FIG. 79–SELDEN "EXPLOSION BUGGY." FORERUNNER OF THE MODERN AUTOMOBILEFIG. 79–SELDEN "EXPLOSION BUGGY." FORERUNNER OF THE MODERN AUTOMOBILEThe Steam LocomotiveLate in the eighteenth century a mischievous boy put some water in a gun-barrel, rammed down a tight wad, and placed the barrel in the fire of a blacksmith's forge. The wad was thrown out with a loud report, and the boy's play-mate, Oliver Evans, thought he had discovered a newpower. The prank with the gun-barrel set young Evans thinking about the power of steam. It was not long until he read a description of a Newcomen engine. In the Newcomen engine, you will remember, it was the pressure of air, not the pressure of steam, that lifted the weight. Evans soon set about building an engine in which the pressure of steam should do the work. He is sometimes called the "Watt of America," for he did in America much the same work that Watt did in Scotland. Evans built the first successful non-condensing engine—that is, an engine in which the steam, after driving the piston, escapes into the air instead of into a condenser. The non-condensing engine made the locomotive possible, for a locomotive could not conveniently carry a condenser. Evans made a locomotive which travelled very slowly. He said, however: "The time will come when people will travel in stages moved by steam-engines from one city to another, almost as fast as birds can fly, fifteen or twenty miles an hour."The inventor who made the first successful locomotive was George Stephenson, and it is worth noting that one of his engines, the "Rocket," possessed all the elements of the modern locomotive. He combined in the "Rocket" the tubular boiler, the forced draft, and direct connection of the piston-rod to the crank-pin of the driving-wheel.The "Rocket" was used on the first steam railway (the Stockton & Darlington, in England), which was opened in 1825. There had been other railways for hauling coal by means of horses over iron tracks, and other locomotives that travelled over an ordinary road; but this was the first roadon which a steam-engine pulled a load over an iron track, the first real railroad. Fig. 80 shows the "Rocket" and two other early locomotives.FIG. 80–SOME EARLY LOCOMOTIVESFIG. 80–SOME EARLY LOCOMOTIVESThe one on the right is Stephenson's "Rocket."Photo by Claudy.In order to build a railroad between Liverpool and Manchester for carrying both passengers and freight it was necessary to secure an act of Parliament. Stephenson was compelled to undergo a severe cross-examination by a committee of Parliament, who feared there would be great danger if the speed of the trains were as high as twelve miles an hour. He was asked:"Have you seen a railroad that would stand a speed of twelve miles an hour?""Yes.""Where?""Any railroad that would bear going four miles an hour. I mean to say that if it would bear the weight at four miles an hour it would bear it at twelve.""Do you mean to say that it would not require a stronger railway to carry the same weight at twelve miles an hour?""I will give an answer to that. I dare say every person has been over ice when skating, or seen persons go over, and they know that it would bear them better at a greater velocity than it would if they went slower; when they go quickly the weight, in a measure, ceases.""Would not that imply that the road must be perfect?""It would, and I mean to make it perfect."For seven miles the road must be built over a peat bog into which a stone would sink to unknown depths. To convince the committee, however, and secure the act of Parliament was more difficult than to build the road. ButStephenson was one of the men who do things because they never give up, and the road was built.How a Locomotive WorksTo understand how a locomotive works, let us consider how the steam is produced, how it acts on the piston, and how it is controlled. The steam is produced in a locomotive in exactly the same way that steam is produced in a tea-kettle. Now everybody knows that a quart of water in a tea-kettle with a wide bottom placed on a stove will boil more quickly than the same amount of water in a tea-pot with a narrow bottom. The greater the heating-surface—that is, the greater the surface of heated metal in contact with the water—the more quickly the water will boil and the more quickly steam can be produced. In a locomotive the aim is to use as large a heating-surface as possible. This is done by making the fire-box double and allowing the water to circulate in the space between the inner and outer parts, except underneath; also by placing tubes in the boiler through which the heated gases and smoke from the fire must pass. An ordinary locomotive contains two hundred or more of these tubes. The water surrounds these tubes, and is therefore in contact with a very large surface of heated metal. In some engines the water is in the tubes, and the heated gases surround the tubes.The steam as it enters the cylinder should be dry—that is, it should not contain drops of water. This is accomplished by allowing the steam from the boiler to pass into a dome above the boiler. Here the steam, which is nearlydry, enters a steam-pipe leading to the cylinder (Fig. 81). The steam is admitted to the cylinder by means of a slide-valve. From the diagram it can easily be seen that the valve admits steam first on one side of the piston, then on the other. It can also be seen that the valve closes the admission-port, and so cuts off the steam before the piston has made a full stroke. The steam that is shut up in the cylinder continues to expand and act on the piston. At the same time the valve opens the exhaust-port, allowing the steam to escape from the other side of the piston; but it closes this port before the piston has quite finished the stroke. The small quantity of steam thus shut up acts like a cushion to prevent the piston striking the end of the cylinder with too great force. The exhaust-steam escapes through a blast-pipe into the chimney, drives the air before it up the chimney, and thus makes a greater draft of air through the fire-box. This is called the forced draft. The escape of the exhaust-steam causes the puffing of the locomotive just after starting. After the engine is under way the engineer partly shuts off the steam by means of the reversing lever and the puffing is less noticeable.FIG. 81–HOW A LOCOMOTIVE WORKSFIG. 81–HOW A LOCOMOTIVE WORKSThe arrows show the course of the steam.The action of the steam may be summed up as follows:1. Steam admitted to the cylinder (admission).2. Valve closes admission-port (cut-off).3. Steam shut up in the cylinder expands, acting on the piston (expansion period).4. Valve opens exhaust-port to allow used steam to escape (exhaust).The devices for controlling the steam are the throttle-valve and the valve-gear. The throttle-valve is at the entrance to the steam-pipe in the steam-dome. This valve is opened and closed by means of a rod in the engineer's cab.Stephenson's link-motion valve-gear is used on most locomotives. The forward rod in the diagram is in position to act upon the valve-rod through the leverL. Suppose the reversing-lever is drawn back to the dotted line; then the forward rod will be raised and the backward rod will come into position to act on the leverL. If this is done while the locomotive is at rest the valve is moved through one-half a complete stroke. In the diagram the steam enters the cylinder on the right of the piston. After this movement of the valve the steam would enter on the left side of the piston. In the present position the locomotive would move forward, but if the valve is changed so as to admit steam to the left of the piston while the connecting-rod is in the position shown then the engine will move backward. Thus the direction can be controlled by the engineer in the cab. Of course, this can be done while the engine is in motion. The forward rod and the backward rod are each moved by an eccentric on the axle of the front driving-wheel. The two eccentrics are in opposite positions on the axle. An eccentric acts just like a crank, causing the rod to move forward and backward as the axle turns, and of course this motion is given to the valve-rod through the lever. When the link is set midway between the forward and the backward rod the valve cannot move. When the link is raised or lowered part way the valve makes a short stroke, and less steam is admitted to the cylinder than with a full stroke. In starting the locomotive the valve is set to make a full stroke.When the train is under headway the valve is set for a short stroke to economize steam. The valve-gear and the throttle-valve together take the place of the governor in the stationary engine, but while the governor acts automatically these are controlled by the engineer.In reality a locomotive is two engines, one on either side, connected to the same driving-wheels. But the two piston-rods are connected to the driving-wheels at points which are at right angles with each other, so that when the crank on one side is at the end of a stroke—the "dead centre"—that on the other side is on the quarter, either above or below the axle, ready for applying the greatest turning force.The expansion-engine was designed to use more of the power of the steam than can be done in the single-cylinder engine. In the double expansion-engine the steam expands from one cylinder into another. The second cylinder must be larger in diameter than the first. In the triple expansion-engine the steam expands from the second cylinder into a third, still larger. The second and third cylinders use a large part of the power that would be wasted with only one cylinder.The TurbineOne of the great inventions relating to steam-power is the steam-turbine. The water-turbine is equally useful in relation to water-power. The water-turbine and the steam-turbine work in very much the same way, the difference being due to the fact that steam expands as it drives the engine, while water drives it by its weight in falling, or byits motion as it rushes in a swift stream or jet against the blades of the turbine.The first steam-engine, that of Hero in the time of Archimedes, was a form of turbine (Fig. 82). It was driven by the reaction of the steam as it escaped into the air. The common lawn-sprinkler, that whirls as the water rushes through it, is a water-turbine that works in the same way. "Barker's Mill" is the name applied to a water-turbine that works like the lawn-sprinkler. As the water rushes out of the opening it pushes against the air. It cannot push against the air without pushing back at the same time. Never yet has any person or object in nature been able to push in one direction only. It cannot be done. If you push a cart forward you push backward against the ground at the same time. If there were nothing for you to push back against your forward push would not move the cart a hair's-breadth. If you doubt this, try to push a cart when you are standing on ice so slippery that you cannot get a foothold. It is the backward push of the water in the lawn-sprinkler and the backward push of the steam in Hero's engine that cause the machine to turn.FIG. 82–HERO'S ENGINEFIG. 