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.
[Illustration: FIG. 89--BRITISH ARMY AIR-SHIP "NULLI SECUNDUS" READY FOR
FLIGHT]
[Illustration: 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 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.
[Illustration: 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.
[Illustration: FIG. 92--COUNT ZEPPELIN'S "DEUTSCHLAND," THE FIRST
AIR-SHIP IN REGULAR PASSENGER SERVICE]
[Illustration:
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 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.
[Illustration: FIG. 94--IN FULL FLIGHT]
[Illustration:
Copyright, 1908, by Pictorial News Co.
FIG. 95--WRIGHT AIR-SHIP IN FLIGHT
Rear view, showing propellers.]
[Illustration: 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.
[Illustration: 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.
[Illustration:
Copyright by M. Brauger, Paris
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.
[Illustration: FIG. 99--THE "PLUNGER"
Photo by Pictorial News Co.]
[Illustration: FIG. 100--U. S. SUBMARINE "SHARK" READY FOR A DIVE
Photo by Pictorial News Co.]
[Illustration: 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.
[Illustration: 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.
[Illustration: 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.
[Illustration: 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.
[Illustration: FIG. 105--MANUFACTURING DIAMONDS--FIRST OPERATION
Preparing the furnace. Charcoal and iron ore placed in a crucible and
subjected to enormous heat electrically.]
[Illustration: FIG. 106--MANUFACTURING DIAMONDS--SECOND OPERATION
The furnace at work.]
[Illustration: 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.
[Illustration: 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.
[Illustration: 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.
[Illustration: FIG. 110--DIAGRAM OF MARCONI WIRELESS-TELEGRAPH RECEIVING
APPARATUS
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.
[Illustration: 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.
[Illustration: 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.
[Illustration: 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.
[Illustration: 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.
[Illustration: FIG. 115--AN ELECTRIC DISCHARGE AT A PRESSURE OF
12,000,000 VOLTS, A CURRENT OF 800 AMPERES IN THE SECONDARY COIL]
[Illustration: 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.
[Illustration: FIG. 117--A PHYSICIAN EXAMINING THE BONES OF THE ARM BY
MEANS OF X-RAYS]
[Illustration: 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.
[Illustration: 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.
APPENDIX
BRIEF NOTES ON IMPORTANT INVENTIONS
Aerial Navigation
First air balloon--Montgolfier Brothers, France, 1783.
First balloon ascension--Rozier, France, 1783.
First gas balloon--Charles, France, 1783.
First crossing of the English Channel in a balloon--Blanchard,
1785.
First successful dirigible balloon--La France, Renard and
Krebs, France, 1884.
First successful motor-driven aeroplane--Wright Brothers,
United States; date of patent, 1906.
First crossing of the English Channel by an aeroplane--Blériot,
1909.
First air-ship in regular passenger service--Count Zeppelin,
Germany, 1910.
Agriculture
Plough with cast-iron mold-board and iron shares--James Small,
Scotland, 1784.
Grain-threshing machine--Andrew Meikle, England, 1788.
McCormick reaper, first practical grain-harvesting
machine--Cyrus H. McCormick, United States, 1831.
Self-raker for harvesters--McCormick, 1845.
Inclined platform and elevator in the reaper, to enable men
binding the grain to ride with the machine--J. S. Marsh, United
States, 1858.
Barbed-wire fence introduced--United States, 1861.
Self-binder, first automatic grain-binding device for the
reaper--Jacob Behel, United States, 1864.
Sulky plough--B. Slusser, United States, 1868.
Twine-binder for harvesters--M. L. Gorham, United States, 1873.
Improved self-binding reaper--Lock and Wood, United States,
1873.
Barbed-wire machine--Glidden and Vaughn, United States, 1874.
Rotary disk cultivator--Mallon, United States, 1878.
Steam-plough--W. Foy, United States, 1879.
Combined harvester and thresher--Matteson, United States, 1886.
Automobile mower--Deering Harvestor Company, United States,
1901.
Automobile
First steam-automobile--Cugnot, France, 1769.
