpowder beneath the piston. The gunpowder engine had been tried by others and found wanting. He next turned his attention to steam, and discovered that if the piston were forced up by steam and then the steam condensed, a vacuum was formed beneath the piston, and air-pressure forced the piston to descend. If the piston were attached to a weight by a rope passing over a pulley, then, as the piston descended, it would lift the weight. Papin's engine consisted simply of a cylinder and piston (Fig. 12). There was no boiler, but the water was placed in the cylinder beneath the piston. A fire was placed under the cylinder and, asthe water boiled, the steam raised the piston. Then the fire was removed and, as the cylinder cooled, the steam condensed, and the piston was forced down by air-pressure. This was a slow and awkward method. The engine required several minutes to make one stroke.FIG. 12–PAPIN'S ENGINEFIG. 12–PAPIN'S ENGINEThe first steam-engine with a piston. When the pistonBwas forced down by air-pressure, a weight was lifted by means of a ropeTTpassing over pulleys.The principle of Papin's engine was first successfully applied by Thomas Newcomen. Newcomen was a blacksmith by trade, and his great successor, Watt, was a mechanic. Thus we see that great discoveries soon become common property. The blacksmith and the mechanic soon learn to use the discoveries of the scientist.Newcomen's EngineIn the Newcomen engine the piston moved a walking-beam to which was attached a pump-rod. Steam was used merely to balance the air-pressure on the piston and allow the pump-rod to descend by its own weight. The steam was condensedin the cylinder, and the pressure of the air forced the piston down. Thus the work of raising water in the pump was done by the air. Newcomen's first engine made twelve strokes a minute, and at each stroke lifted fifty gallons of water fifty yards. He used this engine in pumping water from the mines, and also made engines for lifting coal.At first the steam was condensed by throwing cold water on the outside of the cylinder. But one day the engine suddenly increased its speed and continued to work with unusual rapidity. The upper side of the piston was covered with water to make the piston air-tight, and it was found that this water was entering the cylinder through a hole that had worn in the piston, and this jet of cold water was rapidly condensing the steam. This was the origin of "jet condensation."After this steam and water were alternately admitted to the cylinder through cocks turned by hand. A boy, Humphrey Potter, to whom this work was intrusted, won fame by tying strings to the cocks in such a way that the engine would turn the cocks itself and the boy, Humphrey, was free to play. This device was the origin of valve-gear.[1][1]Any device by which a steam-engine operates the valves which admit steam to the cylinder is called "valve-gear." One form of valve-gear is the link motion invented by Stephenson. This form will be described in connection with the locomotive. A simple valve-rod, worked by an eccentric such as is used on most stationary engines, is also a form of valve-gear.Newcomen's engine was extensively used. The tin and copper mines of Cornwall were deepened. Coal-mines were sunk to twice the depth that had been possible. But asthe mines were deepened the cost of running the engines increased. The largest engines consumed about $15,000 worth of coal per year. The Newcomen engine required about twenty-eight pounds of coal per hour per horse-power, while a modern engine consumes less than two pounds. Again, because of increased cost, mines were being abandoned. Such was the situation when James Watt came into the field of action.Watt had learned the mechanic's trade in one year in a London shop, and, because he had not passed through an apprenticeship of seven years, the Guild of Hammermen, a labor-union of his time, refused him admission, and this refusal meant no employment. He found shelter, however, in the University of Glasgow, and was there provided with a small workshop where he could make instruments for sale.Watt's EngineA small Newcomen engine belonging to the University of Glasgow was out of repair. London mechanics had failed to make it work. The job was given to Watt. That he might do a perfect piece of work on this engine, he made a study of all that was then known relating to steam (Fig. 13).FIG. 13–THE NEWCOMEN ENGINE, IN REPAIRING WHICH WATT WAS LED TO HIS GREAT DISCOVERIESFIG. 13–THE NEWCOMEN ENGINE, IN REPAIRING WHICH WATT WAS LED TO HIS GREAT DISCOVERIESPreserved in the University of Glasgow.He saw that there was a great loss of heat in admitting cold water into the cylinder to condense the steam, and that, to prevent this loss, the cylinder must be kept always as hot as the steam that enters it. While thinking upon this problem the idea came to him that, if connection were made between the cylinder and a tank from which the airhad been pumped out, the steam would rush into the tank, and might there be condensed without cooling the cylinder. This was the origin of the condenser.We have seen that, in the Newcomen engine, the steam acted only on the under side of the piston, air acting on the upper side. It occurred to Watt that the steam should act on both sides of the piston. So he proposed to put an air-tight cover on the cylinder with a hole and stuffing-box for the piston to slide through and to admit steam to act upon it instead of air. Thus he was led to invent the double-acting engine. The action in the cylinder of Watt's engine was the same as that of the modern engine.To save the power of steam, Watt arranged the valve in his engine in such a way that the steam was cut off from the cylinder when the piston had made about one-fourth of a stroke. The steam in the cylinder continues to expand and drive the piston. This device more than doubles the amount of work that the steam will do (Fig. 14).FIG. 14–CYLINDER OF WATT'S STEAM-ENGINEFIG. 