82–HERO'S ENGINEThe turbines in common use for both water and steam power have curved blades. The reason for curving the blades can best be seen by referring to an early form of water-wheel. The best water-turbine is only an improved form of water-wheel. The first water-wheels had flat blades, and these answered very well so long as only a low power was needed and it was not necessary to save the power of the water. It was found, however, that there was a great waste of power in the wheel with flat blades. One inventor proposed to improve the wheel by curving the blades in such a way that the water would glide up the curve and then drop directly downward (Fig. 83). The water then gives up practically all of its power to the wheel and falls from the wheel. It would have no power tomove a second wheel. In this way he used practically all the power of the water. To save the power of the water by making all of the water strike the wheel at high speed the channel was made narrow just above the wheel, forming a mill-race. This applies to the undershot wheel. In the overshot wheel (Fig. 84) the power depends on the weight of the water and on its height. The water runs into buckets attached to the wheel, and, as it falls in these buckets, turns the wheel. The undershot wheel and themill-race represent a common form of turbine, that form in which the steam or the water is forced in a jet against a set of curved blades. Fig. 85 shows a steam-turbine run by a jet of steam. In the water-turbine there are two sets of blades. One set rotates, the other remains fixed. The use of the fixed blades is to turn the water and drive it in the right direction against the moving blades. In some forms of turbine there are more than two sets of blades. The steam, as it passes through, gives up some of its power to each set of blades until, after passing the last set, it has given up nearly all its power. The action of the steam in this turbine is somewhat like that in the expansion-engine, in which the steam gives up a portion of its power in each cylinder. Fig. 86 is from a photograph of a modern steam-turbine, and Fig. 87 is a drawing of the same turbine showing the course of the steam. Fig. 88 is a turbine that runs a large dynamo.FIG. 83–AN UNDERSHOT WATER-WHEEL WITH CURVED BLADESFIG. 83–AN UNDERSHOT WATER-WHEEL WITH CURVED BLADESFIG. 84–AN OVERSHOT WATER-WHEELFIG. 84–AN OVERSHOT WATER-WHEELFIG. 85–DE LAVAL STEAM-TURBINEFIG. 85–DE LAVAL STEAM-TURBINEDriven by a jet of steam striking the blades.FIG. 86–A MODERN STEAM-TURBINE WITH TOP CASING RAISED SHOWING BLADESFIG. 86–A MODERN STEAM-TURBINE WITH TOP CASING RAISED SHOWING BLADESFIG. 87–DIAGRAM OF TURBINE SHOWN IN FIG. 86FIG. 87–DIAGRAM OF TURBINE SHOWN IN FIG. 86The arrows show the course of the steam.FIG. 88–A STEAM-TURBINE THAT RUNS A DYNAMO GENERATING 14,000 ELECTRICAL HORSE-POWERFIG. 88–A STEAM-TURBINE THAT RUNS A DYNAMO GENERATING 14,000 ELECTRICAL HORSE-POWERThe steam enters through the large pipe at the left.In 1897, as the battle-ships of the British fleet were assembled to celebrate the Diamond jubilee of Queen Victoria, a little vessel a hundred feet long darted in and out amongthe giant ships, defied the patrol-boats whose duty it was to keep out intruders, and raced down the lines of battle-ships at the then unheard-of speed of thirty-five knots an hour. It was theTurbinia, fitted with the Parsons turbine. This event marked the beginning of the modern turbine. It also marked the beginning of a revolution in steam propulsion.The Parsons turbine does not use the jet method, but the steam enters near the centre of the wheel and flowstoward the rim, passing over a number of rows of curved blades. The Parsons turbine is used on the fastest ocean liners. TheLusitania, one of the fastest steamships in the first decade of the twentieth century, has two sets of high and low pressure turbines with a total of 68,000 horse-power.The windmill is a form of turbine driven by the air. As the air rushes against the blades of the windmill, it forces them to turn. If the windmill were turned by some mechanical power, it would drive the air back, and we should have a blower. This is what we have in the electric fan, a small windmill driven by an electric motor so that it drives the air instead of being driven by it. The blades of the windmill and the electric fan are shaped very much like the screw propeller. The screw propeller, driven by an engine, would drive the water back if the ship were firmly anchored, just as the fan drives the air. But it cannot drive the water back without pushing forward on the ship at the same time, and this forward push propels the ship. It is difficult to attain what is now regarded as high speed with a single screw. With engines in pairs and two lines of shafting higher power can be used. The best steamers, therefore, are fitted with the twin-screw propeller. Some large steamers have three and some four screws.The screw propellers of turbine steamships are made of small diameter, that they may rotate at high speed without undue waste of power. By the use of turbine engines and twin-screw propellers, the weight of the machinery has been greatly reduced. The old paddle-wheels, with low-pressure engines, developed only about two horse-power for eachton of machinery. The turbine, with the twin-screw propeller, develops from six to seven horse-power for every ton of machinery. The modern steamer, with all its machinery and coal for an Atlantic voyage, weighs no more than the engines of the old paddle-wheel type and coal would weigh for the same horse-power. The steam-turbine and the twin-screw propeller have made rapid ocean travel possible.Chapter VITHE TWENTIETH-CENTURY OUTLOOKWe have seen that the latter half of the nineteenth century was a time of invention. It was a time when the great discoveries of many centuries bore fruit in great inventions. It was thought by some scientists that all the great discoveries had been made, and that all that remained was careful work in applying the great principles that had been discovered. So far was this from being true that in the last ten years of the nineteenth century discoveries were made more startling, if possible, than any that had preceded. The nineteenth century not only brought forth many great inventions, but handed down to the twentieth century a series of discoveries that point the way to still greater inventions.Air-ShipsFor centuries men sailed over the water at the mercy of the wind. The sailing vessel is helpless in a storm. Early in the nineteenth century they learned to use the power of steam for ocean travel, and the wind lost its terrors. Late in the eighteenth century men learned to sail through the air in balloons even more at the mercy of the wind than thesailing vessels on the ocean. More than a hundred years later they learned to propel air-ships in the teeth of the wind. The nineteenth century saw the mastery of the water. The twentieth is witnessing the mastery of the air.The first balloon ascension was made in 1783, two men being carried over Paris by what Benjamin Franklin called a "bag of smoke." The balloon was a bag of oiled silk open at the bottom. In the middle of the opening was a grate in which bundles of fagots and sheaves of straw were burned. The heated air filled the balloon, and as the heated air was lighter than the air around it the balloon could rise and carry a load. Beneath the grate was a wicker car for the men. They were supplied with straw and fagots with which to feed the fire. When they wanted to rise higher they added fuel to heat the air in the balloon. When they wished to descend they allowed the fire to die out, so that the air in the balloon would cool. They could not guide the balloon, but drifted with the wind. That great philosopher Benjamin Franklin, who saw the ascension, said that the time might come when the balloon could be made to move in a calm and guided in a wind. In the second ascension bags of sand were taken as ballast, and the car was suspended from a net which enclosed the balloon. In this second ascension hydrogen gas was used in place of heated air.The greatest height ever reached by a human being is about seven miles. This height was first reached in 1862 by two balloonists who nearly lost their lives in the adventure. At a height of nearly six miles one of the men became unconscious. The other tried to pull the valve-cord to allowthe gas to escape, but found that the cord was out of his reach. His hands were frozen, but he climbed out of the car into the netting of the balloon, secured the cord in his teeth, returned to the car, and