[Ill.u.s.tration: FIG. 96--HOW THE WRIGHT AIR-SHIP IS KEPT AFLOAT 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 at _d_ and _c_, and pa.s.ses through pulleys at _g_ and _h_. 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 corner _d_, and raises _e_. The corner _a_ is raised by the post which connects _a_ and _e_. The rope 4, pa.s.sing from _a_ to _b_ through pulleys at _m_ and _n_, is thus drawn toward _a_ and pulls down the corner _b_. Thus _a_ is raised and _b_ is lowered. At the same time rope 4 turns the rear rudder to the left, as shown by the dotted lines, thus forcing the side _R_ against 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 place in 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 princ.i.p.al 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 Bleriot (Fig. 98). The Bleriot 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 Bleriot represent the two leading types of early successful flying-machines.
[Ill.u.s.tration: Copyright by M. Brauger, Paris FIG. 98--THE BLeRIOT MONOPLANE]
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 princ.i.p.al 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 either of 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 sh.o.r.e 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 submerged is 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, sh.e.l.ls 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 compa.s.s 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 of the compa.s.s, 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 compa.s.s.
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 raise it 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.
[Ill.u.s.tration: FIG. 99--THE "PLUNGER"
Photo by Pictorial News Co.]
[Ill.u.s.tration: FIG. 100--U. S. SUBMARINE "SHARK" READY FOR A DIVE Photo by Pictorial News Co.]
[Ill.u.s.tration: FIG. 101--FIRST SUBMARINE CONSTRUCTED IN UNITED STATES.
IT WENT TO THE BOTTOM WITH SEVEN MEN, WHO WERE DROWNED Photo by Pictorial News Co.]
There is one kind of submarine built for peaceful pursuits which deserves mention. It is the _Argonaut_, invented by Simon Lake. This remarkable boat crawls along the bottom of the sea, but not at a very great depth. It is equipped with divers" appliances, and is used in saving wreckage. Divers can go out through the bottom of the boat, walk about on the sea bottom, and when through with their work re-enter the boat; all the while boat and men are, perhaps, a hundred feet below the surface. The divers" compartment, from which the divers go out into the water, is separated by an air-tight part.i.tion from the rest of the boat.
Compressed air is forced into this compartment until the pressure of the air equals the pressure of the water outside. Then the door in the bottom is opened, and the air keeps the water out. The men in their diving-suits can then go out and in as they please.
For every boat there is a depth beyond which it must not go. The penalty for going beyond this depth is a battered-in vessel, for the pressure increases with the depth. Every time the depth is increased thirty-two feet the pressure is increased fifteen pounds on every square inch.
Beyond a certain depth the vessel cannot resist the pressure. Submarines have been made strong enough to withstand the pressure at a depth of five thousand feet, or nearly a mile. Most submarines, however, cannot go deeper than a hundred and fifty feet.
Air is supplied to the occupants of the boat either from reservoirs containing compressed air or oxygen, or by means of chemicals which absorb the carbon dioxide produced in breathing and restore the needed quant.i.ty of oxygen to the air.
While the men in the boat cannot see in the water, they can see objects on the surface of the water, even when their boat is several feet below the surface, by means of the periscope. This is an arrangement of lenses and mirrors in a tube bent in two right angles, which projects a short distance above the surface and can be turned in any direction (Fig.
102). Thus the boat, while itself nearly invisible, can have a clear view of the battle-ship which it is about to attack.
[Ill.u.s.tration: FIG. 102--HOW MEN IN A SUBMARINE SEE WHEN UNDER THE WATER]
Some Spinning Tops that Are Useful
Every one knows that a top will stand upright only when it is spinning.
Most tops when spinning will stand very rough treatment without being upset. The whip-top will stand a severe lashing. Spin a top upright and give it a knock. It will go round in a circle in a slanting position, and after a time will right itself. If the top is struck toward the south it will not bow toward the south but toward the east or west. In throwing a quoit, the quoit must be given a spinning motion or the thrower cannot be certain how it will alight. A coin thrown up with a spinning motion will not turn over. The quoit and the coin are like the top. They will not turn over easily when spinning. For the same reason a rifle bullet is set spinning by the spiral grooves in the bore of the gun, and it goes straight to its mark. With a smooth-bore gun that does not set the bullet spinning the gunner cannot be sure of his aim.
It took a long time to discover that the spinning top is a useful machine. It is useful because of its steady motion, because it is difficult to turn over. It was discovered by Newton long ago that every moving object tries to keep on in the direction in which it is moving. A moving object always requires some force to change its direction. The spinning top is a beautiful ill.u.s.tration of this principle. The top that is most useful is the gyroscope top (Fig. 103). It is mounted on pivots so arranged that the top can turn in any direction within the frame that supports it. If the top is set spinning one may turn the frame in any direction, but the top does not change direction. The axis of the top will point in the same direction all the while the top is spinning, no matter how the supporting frame is moved about. The top will spin on a string. If attached inside a box the box can be made to stand on one corner while the top is spinning.
[Ill.u.s.tration: FIG. 103--A TOP THAT SPINS ON A STRING]
This top, which is so hard to upset, has been used in ships to prevent the ship being rolled by the waves. A large fly-wheel is mounted in the middle of the vessel on a horizontal axle. A fly-wheel is only a large top. It spins with a steady motion, and because of its larger size it is very much harder to overturn than a toy top. The fly-wheel in the ship resists the rolling force of the waves and steadies the ship, so that even with high waves the rolling can scarcely be felt. The waves do not so readily break over the ship when thus steadied by the revolving wheel.
