GREAT INVENTIONS OF THE NINETEENTH CENTURY
The discoveries of Faraday prepared the way for the great inventions of
the nineteenth century. By the middle of the century men knew how to
control the wonderful power of electricity. They did not know what
electricity is, nor do we know to-day, though we have made some progress
in that direction; but to control it and make it furnish light, heat,
and power was more important.
Before the inventions of James Watt made it possible to use steam-power,
factories were built near falling water, so that water-power could be
used. But the steam-engine made it possible to build great factories
wherever a supply of water for the boilers could be obtained. Cities
were built around the factories. Cities already great became greater.
With the growth of cities the need of a new means of producing light and
power made itself felt. Electricity promised to become the Hercules that
should perform the tasks of the modern world.
Discovery gave way to invention. During the second half of the
nineteenth century many great inventions were made and industries were
developed, while discoveries were few until near the close of the
century. Within this period the great industries which characterize our
modern civilization, and which arose out of the discoveries that science
had made in the centuries preceding, attained a high degree of
development. In this chapter we shall trace the applications of some of
the discoveries with which we have now become familiar. This will lead
us into the field of electrical invention, for we are dealing now with
the beginning of the world's electrical age.
Electric Batteries
From the time of Volta to the time of Faraday the only means of
producing an electric current was the "voltaic battery," so called in
honor of Volta. The voltaic cell is the simplest form of electric
battery. In this cell the zinc and copper plates are placed in sulphuric
acid diluted with water. As the acid eats the zinc, hydrogen gas is
formed. This gas collects in bubbles on the copper plate and weakens the
current. The aim of inventors was to produce a steady current, to devise
a battery in which no gas would collect on the copper plate. They saw
the need of a battery that would give out a current of unchanging
strength until the zinc or the acid was used up.
The first real improvement in the battery was made by Professor Daniell,
of King's College, London. In the Daniell cell the zinc plate is in
dilute sulphuric acid, and the copper plate is in a solution of blue
vitriol or copper sulphate. Professor Daniell separated the two liquids
by placing one of them in a tube formed of the gullet of an ox. This
tube dipped into the other liquid. The hydrogen gas, as it was formed
by the acid acting on the zinc, could go through the walls of the tube,
but was stopped by the copper sulphate, and copper was deposited on the
copper plate. This copper deposit in no way interfered with the current,
so that the current was not weakened until the zinc plate or one of the
solutions was nearly consumed. A cup of porous earthenware is now used
in Daniell cells to separate the liquids (Fig. 37). By placing crystals
of blue vitriol in the battery jar, the solution of blue vitriol can be
kept up to its full strength for a very long time. The zinc in time is
consumed, and must be replaced.
[Illustration: FIG. 37--A DANIELL CELL]
In the gravity cell (Fig. 38) the same materials are used as in the
Daniell cell--copper in copper sulphate, and zinc in sulphuric acid; but
there is no porous cup. The solutions are kept separate by gravity, the
heavy copper sulphate being at the bottom. The gravity cell has until
recently been extensively used in telegraphy, and continues in use in
short-distance telegraphy and in automatic block signals. The gravity
and Daniell cells are used for closed-circuit work--that is, for work in
which the current is flowing almost constantly.
[Illustration: FIG. 38--A GRAVITY CELL]
The Dry Battery
Another important improvement was the invention of the dry battery. You
will remember that the first battery, the one invented by Volta, was a
form of dry battery; but it was a very feeble battery compared with the
dry batteries now in use, so that we may call the dry battery a new
invention. The dry battery is falsely named. There can be no battery
without a liquid. In the dry battery the zinc cup forming the outside of
the cell is one of the plates of the cell (Fig. 39). The battery appears
to be dry because the solution of sal ammoniac is absorbed by
blotting-paper or other porous substance in contact with the zinc. The
inner plate is carbon, and this is surrounded by powdered carbon and
manganese dioxide--the latter to remove the hydrogen gas which collects
on the carbon plate. This gas weakens the current when the circuit has
been closed for a short time, but is slowly removed when the circuit is
broken. Thus the battery is said to "recover."
[Illustration: FIG. 39--SHOWING WHAT IS IN A DRY BATTERY]
The dry cell will give a strong current, but for a short time only. It
recovers, however, if allowed to rest. It can be used, therefore, only
in "open-circuit" work--such as door-bell circuits, and some forms of
fire and burglar alarm. A door-bell circuit is open nearly all the time,
the current flowing only while the button is being pressed. Some forms
of wet battery work in the same way as the dry battery, and are used
like-wise for open-circuit work. In these batteries carbon and zinc
plates in a solution of sal ammoniac are used, the same materials as in
the dry battery. The only difference is that in the dry battery the
solution is absorbed by some porous substance and the battery sealed so
that it appears to be dry.
The Storage Battery
One of the greatest improvements in electric batteries is the storage
battery. A simple storage battery may be made by placing two strips of
lead in sulphuric acid diluted with water and connecting the lead strips
to a battery of Daniell cells or dry cells. In a short time one of the
lead strips will be found covered with a red coating. The surface of
this lead strip is no longer lead but an oxide of lead, somewhat like
the rust that forms on iron. If the lead strips are now disconnected
from the other battery and connected to an electric bell, the bell will
ring. We have here two plates, one of lead and one of oxide of lead, in
dilute sulphuric acid. This forms a storage battery.
The first storage battery was made of two sheets of lead rolled together
and kept apart by a strip of flannel. The lead strips thus separated
were immersed in dilute sulphuric acid. A current from another battery
was passed through this cell for a long time--first in one direction,
then in the other. This roughened the surface of the lead plates, so
that the battery would hold a greater charge. The battery was then
charged by passing a current through it in one direction only for a
considerable length of time. Feeble cells were used for charging. It
took days, and sometimes weeks, to charge the first storage batteries.
Then the storage battery would give out a strong current lasting for a
few hours. It slowly accumulated energy while being charged, and then
gave out this energy rapidly in the form of a strong electric current.
For this reason the storage battery was called an "accumulator."
While charging the storage cell there was formed on the negative plate a
coating of soft lead, and on the positive plate a coating of dark-brown
oxide of lead. It was found better to apply these coatings to the lead
plates before making up the battery. Later it was found that the battery
would hold a still greater charge if the plates were made in the form of
"grids" (Fig. 40), and the cavities filled with the active material--the
negative with spongy lead, and the positive with dark-brown lead oxide.
Some excellent commercial storage batteries are made from lead plates by
the action of an electric current, very much as Planté made his
batteries. Fig. 41 shows one of these plates.
[Illustration: FIG. 40--A STORAGE BATTERY, SHOWING THE "GRIDS"]
[Illustration: FIG. 41--A STORAGE-BATTERY PLATE MADE FROM A SHEET OF
LEAD]
The storage battery does not store up electricity. It produces a current
in exactly the same way as any other battery--by the action of the acid
on the plates. When this action ceases it is no longer a battery, though
it may be made one again by passing a current through it in the opposite
direction from that which it gives out. In this it differs from the
voltaic battery, for when such a battery is run down it can be restored
only by adding new solution or new plates. The storage battery is
especially useful for "sparking" in gas or gasolene motors.
Edison has invented a storage battery that will do as much work as a
lead battery of twice its weight. Edison's battery is intended
especially for use in electric automobiles. By reducing the weight of
the battery which the machine must carry the weight of the truck may
also be reduced. In the Edison battery the positive plates are made of a
grid of nickel-plated steel containing tubes filled with pure nickel.
The negative plate consists of a nickel-plated steel grid containing an
oxide of iron similar to common iron-rust.
After working a number of years on this battery and making nine thousand
experiments, Edison thought he had it perfected, and indeed it was a
great improvement over the storage batteries that had been used--much
lighter and cheaper, and more successful in operation. Two hundred and
fifty automobiles were equipped with it, and it proved superior to lead
batteries for this purpose. But it was not to Edison's liking. He threw
the machinery, worth thousands of dollars, on the scrap-heap, and worked
on for six years. He had then produced a battery as much better than the
first as the first was better than the lead battery, and he was content
to have the new battery placed on the market.
The Dynamo
For the purpose of lighting and power the electric battery proved too
costly. Davy produced an arc light with a battery of four thousand
cells. The arc was about four inches in length and yielded a brilliant
light, but as the cost was six dollars a minute it was not thought
practical. Attempts were made early in the century to use a battery
current for power, but they failed because of the cost and the fact that
no good working motor had been invented.
Light and power were needed. Electricity could supply both. But how
overcome the difficulty of cost, and produce an electric current from
burning coal or falling water? For answer man looked to the great
discovery of Faraday and his "new electrical machine." Inventors in
Germany, France, England, Italy, and America made improvements until
from the disk dynamo of Faraday there had evolved the modern dynamo.