First chain transmission of power in an automobile--Gurney,
England, 1829.
Application of gas-engine to road vehicles, beginning of the
modern motor-car--Gottlieb Daimler and Carl Benz working
independently, Germany, 1886. Daimler's invention consisted of
a two-cylinder air-cooled motor. It was taken up in 1889, by
Panhard and Levassor, of Paris, who began immediately the
construction of the motor-car. This was the beginning of the
motor-car industry.
Bicycle
First bicycle--Branchard and Magurier, France, 1779.
Rear-driven chain safety bicycle--George W. Marble, United
States, 1884.
Bicycles first equipped with pneumatic tires--1890.
Electrical Inventions
William Gilbert, England, 1540-1603, called "the father of
magnetic philosophy," first to use the terms "electric force,"
"electric attraction," "magnetic pole."
First electrical machine, a machine for producing electricity
by friction--Otto von Guericke, Germany, about 1681.
Discovery of conductors and insulators--Stephen Gray, England,
1696-1736.
First to discover that electric charges are of two
kinds--Cisternay du Fay, France, 1698-1739; Du Fay was also the
first to attempt an explanation of electrical action. He
supposed that electricity consists of two fluids which are
separated by friction, and which neutralize each other when
they combine. This theory was more fully set forth by Robert
Symmer.
Leyden jar--Discovered first by Von Kleist in 1745. The same
discovery was made and the Leyden jar brought to the attention
of the public in 1746 by Pieter van Musschenbroek in Holland.
Lightning-rod--Benjamin Franklin, 1732.
Electroplating--Luigi Brugnatelli, Italy, 1805.
Voltaic arc, a powerful arc light produced with a battery
current--Sir Humphry Davy, England, 1808.
Storage battery--Ritter, Germany, 1803. Platinum wires were
dipped in water and a battery current passed through. Hydrogen
collected on one wire and oxygen on the other. If the platinum
wires were disconnected from the battery and connected with
each other by a conductor, the two wires acted like the plates
of a battery, and a current would flow for a short time in the
new circuit.
Electromagnetism discovered--H. C. Oersted, Denmark, 1819.
Galvanometer, a coil of wire around a magnetic needle for
measuring the strength of an electric current--Schweigger,
Germany, 1820.
Motion of magnet produced by an electric current--M. Faraday,
England, 1821.
Thermo-electricity, an electric current produced by heating the
junction of two unlike metals--Discovered by Professor Seebeck
England, 1821.
Principles of electrodynamics, motion produced by an electric
current--Ampère, France. Announced in 1823.
Law of electric circuits, Ohm's law, current strength equals
electromotive force divided by resistance of the
circuit--George S. Ohm, Germany. Proven by experiment in 1826;
mathematical proof published in 1827.
Magneto-electric induction, induction of electric currents by
means of a magnetic field--M. Faraday, England, 1831.
Electric telegraph--Prof. S. F. B. Morse, United States, 1832.
First telegram sent in 1844--Morse.
Constant electric battery--J. P. Daniell, England, 1836.
First electric motor-boat--Jacobi, Russia, 1839.
Induction-coil--Rhumkorff, Germany, 1851.
Duplex telegraph, first practical system--Stearns, United
States, about 1855-1860.
Storage battery, lead plates in sulphuric acid--Gaston Planté,
France, 1859.
Telephone, make-and-break system, first electrical transmission
of speech--Philip Reiss, Germany, 1860.
Atlantic cable laid--Cyrus W. Field, 1866.
Dynamo, armature coil rotates in the field of an electromagnet,
armature supplies current for the electromagnet as well as for
the external circuit--William Siemens, Germany, 1866.
Gramme ring armature for dynamo--Gramme, France, 1868.
Theory that light consists of electromagnetic
waves--Clerk-Maxwell, England, 1873.
Quadruplex telegraph, sending four messages over one wire at
the same time--Edison, 1873.
Siphon recorder for submarine telegraph, sensitive to very
feeble currents--Sir William Thomson, England, 1874.
Telephone, varying current, first practical working
telephone--Alexander Graham Bell, United States, 1876.