threw the weight of his body on the cord. This opened the valve and the balloon descended.Those who go to great heights now provide themselves with tanks of compressed oxygen. Then when the air becomes so thin and rare that breathing is difficult they can breathe from the oxygen tanks.A captive balloon in war serves as an observation tower from which to observe the enemy. It is connected to the ground by a cable. This cable is wound on a drum carried by the balloon wagon. The balloon can be lowered or raised by winding or unwinding the cable.The gas-bag is sometimes made of oiled silk, sometimes of two layers of cotton cloth with vulcanized rubber between. The cotton cloth gives the strength needed, and the rubber makes the bag gas-tight.The most convenient gas for filling balloons is heated air, but the air cools rapidly and loses its lifting power. Coal-gas furnished by city gas-plants is sometimes used. This gas will lift about thirty-five pounds for every thousand cubic feet. A balloon holding thirty-five thousand cubic feet of coal gas will easily lift the car and three persons. The lightest gas is hydrogen. This gas will lift about seventy pounds for every thousand cubic feet. Hydrogen is made by the action of sulphuric acid and water on iron. If a bit of iron is thrown into a mixture of sulphuric acid and water bubbles of hydrogen gas will rise through theliquid. This gas will burn if a lighted match is brought near.A balloon without propelling or steering apparatus is not an air-ship. It may be raised by throwing out ballast or lowered by letting out gas, but further than this the aeronaut has no control over its movements. The balloon moves with the wind. No breeze is felt, for balloon and air move together. To the aeronaut the balloon seems to be in a dead calm. It is only when he catches sight of houses and trees and rivers darting past below that he realizes that the balloon is moving.If a balloon has a propelling apparatus it may move against the wind, or it may outspeed the wind. A balloon with propelling and steering apparatus is called a "dirigible" balloon, which means a balloon that can be guided. Figs. 89 and 90 are from photographs of a "dirigible" used in the British army. Such a balloon is usually long and pointed like a spindle or a cigar. It is built to cut the air, just as a rowboat built for speed is long and pointed so that it may cut the water. The propeller acts like an electric fan. An electric fan drives the air before it, but the air pushes back on the fan just as much as the fan pushes forward on the air, and if the fan were suspended by a long cord it would move backward. So the large fan or screw propeller on an air-ship drives the air backward, and the air reacts and drives the ship forward. In the same way the screw-propeller of an ocean liner drives the vessel forward by the reaction of the water.FIG. 89–BRITISH ARMY AIR-SHIP "NULLI SECUNDUS" READY FOR FLIGHTFIG. 89–BRITISH ARMY AIR-SHIP "NULLI SECUNDUS" READY FOR FLIGHTFIG. 90–BASKET, MOTOR, AND PROPELLER OF THE BRITISH ARMY AIR-SHIP "NULLI SECUNDUS"FIG. 90–BASKET, MOTOR, AND PROPELLER OF THE BRITISH ARMY AIR-SHIP "NULLI SECUNDUS"A balloon rises for the same reason that wood floats on water. The wood is lighter than water, and the waterholds it up. The balloon is lighter than air and the air pushes it up. The upward push of the air is just equal to the weight of the air that would fill the same space the balloon fills. The balloon can support a load that makes the whole weight of the balloon and its load together equal to the weight of the air that would fill the same space. For the balloon to rise the load must be somewhat lighter than this. A balloon may be made lighter than air by filling it with heated air or coal-gas. Hydrogen, however, is used in the better balloons and in air-ships of the "lighter than air" type.The air-ship must, of course, use a very light motor. A steam-engine cannot be made light enough. Neither can an electric motor, if we add the weight of the storage battery that would be required. Air-ships have been propelled by both steam-engines and electric motors, but with low speed because of the weight of the engine or motor. The only successful motor for this purpose is the gasolene motor, which is a form of gas-engine using gas formed by the evaporation of gasolene.The first air-ship that could be controlled and brought back to the starting-point was made in France, in 1885, by Captain Renard, of the French army. It was a cigar-shaped balloon, with a screw propeller run by an electric motor of eight horse-power. The ship attained a speed of thirteen miles an hour.A more successful air-ship was that built by Santos Dumont. With this ship, in 1901, he won a prize of $20,000, which had been offered to the builder of the first air-ship that would sail round the Eiffel Tower in Paris from the AerostaticPark of Vaugirard, a distance of about three miles, and return in half an hour.The balloon part of this air-ship was 112-1/2 feet long and 19-1/2 feet in diameter, holding about 6400 cubic feet of gas. The car was built of pine beams no larger in section than two fingers and weighing only 110 pounds. This car could be taken apart and put in a trunk. A gasolene automobile motor was used, and thus it is seen that the automobile aided in solving the problem of sailing through the air. It was the automobile that led to the construction of light and powerful gasolene motors. The car and motor were suspended from the balloon by means of piano wires, which at a short distance were invisible, so that the man in the car appeared in some mysterious way to follow the balloon. The ship was turned to the left or right by means of a rudder. It was made to ascend or descend by shifting the weight of a heavy rope that hung from the car, thus inclining the ship upward or downward.Count Zeppelin, of Germany, constructed a much larger dirigible balloon than that of Santos Dumont. The balloon of the first Zeppelin air-ship was 390 feet in length, with a diameter of about 39 feet. It was divided into seventeen sections, each section being a balloon in itself. These sections serve the same purpose as the water-tight compartments of a battle-ship. An accident to one section would not mean the destruction of the entire ship. Within the balloon is a framework of aluminum rods extending from one end to the other and held in place by aluminum rings twenty-four feet apart. The balloon contains about 108,000 cubic feet of gas, and it costs about $2500 to fill it. Onefilling of gas will last about three weeks. There are two cars, each about ten feet long, five feet wide, and three feet deep. The cars are connected by a narrow passageway made of aluminum wires and plates, making a walking distance of 326 feet—longer than the decks of many ocean steamers. A sliding weight of 300 kilograms (about 600 pounds) serves the same purpose as the guide-ropes in the Santos Dumont air-ship. By moving this weight forward or backward the ship is raised or lowered at the bow or stern, and thus caused to glide up or down. Anchor-ropes are carried for use in landing. The ship is propelled byfour screws, and guided by a number of rudders placed some in front and some in the rear. The first Zeppelin air-ship carried four passengers. The work of Dumont and Zeppelin has led the great powers to manufacture dirigible balloons for use in time of war. Fig. 91 shows one of the Zeppelin air-ships sailing over a lake.FIG. 91–A ZEPPELIN AIR-SHIPFIG. 91–A ZEPPELIN AIR-SHIPA larger air-ship, theDeutschland, built later by Count Zeppelin, was the first air-ship to be used for regular passenger service. TheDeutschlandis shown in Fig. 92. TheDeutschlandcarried the crew and twenty passengers. Itoperated for a time as a regular passenger air-ship between Friedrichshafen and Düsseldorf, a distance of three hundred miles. TheDeutschlandwas wrecked in a storm on June 28, 1910, but it was successfully operated long enough to give Germany the honor of establishing the first air-ship line for regular passenger service. This is an honor perhaps equally as great as that of establishing the first commercial electric railway, which also belongs to Germany. An American army air-ship is shown in Fig. 93.FIG. 92–COUNT ZEPPELIN'S "DEUTSCHLAND," THE FIRST AIR-SHIP IN REGULAR PASSENGER SERVICEFIG. 92–COUNT ZEPPELIN'S "DEUTSCHLAND," THE FIRST AIR-SHIP IN REGULAR PASSENGER SERVICEFIG. 93–THE BALDWIN AIR-SHIP USED IN THE UNITED STATES ARMYFIG. 