Electroplating and the telegraph are the only applications of the
electric current that became factors in the world's industry before the
dynamo, yet in long-distance telegraphy and in electroplating to-day the
dynamo is used. Without the dynamo, electric lighting, electric power,
and electric traction as developed in the nineteenth century would have
been impossible; in fact, the dynamo with the electric motor (which, as
we shall see, is only a dynamo reversed) is master of the field.
The way had been prepared for the application of Faraday's discovery by
William Sturgeon, an Englishman, and Joseph Henry, an American. Sturgeon
discovered that soft iron is more quickly magnetized than steel, and
found that the strength of an electromagnet can be greatly increased by
making the core of a soft-iron rod and bending the rod into the form of
a horseshoe (Fig. 42). The iron rod was coated with sealing-wax and
wound with a single layer of copper wire, the turns of wire not
touching. This was in 1825, before Faraday discovered the principle of
the dynamo.
[Illustration: FIG. 42--STURGEON'S ELECTROMAGNET]
Professor Henry still further increased the strength of the
electromagnet by covering the wire with silk, which made it possible to
wind several layers of wire on the iron core, and many times the length
of wire that had been used by Sturgeon. Fig. 43 shows such a magnet. One
of Henry's magnets weighed fifty-nine and a half pounds, and would hold
up a ton of iron. Sturgeon said: "Professor Henry has produced a
magnetic force which completely eclipses every other in the whole annals
of magnetism." With Professor Henry's invention the electromagnet was
ready for use in the dynamo. Fig. 44 shows a strong electromagnet.
[Illustration: FIG. 43--AN ELECTROMAGNET WITH MANY TURNS OF INSULATED
WIRE]
[Illustration: FIG. 44--AN ELECTROMAGNET LIFTING TWELVE TONS OF IRON]
A moving magnet causes a current to flow in a coil, but a magnet at rest
has no effect. A moving magnet is equal to a battery. In Faraday's
experiments a current was induced in a coil of wire by moving a magnet
in the coil or by making and breaking the circuit in another coil wound
on the same iron core. A current was induced in a metal disk by
revolving it between the poles of a magnet. In every case there was
motion in a magnetic field, or the field itself was changed. A changing
magnetic field is equal to a moving magnet. What is needed to induce a
current in a coil, whether it be in a dynamo, an induction-coil, or a
transformer, is a changing magnetic field about the coil or motion of
the coil in the magnetic field.
If fine iron filings are sprinkled over the poles of a magnet the
filings arrange themselves in definite lines. This is a simple
experiment which any boy can try for himself. Faraday called the lines
marked out by the iron filings "lines of force" (the lines of force of a
horseshoe magnet are shown in Fig. 36), because they indicate the
direction in which the magnet pulls a piece of iron--that is, the
direction of the magnetic force. Now, if a current is to be induced in
a wire, the wire must move across the lines of force. If the wire moves
along the lines marked out by the iron filings, there will be no
current. When a coil rotates between the poles of a magnet, the wire
moves across the lines of force and a current is induced in the coil if
the circuit is closed. This is the way a current is produced in a
dynamo.
Faraday produced a current by rotating a coil between the poles of a
steel magnet. He made a number of such machines, and used them with some
success in producing lights for lighthouses, but the defects of these
machines were so great that the lighting of a city or the development of
power on a large scale was impractical. The electromagnet was needed to
solve the problem.
Siemens' Dynamo
The war of 1866 between Austria and Prussia and the certainty of a
coming struggle with France turned the attention of German inventors to
the use of electricity in warfare. Werner von Siemens, an artillery
officer, was improving an exploding device for mines. An electric
current was needed to produce a spark or heat a wire to redness in the
powder. Faraday had used a coil of wire turning between the poles of a
steel magnet to produce a current. In England a coil turning between the
poles of an electromagnet had been used, but the electromagnet received
its current from another machine in which a steel magnet was used.
Siemens found that the steel magnet could be dispensed with, and that a
coil turning between the poles of an electromagnet could furnish the
current for the electromagnet. Two things are needed, then, to make a
dynamo: an electromagnet and a coil to turn between the poles of that
magnet. The rotating coil, which usually contains a soft-iron core, is
called the "armature." The coil will furnish current for the magnet and
some to spare; in fact, only a small part of the current induced in the
coil is needed to keep the magnet up to its full strength, and the
greater part of the current may be used for lighting or power. The new
machine was named by its inventor "the dynamo-electric machine." The
name has since been shortened to "dynamo." The first practical problem
which the dynamo solved was the construction of an electric exploding
apparatus without the use of steel magnets or batteries. A dynamo with
Siemens' armature is shown in Fig. 45.
[Illustration: FIG. 45--A DYNAMO WITH SIEMENS' ARMATURE]
In his first enthusiasm the inventor dreamed of great things for the new
machine, among others an electric street railway in Berlin. But the
dynamo was not yet ready. The difficulty was the heating of the iron
core of the armature, caused by the action of induced currents. There
are induced currents in the iron core as well as in the coil, and, for
the same reason, the coil and the iron core within it are both moving in
a magnetic field. These little currents circling round and round in the
iron core produce heat. The rapid changing of the magnetism of the iron
also heats the iron.
It remained for Gramme, in France, to apply the proper remedy. This
remedy was an armature in which the coil was wound on an iron ring,
invented by an Italian, Pacinotti. Gramme applied the principle
discovered by Siemens to Pacinotti's ring, and produced the first
practical dynamo for strong currents. This was in 1868. A ring armature
is shown in Fig. 46. The first dynamo patented in the United States is
shown in Fig. 47. This dynamo is only a curiosity.
[Illustration: FIG. 46--RING ARMATURE]
[Illustration: FIG. 47--FIRST DYNAMO PATENTED IN THE UNITED STATES
Intended to be used for killing whales.
Photo by Claudy.]
The Drum Armature
An improvement in the Siemens armature was made four years later by Von
Hefner-Alteneck, an engineer in the employ of Siemens. This improvement
consisted in winding on the iron core a number of coils similar to the
one coil of the Siemens armature, but wound in different directions.
This is called the "drum armature" (Fig. 48). The heating of the core is
prevented by building it up of a number of thin iron plates insulated
from one another and by air-spaces within the core. The insulation
prevents the small currents from flowing around in the core. The
air-spaces serve for cooling. The drum armature was a great improvement
over both the Siemens and the Gramme armatures. With the Siemens
one-coil armature there is a point in each revolution at which there is
no current. The current, therefore, varies during each revolution of the
armature from zero to full strength. In the Gramme armature only half
the wire, the part on the outside of the ring, receives the full effect
of the magnetic field. The inner half is practically useless, except to
carry the current which is generated in the outer half. Both these
difficulties are avoided in the drum armature. The dynamos of to-day are
modifications of the two kinds invented by Siemens and Gramme. Many
special forms have been designed for special kinds of work.
[Illustration: FIG. 48--A DRUM ARMATURE, SHOWING HOW AN ARMATURE OF FOUR
COILS IS WOUND]
Edison's Compound-Wound Dynamo
Edison, in his work on the electric light and the electric railway, made
some important improvements in the dynamo. The armature of a dynamo is
usually turned by a steam-engine. Edison found that much power was
wasted in the use of belts to connect the engine and the dynamo. He
therefore connected the engine direct to the dynamo, placing the
armature of the dynamo on the shaft of the engine. He also used more
powerful field-magnets than had been used before. His greatest
improvement, however, was in making the dynamo self-regulating, so that
the dynamo will send out the strength of current that is needed. Such a
dynamo will send out more current when more lights are turned on.
Whether it supplies current for one light or a thousand, it sends out
just the current that is needed--no more, no less. It will do this if no
human being is near. An attendant is needed only to keep the machinery
well oiled and see that each part is in working order. Edison brought
about this improvement by his improved method of winding. This method is
known as "compound winding."
To understand compound winding we must first understand two other
methods of winding. In the series winding (Fig. 49), all the current
generated in the armature flows through the coils of the field-magnet.
There is only one circuit. The same current flows through the coils of
the magnet and through the outer circuit, which may contain lights or
motors. Such a dynamo is commonly used for arc lights. It will not
regulate itself. If left to itself it will give less electrical pressure
when more pressure is needed. It requires a special regulator.
[Illustration: FIG. 49--A SERIES-WOUND DYNAMO]
In the second form of winding the current is divided into two branches.
One branch goes through the coils of the field-magnet. The other branch
goes through the line wire for use in lights or motors. This is called
the "shunt winding" (Fig. 50). The shunt-wound dynamo is used for
incandescent lights. It also requires a special regulator, for if left
to itself it gives less electrical pressure when the pressure should be
kept the same.
[Illustration: FIG. 50--A SHUNT-WOUND DYNAMO]
The compound winding (Fig. 51), which was first used by Edison, is a
combination of the series and shunt windings.
