The Story of Great Inventions

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 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 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.

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 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 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 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 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 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-SHIP 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 passenger service. The Deutschland is shown in Fig. 92. The Deutschland carried the crew and twenty passengers. It operated for a time as a regular passenger air-ship between Friedrichshafen and DÜsseldorf, 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 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 SERVICE FIG. 92–COUNT ZEPPELIN'S "DEUTSCHLAND," THE FIRST AIR-SHIP IN REGULAR PASSENGER SERVICE

FIG. 93–THE BALDWIN AIR-SHIP USED IN THE UNITED STATES ARMY 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 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 FLIGHT FIG. 94–IN FULL FLIGHT

FIG. 95–WRIGHT AIR-SHIP IN FLIGHT FIG. 95–WRIGHT AIR-SHIP IN FLIGHT

Rear view, showing propellers.

FIG. 97–THE SEAT AND MOTOR OF THE WRIGHT AEROPLANE 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.

FIG. 96–HOW THE WRIGHT AIR-SHIP IS KEPT AFLOAT 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 passes 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, passing 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 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 MONOPLANE FIG. 98–THE BLÉRIOT 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 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 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 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 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, 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 of the 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 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.

FIG. 99–THE "PLUNGER" FIG. 99–THE "PLUNGER"

Photo by Pictorial News Co.

FIG. 100–U. S. SUBMARINE "SHARK" READY FOR A DIVE FIG. 100–U. S. SUBMARINE "SHARK" READY FOR A DIVE

Photo by Pictorial News Co.

FIG. 101–FIRST SUBMARINE CONSTRUCTED IN UNITED STATES. IT WENT TO THE BOTTOM WITH SEVEN MEN, WHO WERE DROWNED 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 partition 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 quantity 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.

FIG. 102–HOW MEN IN A SUBMARINE SEE WHEN UNDER THE WATER 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 illustration 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.

FIG. 103–A TOP THAT SPINS ON A STRING 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.

FIG. 104–A CAR THAT RUNS ON ONE RAIL FIG. 104–A CAR THAT RUNS ON ONE RAIL

Louis Brennan's full-size monorail.

The gyroscope may be used in place of a compass. 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 compass, 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 quantities.

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 space 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 Institution, 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 space 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 space 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.

If an electric arc is enclosed by something that will hold the heat in we have an electric furnace, and any substance placed in the furnace may be made nearly as hot as the arc itself. In the electric furnace any substance, whether found in nature or prepared artificially, may be melted or vaporized.

It was Henri Moissan, Professor of Chemistry at the Sorbonne in Paris, who made the first great discoveries in the use of the electric furnace and produced the first artificial diamonds. The study of diamonds led Moissan to believe that in nature they are formed by the cooling of a melted mixture of iron and carbon. He could prepare such a mixture with his electric furnace, he thought, and so make diamonds like those of the diamond mines. So, with an electric furnace having electrodes as large as a man's wrist, a mixture of iron and charcoal in a carbon crucible, and a glass tank filled with water, Moissan set out to change the charcoal to diamonds. At a temperature of more than six thousand degrees the iron and charcoal were melted together. For a time of from three to six minutes the mixture was in the intense heat. Then the covering of the furnace was removed and the crucible with the melted mixture dropped into the tank of water. With some fear this was done for the first time, for it was not known what would happen when such a hot object was dropped into cold water. But no explosion occurred, only a violent boiling of the water, a fierce blazing of the molten mass, and then a gradual change of color from white to red and red to black. With boiling acids and other chemicals the refuse was removed, and the fragments that remained were found to be diamonds, small, it is true, so small that they could be seen only with the aid of a microscope, but giving promise of greater things to come. The outer crust of iron held the melted charcoal under enormous pressure while it slowly cooled and formed the diamond crystals. The process of manufacturing diamonds is illustrated in Figs. 105, 106, and 107.

FIG. 105–MANUFACTURING DIAMONDS—FIRST OPERATION FIG. 105–MANUFACTURING DIAMONDS—FIRST OPERATION

Preparing the furnace. Charcoal and iron ore placed in a crucible and subjected to enormous heat electrically.