14–CYLINDER OF WATT'S STEAM-ENGINEArrows show the course of the steam.Horse-Power of an EngineWhen horses were about to be replaced by the steam-engine at the mines, the question was asked: "How many horses will the engine replace?" Tests were made by Watt and others before him of the rate at which a horse could work in pumping water or in lifting a weight by means of a pulley. Watt's experiments showed that "a good London horse could go on lifting 150 pounds over a pulley at the rate of 2-1/2 miles an hour or 220 feet per minute, and continue the work eight hours a day." This would beequal to lifting 33,000 pounds one foot high every minute. This rate of doing work he called a horse-power. It is more than the average horse can do, but this number was used by Watt that he might give good measure in his engines. The horse-power of an engine at that time meant the rate of work in lifting water or coal. Now it means the rate of work done by the steam upon the piston, so that to find the useful horse-power of an engine we must deduct the work wasted in friction.The indicator for measuring the pressure of steam in the cylinder and the fly-ball governor are also inventions madeby Watt (Fig. 15). The fly-ball governor replaced the throttle-valve which was at first used by Watt to regulate the speed of his engines. The throttle-valve is still used on locomotives.FIG. 15–A FLY-BALL GOVERNORFIG. 15–A FLY-BALL GOVERNORThe balls as they rotate regulate the admission of steam to the cylinder by means of the leverLand the rodR.At the end of the eighteenth century the steam-engine was full grown. It remained for the nineteenth century to apply the engine to locomotion on sea and land, to develop the steam-turbine, and so to increase the power of the steam-engine that, early in the twentieth century, a 68,000-horse-power engine should speed an ocean liner across the Atlantic in five days.The Leyden JarThe first electrical invention of practical use was made by Benjamin Franklin. In Franklin's time great interest in electricity had been aroused by the strange discovery of a German professor, Pieter van Musschenbroek, of the University of Leyden. This professor had tried what he called a new but terrible experiment. He had suspended by two silk threads a gun-barrel which received electricity from an electrical machine. From one end of the gun-barrel hung a brass wire. The lower end of this wire dipped in a jar of water. He held the jar in one hand, while with the other he tried to draw sparks from the gun-barrel. Suddenly he received a shock which seemed to him like a lightning stroke. So violent was the shock that he thought for a moment it would end his life.Out of this experiment came the Leyden jar, which for a century and a half was of no practical use, but which now forms an important part of every wireless telegraph equipment. The Leyden jar is simply a glass bottle or jar coated with tin-foil both inside and outside (Fig. 16). When charged with electricity the jar will hold its charge until the two coatings are connected by a metal wire or othergood conductor of electricity. A person may receive a strong shock by holding the jar in one hand and touching a knob connected to the inner coating with the other hand.FIG. 16–A LEYDEN JARFIG. 16–A LEYDEN JARPopular interest in electricity was aroused by this discovery. The friction electrical machine and the Leyden jar were simple and easy to make. People of fashion found them interesting and amusing, the more so because of the shock felt on taking through the body the discharge from the "wonderful bottle," and the fact that several persons could receive the shock at the same instant. On one occasion the Abbé Nollet discharged a Leyden jar through a line composed of all the monks of the Carthusian Monastery in Paris. As the line of serious-faced monks a mile in length jumped into the air, the effect was ridiculous in the extreme.Conductors and InsulatorsAbout this time other great electrical discoveries were made. Early in the century, Stephen Gray discovered that some objects conduct electricity and others do not. He discovered that, when a glass tube is electrified by rubbing, it will attract and repel light objects. In the same way a comb or penholder of rubber may be electrified by rubbing it on the sleeve. A bit of paper which touches the comb becomes electrified. Electricity can be transferred from one object to another. Gray discovered further that contact is not necessary, that a hempen thread or a wire will carry an electric charge from one object to another. A silk thread will not carry the electric charge. "Some things convey electricity," he said, "and some donot, and those which do not can be used to prevent the electricity escaping from those which do." Could this obscure inventor have seen a modern telegraph line with the glass insulators on the poles, which prevent the electric current escaping from the telegraph wire, he might have realized the importance of his discovery. He set up a line of hempen thread six hundred and fifty feet long, and with an electrical machine at one end of the line electrified a boy suspended from the other end.Two Kinds of Electric ChargeA Frenchman, DuFay, while carrying further the experiments of Gray, was watching a bit of gold-leaf floating in the air. The gold-leaf had been repelled after contact with his electrified glass tube. Thinking to try the action of two electrified objects on the gold leaf, he rubbed a piece of gum-copal and brought it near the leaf. To his astonishment the leaf, which was repelled by the glass tube, was attracted by the gum-copal. He repeated the experiment again and