93–THE BALDWIN AIR-SHIP USED IN THE UNITED STATES ARMYCopyright by Pictorial News Co.The AeroplaneThe aeroplane is a later development than the dirigible balloon. The aeroplane is heavier than air. So is a bird and so is a kite. What supports a kite or a bird as it soars? Every boy knows that the strings of a kite must be attached so that the kite is inclined and catches the wind underneath. Then the wind lifts the kite. In still air the kite will not fly unless the boy who holds the string runs very fast and so causes an artificial breeze to blow against the kite. In much the same way a hovering bird is held aloft by the wind. In a dead calm the bird must flap its wings to keep afloat. If the kite string is cut the kite tips over and drops to the earth because it has lost its balance. The lifting power of the wind is well shown in the man-lifting kites which are used in the British army service. In a high wind a large kite is used in place of a captive balloon. It is a box-kite made of bamboo and carries a passenger in a car, the car running on the cable which attaches the kite to the ground. Now suppose a kite with a motor and propeller in place of a string and a boy to run with it, and that the kite is able to balance itself, then it will sail against a wind of its own making and you have a flying-machine heavier than air.The first aeroplane that would fly under perfect control of the operator was built by the Wright brothers at Dayton, Ohio. When they were boys, Bishop Wright gave his two sons, Orville and Wilbur, a toy flyer. From that time on the thought of flying through the air was in their minds. A few years later the death of Lilienthal, who was killed by a fall with his glider in Germany, stirred them, and they took up the problem in earnest. They read all the writings of Lilienthal and became acquainted with Mr. Octave Chanute, an engineer of Chicago who had made a successful glider. They soon built a glider of their own, and experimented with it each summer on the huge sand-dunes of the North Carolina coast.A glider is an aeroplane without a propeller. With it one can cast off into the air from a great height and sail slowly to the ground. Before attempting to use a motor and propeller, the Wrights learned to control the glider perfectly. They had to learn how to prevent its being tipped over by the wind, and how to steer it in any direction. This took years of patient work. But the problem was conquered at last, and they attached a motor and propeller to the glider, and had an air-ship under perfect control and with the speed of an express-train. Their flyer of 1905, which made a flight of twenty-four miles at a speed of more than thirty-eight miles an hour, carried a twenty-five-horse-power gasolene motor, and weighed, with its load,925 pounds. Figs. 94 and 95 show the Wright air-ship in flight. Fig. 97 shows the mechanism.FIG. 94–IN FULL FLIGHTFIG. 94–IN FULL FLIGHTFIG. 95–WRIGHT AIR-SHIP IN FLIGHTFIG. 95–WRIGHT AIR-SHIP IN FLIGHTCopyright, 1908, by Pictorial News Co.Rear view, showing propellers.FIG. 97–THE SEAT AND MOTOR OF THE WRIGHT AEROPLANEFIG. 97–THE SEAT AND MOTOR OF THE WRIGHT AEROPLANEPhoto by Pictorial News Co.How the Wright Aeroplane Is Kept AfloatThe Wright aeroplane is balanced by a warping or twisting of the planes 1 and 2, which form the supporting surfaces (Fig. 96). If left to itself the machine would tip over like a kite when the string is cut and drop edgewise to the ground. Suppose the sideRstarts to fall. The cornersaandeare raised by the operator whilebandfare lowered, thus twisting the planes, as shown in the dotted lines of the figure. The sideRthen catches more wind than the sideL. The wind exerts a greater lifting force onRthan onL, and the balance is restored. The twist is then taken out of the machine by the operator. A ship when sailing on an even keel presents true unwarped planes to the wind.FIG. 96–HOW THE WRIGHT AIR-SHIP IS KEPT AFLOATFIG. 96–HOW THE WRIGHT AIR-SHIP IS KEPT AFLOATThis picture represents a glider. The motor-driven aeroplane is balanced by the warping of the planes in the same way as the glider.The twisting is brought about by a pull on the rope 3, which is attached atdandc, and passes through pulleys atgandh. When the rope is pulled toward the left the right end is tightened and slack is paid out at the left end. This pulls down the cornerd, and raisese. The cornerais raised by the post which connectsaande. The rope 4, passing fromatobthrough pulleys atmandn, is thus drawn towardaand pulls down the cornerb. Thusais raised andbis lowered. At the same time rope 4 turns the rear rudder to the left, as shown by the dotted lines, thus forcing the sideRagainst the wind. Of course, if the left side of the machine starts to fall, the rope 3 is pulled toward the right, and all the movements take placein the opposite direction. The ropes are connected to a lever, by which the operator controls the warping of the planes. These movements are possible because the joints are all universal, permitting movement in any direction. In whatever position the planes may be set, they are held perfectly rigid by the two ropes, together with others not shown in the figure. The machine is guided up or down by the front horizontal rudder.When the aeroplane swings round a curve the outer wing is raised because it moves faster than the inner wing, and therefore has greater lifting force. Thus the aeroplane banks its own curves.The Wright flying-machine is called a biplane because it has two principal planes, one above the other. A number of successful flying-machines have been built with only one plane, and these are called monoplanes. A monoplane that early became famous is that of Blériot (Fig. 98). The Blériot monoplane was the first flying-machine to cross the English Channel. This machine is controlled by a single lever mounted with a ball-and-socket coupling, so that it can move in any direction. When on the ground it is supported by three wheels like bicycle wheels, so that it does not require a track for starting, but can start anywhere from level ground. The Wright and the Blériot represent the two leading types of early successful flying-machines.FIG. 98–THE BLÉRIOT MONOPLANEFIG. 98–THE BLÉRIOT MONOPLANECopyright by M. Brauger, ParisSubmarinesSuccessful navigation beneath the surface of the water, though not carried to the extent imagined by Jules Verne,was a reality at the beginning of the twentieth century. Instead of twenty thousand leagues under the sea, less than a hundred leagues had been accomplished, but no one can foretell what the future may have in store.The principal use of the submarine is in war. It is a diving torpedo-boat, and acts under cover of water, as the light artillery on land is secured behind intrenchments. The weapon used by the submarine is the torpedo. The torpedo is itself a small submarine able to propel itself, and if started in the water toward a certain object, to go under water straight to the mark. It carries a heavy charge eitherof guncotton or dynamite, which explodes when the torpedo strikes a solid object, such as a battle-ship. The first torpedo was intended to be steered from the shore by means of long tiller-ropes, and to be propelled by a steam-engine or by clockwork. The Whitehead fish torpedo, invented in 1866, is self-steering. At the head of the torpedo is a pointed steel firing-pin. When the torpedo strikes a ship or any rigid object this steel pin is driven against a detonator cap which is in the centre of the charge of dynamite. The blow causes the cap to explode, and the explosion of the cap explodes the dynamite. The torpedo is so arranged that it cannot explode until it is about thirty yards away from the ship from which it is fired. The steel pin cannot strike the cap until a small "collar" has been revolved off by a propeller fan, and this requires a distance of about thirty yards. The screw propeller is driven by compressed air. A valve which is worked by the pressure of the water keeps the torpedo at any depth for which the valve is set. The torpedo contains many ingenious devices for bringing it quickly to the required depth and keeping it straight in its course. One of these devices is the gyroscope, which will be described under the head of "spinning tops." Whitehead torpedoes are capable of running at a speed of over thirty-seven miles an hour for a range of two thousand yards and hitting the mark aimed at almost as accurately as a gun. The submarine boat carries a number of torpedoes, and has one torpedo-tube near the forward end from which to fire the torpedoes.It would be very difficult for one submarine to fight another submarine, for the submarine when completely submergedis blind. It could not see in the water to find its enemy. The torpedo-boat-destroyer is able to destroy a submarine by means of torpedoes, shells full of high explosives, or quick-firing guns. Advantage must be taken of the moment when the submarine comes to the surface to get a view of her enemy.One of the great enemies of the submarine will probably be the air-ship, for while the submarine when under water cannot be seen from a ship on the surface, it can, under favorable conditions, be seen from a certain height in the air.Most submarines use a gasolene motor for surface travel, and an electric motor run by a storage battery for navigation below the surface. The best submarines can travel at the surface like an ordinary boat, or "awash"—that is, just below the surface—with only the conning tower projecting above the water, or they can travel completely submerged.The rising and sinking of the submarine depend on the principle of Archimedes. The upward push of the water is just equal to the weight of the water displaced. If the water displaced weighs more than the boat, then the upward push of the water is greater than the weight of the boat and the boat rises. However, the boat can be made to dive when its weight is just a little less than the weight of the water displaced. This is done by means of horizontal rudders which may be inclined so as to cause the boat to glide downward as its propeller drives it forward.The magnetic compass is not reliable in a submarine with a hull made of steel. The electric motor used for propelling the boat under water also interferes with the action ofthe compass, because of its magnetic field. The gyroscope, which we shall describe later, is not affected by magnetic action, and may take the place of the compass.Water ballast is used, and when the submarine wishes to dive, water is admitted into the tanks until the boat is nearly heavy enough to sink of its own weight. It is then guided downward by the horizontal rudder. The submarine is driven by a screw propeller, and some submarines are lowered by means of a vertical screw. Just as a horizontal screw propels a vessel forward, so a vertical screw will propel it downward. When the submarine wishes to rise, it may do so by the action of its rudder, or the water may be pumped out of its tanks, when the water will raiseit rapidly. A submarine which is kept always a little lighter than water will rise to the surface in case of accident to its machinery. Figs. 99, 100, and 101 are from photographs of United States submarines.FIG. 99–THE "PLUNGER"FIG. 99–THE "PLUNGER"Photo by Pictorial News Co.