FIG. 106–MANUFACTURING DIAMONDS—SECOND OPERATION FIG. 106–MANUFACTURING DIAMONDS—SECOND OPERATION

The furnace at work.

FIG. 107–MANUFACTURING DIAMONDS—THIRD OPERATION FIG. 107–MANUFACTURING DIAMONDS—THIRD OPERATION

Plunging the crucible into cold water. Observe the white-hot carbon just removed from the furnace.

The electric furnace has made possible the preparation of substances unknown before, and the production in large quantities at low cost of substances that before were too costly for general use. One of the best known of these substances is aluminum. With the discovery of the electric-furnace method of extracting aluminum from its ores, the price of aluminum fell from one hundred and twenty-four dollars per pound to twelve cents per pound.

Among the many uses of the electric furnace we may mention the preparation of calcium carbide, which is used in producing the acetylene light; carborundum, a substance almost as hard as diamond; and phosphorus, which is used in making the phosphorus match. It is used also to some extent in the manufacture of glass, and, in some cases, for extracting iron from its ores.

The Wireless Telegraph

A ship in a fog is struck by another ship. The water rushes in, puts out the fires in the boilers, the engines stop, the ship is helpless in mid-ocean in the darkness of the night. But the snapping of an electric spark is heard in one of the cabins. Soon another vessel steams alongside. The life-boats are lowered and every person is saved. The call for help had gone out over the sea in every direction for two hundred miles. Another ship had caught the signal and hastened to the rescue, and the world realized that the wireless telegraph had robbed the sea of its terrors.

Without the curious combination of magnets, wires, and batteries on the first ship no signal could have been sent, and without such a combination on the second ship the signal would have passed unheeded. How was this combination discovered, and how does it work?

Faraday, as we have seen, discovered the principle of the induction-coil. With the induction-coil a powerful electric spark can be produced. The friction electrical machine was known long before the time of Faraday. Franklin proved that a stroke of lightning is like a spark from an electrical machine, only more powerful. These great discoverers did not know, however, that an electric spark sends out something like light which travels in all directions. They did not know it, because they had no eyes to see this strange light.

I will tell you a fable to make the meaning clear. There once lived a race of blind men. Not one of them could see. They built houses and cities, railroads and steamships, but they did everything by touch and sound. When they met they touched each other and spoke, and each man knew his friend by the sound of his voice. One day a wise man among them said he believed there was something besides the sound of the voice with which they could make signals to each other. Another wise man thought upon this matter for some time and brought forth a proof that there is something called light, though no man could see it. Another, wiser and more practical, invented an eye which any man could carry about with him and see the light when he turned it in the direction from which the light was coming. Thereafter each man carried a light that flashed like the flashing of a firefly. Each man also carried an eye, and each could see his friend as well as hear the sound of his voice.

The fable is true. The light which no man had seen we now call electric waves. The eye with which any one can perceive this light is the receiving instrument of the wireless telegraph. The strange light flashed out whenever an electric spark passed from an electrical machine, a Leyden jar, an induction-coil, or as lightning in the clouds, but for hundreds of years this light was unseen. The human eye could not see it, and no artificial eye that would catch electric waves had been invented. A man in England, James Clerk-Maxwell, first proved that there is such a light. Heinrich Hertz, a German, first made an eye that would catch the waves from the electric spark, and the man who first perfected an eye with which one could catch the electric waves at a great distance and improved the instruments for sending out such waves was Marconi.