again, and each time the leaf was repelled by the glass and attracted by the gum. He concluded from this that there are two kinds of electricity, which he named "vitreous" and "resinous." The two kinds of electric charge were called by Franklin "positive" and "negative."Franklin made a battery of Leyden jars, connecting the inner coating of one to the outer coating of the next throughout the series. In this way he could get a much stronger spark than with a single jar. On one occasion he nearly lost his life by taking a shock from his battery of Leyden jars.He magnetized and demagnetized steel needles by passing the discharge from his Leyden jars through the needles.Franklin's Kite ExperimentThe conjecture that lightning is of the same nature as the spark from the Leyden jar or the electrical machine had gained a hold on the minds of others before Franklin. In France sparks had been drawn from a rod ninety-nine feet high, but this did not reach into the clouds. Franklin determined to send a kite into a thunder-cloud, thinking electricity from the cloud would follow the string of the kite and could be stored in a Leyden jar, and used like the charge from an electrical machine. He had felt the power of a Leyden-jar discharge, and through it had nearly lost his life. He knew that lightning is far more powerful than any battery of Leyden jars, and yet to test the truth of his theory, that lightning is an electrical discharge, he was about to draw the lightning to his hand. He knew little of conductors of electricity. Whether the cord would draw little or much of the "electric fire" he knew not. So far as he knew he was toying with death.The kite was made of two light strips of cedar placed crosswise, and a large silk handkerchief fastened to the strips. A sharp wire about a foot long was fastened to one of the strips. To the lower end of the cord he attached a key and a silk ribbon. By means of the ribbon he held the cord to insulate it from his hand. The kite soared into the clouds, and Franklin and his son stood under a shed awaiting the coming of the "electric fire" (Fig. 17). Soonthe fibres of the cord began to bristle up. He approached his knuckles to the key. A spark passed. He brought up a Leyden jar and charged it with electricity from the cloud, and found that with this charge he could do everything that could be done with electricity from his machine. He had proved the identity of lightning and electricity.
Galileo and the Battle for Truth
Galileo and the Battle for Truth
For eighteen centuries after the time of Archimedes no inventions of importance were made. Men sought for truth where truth could not be found. They looked within their mouldy manuscripts and asked, "What do the great philosophers say ought to happen?" instead of looking at nature and asking, "What does happen?" And when a man arose who dared to doubt the authority of the old masters and turn to nature to find out the truth, all the weapons at the command of the old school were hurled against him.
Let us, at this distance, blame neither the one side nor the other. The conflict was inevitable. It was an accident of history that the brunt of the attack fell upon a man born in Italy in 1564, and that the battle was fought chiefly in the "Eternal City," from which centuries before had marched the legions that conquered the world.
The boy, Galileo, who was to become the central figure of the great conflict, was talented in many ways. In lute-playing his skill excelled that of his father, who was one of the noted musicians of his day. His skill in drawing wassuch that noted artists submitted their work to him for criticism. He wrote essays on the works of Dante and other classical writers. He amused his boy companions by constructing toy machines which, though ingenious, did not always work.
His preference was for mechanics, but, as this subject offered little prospect of profitable work, he took up the study of medicine in accordance with his father's wishes.
In his eighteenth year he entered the University of Pisa. Here he found men who refused to think for themselves, but decided every question by referring to what the ancient philosophers said. Galileo could not endure such slavish submission to authority. So strongly did he assert himself that he was nicknamed "The Wrangler," and, by his wrangling, he lost a scholarship in the university.
He neglected his medical studies and secretly studied mathematics. His father, learning of this, consented to his becoming a mathematician. Thus he followed his bent, though it seemed to lead directly to poverty.
The Pendulum Clock
It was while a student at the University of Pisa that he discovered a law of pendulums which makes possible our pendulum clocks. While at his devotions in the cathedral, he observed the swinging of the bronze lamp which had been drawn back for lighting. Timing its swinging by means of his pulse, the only timepiece in his possession, he found that the time of one swing remained the same, though the length of the swing grew smaller and smaller. Thisdiscovery led to his invention of an instrument for physicians' use in timing the pulse. About fifty years later he invented the pendulum clock (Fig. 2).
FIG. 2–GALILEO'S PENDULUM CLOCKFIG. 2–GALILEO'S PENDULUM CLOCKIt had only one hand, which is not shown in the picture.
It had only one hand, which is not shown in the picture.
Lack of funds compelled him to leave the university without completing his course. He returned to the parental roof and continued his scientific studies. The writings of Archimedes were his favorite study. With Archimedes' famous experiment on King Hiero's crown as a starting-point, he discovered the laws of floating bodies, which explain why a ship or other object floats on water, and invented a balance for weighing objects in water.