[Illustration: FIG. 51--A COMPOUND-WOUND DYNAMO]
The current is divided into two branches. One branch goes only through
the field-coils. The other branch goes through additional coils which
are wound on the field-magnet, and also through the external circuit.
Such a dynamo can be made self-regulating, so that it will give always
the same electrical pressure whatever the number of lamps or motors
thrown into the circuit. In maintaining always the same pressure it of
course supplies more or less current, according to the amount of current
that is needed. This is clear if we compare the flow of electric current
with the flow of water. Open a water-faucet and notice how fast the
water flows. Then open several other faucets connected with the same
water-pipe. Probably the water will not flow so fast from the first
faucet. That is because the pressure has been lowered by the flow of
water from the other faucets. If we could make the water adjust its own
pressure and keep the pressure always the same, then the water would
always flow at the same rate through a faucet, no matter how many
other faucets were opened. This is what happens in the Edison
compound-wound dynamo. Turn on one 16-candle-power carbon lamp. It takes
about half an ampere of current. Turn on a hundred lamps connected to
the same wires, and the dynamo of its own accord keeps the pressure the
same, and supplies fifty amperes, or half an ampere for each lamp. With
this invention of Edison the dynamo was practically complete, and ready
to furnish current for any purpose for which current might be needed.
Fig. 52 shows one of Edison's first dynamos. Fig. 53 shows a dynamo used
for lighting a railway coach.
[Illustration: FIG. 52--ONE OF EDISON'S FIRST DYNAMOS
Permission of Association of Edison Illuminating Companies.]
[Illustration: FIG. 53--A DYNAMO MOUNTED ON THE TRUCK OF A RAILWAY CAR
The dynamo furnishes current for the electric lights in the car. When
the train is not running the current is furnished by a storage
battery.]
Electric Power
It has been said that the nineteenth century was the age of steam, but
the twentieth will be the age of electricity. Before the end of the
nineteenth century, however, electric power had become a reality, and
there remained only development along practical lines.
We must turn to Oersted, Ampère, and Faraday to find the beginning of
electric power. In Oersted's experiment, motion of a magnet was produced
by an electric current. Ampère found that electric currents attract or
repel each other, and this because of their magnetic action. Faraday
found that one pole of a magnet will spin round a wire through which a
current is flowing. Here was motion produced by an electric current.
These great scientists discovered the principles that were applied later
by inventors in the electric motor.
A number of motors were invented in the early years of the century, but
they were of no practical use. It was not until after the invention of
the Gramme and Siemens dynamos that a practical motor was possible. It
was found that one of these dynamos would run as a motor if a current
were sent through the coils of the armature and the field-magnet; in
fact, the current from one dynamo may be made to run another similar
machine as a motor. Thus the dynamo is said to be reversible. If the
armature is turned by a steam-engine or some other power, a current is
produced. If a current is sent through the coils, the armature turns and
does work. If the machine is used to supply an electric current, it is a
dynamo. If used to do work--as, for example, to propel a street-car and
for that purpose receives a current--it is a motor. The same machine may
be used for either purpose. In practice there are some differences in
the winding of the coils of dynamos and motors, yet any dynamo can be
used as a motor and any motor can be used as a dynamo. This discovery
made it possible to transmit power to a distance with little waste as
well as to divide the power easily. The current from one large dynamo
may light streets and houses, and at the same time run a number of
motors in factories or street-cars at great distances apart. A
central-station dynamo may run the motors that propel hundreds of
street-cars. Dynamos at Niagara furnish current for motors in Buffalo
and other cities. One great scientist, who no doubt fore-saw the wonders
of electricity which we know so well to-day, said that the greatest
discovery of the nineteenth century was that the Gramme machine is
reversible.
The First Electric Railway
The electric railway was made possible by the invention of the dynamo
and the discovery that the dynamo is reversible. At the Industrial
Exposition in Berlin in 1879 there was exhibited the first practical
electric locomotive, the invention of Doctor Siemens. The locomotive and
its passenger-coach were absurdly small. The track was circular, and
about one thousand feet in length. This diminutive railway was referred
to by an American magazine as "Siemens' electrical merry-go-round." But
the electrical merry-go-round aroused great interest because of the
possibilities it represented (Fig. 54).
[Illustration: FIG. 54--FIRST ELECTRIC LOCOMOTIVE]
The current was generated by a dynamo in Machinery Hall, this dynamo
being run by a steam-engine. An exactly similar dynamo mounted on wheels
formed the locomotive. The current from the dynamo in Machinery Hall was
used to run the other as a motor and so propel the car. The rails served
to conduct the current. A third rail in the middle of the track was
connected to one pole of the dynamo and the two outer rails to the other
pole. A small trolley wheel made contact with the third rail. The rails
were not insulated, but it was found that the leakage current was very
small, even when the ground was wet.
The success of this experiment aroused great interest, not only in
Germany, but in Europe and America. America's greatest inventor, Edison,
took up the problem. Edison employed no trolley line or third rail, but
only the two rails of the track as conductors, sending the current out
through one rail and back through the other. Of course, this meant that
the wheels must be insulated, so that the current could flow from one
rail to the other only through the coils of the motor.
As in Siemens' experiment, the motor was of the same construction as the
dynamo. The rails were not insulated, and it was found that, even when
the track was wet, the loss of electric current was not more than 5 per
cent. Edison found that he could realize in his motor 70 per cent. of
the power applied to the dynamo, whereas the German inventor was able to
realize only 60 per cent. The improvement was largely due to the
improved winding. Edison was the first to use in practical work the
compound-wound dynamo, and this was done in connection with his electric
railway. Fig. 55 shows Edison's first electric locomotive.
[Illustration: FIG. 55--FIRST EDISON ELECTRIC LOCOMOTIVE]
The question of gearing was a troublesome one. The armature shaft of the
motor was at first connected by friction gearing to the axle of two
wheels of the locomotive. Later a belt and pulleys were used. An idler
pulley was used to tighten the belt. When the motor was started and the
belt quickly tightened the armature was burned out. This happened a
number of times. Then Mr. Edison brought out from the laboratory a
number of resistance-boxes, placed them on the locomotive, and connected
them in series with the armature. These resistances would permit only a
small current to flow through the motor as it was starting, and so
prevent the burning-out of the armature coils. The locomotive was
started with the resistance-boxes in circuit, and after gaining some
speed the operator would plug the various boxes out of circuit, and in
that way increase the speed. When the motor is running there is a
back-pressure, or a pressure that would cause a current to flow in the
opposite direction from that which is running the motor. Because of this
back-pressure the current which actually flows through the motor is
small, and the resistance-boxes may be safely taken out of the circuit.
Finding the resistance-boxes scattered about under the seats and on the
platform as they were a nuisance, Mr. Edison threw them aside, and used
some coils of wire wound on the motor field-magnet which could be
plugged out of the circuit in the same way as the resistance-boxes. This
device of Edison's was the origin of the controller, though in the
controller now used on street-cars not only is the resistance cut out as
the speed of the car increases, but the electrical connections of the
motor are changed in such a way as to increase its speed gradually.
Fig. 56 shows Edison's first passenger locomotive.
[Illustration: FIG. 56--EDISON'S FIRST PASSENGER LOCOMOTIVE]
The news of the little electric railway at the Industrial Exposition in
Berlin was soon noised abroad, and the German inventor received
inquiries from all parts of the world, indicating that efforts would be
made in other countries to develop practical electrical railways. The
firm of Siemens & Halske therefore determined to build a line for actual
traffic, not for profit, but that Germany might have the honor of
building the first practical electric railway. The line was built
between Berlin and Lichterfelde, a distance of about one and a half
miles. A horse-car seating twenty-six persons was pressed into service.
A motor was mounted between the axles, and a central-station dynamo
exactly like the motor was installed. As in Edison's experimental
railway, the two rails of the track were used to carry the current. This
electric line replaced an omnibus line, and was immediately used for
regular traffic, and thus the electric railway was launched upon its
remarkable career. The first electric car used for commercial service is
shown in Fig. 57.
[Illustration: FIG. 57--FIRST COMMERCIAL ELECTRIC RAILWAY
An old horse-car converted into an electric car.]
Electric Lighting
From the time when the night-watchman carried a lantern to the time of
brilliantly lighted streets was less than a century. It was a time when
the rapid growth of railways and commerce brought about a rapid growth
of cities, and with the growth of cities the need of illumination.
Factories must run at night to meet the world's demands. Commerce cannot
stop when the sun sets. The centres of commerce must have light.
During this time scientists were at work in their laboratories
developing means for producing a high vacuum. They were able to pump the
air out of a glass bulb until less than a millionth part of the air
remained. They little dreamed that there was any connection between the
high vacuum and the problem of lighting. Discoverers were at work
bringing to light the principles now utilized in the dynamo. In the
fulness of time these factors were brought together to produce an
efficient system of lighting.