The fable is true, for electric waves are like the light from the sun. They go through space in all directions as light does. They will not merely go through air, but through what we call empty space, or a vacuum, as light will. If we think of waves somewhat like water waves, but not exactly like them, rushing through space, we have about as good a picture of electric waves as we can well form in our minds. As the light of a lamp goes out in all directions, so do the electric waves go out in all directions from the place where the electric spark passes. Since these waves go through what we call empty space, we must think of something in that space and that it is not really empty. Examine an incandescent electric lamp. The bulb was full of air when the carbon thread was placed in it. The air was then pumped out until only about a millionth part remained. The bulb was then sealed at the tip and made air-tight. We say the space inside is a vacuum. If the bulb is broken there is a loud report as the air rushes in. Is the bulb really empty after the air is pumped out? Is anything left in the bulb around the carbon thread? Turn on the electric current and the carbon thread becomes white hot. The light from the white-hot carbon thread goes out through the vacuum. There is nothing in the vacuum that we can see or feel or handle, but something must be there to carry the light from the carbon thread. The light of the sun comes to the earth through ninety-three million miles of space. Is there anything between the earth and the sun through which this light can pass? Light, we know, is made up of waves, and we cannot think of waves going through empty space. There must be something between the sun and the earth. That something through which the light of the sun comes to the earth we call the ether. It is the ether that carries the light across the vacuum in the light bulb as well as from the sun to the earth. Electric waves used in wireless telegraphy go through this same ether. The light of the sun is made up of the same kind of waves, and we do not think it strange because it is so common. It is true we do not see light waves, but they affect our eyes so that by means of them we can see objects and perceive the flashing of a light. So with the wireless receiving instrument we do not see the electric waves, but we perceive the flashing of the strange light. Electric waves and light travel with the same speed—186,000 miles in a second. A wireless message will go around the earth in about one-seventh of a second.

Electric waves will go through a brick wall as readily as sunlight will go through a glass window, but that is not so strange as it may seem. Red light will not go through blue glass. Blue glass holds back the red light, but lets the blue light go through. So the brick wall holds back common light, but allows the light which we call electric waves to go through.

Some waves on water are longer than others. So electric waves are longer than light waves. That is the only difference between them. In fact, the light of the sun is made up of very short electric waves. These short waves affect our eyes, but the longer electric waves do not. We are daily receiving the wireless-telegraph waves from the sun, which we call light. Electric waves used in wireless telegraphy vary from about six hundred feet to two miles in length, while the longest light waves that affect our eyes are only one thirty-three-thousandth of an inch in length.

The sensitive part of the Marconi receiving apparatus is the coherer. The first coherer was made in 1890 by Prof. Edward Branly, of the Catholic University of Paris. Very fine metal filings were enclosed in a tube of ebonite and connected in a circuit with a battery and a galvanometer. The filings have so high a resistance that no current flows. The waves from an electric spark, however, affect the filings so that they allow the current to flow. The electric waves are said to cause the filings to cohere—that is, to cling together more closely. It is a peculiar form of electric welding. Branly discovered that a slight tapping of the tube loosens the filings and stops the flow of the current.

All that was needed for wireless telegraphy was at hand. Men knew how to produce electric waves of any desired length. They knew how they would act. A sensitive receiver had been discovered. There was needed the practical man who should combine the parts, improve details, and apply the wireless telegraph to actual use. This was the work of Guglielmo Marconi. In 1894, at the age of twenty, Marconi began his experiments on his father's estate, the Villa Grifone, Bologna, Italy. Fig. 108 is from a photograph of Marconi and his wireless sending and receiving instruments.

FIG. 108–MARCONI AND HIS WIRELESS-TELEGRAPH SENDING AND RECEIVING INSTRUMENTS FIG. 108–MARCONI AND HIS WIRELESS-TELEGRAPH SENDING AND RECEIVING INSTRUMENTS

To Marconi, telegraphing through space without wires appears no more wonderful than telegraphing with wires. In the wire telegraph electric waves, which we then call an electric current, follow a wire somewhat as the sound of the voice goes through a speaking-tube. In the wireless telegraph the electric waves go out through space without any wire to guide them. The light and heat waves of the sun travel to us through millions of miles of space without requiring any conducting wire. That electric waves should go though space in the same way that light does is no more wonderful than that the waves should follow all the turns of a wire.

The sending instrument used by Marconi includes an induction-coil, one side of the spark-gap being connected to the earth and the other to a vertical wire (Fig. 109). There must be a battery of Leyden jars in the circuit of the secondary coil. The induction-coil may be operated by a storage battery or dynamo. The vertical wire, or antenna, is to the sending instrument what the sounding-board is to a violin. It is needed to increase the strength of the waves. In the wireless telegraph some wires must be used. It is called wireless because the stations are not connected by wires. The antenna for long-distance work consists of a network of overhead wires. When the key is pressed a rapid succession of sparks passes across the spark-gap. The antenna, or overhead wire, is thus made to send out electric waves. By pressing the key for a longer or shorter time, a longer or shorter series of waves may be produced and a correspondingly longer or shorter effect on the receiver. In this manner the dots and dashes of the Morse alphabet may be transmitted.