The gyroscope is also used in some forms of torpedo to give the torpedo steady motion. By means of a spring released by a trigger the gyroscope within the torpedo is set spinning before the torpedo enters the water.
The gyroscope keeps its direction unchanged, and as the torpedo turns one way or the other the gyroscope acts upon one or the other of two valves connected with the compressed-air chambers from which the screws of the torpedo are driven. The air thus set free by the gyroscope drives a piston-rod connected with a rudder in such a way as to right the torpedo. The torpedo goes through the water with a slightly zigzag motion, but never more than two feet out of the line in which it was aimed.
The Monorail-Car
Another use of the gyroscope is in the monorail-car. To make a car run on a single rail, with its weight above the rail, was impossible until the use of the gyroscope was discovered. In the monorail-car invented by Brennan (Fig. 104) there are two gyroscopes, each weighing fifteen hundred pounds, driven at a speed of three thousand revolutions a minute by an electric motor. Each gyroscope wheel with its motor is mounted in an air-tight casing from which the air is pumped out. The wheel will run much more easily in a vacuum than in air, for the air offers very great resistance to its motion. The wheels are placed one on each side of the car with their axles horizontal. When the car starts to fall the spinning gyroscopes right it much as a spinning top rights itself if tipped to one side by a blow. If the wind tips the car to the left the gyroscopes incline to the right until the car is again upright. If the load is heavier on the right side the car inclines itself toward the left just as a man leans to the left when carrying a load on his right shoulder. In rounding a curve the car leans to the inside of the curve just as a bicycle rider does, and as a railway train is made to do by laying the outer rail of the curve higher than the inner rail. Two gyroscopes spinning in opposite directions are necessary to keep the car from falling when rounding a curve.
[Ill.u.s.tration: FIG. 104--A CAR THAT RUNS ON ONE RAIL Louis Brennan"s full-size monorail.]
The gyroscope may be used in place of a compa.s.s. If it is set spinning in a north and south direction it will continue to spin in a north and south direction, no matter how the ship may turn. It is even more reliable than the compa.s.s, for it is not affected by magnetic action.
Possibly some of the great inventions yet to be made will be new uses of the spinning top.
Liquid Air and the Greatest Cold
For a long time after men had learned the use of the furnace and could produce great heat, the greatest cold known was that of the mountain-top. Men wondered what would happen if air could be made colder than the frost of winter, but knew not how to bring about such a result.
They wondered what things could be frozen that remain liquid or gaseous even in the cold of winter.
The first artificial cold was produced by a mixture of salt and ice, such as we now use in an ice-cream freezer. In time men learned other ways of producing great cold and even to manufacture ice in large quant.i.ties.
The cold of liquid air is far greater than that of ice or even a freezing mixture of salt and ice. Liquid air is simply air that is so cold that it becomes a liquid just as steam when cooled forms water.
Steam has only to be cooled to the temperature of boiling water, while air must be cooled to 314 degrees below zero on the Fahrenheit scale.
If it were possible for us to live in such a climate, and the world were cooled to the temperature of liquid air, we should have a curious world.
Watch-springs might be made out of pewter, bells of tin, and piano wires of solder, for these metals are made stronger by the extreme cold of liquid air. There would be no air to breathe. Oceans and rivers would be frozen solid, and the air would form a liquid ocean about thirty-five feet deep. This ocean of liquid air would be kept boiling a long time by the heat of the ice beneath it, for ice is hot compared with liquid air.
The ice would cool as it gave up its heat to the liquid air and in time become as cold as the liquid air itself.
Liquid air has been shipped thousands of miles in a double walled tin can, the s.p.a.ce between the two walls being filled with felt. The felt protects the liquid air from the heat of the air without. The liquid air evaporates slowly, and escapes through a small opening at the top.
Professor Dewar, a successor of Faraday in the Royal Inst.i.tution, invented the Dewar bulb, by means of which the evaporation of the liquid air is prevented. This bulb is a double-walled flask. In the s.p.a.ce between the two walls of the flask is a vacuum. Now a vacuum is the best possible protection against heat. If we were to take a bottle full of air and pump out from the bottle all except about a thousandth of a millionth of the air it contained at first we should have such a vacuum as that of the Dewar bulb. With such a vacuum around it ice could be kept from melting for many days even in the hottest weather, for no heat can go through a vacuum.
But the greatest cold is not the cold of liquid air. Liquid hydrogen is so cold that it freezes air. When a flask of liquid hydrogen is opened there is a small snow-storm of frozen air in the mouth of the flask. But even this is not the greatest cold. The liquid hydrogen may be frozen, forming a hydrogen snow whose temperature is 435 degrees below zero.
This is nearly equal to the cold of the s.p.a.ce beyond the earth"s atmosphere, which is the greatest possible cold.
The Electric Furnace and the Greatest Heat
The greatest heat that has yet been produced artificially is that of the electric arc. The exact temperature of the electric arc is not known with certainty. It is known, however, that the temperature of the hottest part of the arc is not less than 6500 degrees Fahrenheit. When we compare this with the temperature of the hottest coal furnace, which is about 4000 degrees, we can very easily understand that something is likely to happen at the temperature of the electric arc that could not happen in an ordinary furnace.