For a time gas replaced the lantern of the night-watchman, only to yield
the greater portion of the field to its rival, electricity.
The first efforts were in the direction of the arc light. From the
earliest times the light given out by an electric spark had been
observed. It was the aim of inventors to produce a continuous spark that
should give out a brilliant light. It was thought for a time that the
electric battery would solve the problem, but the cost of the battery
current was too great. Again we are indebted to Faraday, for it was the
dynamo that made electric lighting possible.
An arc light is produced by an electric current flowing across a gap
between two sticks of carbon. The air offers very great resistance to
the flow of electric current across this gap. Now whenever an electric
current flows through something which resists its flow, heat is
produced. The high resistance of the air-gap causes such intense heat
that the tips of the carbons become white hot and give out a brilliant
light. If examined through a smoked glass a beautiful blue arc of carbon
vapor may be seen between the carbon tips. If the current flows in one
direction only, one of the carbons, the positive, becomes hotter and
brighter than the other.
In 1878 the streets of Paris were lighted with the "Jablochkoff candle,"
a form of arc light supplied with current by the Gramme machine. In the
same year the Brush system of arc lighting was given to the public. This
was the beginning of our present system of arc lighting.
The electric arc is suitable for lighting streets and for large
buildings, but cannot be used for lighting houses. The light is too
intense. One arc would furnish enough light for a number of houses if
the light could be divided so that there might be just the right amount
of light in each room. But this is impossible with the electric arc.
The Edison system of incandescent lighting was required to solve the
problem of lighting houses by electricity.
In 1880 the Edison system was brought out for commercial use. Edison's
problem was to produce a light that could be divided into a number of
small lights, and one that would require less attention than the arc
light. He tried passing a current through platinum wire enclosed in a
vacuum. This gave a fairly good light, but was not wholly satisfactory.
He sat one night thinking about the problem, unconsciously fingering a
bit of lampblack mixed with tar which he had used in his telephone. Not
thinking what he was doing, he rolled this mixture of tar and lampblack
into a thread. Then he noticed what he had done, and the thought
occurred to him: "Why not pass an electric current through this thread
of carbon?" He tried it. A faint glow was the result. He felt that he
was on the right track. A piece of cotton thread must be heated in a
furnace in an iron mold, which would prevent the thread from burning by
keeping out the air. Then all the other elements that were in the thread
would be driven out and only the carbon remain. For three days he worked
without sleep to prepare this carbon filament. At the end of two days he
succeeded in getting a perfect filament, but when he attempted to seal
it in the glass bulb it broke. He patiently worked another day, and was
rewarded by securing a good carbon filament, sealed in a glass globe. He
pumped the air out of this globe, sealed it, and sent a current through
the carbon thread. He tried a weak current at first. There was a faint
glow. He increased the current. The thread glowed more brightly. He
continued to increase the current until the slender thread of carbon,
which would crumble at a touch, was carrying a current that would melt a
wire of platinum strong enough to support a weight of several pounds.
The carbon gave a bright light. He had found a means of causing the
electric current to furnish a large number of small lights. Fig. 58 is
an excellent photograph of Edison at work in his laboratory. Fig. 59
shows some of Edison's first incandescent lamps. He next set out in
search of the best kind of carbon for the purpose. He carbonized paper
and wood of various kinds--in fact, everything he could find that would
yield a carbon filament. He tried the fibres of a Japanese fan made of
bamboo, and found that this gave a better light than anything he had
tried before. He then began the search for the best kind of bamboo. He
learned that there are about twelve hundred varieties of bamboo. He must
have a sample of every variety. He sent men into every part of the world
where bamboo grows. One man travelled thirty thousand miles and had many
encounters with wild beasts in his search for the samples of bamboo. At
last a Japanese bamboo was found that was better than any other. The
search for the carbon fibre had cost about a hundred thousand dollars.
Later it was found that a "squirted filament" could be made that worked
as well as the bamboo fibre. This was made by dissolving cotton wool in
a certain solution, and then squirting this solution through a small
hole into a small tank containing alcohol. The alcohol causes the
substance to set and harden, and thus forms a carbon thread the size of
the hole. Fig. 60 shows the first commercial electric-lighting plant,
which was installed on the steamship _Columbia_ in 1880.
[Illustration:
Copyright, 1904, by Byron, N. Y.
FIG. 58--EDISON, AMERICA'S GREATEST INVENTOR, AT WORK IN HIS LABORATORY]
[Illustration:
Copyright, 1904, by William J. Hammer
FIG. 59--EDISON'S FAMOUS HORSESHOE PAPER-FILAMENT LAMP OF 1870]
[Illustration: FIG. 60--FIRST COMMERCIAL EDISON ELECTRIC-LIGHTING PLANT;
INSTALLED ON THE STEAMSHIP "COLUMBIA" IN MAY, 1880]
The carbon thread in the incandescent light is heated to a white heat,
and because it is so heated it gives out light. In air such a tiny
thread of white-hot carbon would burn in a fraction of a second. The
carbon must be in a vacuum, and so the air is pumped out of the light
bulb with a special kind of air-pump invented not long before Edison
began his work on the electric light. This pump is capable of taking out
practically all the air that was in the bulb. Perhaps a millionth part
of the original air remains.
A great invention is never completed by one man. It was to be expected
that the electric light would be improved. A number of kinds of
incandescent light have been devised, using different kinds of filaments
and adapted to a variety of uses. The original Edison carbon lamp,
however, continues in use, being better adapted to certain purposes than
the newer forms.
The mercury vapor light deserves mention as a special form of arc light.
In the ordinary arc light the arc is formed of carbon vapor, and the
light is given out from the tips of the white-hot carbons. In the
mercury vapor light the light is given out from the mercury vapor which
forms the arc. This arc may be of any desired length, and yields a soft,
bluish-white light which is a near approach to daylight.
The Telegraph
The need of some means of giving signals at a distance was early felt in
the art of war. Flag signals such as are now used by the armies and
navies of the world were introduced in the middle of the seventeenth
century by the Duke of York, admiral of the English fleet, who afterward
became James II. of England. Other methods of communicating at a
distance were devised from time to time, but the distance was only that
at which a signal could be seen or a sound heard. No means of
communicating over very long distances was possible until the magnetic
action of an electric current was discovered. When Oersted's discovery
was made known men began to think of signalling to a distance by means
of the action of an electric current on a magnetic needle. A current may
be sent over a very long wire, and it will deflect a magnetic needle at
the other end. The movements of the needle may be controlled by opening
and closing the circuit, and a system of signals or an alphabet may be
arranged. A number of needle telegraphs were invented, but they were too
slow in action. Two other great inventions were needed to prepare the
way for the telegraph. One was the electromagnet in the form developed
by Professor Henry, a horseshoe magnet with many turns of silk-covered
wire around the soft-iron core, so that a very feeble current will
produce a magnet strong enough to move an armature of soft iron. The
magnet has this strength because the current flows so many times around
the iron core. Another need was that of a battery that could be depended
on to give a constant current for a considerable length of time. This
need was met by the Daniell cell.
The electromagnet made the telegraph possible. The locomotive made it a
necessity. Without the telegraph it would be impossible to control a
railway system from a central office. A train after leaving the central
station would be like a ship at sea before the invention of the wireless
telegraph. Nothing could be known of its movements until it returned.
The need of a telegraph was keenly felt in America when the new republic
was extended to the Pacific Coast. An English statesman said, after the
United States acquired California, that this marked the end of the great
American Republic, for a people spread over such a vast area and
separated by such natural barriers could not hold together. He did not
know that the iron wire of the telegraph would bind the new nation
firmly together.
The Morse telegraph system now in use throughout the civilized world was
made possible by the work of Sturgeon and Henry. Sturgeon's
electromagnet might have been used for telegraphy through very short
distances, but Henry's magnet, with its coils of many turns of insulated
wire, was needed for long-distance signalling. In one of the rooms of
the Albany Academy, Professor Henry caused an electromagnet to sound a
bell when the current was transmitted through more than a mile of wire.
This might be called the first electromagnetic telegraph. But the
application to actual practice was made by Morse, and the man who first
makes the practical application of a principle is the true inventor.
In 1832, on board the packet-ship _Sully_, Samuel F. B. Morse, an
American artist, forty-one years of age, was returning from Europe. In
conversation a Doctor Jackson referred to the electrical experiments of
Ampère, which he had witnessed while in Europe, and, in reply to a
question, said that electricity passes instantaneously over any known
length of wire. The thought of transmitting words by means of the
electric current at once took possession of the artist's mind. After
many days and sleepless nights he showed to friends on board the
drawings and notes he had made of a recording telegraph.