Electric candle, beginning of present arc light--Paul
Jablochkoff, Russia, 1876.
Telephone transmitter of variable resistance--Emil Berliner and
Edison working independently, United States, 1877. Edison used
carbon contacts, Berliner used metal contacts.
Brush system of arc lighting--1878.
Incandescent electric lamp with carbon filament--Edison, 1878.
First electric locomotive--Siemens, Germany, 1879.
Blake telephone transmitter--Blake, United States, 1880.
Storage battery, lead grids filled with active material--Faure,
France, 1881.
Electric Welding--Elihu Thompson, United States, 1886.
Electric Waves discovered by experiment--Heinrich Hertz,
Germany, 1888.
Coherer for receiving electric Waves--Edward Branly, France,
1890.
X-rays--Discovered by Prof. W. C. Roentgen, Germany; announced
to the public in 1895.
Wireless telegraphy--G. Marconi, Italy, 1896.
Nernst electric light, a clay capable of conducting electricity
when heated is used; it becomes incandescent without a
vacuum--Walter Nernst, Germany, 1897.
Radium discovered by Madame Curie, France, 1898.
Explosives
Gunpowder--Inventor and date unknown.
Guncotton--Schönbein, Germany, 1845.
Nitroglycerine--Sobrero, 1847.
Explosive gelatine--A. Nobel, France, 1863.
Dynamite--A. Nobel, France, 1866.
Smokeless powder--Vielle, France, 1866.
Firearms and Ordnance
Spirally grooved rifle barrel--Koster, England, 1620.
Breech-loading shot-gun--Thornton and Hall, United States,
1811.
The revolver; a device "for combining a number of long barrels
so as to rotate upon a spindle by the act of cocking the
hammer"--Samuel Colt, United States, 1836.
Breech gun-lock, interrupted thread--Chambers, United States,
1849.
Magazine gun--Walter Hunt, United States, 1849.
Breech-loading rifle--Maynard, United States, 1851.
Iron-clad floating batteries first used in Crimean War--1855.
Breech-loading ordnance--Wright and Gould, United States, 1858.
Revolving turret for floating batteries--Theodore Timby, United
States, 1862.
First iron-clad floating battery propelled by steam: the
_Monitor_--John Ericsson, United States, 1862.
Gatling gun--Dr. R. J. Gatling, United States, 1862.
Automatic shell-ejector for revolver--W. C. Dodge, United
States, 1865.
Torpedo--Whitehead, United States, 1866.
Disappearing gun-carriage--Moncrief, England, 1868.
Rebounding gun-lock--L. Hailer, United States, 1870.
Magazine rifle--Lee, United States, 1879.
Hammerless gun--Greener, United States, 1880.
Gun silencer, to be attached to barrel of gun; gun can be fired
without noise--Maxim, 1909.
Gas Used for Light and Power
Gas first used for illuminating purposes--William Murdoch,
England, 1792.
First street gas-lighting in England--F. A. Winsor, 1814.
Gas-meter--S. Clegg, England, 1815.
Water-gas, prepared by passing steam over white-hot anthracite
coal--First produced in England in 1823.
Illuminating water-gas--Lowe, United States, 1875.
Gas-engine, 4-cycle, beginning of modern gas-engine--Otto and
Langen, Germany, 1877.
Incandescent gas-mantle--Carl A. von Welsbach, Austria, 1887.
Iron and Steel
Blast-furnace, beginning of iron industry--Belgium, 1340.
Use of coke in blast-furnace--Abram Darby, England, about 1720.
Puddling iron--Henry Cort, England, 1783-84.
Process of making malleable-iron castings--Lucas, England,
1804.
Hot-air blast for iron furnaces--J. B. Neilson, Scotland, 1828.
The galvanizing of iron--Henry Craufurd, England, 1837.
Process of making steel, blowing air through molten pig-iron to
burn out carbon, then adding spiegel iron; first production of
cheap steel--Sir Henry Bessemer, England, 1855.
Regenerative furnace, a gas-furnace in which gas and air are
heated before being introduced into the furnace, giving an
extremely high temperature--William Siemens, England, 1856.