But such employment won nothing more substantial than honor and fame. Food and clothing were needed. For two years he strove without success to secure employment. At the end of that time he was appointed professor of mathematics in the University of Pisa at the magnificent salary of sixty scudi (about sixty-three dollars) per year. "But any port in a storm; and in Galileo's needy circumstances even this wretched salary was not to be rejected." Moreover, he could add somewhat to his income by private tutoring.
Galileo's Experiment with Falling Shot
While teaching at the University of Pisa, he performed his famous experiment of dropping from the top of the leaning tower two shot, one weighing ten pounds, the other one pound. Now, according to Aristotle, the ten-pound shot should fall in one-tenth the time required by the one-pound shot. But the assembled company of professors and students saw the two shot start together, fall together, andstrike the ground at the same instant, and still refused to believe their own eyes. They continued to affirm that a weight of ten pounds would reach the ground in a tenth of the time taken by a one-pound weight, because they were able to quote chapter and verse in which Aristotle assured them that such is the fact. Thus Galileo made enemies of the other professors, but for a time they could do nothing more than annoy him.
About this time Galileo incurred the wrath of the Grand Duke of Tuscany, from whom he had received his appointment. He was commissioned to examine a machine invented by a nephew of the Grand Duke for the purpose of cleaning harbors. Galileo plainly said that the machine was worthless. It was tried, and his opinion proved true. But like the kings of olden time who killed the bearer of evil tidings even though the tidings were true, his enemies made his position so unpleasant that he resigned.
He had neither employment nor money. His father's death occurring about this time, threw upon him the care of a mother, a worthless brother, and two sisters. In his distress he sought help from a friend, and secured an appointment as professor of mathematics in the University of Padua. His salary was one hundred and eighty florins (about ninety-five dollars), while other professors received more than ten times as much.
While at Padua, Galileo was busy inventing. He invented the sector, which is to be found in most cases of mathematical instruments and is used in certain kinds of drawing. He also invented an air thermometer (Fig. 3), the first instrument for measuring temperature.
FIG. 3–AN AIR THERMOMETERFIG. 3–AN AIR THERMOMETERWhen the air in the bulb grows cooler it contracts, and the air outside forces the Water up the tube. When the air in the bulb grows warmer it expands and forces the water down in the tube.
When the air in the bulb grows cooler it contracts, and the air outside forces the Water up the tube. When the air in the bulb grows warmer it expands and forces the water down in the tube.
In 1604 there appeared a new star of great brilliancy. It continued to shine with varying brightness for eighteen months, and then vanished. This was a strange event, and Galileo made use of it. He proved that the new star must lie among the most distant of the heavenly bodies, and this fact did not agree with Aristotle's view that the heavens are perfect, and therefore never change. A heated controversy followed, and Galileo came out boldly in favor of the theory that the earth revolves about the sun, the prevailing notion then being that the earth does not move, but that the sun and other heavenly bodies revolve around it.
The Telescope
In 1609 Galileo learned of a discovery that was to be of great value to the world, but a source of untold trouble to himself. An apprentice of a Dutch optician, while playing with spectacle lenses, chanced to observe that if two of the lenses were placed in a certain position objects seen through them appeared much nearer. Galileo, learning of this, set to work to construct a spy-glass, applying his knowledge of light. In one day he had constructed such an instrument, in which he used two lenses like the lenses of the modern opera-glass. Thus, while the Dutchman's discovery was by accident, Galileo's was by reasoning, and was the more fruitful, as we shall see.
Galileo continued improving his telescope until he had made one which would magnify thirty times. He was the first to apply the telescope to the study of the heavenly bodies. The most startling of his discoveries was that ofthe moons of the planet Jupiter, which he called new planets.
This aroused the fury of his enemies, who ridiculed the idea of there being new planets; "for," they said, "to see these planets they must first be put inside the telescope." The excitement was intense. Poets chanted the praise of Galileo. A public fête was held in his honor. One of his pupils was imprisoned in the tower of San Marco, where he had gone to make observations with his telescope, and could not escape until the crowd had satisfied their curiosity. Some of the philosophers refused to look lest they should see and be convinced.
Galileo's Struggle
His enemies sought to steal from him the honor of his discoveries. Some claimed to have made the discoveries before Galileo did. Others claimed that his discoveries were false, that their only use was to gratify Galileo's vanity and thirst for gold. In these trying times the friendship of the great astronomer Kepler warded off some of the most exasperating attacks.
Galileo's fame spread throughout Europe. Students came in great numbers, so that he had little leisure left for his own studies. He therefore decided to leave Padua, and secured an appointment as mathematician and philosopher to the Grand Duke of Tuscany. This appointment took him to Florence. It was here that an incident occurred that marked the beginning of a persecution which continued to the end of his life.
As we read the story of this conflict let us remember thatit was not primarily a conflict between the Roman Catholic Church and Galileo. It was a conflict of principles. On the one side were arrayed those who said that men should always believe as the ancient writers did; on the other, those who said men should think for themselves. In the first party were most of the university professors and others who dreaded the introduction of new beliefs, whether in religion or science. In the second party were Galileo and a small band of devoted followers.