In New York, in a room provided by his brothers, he gave himself up to
the working-out of his idea, sleeping little and eating the simplest
food. Receiving an appointment as professor in the University of the
City of New York, he moved to one of the buildings of that university
and continued his experiments in extreme poverty, and at times facing
starvation, as his salary depended on the tuition fees of his pupils.
A story told by one of his pupils describes his condition at the time.
"I engaged to become one of Morse's pupils. He had three others. I soon
found that the professor had little patronage. I paid my fifty dollars;
that settled one quarter's tuition. I remember, when the second was due,
my remittance from home did not come as expected, and one day the
professor came in and said, courteously:
"'Well, Strother, my boy, how are we off for money?'
"'Why, professor, I am sorry to say I have been disappointed; but I
expect a remittance next week.'
"'Next week!' he repeated, sadly; 'I shall be dead by that time.'
"'Dead, sir?'
"'Yes; dead by starvation!'
"I was distressed and astonished. I said, hurriedly: 'Would ten dollars
be of any service?'
"'Ten dollars would save my life; that is all it would do.'"
The money was paid, all the student had, and the two dined together. It
was Morse's first meal in twenty-four hours.
The Morse telegraph sounder (Fig. 61) consists of an electromagnet and a
soft-iron armature. When no current is flowing the armature is held away
from the magnet by a spring. When the circuit is closed a current flows
through the coils of the magnet and the armature is attracted, causing
a click. When the circuit is broken the spring pulls the armature away
from the magnet, causing another click. The circuit is made and broken
by means of a key at the other end of the line. In Morse's first
instrument (Fig. 62) the armature carried a pen, which was drawn across
a ribbon of paper when the armature was attracted by the magnet. If the
pen was held by the magnet for a very short time, a dot was made; if for
a longer time, a dash. The pen was soon discarded, and the message taken
by sound only. The Morse alphabet now in use was devised by a Mr. Vail,
who assisted Morse in developing the telegraph. The thought occurred to
Mr. Vail that he could get help from a printing-office in deciding the
combinations of dots and dashes that should be used for the different
letters. The letters requiring the largest spaces in the type-cases are
the ones that occur most frequently, and for these letters he used the
simplest combinations of dots and dashes.
[Illustration: FIG. 61--A TELEGRAPH SOUNDER]
[Illustration: FIG. 62--MORSE'S FIRST TELEGRAPH INSTRUMENT
A pen was attached to the pendulum and drawn across the strip of paper
by the action of the electromagnet. The lead type shown in the lower
right-hand corner was used in making electrical contact when sending a
message. The modern instrument shown in the lower left-hand corner is
the one that sent a message around the world in 1896.
Photo by Claudy.]
Morse repeatedly said that, if he could make his telegraph work through
ten miles, he could make it work around the world. This promise of
long-distance telegraphy he fulfilled by the use of the relay. The relay
works in the same way as the sounder. The current coming over a long
line may be too feeble to produce a click that can be easily heard, yet
strong enough to magnetize the coils of the relay and cause the armature
to close another circuit. This second circuit includes the sounder and a
battery in the same station as the sounder, which we shall call "the
local battery." The relay simply acts as a contact key, and closes the
circuit of the local battery. Thus the current from the local battery
flows through the sounder and produces a loud click. Sometimes a relay
is used to control a second very long circuit. At the farther end of the
second circuit may be a sounder or a second relay which controls a third
circuit. Any number of circuits may be thus connected by means of
relays. This is a form of repeating system used for telegraphing over
very long distances. Fig. 63 shows a circuit with relay and sounder.
[Illustration: FIG. 63--A TELEGRAPHIC CIRCUIT WITH RELAY AND SOUNDER]
In the telegraphic circuit only one connecting wire is needed. The
earth, being a good conductor of electricity, is used as part of the
circuit. It is necessary, therefore, to make a ground connection at each
end of the line, the instruments being connected between the line wire
and the earth. For long-distance telegraphy a current from a dynamo is
used instead of a battery current. Fig. 64 shows a simple telegraphic
circuit.
[Illustration: FIG. 64--A SIMPLE TELEGRAPHIC CIRCUIT
Two keys are shown at _K K_, and two switches at _S S_. When one key
is to be used the switch at that station must be open, and the switch at
the other station closed.]
A telegraphic message travels with the speed of light, for the speed of
electricity and the speed of light are the same. A telegraphic signal
would go more than seven times around the earth in one second if it
travelled on one continuous wire. The relays that must be used, however,
cause some delay.
In 1835 Morse's experimental telegraph was completed, and in 1837 it was
exhibited to the public, but seven years more passed before a line was
established for public use. Aid from Congress was necessary. Going to
Washington, Morse exhibited his instrument in the halls of the Capitol,
sending messages through ten miles of wire wound on a reel. The
invention was ridiculed, but the inventor did not despair. A bill for an
appropriation to establish a telegraphic line between Washington and
Baltimore passed the House by a small majority. The last day of the
session came. Ten o'clock at night, two hours before adjournment, and
the Senate had not acted. A senator advised Morse to go home and think
no more of it, saying that the Senate was not in sympathy with his
project. He went to his hotel, counted his money, and found that he
could pay his bill, buy his ticket home, and have thirty-seven cents
left. All through his work he had firmly believed that a Higher Power
was directing his work, and bringing to the world, through his
invention, a new and uplifting force; and so when all seemed lost he did
not lose heart.
In the morning a friend, Miss Ellsworth, called and offered her
congratulations that the bill had been passed by the Senate and thirty
thousand dollars appropriated for the telegraph. Being the first to
bring the news of his success, Mr. Morse promised her that the first
message over the new line should be hers. In about a year the line was
completed, and Miss Ellsworth dictated the now famous message: "What
hath God wrought!"
Soon afterward the Democratic Convention, in session in Baltimore,
received a telegraphic message from Senator Silas Wright, in Washington,
declining the nomination for the Vice-Presidency, which had been
tendered him. The convention refused to accept a message sent by
telegraph, and sent a committee to Washington to investigate. The
message was confirmed, and Morse and his telegraph became famous. Fig.
65 shows the first telegraph instrument used for commercial work.
[Illustration: FIG. 65--FIRST TELEGRAPH INSTRUMENT USED FOR COMMERCIAL
WORK
Photo by Claudy.]
The desire to telegraph across the ocean came with the introduction of
the telegraph on land. Bare wires in the air with glass insulators at
the poles are used for land telegraphy, but bare wires in the water
could not be used, for ocean water will conduct electricity. Something
was needed to cover the wire, protect it from the water, and prevent the
escape of the electric current. Just when it was needed such a
substance was discovered. In 1843, when Morse was working on his
telegraph, it was found that the juice of a certain kind of tree growing
in the Malayan Archipelago formed a substance somewhat like rubber but
more durable, and especially suited to the insulation of wires in water.
This substance is gutta-percha. Ocean cables are made of a number of
copper wires, each wire covered with gutta-percha, the wires twisted
together and protected with tarred rope yarn and an outer layer of
galvanized iron wires. The earth is used for the return circuit, as in
the land telegraph.
Duplex Telegraphy
The telegraph was a success, but many improvements were yet to be made.
Economy of construction was the thing sought for. To make one wire do
the work of two was accomplished by the invention of the duplex system.
In duplex telegraphy two messages may be sent in opposite directions
over the same wire at the same time. Let us take a look at some of the
methods by which this is accomplished.
One method with a long name but very simple in its working is the
differential system (Fig. 66). In the differential system the current
from the home battery divides into two branches passing around the coils
of the electromagnet in opposite directions. Now if these two branches
are so arranged that the currents flowing through them are equal, the
relay will not be magnetized, because one current would tend to make the
end A a north pole, and the other current would tend to make the same
end a south pole. The result is that the relay coil is not magnetized,
and does not attract the armature. But the current from the distant
battery comes over one of these branches only, and will magnetize the
relay. Hence, with a similar arrangement at the second station, two
messages may be sent at the same time in opposite directions.
[Illustration: FIG. 66--HOW TWO MESSAGES ARE SENT OVER ONE WIRE AT THE
SAME TIME]
Another method not quite so simple in principle is the bridge method.
When the key at station _A_ (see Fig. 67) is closed, the current from
the battery at station _A_ divides at _C_, and if the resistances _1_
and _2_ are equal, and the resistance _3_ is equal to the resistance of
the line, no current will flow through the sounder. But if a current
comes over the line from the distant station this current divides at
_D_, and a part goes through the sounder, causing it to click. The
sounder is not affected, therefore, by the current from the home
battery, but is affected by the current from the distant battery.
Therefore, a message may be sent and another received at the same time.
If there is a similar arrangement at the other station, two messages may
travel over the line in opposite directions at the same time.