Open-hearth process of making steel--Siemens-Martin, England,
1856.
Nickel steel, much stronger than ordinary steel, used for
armorplate--Schneider, United States, 1889.
Mining
Miners' safety-lamp--Sir Humphry Davy, England, 1815.
Compressed-air rock-drill--C. Burleigh, United States, 1866.
Diamond rock-drill, a tube of cast-steel with a number of black
diamonds set at one end. The machine cuts a circular groove,
leaving a core inside the tube. This core is brought to the
surface with a rod, and the powdered rock is washed out by
water forced down the tube and flowing up the sides of the
hole. The drill does not have to stop for cleaning out--Herman,
United States, 1854.
Photography
First photographic picture, not permanent--Thomas Wedgewood,
England, 1791.
Daguerreotype, first developing process--Louis Daguerre,
France, 1839.
First photographic portraits, daguerreotype process--Prof. J.
W. Draper, United States, 1839.
Collodion process in photography--Scott Archer, England, 1849.
Photographic roll films--Melhuish, England, 1854.
Dry-plate photography--Dr. J. M. Taupenot, 1855.
Photographic emulsion, bromide of silver in gelatine, basis of
present rapid photography--R. L. Maddox, England, 1871.
Hand photographic camera for plates--William Schmid, United
States, 1881.
Printing
First printing with movable types in Europe and first
printing-press--Guttenberg, Germany, about 1445.
Screw printing-press--Blaew, Germany, 1620.
First newspaper of importance--_London Weekly Courant_, 1625.
Stereotyping, making plates from casts of the type after it is
set up--William Ged, Scotland, 1731.
First practical steam rotary printing-press, paper printed on
both sides, 1800 impressions per hour--Frederick Koenig,
Germany, 1814.
Printing from curved stereotype plates--H. Cowper, England,
1815.
Hoe's lightning press, 2000 impressions per hour--R. Hoe,
United States, 1847.
Printing from a continuous web, paper wound in rolls, both
sides printed at once--William Bullock, United States, 1865.
"Straightline newspaper perfecting" press, prints 100,000
eight-page papers per hour--Goss Company, United States.
Linotype machine. The operator uses a keyboard like that of a
typewriter. The machine sets the matrices which correspond to
the type, casts the type in lines from molten metal, delivers
the lines of type on a galley, and returns the matrices to
their appropriate tubes. It does the work of five men setting
type in the ordinary way--Othmar Mergenthaler, United States,
1890.
Steam Navigation
First steamboat in the world--Papin, River Fulda, Germany,
1705.
First steamboat in America--John Fitch, Delaware River, 1783.
First passenger steamboat in the world, the _Clermont_--Robert
Fulton, Hudson River, 1807.
First steamer to cross the Atlantic, the _Savannah_, built at
New York--First voyage across the Atlantic, 1819.
The screw propeller first used on a steamboat--John Ericsson,
United States, about 1836.
Compound engines adopted for steamers--1856.
First turbine-steamer, the _Turbinia_--Parsons, 1895.
First mercantile steam-turbine ship, the _King Edward_--Denny
and Brothers, England, 1901.
Steam Used for Power and Land Transportation
First steam-engine with a piston--Denys Papin, France, 1690.
First practical application of the power of steam, pumping
water--Thomas Savery, England, 1698.
Double-acting steam-engine and condenser--James Watt, Scotland,
1782.
Steam-locomotive first used to haul loads on a
railroad--Richard Trevethick, England, 1804.
First passenger steam railway, the "Stockton &
Darlington"--George Stephenson, England, 1825.
First steam-locomotive in the United States, the "Stourbridge
Lion"--1829.
Link motion for locomotives--George Stephenson, England, 1833.
Steam-whistle, adopted for use on locomotives--George
Stephenson, 1833.
Steam-hammer--James Nasmyth, Scotland, 1842.
Steam-pressure gauge--Bourdon, France, 1849.
Corliss engine--G. H. Corliss, United States, 1849.