At a dinner at the table of the Grand Duke in Pisa the conversation turned on the moons of Jupiter. Some praised Galileo. Others condemned him, saying that the Holy Scriptures were opposed to his theory of the motion of the earth. A friend reported the incident to Galileo, and he replied to the arguments of his opponents in a letter which was made public. No doubt the sting of his sarcasm made his enemies more bitter. He admitted that the Scriptures cannot lie or err, but this, he said, does not hold good of those who attempt to explain the Scriptures. In another letter, he quoted with approval a saying of Cardinal Baronius, "The Holy Spirit intended to teach us in the Bible how to go to Heaven, not how the heavens go."
The first shot had been fired. The battle was on, and the Church, because it possessed the most powerful weapons of attack, was used by the combined forces to break the power of Galileo's reasoning. He went to Rome to make his defence, but was commanded by the Holy Office not to hold or teach that the sun is immovable, and that the earth moves about the sun.
During another visit to Rome there was shown to Galileoan instrument which, it was said, would show a flea as large as a cricket. Galileo recalled that some years before he had so arranged a telescope that he had seen flies which he said looked as big as a lamb, and were covered all over with hair. This was the first microscope. Galileo quickly improved the instrument, and soon his microscopes were in great demand.
In violation of the decree of the Church, to which he had submitted, he published his most famous work in which he defended the theory that the earth moves about the sun. The book was the outcome of his life-work, but the Church believed it dangerous. He was summoned to Rome. Confined to a sick-bed, he pleaded for delay, which was granted. Before he recovered, however, the summons was made imperative. He must go to Rome, or be carried in irons. He went in a litter, carried by servants of the Grand Duke. In Rome he was to appear before the Inquisition. There he was treated with a consideration never before accorded to a prisoner of the Inquisition. Nor was he subjected to torture, as has been stated by some. He was found guilty of teaching the doctrine that the sun does not move, and that the earth moves about the sun. He was compelled to recant, and sentenced to the prison of the Holy Office and, by way of penance, to repeat once a week for three years the seven penitential Psalms.
He yielded without reserve to the decree of the Inquisition, renounced his "errors and heresies," and, with his hand on the Bible, took oath never again to teach the forbidden doctrine.
And now, though a shattered old man of seventy-four,enjoined to silence on the chief results of his life-work, nothing could quench his devotion to science. In these last years, he published a new book which, with his earlier work, entitles him to be regarded as the founder of the science of mechanics.
In his study of machines Galileo found that no machine will do work of itself. Whenever a machine is at work, a man or a horse, or some other power, is at work upon the machine. In no case will a machine do work without receiving an equal amount of work.
Torricelli and the Barometer
Galileo had a pump which he found would not work when the water was thirty-five feet below the valve. He thought the pump was injured, and sent for the maker. The maker assured him that no pump would do better. This led Torricelli, one of Galileo's pupils, to the discovery of the barometer. Men had said that water rises in a pump because nature abhors a vacuum. Torricelli believed that air-pressure and not nature's "horror of a vacuum" is the cause of water rising in a pump. He invented the barometer to measure air-pressure.
The first barometer was a glass tube filled with quick-silver or mercury (Fig. 4). The tube was closed at theupper end, and the lower end, which was open, dipped in a dish of mercury. He allowed the tube to stand, and saw that the height of the mercury changed. This he believed was because the air-pressure changed. Wind, Torricelli said, is caused by a difference of air-pressure, which is due to unequal heating of the air. For this reason a cool breeze blows from the mountain top to the heated valley, or from sea to land on a summer day.
FIG. 4–TORRICELLI'S EXPERIMENTFIG. 4–TORRICELLI'S EXPERIMENT
Otto Von Guericke and the Air-Pump
About this time a German burgomaster, Otto von Guericke, of Magdeburg, was performing experiments on air-pressure. The Thirty Years' War had been raging for thirteen years. The Swedish King, Gustavus Adolphus, had landed in Germany, and was winning victory after victory over the imperial troops. Magdeburg had entered into an alliance with the Swedish King, by which he was granted free passage through the city, while, on the other hand, he promised protection to the city.
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 thehorrors 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 passed 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.
FIG. 5–GUERICKE'S AIR-PUMPFIG. 5–GUERICKE'S AIR-PUMPMen lifted from the ground by air-pressure.
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 glass 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 superstitious neighbors to accuse him of being in league with Satan.
FIG. 6–GUERICKE'S WATER BAROMETERFIG. 6–GUERICKE'S WATER BAROMETERIn fair weather the image appeared above the housetop. When a storm was approaching the image dropped below the roof into the house.
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 exertsless 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, andobserving 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.
FIG. 7–A LIFT-PUMPFIG. 7–A LIFT-PUMPAir 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.
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-ship 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).