[Illustration: FIG. 67--HOW TWO MESSAGES ARE SENT OVER ONE WIRE AT THE
SAME TIME. BRIDGE METHOD]
The differential method is used in land telegraphy, the bridge method
almost exclusively in submarine telegraphy. The next step was a
quadruplex system, by means of which four messages may be transmitted
over one wire at the same time. The first quadruplex system was invented
by Edison in 1874, and in four years it saved more than half a million
dollars. Other systems have been invented which make it possible to send
even a larger number of messages at one time over a single wire.
The Telephone
The idea of "talking by telegraph" began to grow in the minds of
inventors soon after the Morse instrument came into use. The sound of
the voice causes vibrations in the air. (This is simply shown in the
string telephone. This telephone is made by stretching a thin membrane,
such as thin sheepskin, or gold-beaters' skin, over a round frame of
wood or metal. Two such instruments are connected by a string, the end
of the string being fastened to the middle of the stretched membrane.
The sound of the voice causes this membrane to vibrate. As the membrane
moves rapidly back and forth, it pulls and releases the string, and so
causes the membrane at the other end to vibrate and give out the sound.
This is the actual carrying of the sound vibrations along the string.)
In the telephone it is not sound vibrations but an electric current that
travels over the line wire. The telephone message, therefore, travels
with the speed of electricity, not with the speed of sound. If it
travelled with the speed of sound in air, a message spoken in Chicago
would be heard in New York one hour later; but we know that a message
spoken in Chicago may be heard in New York the instant it is spoken.
The telephone, like the telegraph, depends on the electromagnet. The
thought of inventors at first was to make the vibrations of a thin
membrane, caused by the sound of the voice, open and close a telegraphic
circuit. An electromagnet at the other end of the line would cause a
thin membrane with a piece of soft iron attached to it to vibrate, just
as the magnet in the telegraph receiver pulls and releases the
soft-iron armature as the circuit is made and broken. The thin membrane
caused to vibrate in this way would give out the sound. A telephone on
this principle was invented by Philip Reis, a schoolmaster in Germany.
The transmitter was carved out of wood in the shape of a human ear, the
thin membrane being in the position of the ear-drum. Musical sounds and
even words were transmitted by this telephone, but it could never have
been successful as a practical working telephone. The membrane in the
receiver would vibrate with the same speed as the membrane in the
transmitter, but sound depends on something more than speed of
vibration.
The Bell telephone, as known to-day, began with a study of the human
ear. Alexander Graham Bell was a teacher of the deaf. His aim was to
teach the deaf to use spoken language, and for this purpose he wished to
learn the nature of the vibrations caused by the voice. His plan was to
cause the ear itself to trace on smoked glass the waves produced by the
different letters of the alphabet, and to use these tracings in teaching
the deaf. Accordingly, a human ear was mounted on a suitable support,
the stirrup-bone removed, leaving two bones attached, and a stylus of
wheat straw attached to one of the bones. The ear-drum, caused to
vibrate by the sound, moved the two small bones and the pointer of
straw, so that when he sang or talked to the ear delicate tracings were
made on the glass.
This experiment suggested to Mr. Bell that a membrane heavier than the
ear-drum would move a heavier weight. If the ear-drum, no thicker than
tissue-paper, could move the bones of the ear, a heavier membrane might
vibrate a piece of iron in front of an electromagnet. He was at the
same time devising a telegraph for transmitting messages by means of
musical sounds. In this telegraph he was using an electromagnet in the
transmitter and another electromagnet in the receiver. He attached the
soft-iron armature of each electromagnet to a stretched membrane of
gold-beaters' skin, expecting that the sound of his voice would cause
the membrane of the transmitter to vibrate, and that, by means of the
electromagnets, the membrane of the receiver would be made to vibrate in
the same way (Fig. 68). At first he was disappointed, but after making
some changes in the armatures a distinct sound was heard in the
receiver. Later the membrane was discarded, and a thin iron disk used
with better effect.
[Illustration: FIG. 68--FIRST BELL TELEPHONE RECEIVER AND TRANSMITTER
The receiver is on the left in the picture. A thin membrane of
gold-beaters' skin tightly stretched and fastened with a cord can be
seen on the end of the transmitter and of the receiver. An electromagnet
is also shown over each membrane. This thin membrane, with a piece of
soft iron attached, was used in place of the soft-iron disk of the
modern receiver.]
The story of Bell's struggles might seem like the repetition of the life
story of many another great inventor. He knew that he had discovered
something of great value to the world. He devoted his time to the
perfecting of the telephone, neglecting his professional work and
finally giving it up, that he might give his whole time to his
invention. He was forced to endure poverty and ridicule. He was called
"a crank who says he can talk through a wire." Men said his invention
could never be made practical. Even after he succeeded in finding a few
purchasers and some of the telephones were in actual use, people were
slow to adopt it. The idea of talking at a piece of iron and hearing
another piece of iron talk seemed like a kind of witchcraft.
In the telephone we see another use of the electromagnet. A very thin
iron disk near the poles of an electromagnet forms the telephone
receiver (Fig. 69). An electric current travels over the telephone wire.
If the current grows stronger, the magnet is made stronger and pulls
the disk toward it. If the current grows weaker, the magnet becomes
weaker and does not pull so hard on the disk. The disk then springs back
from the magnet. If these changes take place rapidly the disk moves back
and forth rapidly and gives out a sound. The sound of the voice at the
other end of the line sets the disk in the mouthpiece vibrating. The
vibrations of this disk cause the changes in the electric current
flowing over the line-wire, and the changes in the electric current
cause the disk of the receiver to vibrate in exactly the same way as the
disk at the mouthpiece. Thus the words spoken into the mouthpiece may be
heard at the receiver.
[Illustration: FIG. 69--A TELEPHONE RECEIVER]
The transmitter used by Bell was like the receiver. Two receivers from
the common telephone connected by two wires may be used as a telephone
without batteries. Fig. 70 shows a complete telephone made of two
receivers connected by two wires. The disk in one receiver which is now
used as a transmitter is made to vibrate by the sound of the voice. Now
when a piece of iron moves back and forth in a magnetic field it
strengthens and weakens the field. So the magnetic field in the
transmitter is rapidly changed by the movement of the iron disk. Now we
have found that whenever a coil of wire is in a changing magnetic field
a current is induced in the coil. The small coil in the transmitter,
therefore, has a current induced in it. We have also found that when the
magnetic field is made stronger the induced current flows in one
direction, and when the field is made weaker the current flows in the
opposite direction. Since the field in the transmitter is made
alternately stronger and weaker, the current in the coil flows first in
one direction, then in the opposite direction--that is, we have an
alternating current. This alternating current, of course, flows over the
line-wire and through the coil in the receiver. In the receiver the
alternating current will alternately strengthen and weaken the magnetic
field, and as it does so the pull of the magnet on the iron disk is
strengthened and weakened. The iron disk in the receiver, therefore,
vibrates in exactly the same way as the disk in the transmitter, and so
gives out a sound just like that which is acting on the transmitter.
[Illustration: FIG. 70--TWO RECEIVERS USED AS A COMPLETE TELEPHONE]
In the Blake transmitter, which is now commonly used, the disk moves a
pencil of carbon which presses against another pencil of carbon. This
varies the pressure between the two pencils of carbon. A battery current
flows through the two carbons, and as the pressure of the carbons
changes the strength of the current changes. When the carbons are
pressed together more closely the current is stronger. When the pressure
is less the current is weaker. We have, then, a varying current through
the carbons. This current flows through the primary coil of an
induction-coil, the secondary being connected to the line-wire. Now a
current of varying strength in the primary induces an alternating
current in the secondary. We have, then, an alternating current flowing
over the line-wire. This alternating current acts on the magnetic field
of the receiver in the way described before, causing the disk in the
receiver to vibrate and give out the sound.
For long-distance work a carbon-dust transmitter (Fig. 71) is used. In
this there are many granules of carbon, so that instead of two
carbon-points in contact there are many. This makes the transmitter more
sensitive.
[Illustration: FIG. 71--CARBON-DUST TRANSMITTER]
The strength of current required for the telephone is very small. To
transmit a telephone message requires less than a hundred-millionth part
of the current required for a telegraphic message. The work done in
lifting the telephone receiver a distance of one foot, if changed into
an alternating current, would be sufficient to keep up a sound in the
receiver for a hundred thousand years. Because of its extreme
sensitiveness the telephone requires a complete wire circuit. The earth
cannot be used for the return circuit, as in the case of the telegraph.
Disturbances in the earth, vibration, leakage currents from trolley
lines, and so forth, would interfere seriously with the action of the
telephone.