FIG. 109–DIAGRAM OF WIRELESS-TELEGRAPH SENDING APPARATUS FIG. 109–DIAGRAM OF WIRELESS-TELEGRAPH SENDING APPARATUS

At the receiving station there are two circuits. One includes a coherer, a local battery, and a telegraph relay (Fig. 110). The other circuit, which is opened and closed by the relay, includes a recording instrument and a tapper. One end of the coherer is connected to the earth and the other to a vertical wire like that used for the transmitter. The electric waves weld the filings in the coherer, and this closes the first circuit. The relay then closes the second circuit, the recording instrument records a dot or a dash, and the tapper strikes the coherer and breaks the filings apart ready for another stream of electric waves.

The second circuit described in the text is not shown here. The relay and the second circuit would take the place of the electric bell. In the circuit as shown here the electric waves would cause the coherer to close the circuit and ring the bell.

With this arrangement it was possible to work only two stations at one time. Though stations were to be established in all the cities of Great Britain, only one message could be sent at one time, and all stations but one must keep silence, because a second series of waves would mingle with the first and confusion would result.

Marconi's next effort was to make it possible to send any number of messages at one time. This led to his system of tuning the sending and receiving instruments. With this system the receiving instrument will take a message only from a sending instrument with which it is in tune. It is possible, therefore, for any number of wireless-telegraph stations to operate at the same time, the waves crossing one another in all directions without interfering, each receiver responding to the waves intended for it. An ocean steamer can, with the tuned system, send one message and receive another from a different station at the same time.

Marconi's ambition was to send a wireless message across the Atlantic. Quietly he made his preparation, building at Poldhu, Cornwall, England, a more powerful transmitter than had yet been used. At noon on the 12th of December, 1901, he sat in a room of the old barracks on Signal Hill, near St. Johns, Newfoundland, waiting for a signal from England. His assistants at the Poldhu station were to telegraph across the ocean the letter "S" at certain times each day. On the table was the receiving apparatus, made very sensitive, and including a telephone receiver. A wire led out of the window to a huge kite, which the furious wind held four hundred feet above him. One kite and a balloon used for supporting the antenna had been carried out to sea. He held the telephone receiver to his ear for some time. The critical time had come for which he had worked for years, for which his three hundred patents had prepared the way, and for which his company had erected the costly power station at Poldhu. Calmly he listened, his face showing no sign of emotion. Suddenly there sounded the sharp click of the tapper as it struck the coherer. After a short time Marconi handed the telephone receiver to his assistant. "See if you can hear anything," he said. A moment later, faintly and yet distinctly, came the three little clicks, the dots of the letter "S" tapped out an instant before in England. Marconi's victory was won.

A flying-machine can be equipped with a wireless-telegraph outfit, so that a man can telegraph while flying through the air. Two men are needed, one to operate the flying-machine, the other to send the telegraphic messages. This has been done with the Wright machine and with some dirigible balloons. Of course, the wireless instruments on the flying-machine cannot be connected to the ground. Instead of the ground connection there is a second antenna.—one antenna on each side of the spark-gap. While in the ordinary wireless instruments the discharge surges back and forth between the antenna and the earth, in the flying-machine wireless the discharge surges back and forth between the two antennÆ. In the Wright machine, when equipped for wireless telegraphy, the two antennÆ are placed one under the upper plane, the other under the lower plane of the flying-machine.

More power is required for the wireless than for the wire telegraph. In the wire telegraph about one-hundredth horse-power is required to send a message one hundred and twenty miles. To send a message the same distance with the wireless requires about ten horse-power, or a thousand times as much as with the wire telegraph. This is because in the wireless telegraph the waves go out in all directions, and much of the power is wasted. In the wire telegraph the electric waves are directed along the wire and very little of the power is wasted. For the same reason a person's voice can be heard a long distance through a speaking-tube. The speaking-tube guides the sound and prevents it from scattering somewhat as the wire guides the electric waves.