FIG. 8–A SIMPLE HYDRAULIC PRESSFIG. 8–A SIMPLE HYDRAULIC PRESSA one-pound weight holds up a hundred pounds.
A one-pound weight holds up a hundred pounds.
The hydraulic press has two cylinders. One cylindermust 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 illustrated in Fig. 10.
FIG. 9–HOW AN HYDRAULIC PRESS WORKSFIG. 9–HOW AN HYDRAULIC PRESS WORKSOne 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 plungerp. The large pistonPis forced up, thus compressing the paper.
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 plungerp. The large pistonPis forced up, thus compressing the paper.
FIG. 10–AN HYDRAULIC PRESS WITH BELT-DRIVEN PUMPFIG. 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 class gave him a kick in the stomach. This roused him and, to avenge the insult, he applied himself to study and quickly passed above his offending classmate. His strong spirit was aroused, and he soon took up his position at the head of his class.
It was his delight to invent amusements for his classmates. 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 tothese kites and fly them on dark nights, to the delight of his companions and the dismay of the superstitious 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 handleworked 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 orbit, 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 orbit. As the earth and moon attract eachother, 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 pass through a glass 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 glass 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 passing 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 shine through a gray sky, and the beauty of the setting sun would be replaced by the gray of twilight (Fig. 11).
FIG. 11–NEWTON'S EXPERIMENT WITH THE PRISMFIG. 11–NEWTON'S EXPERIMENT WITH THE PRISMSunlight separated into the colors of the rainbow. The seven colors are: violet, indigo, blue, green, yellow, orange, red.
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. Herefused it, whereupon the agent who made the offer said to him that it came from a great duchess. 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-shore and diverting myself in now and then finding a smoother pebble or a prettier shell than the ordinary, whilst the great ocean of truth lay all undiscovered before me."
THE EIGHTEENTH CENTURY
James Watt and the Steam-Engine
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 windlass 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 inventionit 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.
The First Steam-Engine with a Piston
The first steam-engine with a piston was made by Denys Papin, a Frenchman. Papin had observed that, in Guericke's experiment, air-pressure lifted several men off their feet. So he thought the air could be made to lift heavy weights and do useful work. But how should he produce the vacuum? His first thought was to explode gunpowder beneath the piston. The gunpowder engine had been tried by others and found wanting. He next turned his attention to steam, and discovered that if the piston were forced up by steam and then the steam condensed, a vacuum was formed beneath the piston, and air-pressure forced the piston to descend. If the piston were attached to a weight by a rope passing over a pulley, then, as the piston descended, it would lift the weight. Papin's engine consisted simply of a cylinder and piston (Fig. 12). There was no boiler, but the water was placed in the cylinder beneath the piston. A fire was placed under the cylinder and, asthe water boiled, the steam raised the piston. Then the fire was removed and, as the cylinder cooled, the steam condensed, and the piston was forced down by air-pressure. This was a slow and awkward method. The engine required several minutes to make one stroke.
FIG. 12–PAPIN'S ENGINEFIG. 12–PAPIN'S ENGINEThe first steam-engine with a piston. When the pistonBwas forced down by air-pressure, a weight was lifted by means of a ropeTTpassing over pulleys.
The first steam-engine with a piston. When the pistonBwas forced down by air-pressure, a weight was lifted by means of a ropeTTpassing over pulleys.
The principle of Papin's engine was first successfully applied by Thomas Newcomen. Newcomen was a blacksmith by trade, and his great successor, Watt, was a mechanic. Thus we see that great discoveries soon become common property. The blacksmith and the mechanic soon learn to use the discoveries of the scientist.
Newcomen's Engine
In the Newcomen engine the piston moved a walking-beam to which was attached a pump-rod. Steam was used merely to balance the air-pressure on the piston and allow the pump-rod to descend by its own weight. The steam was condensedin the cylinder, and the pressure of the air forced the piston down. Thus the work of raising water in the pump was done by the air. Newcomen's first engine made twelve strokes a minute, and at each stroke lifted fifty gallons of water fifty yards. He used this engine in pumping water from the mines, and also made engines for lifting coal.
At first the steam was condensed by throwing cold water on the outside of the cylinder. But one day the engine suddenly increased its speed and continued to work with unusual rapidity. The upper side of the piston was covered with water to make the piston air-tight, and it was found that this water was entering the cylinder through a hole that had worn in the piston, and this jet of cold water was rapidly condensing the steam. This was the origin of "jet condensation."
After this steam and water were alternately admitted to the cylinder through cocks turned by hand. A boy, Humphrey Potter, to whom this work was intrusted, won fame by tying strings to the cocks in such a way that the engine would turn the cocks itself and the boy, Humphrey, was free to play. This device was the origin of valve-gear.[1]
[1]Any device by which a steam-engine operates the valves which admit steam to the cylinder is called "valve-gear." One form of valve-gear is the link motion invented by Stephenson. This form will be described in connection with the locomotive. A simple valve-rod, worked by an eccentric such as is used on most stationary engines, is also a form of valve-gear.