When the telephone was invented it was commonly remarked that it could
not take the place of the telegraph in commerce, for the latter gave the
merchant some evidence of a business transaction, while the telephone
left no sign. There was a time when men feared to trust each other, but
now large business deals are made by telephone; products of the farm,
the factory, and the mine are bought and sold in immense quantities
without a written contract or even the written evidence of a telegram.
Thus the telephone has developed a spirit of business honor.
The Phonograph
The phonograph grew out of the telephone. It is said to be the only one
of Edison's inventions that came by accident, yet only a man of genius
would have seen the meaning of such an accident. He was singing into the
mouthpiece of a telephone when the vibrations of the disk caused a fine
steel point to pierce one of his fingers held just behind the disk. This
set him to thinking. If the sound of his voice could cause the disk to
vibrate with force enough to pierce the skin, would it not make
impressions on tin-foil, and so make a record of the voice that could be
reproduced by passing the point rapidly over the same impressions? He
gave his assistants the necessary instructions, and soon the first
phonograph was made.
This disk in the phonograph is set in vibration by sound vibrations in
the air in the same way as the disk in the telephone transmitter.
Attached to the disk is a needle-point which, of course, vibrates with
the disk. If a cylinder with a soft surface is turned rapidly under the
steel point as it vibrates, impressions are made in the cylinder
corresponding to the movements of the disk. The cylinder must move
forward as it turns, so that its path will be a spiral. If, now, the
stylus is placed at the starting-point and the cylinder turned rapidly
the stylus will move rapidly up and down as it goes over the
indentations in the cylinder, and so cause the metal disk to vibrate and
give out a sound like that received at first. In the earliest
phonographs the cylinder was covered with tin-foil. Later the so-called
"wax records" came into use. These cylinders are not made of wax, but of
very hard soap. Fig. 72 shows an instrument in which the sound of the
voice caused a pencil-point to trace a wavy line on a cylinder. This
instrument may be called a forerunner of the phonograph. Fig. 73 shows
Edison's first phonograph with a modern instrument placed beside it for
comparison.
[Illustration: FIG. 72--THE PHONAUTOGRAPH, A FORERUNNER OF THE
PHONOGRAPH]
[Illustration: FIG. 73 EDISON'S FIRST PHONOGRAPH AND A MODERN INSTRUMENT
Photo by Claudy.]
Gas-Engines
Cannons are the oldest gas-engines. Indeed, the principle of the cannon
is the same as that of the modern gas-engine, the piston in the engine
taking the place of the cannon-ball. The power in each case is obtained
by explosion--in the cannon the explosion of powder, in the engine the
explosion of a mixture of air and gas. Powder-engines with pistons were
proposed in the seventeenth century, and some were actually built, but
it proved too difficult to control them, and the idea of the gas-engine
was abandoned for more than a hundred years.
The discovery of coal-gas near the close of the eighteenth century gave
a new impetus to the gas-engine. John Barber, an Englishman, built the
first actual gas-engine. He used gas distilled from wood, coal, or oil.
The gas, mixed with the proper proportion of air, was introduced into a
tank which he called the exploder. The mixture was fired and issued out
in a continuous stream of flame against the vanes of a paddle-wheel,
driving them round with great force.
In 1804 Lebon, a French engineer, was assassinated, and the progress of
the gas-engine set back a number of years, for this engineer had
proposed to compress the mixture of gas and air before firing, and to
fire the mixture by an electric spark. This is the method used in
gas-engines to-day.
The first practical working gas-engine was invented by Lenoir, a
Frenchman, in 1860. From this time to the end of the century the
gas-engine developed rapidly, receiving a new impulse from the
increasing demand for the motor-car.
The engine of the German inventors, Otto and Langen, brought out in
1876, marked the beginning of a new era. The greater number of engines
used in automobiles to-day are of the kind known as the Otto cycle, or
four-cycle, engine. This engine is called four-cycle because the piston
makes four strokes for every explosion. There is one stroke to admit the
mixture of gas and air to the cylinder, another to compress the gas and
air, at the beginning of the third stroke the explosion takes place, and
in the fourth stroke the burned-out gases are driven out of the
cylinder. The working of the four-cycle gas-engine is made clear in
Figs. 74, 75, 76, and 77.
[Illustration: FIG. 74--FIRST STROKE. GAS AND AIR ADMITTED TO THE
CYLINDER]
[Illustration: FIG. 75--SECOND STROKE. MIXTURE OF GAS AND AIR
COMPRESSED]
[Illustration: FIG. 76--THIRD STROKE. THE MIXTURE IS EXPLODED AND
EXPANDS, DRIVING THE PISTON FORWARD]
[Illustration: FIG. 77--FOURTH STROKE, EXHAUST. THE BURNED-OUT MIXTURE
OF GAS AND AIR EXPELLED FROM THE CYLINDER]
THE FOUR-CYCLE GAS-ENGINE
In such a gas-engine the power is applied to the piston only in one
stroke out of every four, while in the steam-engine the power is applied
at every stroke. It would seem, therefore, that a steam-engine would do
more work than a gas-engine for the same amount of heat, but such is not
the case; in fact, a good gas-engine will do about twice as much work as
a good steam-engine for the same amount of fuel. The reason is that the
steam-engine wastes its heat. Heat is given to the condenser, to the
iron of the boiler, to the connecting pipes and the air around them,
while in the gas-engine the heat is produced in the cylinder by the
explosion and the power applied directly to the piston-head. More than
this, a steam-engine when at rest wastes heat; there must be a fire
under the boiler if the engine is to be ready for use on short notice.
When a gas-engine is at rest there is no fire, nothing is being used up,
and yet the engine can be started very quickly. A gas-engine can be made
much lighter than a steam-engine of the same horse-power. The automobile
and the flying-machine require very light engines. Without the
gas-engine the automobile would have remained imperfect and crude, while
the flying-machine would have been impossible.
In a two-cycle gas-engine there is an explosion for every two strokes of
the piston, or one explosion for every revolution of the crank-shaft.
During one stroke the mixture of gas and air on one side of the piston
is compressed and a new mixture enters on the opposite side of the
piston. At the end of this stroke the compressed mixture is exploded,
and power is applied to the piston during about one-fourth of the next
stroke. During the remainder of the second stroke the burned-out gas
escapes, and the fresh mixture passes over from one side of the piston
to the other ready for compression. The two-cycle engine is simpler in
construction than the four-cycle, having no valves. It also has less
weight per horse-power. The cylinder of a two-cycle engine is shown in
Fig. 78.
[Illustration: FIG. 78--TWO-CYCLE GAS-ENGINE. CRANK AND CONNECTING-ROD
ARE ENCLOSED WITH THE PISTON]
A steam-engine is self-starting. The engineer has only to turn the steam
into the cylinder, but the gas-engine requires to be turned until at
least one explosion takes place, for until there is an explosion of gas
and air in the cylinder there is no power.
A gas-engine may have a number of cylinders. Four-cylinder and
six-cylinder engines are common. In a four-cylinder, four-cycle engine,
while one cylinder is on the power stroke the next is on the compression
stroke, the third on the admission stroke, and the fourth on the exhaust
stroke. Fig. 79 shows the Selden "explosion buggy" propelled by a
gas-engine. This machine was the forerunner of the modern automobile.
[Illustration: FIG. 79--SELDEN "EXPLOSION BUGGY." FORERUNNER OF THE
MODERN AUTOMOBILE]
The Steam Locomotive
Late in the eighteenth century a mischievous boy put some water in a
gun-barrel, rammed down a tight wad, and placed the barrel in the fire
of a blacksmith's forge. The wad was thrown out with a loud report, and
the boy's play-mate, Oliver Evans, thought he had discovered a new
power. The prank with the gun-barrel set young Evans thinking about the
power of steam. It was not long until he read a description of a
Newcomen engine. In the Newcomen engine, you will remember, it was the
pressure of air, not the pressure of steam, that lifted the weight.
Evans soon set about building an engine in which the pressure of steam
should do the work. He is sometimes called the "Watt of America," for he
did in America much the same work that Watt did in Scotland. Evans built
the first successful non-condensing engine--that is, an engine in which
the steam, after driving the piston, escapes into the air instead of
into a condenser. The non-condensing engine made the locomotive
possible, for a locomotive could not conveniently carry a condenser.
Evans made a locomotive which travelled very slowly. He said, however:
"The time will come when people will travel in stages moved by
steam-engines from one city to another, almost as fast as birds can fly,
fifteen or twenty miles an hour."
The inventor who made the first successful locomotive was George
Stephenson, and it is worth noting that one of his engines, the
"Rocket," possessed all the elements of the modern locomotive. He
combined in the "Rocket" the tubular boiler, the forced draft, and
direct connection of the piston-rod to the crank-pin of the
driving-wheel.
