[Ill.u.s.tration: FIG. 85--DE LAVAL STEAM-TURBINE Driven by a jet of steam striking the blades.]

[Ill.u.s.tration: FIG. 86--A MODERN STEAM-TURBINE WITH TOP CASING RAISED SHOWING BLADES]

[Ill.u.s.tration: FIG. 87--DIAGRAM OF TURBINE SHOWN IN FIG. 86 The arrows show the course of the steam.]

[Ill.u.s.tration: FIG. 88--A STEAM-TURBINE THAT RUNS A DYNAMO GENERATING 14,000 ELECTRICAL HORSE-POWER The steam enters through the large pipe at the left.]

In 1897, as the battle-ships of the British fleet were a.s.sembled to celebrate the Diamond jubilee of Queen Victoria, a little vessel a hundred feet long darted in and out among the 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 the _Turbinia_, 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 flows toward the rim, pa.s.sing over a number of rows of curved blades. The Parsons turbine is used on the fastest ocean liners. The _Lusitania_, 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 anch.o.r.ed, 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 each ton 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 VI

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 the sailing 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 f.a.gots 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 f.a.gots 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 allow the 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 the liquid. 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.

[Ill.u.s.tration: FIG. 89--BRITISH ARMY AIR-SHIP "NULLI SECUNDUS" READY FOR FLIGHT]

[Ill.u.s.tration: 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 water holds 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 s.p.a.ce 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 s.p.a.ce. 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 Aerostatic Park 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. One filling 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 pa.s.sageway 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 by four screws, and guided by a number of rudders placed some in front and some in the rear. The first Zeppelin air-ship carried four pa.s.sengers. 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.

[Ill.u.s.tration: FIG. 91--A ZEPPELIN AIR-SHIP]

A larger air-ship, the _Deutschland_, built later by Count Zeppelin, was the first air-ship to be used for regular pa.s.senger service. The _Deutschland_ is shown in Fig. 92. The _Deutschland_ carried the crew and twenty pa.s.sengers. It operated for a time as a regular pa.s.senger air-ship between Friedrichshafen and Dusseldorf, a distance of three hundred miles. The _Deutschland_ was 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 pa.s.senger 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.

[Ill.u.s.tration: FIG. 92--COUNT ZEPPELIN'S "DEUTSCHLAND," THE FIRST AIR-SHIP IN REGULAR Pa.s.sENGER SERVICE]

[Ill.u.s.tration: Copyright by Pictorial News Co.

FIG. 93--THE BALDWIN AIR-SHIP USED IN THE UNITED STATES ARMY]

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 pa.s.senger 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.

[Ill.u.s.tration: FIG. 94--IN FULL FLIGHT]

[Ill.u.s.tration: Copyright, 1908, by Pictorial News Co.

FIG. 95--WRIGHT AIR-SHIP IN FLIGHT Rear view, showing propellers.]

[Ill.u.s.tration: FIG. 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 side _R_ starts to fall. The corners _a_ and _e_ are raised by the operator while _b_ and _f_ are lowered, thus twisting the planes, as shown in the dotted lines of the figure.

The side _R_ then catches more wind than the side _L_. The wind exerts a greater lifting force on _R_ than on _L_, 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.