[1]Any device by which a steam-engine operates the valves which admit steam to the cylinder is called "valve-gear." One form of valve-gear is the link motion invented by Stephenson. This form will be described in connection with the locomotive. A simple valve-rod, worked by an eccentric such as is used on most stationary engines, is also a form of valve-gear.
Newcomen's engine was extensively used. The tin and copper mines of Cornwall were deepened. Coal-mines were sunk to twice the depth that had been possible. But asthe mines were deepened the cost of running the engines increased. The largest engines consumed about $15,000 worth of coal per year. The Newcomen engine required about twenty-eight pounds of coal per hour per horse-power, while a modern engine consumes less than two pounds. Again, because of increased cost, mines were being abandoned. Such was the situation when James Watt came into the field of action.
Watt had learned the mechanic's trade in one year in a London shop, and, because he had not passed through an apprenticeship of seven years, the Guild of Hammermen, a labor-union of his time, refused him admission, and this refusal meant no employment. He found shelter, however, in the University of Glasgow, and was there provided with a small workshop where he could make instruments for sale.
Watt's Engine
A small Newcomen engine belonging to the University of Glasgow was out of repair. London mechanics had failed to make it work. The job was given to Watt. That he might do a perfect piece of work on this engine, he made a study of all that was then known relating to steam (Fig. 13).
FIG. 13–THE NEWCOMEN ENGINE, IN REPAIRING WHICH WATT WAS LED TO HIS GREAT DISCOVERIESFIG. 13–THE NEWCOMEN ENGINE, IN REPAIRING WHICH WATT WAS LED TO HIS GREAT DISCOVERIESPreserved in the University of Glasgow.
Preserved in the University of Glasgow.
He saw that there was a great loss of heat in admitting cold water into the cylinder to condense the steam, and that, to prevent this loss, the cylinder must be kept always as hot as the steam that enters it. While thinking upon this problem the idea came to him that, if connection were made between the cylinder and a tank from which the airhad been pumped out, the steam would rush into the tank, and might there be condensed without cooling the cylinder. This was the origin of the condenser.
We have seen that, in the Newcomen engine, the steam acted only on the under side of the piston, air acting on the upper side. It occurred to Watt that the steam should act on both sides of the piston. So he proposed to put an air-tight cover on the cylinder with a hole and stuffing-box for the piston to slide through and to admit steam to act upon it instead of air. Thus he was led to invent the double-acting engine. The action in the cylinder of Watt's engine was the same as that of the modern engine.
To save the power of steam, Watt arranged the valve in his engine in such a way that the steam was cut off from the cylinder when the piston had made about one-fourth of a stroke. The steam in the cylinder continues to expand and drive the piston. This device more than doubles the amount of work that the steam will do (Fig. 14).
FIG. 14–CYLINDER OF WATT'S STEAM-ENGINEFIG. 14–CYLINDER OF WATT'S STEAM-ENGINEArrows show the course of the steam.
Arrows show the course of the steam.
Horse-Power of an Engine
When horses were about to be replaced by the steam-engine at the mines, the question was asked: "How many horses will the engine replace?" Tests were made by Watt and others before him of the rate at which a horse could work in pumping water or in lifting a weight by means of a pulley. Watt's experiments showed that "a good London horse could go on lifting 150 pounds over a pulley at the rate of 2-1/2 miles an hour or 220 feet per minute, and continue the work eight hours a day." This would beequal to lifting 33,000 pounds one foot high every minute. This rate of doing work he called a horse-power. It is more than the average horse can do, but this number was used by Watt that he might give good measure in his engines. The horse-power of an engine at that time meant the rate of work in lifting water or coal. Now it means the rate of work done by the steam upon the piston, so that to find the useful horse-power of an engine we must deduct the work wasted in friction.
The indicator for measuring the pressure of steam in the cylinder and the fly-ball governor are also inventions madeby Watt (Fig. 15). The fly-ball governor replaced the throttle-valve which was at first used by Watt to regulate the speed of his engines. The throttle-valve is still used on locomotives.
FIG. 15–A FLY-BALL GOVERNORFIG. 15–A FLY-BALL GOVERNORThe balls as they rotate regulate the admission of steam to the cylinder by means of the leverLand the rodR.
The balls as they rotate regulate the admission of steam to the cylinder by means of the leverLand the rodR.
At the end of the eighteenth century the steam-engine was full grown. It remained for the nineteenth century to apply the engine to locomotion on sea and land, to develop the steam-turbine, and so to increase the power of the steam-engine that, early in the twentieth century, a 68,000-horse-power engine should speed an ocean liner across the Atlantic in five days.