FIG. 79–SELDEN "EXPLOSION BUGGY." FORERUNNER OF THE MODERN AUTOMOBILEFIG. 79–SELDEN "EXPLOSION BUGGY." FORERUNNER OF THE MODERN AUTOMOBILE
The Steam Locomotive
Late in the eighteenth century a mischievous boy put some water in a gun-barrel, rammed down a tight wad, and placed the barrel in the fire of a blacksmith's forge. The wad was thrown out with a loud report, and the boy's play-mate, Oliver Evans, thought he had discovered a newpower. The prank with the gun-barrel set young Evans thinking about the power of steam. It was not long until he read a description of a Newcomen engine. In the Newcomen engine, you will remember, it was the pressure of air, not the pressure of steam, that lifted the weight. Evans soon set about building an engine in which the pressure of steam should do the work. He is sometimes called the "Watt of America," for he did in America much the same work that Watt did in Scotland. Evans built the first successful non-condensing engine—that is, an engine in which the steam, after driving the piston, escapes into the air instead of into a condenser. The non-condensing engine made the locomotive possible, for a locomotive could not conveniently carry a condenser. Evans made a locomotive which travelled very slowly. He said, however: "The time will come when people will travel in stages moved by steam-engines from one city to another, almost as fast as birds can fly, fifteen or twenty miles an hour."
The inventor who made the first successful locomotive was George Stephenson, and it is worth noting that one of his engines, the "Rocket," possessed all the elements of the modern locomotive. He combined in the "Rocket" the tubular boiler, the forced draft, and direct connection of the piston-rod to the crank-pin of the driving-wheel.
The "Rocket" was used on the first steam railway (the Stockton & Darlington, in England), which was opened in 1825. There had been other railways for hauling coal by means of horses over iron tracks, and other locomotives that travelled over an ordinary road; but this was the first roadon which a steam-engine pulled a load over an iron track, the first real railroad. Fig. 80 shows the "Rocket" and two other early locomotives.
FIG. 80–SOME EARLY LOCOMOTIVESFIG. 80–SOME EARLY LOCOMOTIVESThe one on the right is Stephenson's "Rocket."Photo by Claudy.
The one on the right is Stephenson's "Rocket."
Photo by Claudy.
In order to build a railroad between Liverpool and Manchester for carrying both passengers and freight it was necessary to secure an act of Parliament. Stephenson was compelled to undergo a severe cross-examination by a committee of Parliament, who feared there would be great danger if the speed of the trains were as high as twelve miles an hour. He was asked:
"Have you seen a railroad that would stand a speed of twelve miles an hour?"
"Yes."
"Where?"
"Any railroad that would bear going four miles an hour. I mean to say that if it would bear the weight at four miles an hour it would bear it at twelve."
"Do you mean to say that it would not require a stronger railway to carry the same weight at twelve miles an hour?"
"I will give an answer to that. I dare say every person has been over ice when skating, or seen persons go over, and they know that it would bear them better at a greater velocity than it would if they went slower; when they go quickly the weight, in a measure, ceases."
"Would not that imply that the road must be perfect?"
"It would, and I mean to make it perfect."
For seven miles the road must be built over a peat bog into which a stone would sink to unknown depths. To convince the committee, however, and secure the act of Parliament was more difficult than to build the road. ButStephenson was one of the men who do things because they never give up, and the road was built.
How a Locomotive Works
To understand how a locomotive works, let us consider how the steam is produced, how it acts on the piston, and how it is controlled. The steam is produced in a locomotive in exactly the same way that steam is produced in a tea-kettle. Now everybody knows that a quart of water in a tea-kettle with a wide bottom placed on a stove will boil more quickly than the same amount of water in a tea-pot with a narrow bottom. The greater the heating-surface—that is, the greater the surface of heated metal in contact with the water—the more quickly the water will boil and the more quickly steam can be produced. In a locomotive the aim is to use as large a heating-surface as possible. This is done by making the fire-box double and allowing the water to circulate in the space between the inner and outer parts, except underneath; also by placing tubes in the boiler through which the heated gases and smoke from the fire must pass. An ordinary locomotive contains two hundred or more of these tubes. The water surrounds these tubes, and is therefore in contact with a very large surface of heated metal. In some engines the water is in the tubes, and the heated gases surround the tubes.
The steam as it enters the cylinder should be dry—that is, it should not contain drops of water. This is accomplished by allowing the steam from the boiler to pass into a dome above the boiler. Here the steam, which is nearlydry, enters a steam-pipe leading to the cylinder (Fig. 81). The steam is admitted to the cylinder by means of a slide-valve. From the diagram it can easily be seen that the valve admits steam first on one side of the piston, then on the other. It can also be seen that the valve closes the admission-port, and so cuts off the steam before the piston has made a full stroke. The steam that is shut up in the cylinder continues to expand and act on the piston. At the same time the valve opens the exhaust-port, allowing the steam to escape from the other side of the piston; but it closes this port before the piston has quite finished the stroke. The small quantity of steam thus shut up acts like a cushion to prevent the piston striking the end of the cylinder with too great force. The exhaust-steam escapes through a blast-pipe into the chimney, drives the air before it up the chimney, and thus makes a greater draft of air through the fire-box. This is called the forced draft. The escape of the exhaust-steam causes the puffing of the locomotive just after starting. After the engine is under way the engineer partly shuts off the steam by means of the reversing lever and the puffing is less noticeable.
FIG. 81–HOW A LOCOMOTIVE WORKSFIG. 81–HOW A LOCOMOTIVE WORKSThe arrows show the course of the steam.
The arrows show the course of the steam.
The action of the steam may be summed up as follows:
1. Steam admitted to the cylinder (admission).
2. Valve closes admission-port (cut-off).
3. Steam shut up in the cylinder expands, acting on the piston (expansion period).
4. Valve opens exhaust-port to allow used steam to escape (exhaust).
The devices for controlling the steam are the throttle-valve and the valve-gear. The throttle-valve is at the entrance to the steam-pipe in the steam-dome. This valve is opened and closed by means of a rod in the engineer's cab.
Stephenson's link-motion valve-gear is used on most locomotives. The forward rod in the diagram is in position to act upon the valve-rod through the leverL. Suppose the reversing-lever is drawn back to the dotted line; then the forward rod will be raised and the backward rod will come into position to act on the leverL. If this is done while the locomotive is at rest the valve is moved through one-half a complete stroke. In the diagram the steam enters the cylinder on the right of the piston. After this movement of the valve the steam would enter on the left side of the piston. In the present position the locomotive would move forward, but if the valve is changed so as to admit steam to the left of the piston while the connecting-rod is in the position shown then the engine will move backward. Thus the direction can be controlled by the engineer in the cab. Of course, this can be done while the engine is in motion. The forward rod and the backward rod are each moved by an eccentric on the axle of the front driving-wheel. The two eccentrics are in opposite positions on the axle. An eccentric acts just like a crank, causing the rod to move forward and backward as the axle turns, and of course this motion is given to the valve-rod through the lever. When the link is set midway between the forward and the backward rod the valve cannot move. When the link is raised or lowered part way the valve makes a short stroke, and less steam is admitted to the cylinder than with a full stroke. In starting the locomotive the valve is set to make a full stroke.When the train is under headway the valve is set for a short stroke to economize steam. The valve-gear and the throttle-valve together take the place of the governor in the stationary engine, but while the governor acts automatically these are controlled by the engineer.
In reality a locomotive is two engines, one on either side, connected to the same driving-wheels. But the two piston-rods are connected to the driving-wheels at points which are at right angles with each other, so that when the crank on one side is at the end of a stroke—the "dead centre"—that on the other side is on the quarter, either above or below the axle, ready for applying the greatest turning force.
The expansion-engine was designed to use more of the power of the steam than can be done in the single-cylinder engine. In the double expansion-engine the steam expands from one cylinder into another. The second cylinder must be larger in diameter than the first. In the triple expansion-engine the steam expands from the second cylinder into a third, still larger. The second and third cylinders use a large part of the power that would be wasted with only one cylinder.
The Turbine
One of the great inventions relating to steam-power is the steam-turbine. The water-turbine is equally useful in relation to water-power. The water-turbine and the steam-turbine work in very much the same way, the difference being due to the fact that steam expands as it drives the engine, while water drives it by its weight in falling, or byits motion as it rushes in a swift stream or jet against the blades of the turbine.
The first steam-engine, that of Hero in the time of Archimedes, was a form of turbine (Fig. 82). It was driven by the reaction of the steam as it escaped into the air. The common lawn-sprinkler, that whirls as the water rushes through it, is a water-turbine that works in the same way. "Barker's Mill" is the name applied to a water-turbine that works like the lawn-sprinkler. As the water rushes out of the opening it pushes against the air. It cannot push against the air without pushing back at the same time. Never yet has any person or object in nature been able to push in one direction only. It cannot be done. If you push a cart forward you push backward against the ground at the same time. If there were nothing for you to push back against your forward push would not move the cart a hair's-breadth. If you doubt this, try to push a cart when you are standing on ice so slippery that you cannot get a foothold. It is the backward push of the water in the lawn-sprinkler and the backward push of the steam in Hero's engine that cause the machine to turn.