First practical steam-turbine--C. A. Parsons, England, 1884.
Textile Industries
Flying shuttle, first important invention in weaving, leading
to modern weaving machinery--John Kay, England, 1733.
Spinning-jenny--James Hargreaves, England, 1763.
Power loom--James Cartwright, England, 1785.
Cotton-gin, for separating the seeds from the fibre, gave a new
impetus to the cotton industry. The production of cotton
increased in five years from 35,000 to 155,000 bales--Eli
Whitney, United States, 1792.
Pattern loom, for the weaving of patterns--M. J. Jacquard,
France, 1801.
Application of steam to the loom--William Horrocks, England,
1803.
Knitting-machine--Brunel, England, 1816.
Sewing-machine--Elias Howe, United States, 1846.
Mercerized cotton--John Mercer, England, 1850.
Process of making artificial silk--H. de Chardonnet, France,
1888.
Wood-Working
Circular wood-saw--Miller, England, 1777.
Wood-planing machine--Samuel Benthem, England, 1791.
Wood-mortising machine--M. J. Brunel, England, 1801.
Band wood-saw--Newberry, England, 1808.
Lathe for turning irregular wood forms--Thomas Blanchard,
United States, 1819.
Improved planing-machine--William Woodworth, United States,
1828.
Miscellaneous
First fireproof safe--Richard Scott, England, 1801.
Steel pen, quill pen used up to this time--Wise, England, 1803.
First life-preserver--John Edwards, England, 1805.
Calculating machine--Charles Babbage, England, 1822.
First friction matches--John Walker, United States, 1827. Flint
and steel were used for starting fires before matches were
invented.
First portable steam fire-engine--Brithwaite and Ericsson,
England, 1830.
Vulcanizing of rubber--Charles Goodyear, United States, 1839.
Pneumatic tire--R. W. Thompson, England, 1845.
Time-lock for safes--Savage, United States, 1847.
Match-making machinery--A. L. Denison, United States, 1850.
American machine-made watches--United States, 1850.
Safety matches--Lundstrom, Sweden, 1855.
Sleeping-car--Woodruff, United States, 1856.
Printing-machine for the blind, origin of the
typewriter--Alfred E. Beach, United States, 1856.
Cable-car--E. A. Gardner, United States, 1858.
Driven well, an iron tube with the end pointed and perforated
driven into the ground--Col. N. W. Green, United States, 1861.
Passenger elevator--E. G. Otis, United States, 1861.
First practical typewriter--C. L. Sholes, United States, 1861.
Railway air-brake, use of air-pressure in applying brakes to
the wheels of a car. A strong spring presses the brake against
the wheels. Air acts against the spring and holds the brake
away from the wheels. To apply the brake, air is allowed to
escape, reducing the pressure and allowing the spring to
act--George Westinghouse, United States, 1869.
Store-cash carrier--Dr. Brown, United States, 1875.
Roller flour-mills--F. Wegman, United States, 1875.
Kinetoscope, moving-picture machine--Edison, 1893.
INDEX
Aeroplane, 184.
Air-pressure, 23.
Air-pump, 20.
Air-ships, 173.
Air thermometer, 13.
Alternating current, wonders of, 225.
Amber, 8.
Ampère, 67, 111.
Arago, 69.
Archimedes, 1, 12;
inventions of, 7.
Archimedes' principle, 6, 12.
Arc light, 120.
Armature, 101, 103, 104.
Balloons, 174.
Barometer, mercury, 19, 25;
water, 23.
Battle of Syracuse, 2.
Bell, Alexander Graham, 141.
Blake transmitter, 146.
Blériot, 190.
Boyle, 23.
Branly, 214.
Cannon experiment, Rumford's, 59.
Cog-wheels, first used, 8.
Coherer, 214.
Colors in sunlight, 31.
Condenser in steam-engine, 40.
Conductors, electrical, 44.
Controller, 116.
Daniell cell, 89, 127.
Davy, 56, 61, 96.
De Forest, 224.
Diamonds, manufacturing, 206.
Drum armature, 104.
Dry battery, 91.
DuFay, 45.