The overhead wires of a wireless-telegraph station send out a "dark" light while a message is being sent. (See frontispiece.) Standing near the station on a dark night one can see nothing, but can hear only the terrific snapping of the electric discharge. The camera, however, shows that light goes out from the wires. It is light of shorter waves than any that the eye can perceive, but the sensitive film of the photographic plate makes it known to us.

The Wireless Telephone

In sending a message by the wire telegraph the current flows over the line wire when the key is pressed. When the key is released the current stops. The circuit is made and broken for every dot or dash. This we may call an interrupted current. Now we have seen that the attempt to invent a wire telephone using an interrupted current failed. While one is talking over the wire telephone a current (alternating) must be flowing over the line wire. The sound of the voice does not make and break the circuit, but changes the strength of the current. This alternating current is wonderfully sensitive. It can vary in the rate at which it alternates or the number of alternations per second to correspond to sound of every pitch. It varies in strength to correspond to all the variations in the voice, and reproduces in the receiver not merely the words that are spoken but the quality of the voice, so that the voice of a friend can be recognized by telephone almost as well as if talking face to face.

The same things are true of the wireless telegraph and telephone. Instead of an electric current, let us say "a stream of electric waves." Then we may say of the wireless everything that we have said of the wire telegraph and telephone. In sending a message by wireless telegraph the stream of electric waves flows when the key is pressed and stops when the key is released. We have an interrupted stream of electric waves. But an interrupted stream of waves cannot be used for a wireless telephone any more than an interrupted current can be used for a wire-telephone. There must be a constantly flowing stream of electric waves, and these waves must be changed in strength and form by the sound of the voice. Fig. 111 shows a wireless-telephone receiver in which light is used to carry the message. The light acts on the receiver in such a way as to reproduce the sound.

FIG. 111–RECEIVER OF BELL'S PHOTOPHONE FIG. 111–RECEIVER OF BELL'S PHOTOPHONE

An early idea in wireless telephony.

In the wireless-telegraph receiver the interrupted stream of electric waves makes and breaks the circuit of an electric battery. The wireless-telephone receiver must not make and break a circuit, but it must be sensitive to all the changes in the electric waves. One such receiver is the audion, which we shall now describe.

The audion was invented by Dr. Lee de Forest. De Forest had taken the degree of Doctor of Philosophy at Yale University, having written his thesis for that degree on the subject of electric waves. He then entered the employ of the Western Electric Company in Chicago, and while in this position worked at night in his room on experiments with electric waves.

Here he found that a gas flame is sensitive to electric waves (Fig. 112). If a gas flame is made part of the circuit of an electric battery, which includes also an induction-coil connected to a telephone receiver, then when a stream of electric waves comes along there is a click in the receiver. The waves change the resistance of the flame, and so change the strength of the current. The flame is a simple audion. It is the heated gas in the flame that responds to the electric waves.

FIG. 112–A GAS FLAME IS SENSITIVE TO ELECTRIC WAVES FIG. 112–A GAS FLAME IS SENSITIVE TO ELECTRIC WAVES

If instead of a gas flame an incandescent-light bulb is used having a metal filament, and on either side of the filament a small strip of platinum, a more sensitive receiver is obtained. This is the audion, which is the distinguishing feature of the De Forest wireless telegraph and wireless telephone. The metal filament is made white hot by the current from a storage battery. The vacuum in the bulb is about the same as that of the ordinary incandescent electric light. A very small quantity of gas is therefore left in the bulb. The electrified particles of gas respond more freely to electric waves in this bulb than in the gas flame.

The De Forest wireless telephone was adopted for use in the United States Navy shortly before the cruise around the world in 1908. Every ship in the navy was equipped with the wireless telephone, enabling the Admiral to talk with the officers of any vessel up to a distance of thirty-five miles. The wireless telephone in use on a battle-ship is shown in Fig. 113.