FIG. 82–HERO'S ENGINEFIG. 82–HERO'S ENGINE
The turbines in common use for both water and steam power have curved blades. The reason for curving the blades can best be seen by referring to an early form of water-wheel. The best water-turbine is only an improved form of water-wheel. The first water-wheels had flat blades, and these answered very well so long as only a low power was needed and it was not necessary to save the power of the water. It was found, however, that there was a great waste of power in the wheel with flat blades. One inventor proposed to improve the wheel by curving the blades in such a way that the water would glide up the curve and then drop directly downward (Fig. 83). The water then gives up practically all of its power to the wheel and falls from the wheel. It would have no power tomove a second wheel. In this way he used practically all the power of the water. To save the power of the water by making all of the water strike the wheel at high speed the channel was made narrow just above the wheel, forming a mill-race. This applies to the undershot wheel. In the overshot wheel (Fig. 84) the power depends on the weight of the water and on its height. The water runs into buckets attached to the wheel, and, as it falls in these buckets, turns the wheel. The undershot wheel and themill-race represent a common form of turbine, that form in which the steam or the water is forced in a jet against a set of curved blades. Fig. 85 shows a steam-turbine run by a jet of steam. In the water-turbine there are two sets of blades. One set rotates, the other remains fixed. The use of the fixed blades is to turn the water and drive it in the right direction against the moving blades. In some forms of turbine there are more than two sets of blades. The steam, as it passes through, gives up some of its power to each set of blades until, after passing the last set, it has given up nearly all its power. The action of the steam in this turbine is somewhat like that in the expansion-engine, in which the steam gives up a portion of its power in each cylinder. Fig. 86 is from a photograph of a modern steam-turbine, and Fig. 87 is a drawing of the same turbine showing the course of the steam. Fig. 88 is a turbine that runs a large dynamo.
FIG. 83–AN UNDERSHOT WATER-WHEEL WITH CURVED BLADESFIG. 83–AN UNDERSHOT WATER-WHEEL WITH CURVED BLADES
FIG. 84–AN OVERSHOT WATER-WHEELFIG. 84–AN OVERSHOT WATER-WHEEL
FIG. 85–DE LAVAL STEAM-TURBINEFIG. 85–DE LAVAL STEAM-TURBINEDriven by a jet of steam striking the blades.
Driven by a jet of steam striking the blades.
FIG. 86–A MODERN STEAM-TURBINE WITH TOP CASING RAISED SHOWING BLADESFIG. 86–A MODERN STEAM-TURBINE WITH TOP CASING RAISED SHOWING BLADES
FIG. 87–DIAGRAM OF TURBINE SHOWN IN FIG. 86FIG. 87–DIAGRAM OF TURBINE SHOWN IN FIG. 86The arrows show the course of the steam.
The arrows show the course of the steam.
FIG. 88–A STEAM-TURBINE THAT RUNS A DYNAMO GENERATING 14,000 ELECTRICAL HORSE-POWERFIG. 88–A STEAM-TURBINE THAT RUNS A DYNAMO GENERATING 14,000 ELECTRICAL HORSE-POWERThe steam enters through the large pipe at the left.
The steam enters through the large pipe at the left.
In 1897, as the battle-ships of the British fleet were assembled to celebrate the Diamond jubilee of Queen Victoria, a little vessel a hundred feet long darted in and out amongthe giant ships, defied the patrol-boats whose duty it was to keep out intruders, and raced down the lines of battle-ships at the then unheard-of speed of thirty-five knots an hour. It was theTurbinia, fitted with the Parsons turbine. This event marked the beginning of the modern turbine. It also marked the beginning of a revolution in steam propulsion.
The Parsons turbine does not use the jet method, but the steam enters near the centre of the wheel and flowstoward the rim, passing over a number of rows of curved blades. The Parsons turbine is used on the fastest ocean liners. TheLusitania, one of the fastest steamships in the first decade of the twentieth century, has two sets of high and low pressure turbines with a total of 68,000 horse-power.
The windmill is a form of turbine driven by the air. As the air rushes against the blades of the windmill, it forces them to turn. If the windmill were turned by some mechanical power, it would drive the air back, and we should have a blower. This is what we have in the electric fan, a small windmill driven by an electric motor so that it drives the air instead of being driven by it. The blades of the windmill and the electric fan are shaped very much like the screw propeller. The screw propeller, driven by an engine, would drive the water back if the ship were firmly anchored, just as the fan drives the air. But it cannot drive the water back without pushing forward on the ship at the same time, and this forward push propels the ship. It is difficult to attain what is now regarded as high speed with a single screw. With engines in pairs and two lines of shafting higher power can be used. The best steamers, therefore, are fitted with the twin-screw propeller. Some large steamers have three and some four screws.
The screw propellers of turbine steamships are made of small diameter, that they may rotate at high speed without undue waste of power. By the use of turbine engines and twin-screw propellers, the weight of the machinery has been greatly reduced. The old paddle-wheels, with low-pressure engines, developed only about two horse-power for eachton of machinery. The turbine, with the twin-screw propeller, develops from six to seven horse-power for every ton of machinery. The modern steamer, with all its machinery and coal for an Atlantic voyage, weighs no more than the engines of the old paddle-wheel type and coal would weigh for the same horse-power. The steam-turbine and the twin-screw propeller have made rapid ocean travel possible.
THE TWENTIETH-CENTURY OUTLOOK
We have seen that the latter half of the nineteenth century was a time of invention. It was a time when the great discoveries of many centuries bore fruit in great inventions. It was thought by some scientists that all the great discoveries had been made, and that all that remained was careful work in applying the great principles that had been discovered. So far was this from being true that in the last ten years of the nineteenth century discoveries were made more startling, if possible, than any that had preceded. The nineteenth century not only brought forth many great inventions, but handed down to the twentieth century a series of discoveries that point the way to still greater inventions.
Air-Ships
For centuries men sailed over the water at the mercy of the wind. The sailing vessel is helpless in a storm. Early in the nineteenth century they learned to use the power of steam for ocean travel, and the wind lost its terrors. Late in the eighteenth century men learned to sail through the air in balloons even more at the mercy of the wind than thesailing vessels on the ocean. More than a hundred years later they learned to propel air-ships in the teeth of the wind. The nineteenth century saw the mastery of the water. The twentieth is witnessing the mastery of the air.
The first balloon ascension was made in 1783, two men being carried over Paris by what Benjamin Franklin called a "bag of smoke." The balloon was a bag of oiled silk open at the bottom. In the middle of the opening was a grate in which bundles of fagots and sheaves of straw were burned. The heated air filled the balloon, and as the heated air was lighter than the air around it the balloon could rise and carry a load. Beneath the grate was a wicker car for the men. They were supplied with straw and fagots with which to feed the fire. When they wanted to rise higher they added fuel to heat the air in the balloon. When they wished to descend they allowed the fire to die out, so that the air in the balloon would cool. They could not guide the balloon, but drifted with the wind. That great philosopher Benjamin Franklin, who saw the ascension, said that the time might come when the balloon could be made to move in a calm and guided in a wind. In the second ascension bags of sand were taken as ballast, and the car was suspended from a net which enclosed the balloon. In this second ascension hydrogen gas was used in place of heated air.
The greatest height ever reached by a human being is about seven miles. This height was first reached in 1862 by two balloonists who nearly lost their lives in the adventure. At a height of nearly six miles one of the men became unconscious. The other tried to pull the valve-cord to allowthe gas to escape, but found that the cord was out of his reach. His hands were frozen, but he climbed out of the car into the netting of the balloon, secured the cord in his teeth, returned to the car, and threw the weight of his body on the cord. This opened the valve and the balloon descended.
Those who go to great heights now provide themselves with tanks of compressed oxygen. Then when the air becomes so thin and rare that breathing is difficult they can breathe from the oxygen tanks.
A captive balloon in war serves as an observation tower from which to observe the enemy. It is connected to the ground by a cable. This cable is wound on a drum carried by the balloon wagon. The balloon can be lowered or raised by winding or unwinding the cable.
The gas-bag is sometimes made of oiled silk, sometimes of two layers of cotton cloth with vulcanized rubber between. The cotton cloth gives the strength needed, and the rubber makes the bag gas-tight.