Dumont, 179.
Duplex telegraphy, 136.
Dynamo, 55, 79, 81, 96, 99, 100, 105, 111;
series wound, 105;
shunt wound, 107;
compound wound, 108.
Edison, 95, 105, 114, 121.
Electrical machine, 23, 44, 45, 83.
Electric battery, 53, 62, 84, 89.
Electric charge, two kinds, 45.
Electric current, 50, 69, 73, 74, 82, 96;
magnetic action of, 66, 68;
produced by a magnet, 72.
Electric furnace, 205.
Electricity, 8, 50;
theories of, 49;
speed of, 133.
Electric lighting, 97, 118.
Electric motor, 71, 97, 111.
Electric power, 111.
Electric railway, 112.
Electric waves, 212.
Electromagnet, 100, 126, 143.
Electromagnetism, 65.
Faraday, 55, 63, 100, 111;
electrical discoveries, 64.
Force-pump, 8.
Franklin, 43, 45, 46, 65.
Galileo, 9, 63;
experiment with falling shot, 12.
Galvani, 50.
Galvanometer, 74, 75.
Gas-engines, 150.
Glider, 186.
Governor, fly-ball, 42.
Gramme-ring armature, 103.
Gravitation, 30.
Gravity cell, 91.
Gray, Stephen, 44.
Guericke, 20, 35.
Gyroscope, 200.
Heat, 59.
Henry, Joseph, 97, 127.
Hero, 8, 164;
engine, 164.
Hiero, King of Syracuse, 1, 6.
Horse-power, 40.
Hydraulic press, 26.
Incandescent light, 121.
Indicator, 41.
Induction-coil, 76, 82, 99.
Induction, electrical, 74.
Insulators, 44.
Inventions of the ancient Greeks 7;
of the nineteenth century, 88.
Kite experiment, Franklin's, 46.
Kites, 27.
Leyden jar, 43.
Lightning-rod, 48.
Lines of force, 99.
Liquid air, 203.
Locomotive, electric, 114;
steam, 155.
Magdeburg, 21.
Magnetic field, 80, 99.
Magnets, 8, 130.
Marconi, 215.
Mayer, Robert, 61, 85.
Mercury vapor light, 125.
Microscope, 18.
Miner's safety lamp, 61.
Monorail car, 201.
Morse, 128.
Napoleon, 62.
Newcomen, 34, 36.
Newcomen's engine, 36.
Newton, 27.
Niagara, 227.
Oersted, 65, 71, 111, 126.
Papin, 35.
Papin's engine, 35.
Pascal, 25.
Pendulum clock, 10, 12.
Perpetual motion impossible, 87.
Phonograph, 147.
Principle of Work, 19.
Prism, 31.
Pump, 8, 19.
Radium, 232.
Reis, Philip, 141.
Relay, 130.
Roentgen, 232.
Royal institution, 56, 61.
Rumford, 57, 59.
Rumford's cannon experiment, 59.
Safety-lamp, 62.
Screw propeller, 171.
Siemens, 100.
Spinning tops, 199.
Steam-engine, 8, 25, 34.
Steam locomotive, 155.
Steam pressure, 23.
Stephenson, 156.
Storage battery, 93.
Sturgeon, 97, 127.
Submarines, 190.
Suction-pump, 8.
Symmer, Robert, 49.
Telegraph, 96, 126;
wireless, 208.
Telephone, 140;
wireless, 221.
Telescope, invention of, 15;
Newton's, 32.
Tesla, 231.
Thermometer, air, 13.
Torpedo, 192.
Torricelli, 19, 35.
Transformer, 80, 82, 99, 227.
Turbine, 163.
University of Padua, 13.
University of Pisa, 10, 12.
Valve-gear, 37, 162.
Volta, 53, 63, 89.
Voltaic battery, 53, 89.
Water-clock, 8, 29.
Water-wheel, 165.
Watt, James, 34.
Watt's engine, 38.
Wireless telegraph, 208.
Wright aeroplane, 188.
X-rays, 232.
Zeppelin, 180.
THE END