FIG. 113–CAPTAIN INGERSOLL ON BOARD THE U. S. BATTLE-SHIP "CONNECTICUT" USING THE WIRELESS TELEPHONE FIG. 113–CAPTAIN INGERSOLL ON BOARD THE U. S. BATTLE-SHIP "CONNECTICUT" USING THE WIRELESS TELEPHONE

Wonders of the Alternating Current

Before the days of the electric current, men used the power of falling water. The mill or factory using the water-power was placed beside the fall. The water turned a great wheel, to which was connected the machinery of the mill, It was not until the invention of the dynamo and motor that water-power could be used at a great distance. If a hundred years ago a man had said that the time would come when a waterfall could turn the wheels of a mill a hundred miles away he would have been laughed at. Yet this very thing has come to pass. Indeed, one waterfall may turn the wheels of many factories, run street-cars, and light cities up to a distance of a hundred miles and even more. The power of the falling water goes out over slender copper wires from a great dynamo near the fall to the motors in the factories and street-cars.

The falling water of Niagara has about five million horse-power. About the hundredth part of this power is now being used. The water, falling in a wheel-pit 141 feet deep, turns a great dynamo weighing 87,000 pounds with a speed of 250 turns per minute. A number of such dynamos are used supplying an alternating current at a pressure of 22,000 volts, the current alternating or changing direction twenty-five times per second. Such a pressure is too high for the motors and electric lights, but the current is carried at high pressure to the place where it is to be used and there transformed to a current of low pressure. In carrying a current over a long line, there is less loss if the current is carried at high pressure. With an alternating current this can be done and the current changed by means of a transformer to a current of low pressure.

A transformer is simply two coils of wire wound on an iron core. The simplest transformer is the form used by Faraday when he discovered electromagnetic induction. If instead of making and breaking a circuit that flows only in one direction as Faraday did, we cause an alternating current to flow through one of the coils, which we may call the primary, each time the current changes direction in the primary the magnetic field is reversed—that is, the end of the coil which was the north pole becomes the south pole. This rapidly changing magnetic field induces a current in the secondary coil. Each time the magnetic field of the primary coil is reversed the current in the secondary changes direction. Thus an alternating current in the primary induces an alternating current in the secondary. One of these coils is of fine wire, which is wound a great many times around the iron. The other is of coarser wire wound only a few times around the iron. Suppose the current is to be changed from high pressure to low pressure. Then the high-pressure current from the line is made to flow through the coil of many turns, and a current of low pressure is given out from the coil of few turns. By changing the number of turns of wire in the coils we can make the pressure whatever we please. If the pressure or voltage of the secondary coil is less than that of the primary, we have a "step-down" transformer. On the other hand, if we send the current from the line wire through the coil of few turns, then we get a higher voltage from the secondary coil than that of the line wire, and we have a "step-up" transformer. The Niagara current is "stepped down" from 22,000 volts to 220 volts for use in motors.

An electric lamp may be lighted though not connected to any battery or dynamo, but connected only to a coil of wire (Fig. 114). More than this, the coil may be insulated so that no current can enter it from any other coil or wire, and yet the lamp can be lighted. This can be done only by means of an alternating current. If the coil to which the lamp is connected is held in the magnetic field of an alternating current, then another alternating current is induced in the coil, and this second current flows through the lamp.

FIG. 114–INCANDESCENT ELECTRIC LAMP LIGHTED THOUGH NOT CONNECTED TO ANY BATTERY OR DYNAMO FIG. 114–INCANDESCENT ELECTRIC LAMP LIGHTED THOUGH NOT CONNECTED TO ANY BATTERY OR DYNAMO

We have already learned that a changing magnetic field induces a current in a coil. Now the coil through which an alternating current is flowing has a changing magnetic field all around it, and if the lamp-coil is brought into this changing magnetic field an alternating current will flow through the coil and the lamp. The insulation on the lamp-coil does not prevent the magnetic field from acting, though it does prevent a current from entering the coil. The current is induced in the coil itself, and does not enter it from any outside source.

The transformer works in the same way, the only difference being that in the transformer the two coils are on the same iron core. But in the transformer the two coils are insulated so that no current can flow from one coil to the other. When an alternating current and transformers are used, the current that lights the lamps in the houses or on the streets is not the current from the dynamo. It is a new current induced in the secondary coil of the transformer by the magnetic field of the primary coil.