The most convenient gas for filling balloons is heated air, but the air cools rapidly and loses its lifting power. Coal-gas furnished by city gas-plants is sometimes used. This gas will lift about thirty-five pounds for every thousand cubic feet. A balloon holding thirty-five thousand cubic feet of coal gas will easily lift the car and three persons. The lightest gas is hydrogen. This gas will lift about seventy pounds for every thousand cubic feet. Hydrogen is made by the action of sulphuric acid and water on iron. If a bit of iron is thrown into a mixture of sulphuric acid and water bubbles of hydrogen gas will rise through theliquid. This gas will burn if a lighted match is brought near.
A balloon without propelling or steering apparatus is not an air-ship. It may be raised by throwing out ballast or lowered by letting out gas, but further than this the aeronaut has no control over its movements. The balloon moves with the wind. No breeze is felt, for balloon and air move together. To the aeronaut the balloon seems to be in a dead calm. It is only when he catches sight of houses and trees and rivers darting past below that he realizes that the balloon is moving.
If a balloon has a propelling apparatus it may move against the wind, or it may outspeed the wind. A balloon with propelling and steering apparatus is called a "dirigible" balloon, which means a balloon that can be guided. Figs. 89 and 90 are from photographs of a "dirigible" used in the British army. Such a balloon is usually long and pointed like a spindle or a cigar. It is built to cut the air, just as a rowboat built for speed is long and pointed so that it may cut the water. The propeller acts like an electric fan. An electric fan drives the air before it, but the air pushes back on the fan just as much as the fan pushes forward on the air, and if the fan were suspended by a long cord it would move backward. So the large fan or screw propeller on an air-ship drives the air backward, and the air reacts and drives the ship forward. In the same way the screw-propeller of an ocean liner drives the vessel forward by the reaction of the water.
FIG. 89–BRITISH ARMY AIR-SHIP "NULLI SECUNDUS" READY FOR FLIGHTFIG. 89–BRITISH ARMY AIR-SHIP "NULLI SECUNDUS" READY FOR FLIGHT
FIG. 90–BASKET, MOTOR, AND PROPELLER OF THE BRITISH ARMY AIR-SHIP "NULLI SECUNDUS"FIG. 90–BASKET, MOTOR, AND PROPELLER OF THE BRITISH ARMY AIR-SHIP "NULLI SECUNDUS"
A balloon rises for the same reason that wood floats on water. The wood is lighter than water, and the waterholds it up. The balloon is lighter than air and the air pushes it up. The upward push of the air is just equal to the weight of the air that would fill the same space the balloon fills. The balloon can support a load that makes the whole weight of the balloon and its load together equal to the weight of the air that would fill the same space. For the balloon to rise the load must be somewhat lighter than this. A balloon may be made lighter than air by filling it with heated air or coal-gas. Hydrogen, however, is used in the better balloons and in air-ships of the "lighter than air" type.
The air-ship must, of course, use a very light motor. A steam-engine cannot be made light enough. Neither can an electric motor, if we add the weight of the storage battery that would be required. Air-ships have been propelled by both steam-engines and electric motors, but with low speed because of the weight of the engine or motor. The only successful motor for this purpose is the gasolene motor, which is a form of gas-engine using gas formed by the evaporation of gasolene.
The first air-ship that could be controlled and brought back to the starting-point was made in France, in 1885, by Captain Renard, of the French army. It was a cigar-shaped balloon, with a screw propeller run by an electric motor of eight horse-power. The ship attained a speed of thirteen miles an hour.
A more successful air-ship was that built by Santos Dumont. With this ship, in 1901, he won a prize of $20,000, which had been offered to the builder of the first air-ship that would sail round the Eiffel Tower in Paris from the AerostaticPark of Vaugirard, a distance of about three miles, and return in half an hour.
The balloon part of this air-ship was 112-1/2 feet long and 19-1/2 feet in diameter, holding about 6400 cubic feet of gas. The car was built of pine beams no larger in section than two fingers and weighing only 110 pounds. This car could be taken apart and put in a trunk. A gasolene automobile motor was used, and thus it is seen that the automobile aided in solving the problem of sailing through the air. It was the automobile that led to the construction of light and powerful gasolene motors. The car and motor were suspended from the balloon by means of piano wires, which at a short distance were invisible, so that the man in the car appeared in some mysterious way to follow the balloon. The ship was turned to the left or right by means of a rudder. It was made to ascend or descend by shifting the weight of a heavy rope that hung from the car, thus inclining the ship upward or downward.
Count Zeppelin, of Germany, constructed a much larger dirigible balloon than that of Santos Dumont. The balloon of the first Zeppelin air-ship was 390 feet in length, with a diameter of about 39 feet. It was divided into seventeen sections, each section being a balloon in itself. These sections serve the same purpose as the water-tight compartments of a battle-ship. An accident to one section would not mean the destruction of the entire ship. Within the balloon is a framework of aluminum rods extending from one end to the other and held in place by aluminum rings twenty-four feet apart. The balloon contains about 108,000 cubic feet of gas, and it costs about $2500 to fill it. Onefilling of gas will last about three weeks. There are two cars, each about ten feet long, five feet wide, and three feet deep. The cars are connected by a narrow passageway made of aluminum wires and plates, making a walking distance of 326 feet—longer than the decks of many ocean steamers. A sliding weight of 300 kilograms (about 600 pounds) serves the same purpose as the guide-ropes in the Santos Dumont air-ship. By moving this weight forward or backward the ship is raised or lowered at the bow or stern, and thus caused to glide up or down. Anchor-ropes are carried for use in landing. The ship is propelled byfour screws, and guided by a number of rudders placed some in front and some in the rear. The first Zeppelin air-ship carried four passengers. The work of Dumont and Zeppelin has led the great powers to manufacture dirigible balloons for use in time of war. Fig. 91 shows one of the Zeppelin air-ships sailing over a lake.
FIG. 91–A ZEPPELIN AIR-SHIPFIG. 91–A ZEPPELIN AIR-SHIP
A larger air-ship, theDeutschland, built later by Count Zeppelin, was the first air-ship to be used for regular passenger service. TheDeutschlandis shown in Fig. 92. TheDeutschlandcarried the crew and twenty passengers. Itoperated for a time as a regular passenger air-ship between Friedrichshafen and Düsseldorf, a distance of three hundred miles. TheDeutschlandwas wrecked in a storm on June 28, 1910, but it was successfully operated long enough to give Germany the honor of establishing the first air-ship line for regular passenger service. This is an honor perhaps equally as great as that of establishing the first commercial electric railway, which also belongs to Germany. An American army air-ship is shown in Fig. 93.
FIG. 92–COUNT ZEPPELIN'S "DEUTSCHLAND," THE FIRST AIR-SHIP IN REGULAR PASSENGER SERVICEFIG. 92–COUNT ZEPPELIN'S "DEUTSCHLAND," THE FIRST AIR-SHIP IN REGULAR PASSENGER SERVICE
FIG. 93–THE BALDWIN AIR-SHIP USED IN THE UNITED STATES ARMYFIG. 93–THE BALDWIN AIR-SHIP USED IN THE UNITED STATES ARMYCopyright by Pictorial News Co.
Copyright by Pictorial News Co.
The Aeroplane
The aeroplane is a later development than the dirigible balloon. The aeroplane is heavier than air. So is a bird and so is a kite. What supports a kite or a bird as it soars? Every boy knows that the strings of a kite must be attached so that the kite is inclined and catches the wind underneath. Then the wind lifts the kite. In still air the kite will not fly unless the boy who holds the string runs very fast and so causes an artificial breeze to blow against the kite. In much the same way a hovering bird is held aloft by the wind. In a dead calm the bird must flap its wings to keep afloat. If the kite string is cut the kite tips over and drops to the earth because it has lost its balance. The lifting power of the wind is well shown in the man-lifting kites which are used in the British army service. In a high wind a large kite is used in place of a captive balloon. It is a box-kite made of bamboo and carries a passenger in a car, the car running on the cable which attaches the kite to the ground. Now suppose a kite with a motor and propeller in place of a string and a boy to run with it, and that the kite is able to balance itself, then it will sail against a wind of its own making and you have a flying-machine heavier than air.