The Leyden Jar
The first electrical invention of practical use was made by Benjamin Franklin. In Franklin's time great interest in electricity had been aroused by the strange discovery of a German professor, Pieter van Musschenbroek, of the University of Leyden. This professor had tried what he called a new but terrible experiment. He had suspended by two silk threads a gun-barrel which received electricity from an electrical machine. From one end of the gun-barrel hung a brass wire. The lower end of this wire dipped in a jar of water. He held the jar in one hand, while with the other he tried to draw sparks from the gun-barrel. Suddenly he received a shock which seemed to him like a lightning stroke. So violent was the shock that he thought for a moment it would end his life.
Out of this experiment came the Leyden jar, which for a century and a half was of no practical use, but which now forms an important part of every wireless telegraph equipment. The Leyden jar is simply a glass bottle or jar coated with tin-foil both inside and outside (Fig. 16). When charged with electricity the jar will hold its charge until the two coatings are connected by a metal wire or othergood conductor of electricity. A person may receive a strong shock by holding the jar in one hand and touching a knob connected to the inner coating with the other hand.
FIG. 16–A LEYDEN JARFIG. 16–A LEYDEN JAR
Popular interest in electricity was aroused by this discovery. The friction electrical machine and the Leyden jar were simple and easy to make. People of fashion found them interesting and amusing, the more so because of the shock felt on taking through the body the discharge from the "wonderful bottle," and the fact that several persons could receive the shock at the same instant. On one occasion the Abbé Nollet discharged a Leyden jar through a line composed of all the monks of the Carthusian Monastery in Paris. As the line of serious-faced monks a mile in length jumped into the air, the effect was ridiculous in the extreme.
Conductors and Insulators
About this time other great electrical discoveries were made. Early in the century, Stephen Gray discovered that some objects conduct electricity and others do not. He discovered that, when a glass tube is electrified by rubbing, it will attract and repel light objects. In the same way a comb or penholder of rubber may be electrified by rubbing it on the sleeve. A bit of paper which touches the comb becomes electrified. Electricity can be transferred from one object to another. Gray discovered further that contact is not necessary, that a hempen thread or a wire will carry an electric charge from one object to another. A silk thread will not carry the electric charge. "Some things convey electricity," he said, "and some donot, and those which do not can be used to prevent the electricity escaping from those which do." Could this obscure inventor have seen a modern telegraph line with the glass insulators on the poles, which prevent the electric current escaping from the telegraph wire, he might have realized the importance of his discovery. He set up a line of hempen thread six hundred and fifty feet long, and with an electrical machine at one end of the line electrified a boy suspended from the other end.
Two Kinds of Electric Charge
A Frenchman, DuFay, while carrying further the experiments of Gray, was watching a bit of gold-leaf floating in the air. The gold-leaf had been repelled after contact with his electrified glass tube. Thinking to try the action of two electrified objects on the gold leaf, he rubbed a piece of gum-copal and brought it near the leaf. To his astonishment the leaf, which was repelled by the glass tube, was attracted by the gum-copal. He repeated the experiment again and again, and each time the leaf was repelled by the glass and attracted by the gum. He concluded from this that there are two kinds of electricity, which he named "vitreous" and "resinous." The two kinds of electric charge were called by Franklin "positive" and "negative."
Franklin made a battery of Leyden jars, connecting the inner coating of one to the outer coating of the next throughout the series. In this way he could get a much stronger spark than with a single jar. On one occasion he nearly lost his life by taking a shock from his battery of Leyden jars.He magnetized and demagnetized steel needles by passing the discharge from his Leyden jars through the needles.
Franklin's Kite Experiment
The conjecture that lightning is of the same nature as the spark from the Leyden jar or the electrical machine had gained a hold on the minds of others before Franklin. In France sparks had been drawn from a rod ninety-nine feet high, but this did not reach into the clouds. Franklin determined to send a kite into a thunder-cloud, thinking electricity from the cloud would follow the string of the kite and could be stored in a Leyden jar, and used like the charge from an electrical machine. He had felt the power of a Leyden-jar discharge, and through it had nearly lost his life. He knew that lightning is far more powerful than any battery of Leyden jars, and yet to test the truth of his theory, that lightning is an electrical discharge, he was about to draw the lightning to his hand. He knew little of conductors of electricity. Whether the cord would draw little or much of the "electric fire" he knew not. So far as he knew he was toying with death.
The kite was made of two light strips of cedar placed crosswise, and a large silk handkerchief fastened to the strips. A sharp wire about a foot long was fastened to one of the strips. To the lower end of the cord he attached a key and a silk ribbon. By means of the ribbon he held the cord to insulate it from his hand. The kite soared into the clouds, and Franklin and his son stood under a shed awaiting the coming of the "electric fire" (Fig. 17). Soonthe fibres of the cord began to bristle up. He approached his knuckles to the key. A spark passed. He brought up a Leyden jar and charged it with electricity from the cloud, and found that with this charge he could do everything that could be done with electricity from his machine. He had proved the identity of lightning and electricity.