A peculiar transformer which produces an alternating current that changes direction millions of times in a second has been made by Nikola Tesla. This current will do many wonderful things which no ordinary current will do. It will light a room or run a motor without connecting wires. It has produced an electric discharge sixty-five feet in length (Figs. 115 and 116). Though this current is caused to flow by a pressure of millions of volts, it may be taken with safety through the human body. Strange as it may seem, the safety of this current is due to the high pressure and the rapidity with which it changes direction. While the current used at Sing Sing in executing criminals has a pressure of about twenty-five hundred volts, a current having a pressure of a million volts and alternating hundreds of thousands or millions of times per second is harmless; With such a current the human body may become a "live wire," and an electric lamp to be lighted held in one hand while the other hand grasps the wire from the transformer.

FIG. 115–AN ELECTRIC DISCHARGE AT A PRESSURE OF 12,000,000 VOLTS, A CURRENT OF 800 AMPERES IN THE SECONDARY COIL FIG. 115–AN ELECTRIC DISCHARGE AT A PRESSURE OF 12,000,000 VOLTS, A CURRENT OF 800 AMPERES IN THE SECONDARY COIL

FIG. 116–AN ELECTRIC DISCHARGE SIXTY-FIVE FEET IN LENGTH FIG. 116.—AN ELECTRIC DISCHARGE SIXTY-FIVE FEET IN LENGTH

X-Rays and Radium

A strange light which passes through the human body as readily as sunlight through a window was discovered by Prof. Wilhelm Konrad Roentgen, of the University of WÜrzburg. This light, which Professor Roentgen named X-rays, is given out when an electric discharge at high pressure passes through a certain kind of glass tube from which the air has been pumped out until there is a nearly perfect vacuum.

X-rays were discovered by accident. Professor Roentgen was working at his desk with one of the glass tubes when he was called to lunch. He laid the tube with the electric discharge passing through it on a book. Returning from lunch he took a photographic plate-holder which was under the book and made some outdoor exposures with his camera. On developing the plates a picture of a key appeared on one of them. He was greatly puzzled at first, but after a search for the key found it between the leaves of the book. The strange light from the electric discharge in the glass tube had passed through the book and the hard-rubber slide of the plate-holder and made a shadow-picture of the key on the photographic plate. He tried the strange light in many ways, and found that it would go through many objects. It would even go through the human body, so that shadow-pictures of the bones and organs of the body could be obtained. In Fig. 117 is shown a physician using X-rays. Fig. 118 is an X-ray photograph of the eye.

FIG. 117–A PHYSICIAN EXAMINING THE BONES OF THE ARM BY MEANS OF X-RAYS FIG. 117–A PHYSICIAN EXAMINING THE BONES OF THE ARM BY MEANS OF X-RAYS

FIG. 118–X-RAY PHOTOGRAPH OF THE EYE FIG. 118–X-RAY PHOTOGRAPH OF THE EYE

The eye is above and to the left of the larger black circle. The smaller black circle is a shot which has lodged back of the eye.

Not long after the discovery of X-rays it was discovered that light very much like the X-rays is given out by certain minerals. One of the most interesting and the best known of these is radium. Radium gives out a light somewhat like X-rays that will go through copper and other metals. It does many other strange things. It gives out heat as well as light; so much heat, in fact, that it is always about five degrees warmer than the air around it. It continues to give out heat at such a rate that a pound of radium will melt a pound of ice every hour. It can probably keep this up for at least a thousand years. If this heat could be used in running an engine, a hundred pounds of radium would run a one-horse-power engine without stopping for many hundred years. The power of Niagara might be replaced by the power of radium if an engine that could use this power were invented. Fig. 119 is from a photograph made with radium.

FIG. 119–PHOTOGRAPH MADE WITH RADIUM FIG. 119–PHOTOGRAPH MADE WITH RADIUM

A purse containing a coin. The strange light from the radium goes through the purse and the slide of the plate-holder and makes a shadow-picture.

The great inventor of the future may be able to use the heat of radium or some new power now unknown. We have seen how, through the toil of many years and the labors of many men, the great inventions of our age have come into being. It may be that we are now witnessing other great inventions in the making.

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