The first aeroplane that would fly under perfect control of the operator was built by the Wright brothers at Dayton, Ohio. When they were boys, Bishop Wright gave his two sons, Orville and Wilbur, a toy flyer. From that time on the thought of flying through the air was in their minds. A few years later the death of Lilienthal, who was killed by a fall with his glider in Germany, stirred them, and they took up the problem in earnest. They read all the writings of Lilienthal and became acquainted with Mr. Octave Chanute, an engineer of Chicago who had made a successful glider. They soon built a glider of their own, and experimented with it each summer on the huge sand-dunes of the North Carolina coast.
A glider is an aeroplane without a propeller. With it one can cast off into the air from a great height and sail slowly to the ground. Before attempting to use a motor and propeller, the Wrights learned to control the glider perfectly. They had to learn how to prevent its being tipped over by the wind, and how to steer it in any direction. This took years of patient work. But the problem was conquered at last, and they attached a motor and propeller to the glider, and had an air-ship under perfect control and with the speed of an express-train. Their flyer of 1905, which made a flight of twenty-four miles at a speed of more than thirty-eight miles an hour, carried a twenty-five-horse-power gasolene motor, and weighed, with its load,925 pounds. Figs. 94 and 95 show the Wright air-ship in flight. Fig. 97 shows the mechanism.
FIG. 94–IN FULL FLIGHTFIG. 94–IN FULL FLIGHT
FIG. 95–WRIGHT AIR-SHIP IN FLIGHTFIG. 95–WRIGHT AIR-SHIP IN FLIGHT
Copyright, 1908, by Pictorial News Co.
Rear view, showing propellers.
FIG. 97–THE SEAT AND MOTOR OF THE WRIGHT AEROPLANEFIG. 97–THE SEAT AND MOTOR OF THE WRIGHT AEROPLANE
Photo by Pictorial News Co.
How the Wright Aeroplane Is Kept Afloat
The Wright aeroplane is balanced by a warping or twisting of the planes 1 and 2, which form the supporting surfaces (Fig. 96). If left to itself the machine would tip over like a kite when the string is cut and drop edgewise to the ground. Suppose the sideRstarts to fall. The cornersaandeare raised by the operator whilebandfare lowered, thus twisting the planes, as shown in the dotted lines of the figure. The sideRthen catches more wind than the sideL. The wind exerts a greater lifting force onRthan onL, and the balance is restored. The twist is then taken out of the machine by the operator. A ship when sailing on an even keel presents true unwarped planes to the wind.
FIG. 96–HOW THE WRIGHT AIR-SHIP IS KEPT AFLOATFIG. 96–HOW THE WRIGHT AIR-SHIP IS KEPT AFLOATThis picture represents a glider. The motor-driven aeroplane is balanced by the warping of the planes in the same way as the glider.
This picture represents a glider. The motor-driven aeroplane is balanced by the warping of the planes in the same way as the glider.
The twisting is brought about by a pull on the rope 3, which is attached atdandc, and passes through pulleys atgandh. When the rope is pulled toward the left the right end is tightened and slack is paid out at the left end. This pulls down the cornerd, and raisese. The cornerais raised by the post which connectsaande. The rope 4, passing fromatobthrough pulleys atmandn, is thus drawn towardaand pulls down the cornerb. Thusais raised andbis lowered. At the same time rope 4 turns the rear rudder to the left, as shown by the dotted lines, thus forcing the sideRagainst the wind. Of course, if the left side of the machine starts to fall, the rope 3 is pulled toward the right, and all the movements take placein the opposite direction. The ropes are connected to a lever, by which the operator controls the warping of the planes. These movements are possible because the joints are all universal, permitting movement in any direction. In whatever position the planes may be set, they are held perfectly rigid by the two ropes, together with others not shown in the figure. The machine is guided up or down by the front horizontal rudder.
When the aeroplane swings round a curve the outer wing is raised because it moves faster than the inner wing, and therefore has greater lifting force. Thus the aeroplane banks its own curves.
The Wright flying-machine is called a biplane because it has two principal planes, one above the other. A number of successful flying-machines have been built with only one plane, and these are called monoplanes. A monoplane that early became famous is that of Blériot (Fig. 98). The Blériot monoplane was the first flying-machine to cross the English Channel. This machine is controlled by a single lever mounted with a ball-and-socket coupling, so that it can move in any direction. When on the ground it is supported by three wheels like bicycle wheels, so that it does not require a track for starting, but can start anywhere from level ground. The Wright and the Blériot represent the two leading types of early successful flying-machines.
FIG. 98–THE BLÉRIOT MONOPLANEFIG. 98–THE BLÉRIOT MONOPLANECopyright by M. Brauger, Paris
Copyright by M. Brauger, Paris
Submarines
Successful navigation beneath the surface of the water, though not carried to the extent imagined by Jules Verne,was a reality at the beginning of the twentieth century. Instead of twenty thousand leagues under the sea, less than a hundred leagues had been accomplished, but no one can foretell what the future may have in store.
The principal use of the submarine is in war. It is a diving torpedo-boat, and acts under cover of water, as the light artillery on land is secured behind intrenchments. The weapon used by the submarine is the torpedo. The torpedo is itself a small submarine able to propel itself, and if started in the water toward a certain object, to go under water straight to the mark. It carries a heavy charge eitherof guncotton or dynamite, which explodes when the torpedo strikes a solid object, such as a battle-ship. The first torpedo was intended to be steered from the shore by means of long tiller-ropes, and to be propelled by a steam-engine or by clockwork. The Whitehead fish torpedo, invented in 1866, is self-steering. At the head of the torpedo is a pointed steel firing-pin. When the torpedo strikes a ship or any rigid object this steel pin is driven against a detonator cap which is in the centre of the charge of dynamite. The blow causes the cap to explode, and the explosion of the cap explodes the dynamite. The torpedo is so arranged that it cannot explode until it is about thirty yards away from the ship from which it is fired. The steel pin cannot strike the cap until a small "collar" has been revolved off by a propeller fan, and this requires a distance of about thirty yards. The screw propeller is driven by compressed air. A valve which is worked by the pressure of the water keeps the torpedo at any depth for which the valve is set. The torpedo contains many ingenious devices for bringing it quickly to the required depth and keeping it straight in its course. One of these devices is the gyroscope, which will be described under the head of "spinning tops." Whitehead torpedoes are capable of running at a speed of over thirty-seven miles an hour for a range of two thousand yards and hitting the mark aimed at almost as accurately as a gun. The submarine boat carries a number of torpedoes, and has one torpedo-tube near the forward end from which to fire the torpedoes.
It would be very difficult for one submarine to fight another submarine, for the submarine when completely submergedis blind. It could not see in the water to find its enemy. The torpedo-boat-destroyer is able to destroy a submarine by means of torpedoes, shells full of high explosives, or quick-firing guns. Advantage must be taken of the moment when the submarine comes to the surface to get a view of her enemy.
One of the great enemies of the submarine will probably be the air-ship, for while the submarine when under water cannot be seen from a ship on the surface, it can, under favorable conditions, be seen from a certain height in the air.
Most submarines use a gasolene motor for surface travel, and an electric motor run by a storage battery for navigation below the surface. The best submarines can travel at the surface like an ordinary boat, or "awash"—that is, just below the surface—with only the conning tower projecting above the water, or they can travel completely submerged.
The rising and sinking of the submarine depend on the principle of Archimedes. The upward push of the water is just equal to the weight of the water displaced. If the water displaced weighs more than the boat, then the upward push of the water is greater than the weight of the boat and the boat rises. However, the boat can be made to dive when its weight is just a little less than the weight of the water displaced. This is done by means of horizontal rudders which may be inclined so as to cause the boat to glide downward as its propeller drives it forward.
The magnetic compass is not reliable in a submarine with a hull made of steel. The electric motor used for propelling the boat under water also interferes with the action ofthe compass, because of its magnetic field. The gyroscope, which we shall describe later, is not affected by magnetic action, and may take the place of the compass.
Water ballast is used, and when the submarine wishes to dive, water is admitted into the tanks until the boat is nearly heavy enough to sink of its own weight. It is then guided downward by the horizontal rudder. The submarine is driven by a screw propeller, and some submarines are lowered by means of a vertical screw. Just as a horizontal screw propels a vessel forward, so a vertical screw will propel it downward. When the submarine wishes to rise, it may do so by the action of its rudder, or the water may be pumped out of its tanks, when the water will raiseit rapidly. A submarine which is kept always a little lighter than water will rise to the surface in case of accident to its machinery. Figs. 99, 100, and 101 are from photographs of United States submarines.
FIG. 99–THE "PLUNGER"FIG. 99–THE "PLUNGER"Photo by Pictorial News Co.
Photo by Pictorial News Co.