The "Rocket" was used on the first steam railway (the Stockton &
Darlington, in England), which was opened in 1825. There had been other
railways for hauling coal by means of horses over iron tracks, and other
locomotives that travelled over an ordinary road; but this was the first
road on which a steam-engine pulled a load over an iron track, the
first real railroad. Fig. 80 shows the "Rocket" and two other early
locomotives.
[Illustration: FIG. 80--SOME EARLY LOCOMOTIVES
The one on the right is Stephenson's "Rocket."
Photo by Claudy.]
In order to build a railroad between Liverpool and Manchester for
carrying both passengers and freight it was necessary to secure an act
of Parliament. Stephenson was compelled to undergo a severe
cross-examination by a committee of Parliament, who feared there would
be great danger if the speed of the trains were as high as twelve miles
an hour. He was asked:
"Have you seen a railroad that would stand a speed of twelve miles an
hour?"
"Yes."
"Where?"
"Any railroad that would bear going four miles an hour. I mean to say
that if it would bear the weight at four miles an hour it would bear it
at twelve."
"Do you mean to say that it would not require a stronger railway to
carry the same weight at twelve miles an hour?"
"I will give an answer to that. I dare say every person has been over
ice when skating, or seen persons go over, and they know that it would
bear them better at a greater velocity than it would if they went
slower; when they go quickly the weight, in a measure, ceases."
"Would not that imply that the road must be perfect?"
"It would, and I mean to make it perfect."
For seven miles the road must be built over a peat bog into which a
stone would sink to unknown depths. To convince the committee, however,
and secure the act of Parliament was more difficult than to build the
road. But Stephenson was one of the men who do things because they
never give up, and the road was built.
How a Locomotive Works
To understand how a locomotive works, let us consider how the steam is
produced, how it acts on the piston, and how it is controlled. The steam
is produced in a locomotive in exactly the same way that steam is
produced in a tea-kettle. Now everybody knows that a quart of water in a
tea-kettle with a wide bottom placed on a stove will boil more quickly
than the same amount of water in a tea-pot with a narrow bottom. The
greater the heating-surface--that is, the greater the surface of heated
metal in contact with the water--the more quickly the water will boil
and the more quickly steam can be produced. In a locomotive the aim is
to use as large a heating-surface as possible. This is done by making
the fire-box double and allowing the water to circulate in the space
between the inner and outer parts, except underneath; also by placing
tubes in the boiler through which the heated gases and smoke from the
fire must pass. An ordinary locomotive contains two hundred or more of
these tubes. The water surrounds these tubes, and is therefore in
contact with a very large surface of heated metal. In some engines the
water is in the tubes, and the heated gases surround the tubes.
The steam as it enters the cylinder should be dry--that is, it should
not contain drops of water. This is accomplished by allowing the steam
from the boiler to pass into a dome above the boiler. Here the steam,
which is nearly dry, enters a steam-pipe leading to the cylinder (Fig.
81). The steam is admitted to the cylinder by means of a slide-valve.
From the diagram it can easily be seen that the valve admits steam first
on one side of the piston, then on the other. It can also be seen that
the valve closes the admission-port, and so cuts off the steam before
the piston has made a full stroke. The steam that is shut up in the
cylinder continues to expand and act on the piston. At the same time the
valve opens the exhaust-port, allowing the steam to escape from the
other side of the piston; but it closes this port before the piston has
quite finished the stroke. The small quantity of steam thus shut up acts
like a cushion to prevent the piston striking the end of the cylinder
with too great force. The exhaust-steam escapes through a blast-pipe
into the chimney, drives the air before it up the chimney, and thus
makes a greater draft of air through the fire-box. This is called the
forced draft. The escape of the exhaust-steam causes the puffing of the
locomotive just after starting. After the engine is under way the
engineer partly shuts off the steam by means of the reversing lever and
the puffing is less noticeable.
[Illustration: FIG. 81--HOW A LOCOMOTIVE WORKS
The arrows show the course of the steam.]
The action of the steam may be summed up as follows:
1. Steam admitted to the cylinder (admission).
2. Valve closes admission-port (cut-off).
3. Steam shut up in the cylinder expands, acting on the piston
(expansion period).
4. Valve opens exhaust-port to allow used steam to escape (exhaust).
The devices for controlling the steam are the throttle-valve and the
valve-gear. The throttle-valve is at the entrance to the steam-pipe in
the steam-dome. This valve is opened and closed by means of a rod in the
engineer's cab.
Stephenson's link-motion valve-gear is used on most locomotives. The
forward rod in the diagram is in position to act upon the valve-rod
through the lever _L_. Suppose the reversing-lever is drawn back to the
dotted line; then the forward rod will be raised and the backward rod
will come into position to act on the lever _L_. If this is done while
the locomotive is at rest the valve is moved through one-half a complete
stroke. In the diagram the steam enters the cylinder on the right of the
piston. After this movement of the valve the steam would enter on the
left side of the piston. In the present position the locomotive would
move forward, but if the valve is changed so as to admit steam to the
left of the piston while the connecting-rod is in the position shown
then the engine will move backward. Thus the direction can be controlled
by the engineer in the cab. Of course, this can be done while the engine
is in motion. The forward rod and the backward rod are each moved by an
eccentric on the axle of the front driving-wheel. The two eccentrics are
in opposite positions on the axle. An eccentric acts just like a crank,
causing the rod to move forward and backward as the axle turns, and of
course this motion is given to the valve-rod through the lever. When the
link is set midway between the forward and the backward rod the valve
cannot move. When the link is raised or lowered part way the valve makes
a short stroke, and less steam is admitted to the cylinder than with a
full stroke. In starting the locomotive the valve is set to make a full
stroke. When the train is under headway the valve is set for a short
stroke to economize steam. The valve-gear and the throttle-valve
together take the place of the governor in the stationary engine, but
while the governor acts automatically these are controlled by the
engineer.
In reality a locomotive is two engines, one on either side, connected to
the same driving-wheels. But the two piston-rods are connected to the
driving-wheels at points which are at right angles with each other, so
that when the crank on one side is at the end of a stroke--the "dead
centre"--that on the other side is on the quarter, either above or below
the axle, ready for applying the greatest turning force.
The expansion-engine was designed to use more of the power of the steam
than can be done in the single-cylinder engine. In the double
expansion-engine the steam expands from one cylinder into another. The
second cylinder must be larger in diameter than the first. In the triple
expansion-engine the steam expands from the second cylinder into a
third, still larger. The second and third cylinders use a large part of
the power that would be wasted with only one cylinder.
The Turbine
One of the great inventions relating to steam-power is the
steam-turbine. The water-turbine is equally useful in relation to
water-power. The water-turbine and the steam-turbine work in very much
the same way, the difference being due to the fact that steam expands as
it drives the engine, while water drives it by its weight in falling, or
by its motion as it rushes in a swift stream or jet against the blades
of the turbine.
The first steam-engine, that of Hero in the time of Archimedes, was a
form of turbine (Fig. 82). It was driven by the reaction of the steam as
it escaped into the air. The common lawn-sprinkler, that whirls as the
water rushes through it, is a water-turbine that works in the same way.
"Barker's Mill" is the name applied to a water-turbine that works like
the lawn-sprinkler. As the water rushes out of the opening it pushes
against the air. It cannot push against the air without pushing back at
the same time. Never yet has any person or object in nature been able to
push in one direction only. It cannot be done. If you push a cart
forward you push backward against the ground at the same time. If there
were nothing for you to push back against your forward push would not
move the cart a hair's-breadth. If you doubt this, try to push a cart
when you are standing on ice so slippery that you cannot get a foothold.
It is the backward push of the water in the lawn-sprinkler and the
backward push of the steam in Hero's engine that cause the machine to
turn.
[Illustration: FIG. 82--HERO'S ENGINE]
The turbines in common use for both water and steam power have curved
blades. The reason for curving the blades can best be seen by referring
to an early form of water-wheel. The best water-turbine is only an
improved form of water-wheel. The first water-wheels had flat blades,
and these answered very well so long as only a low power was needed and
it was not necessary to save the power of the water. It was found,
however, that there was a great waste of power in the wheel with flat
blades. One inventor proposed to improve the wheel by curving the blades
in such a way that the water would glide up the curve and then drop
directly downward (Fig. 83). The water then gives up practically all of
its power to the wheel and falls from the wheel. It would have no power
to move a second wheel. In this way he used practically all the power
of the water. To save the power of the water by making all of the water
strike the wheel at high speed the channel was made narrow just above
the wheel, forming a mill-race. This applies to the undershot wheel. In
the overshot wheel (Fig. 84) the power depends on the weight of the
water and on its height. The water runs into buckets attached to the
wheel, and, as it falls in these buckets, turns the wheel. The undershot
wheel and the mill-race represent a common form of turbine, that form
in which the steam or the water is forced in a jet against a set of
curved blades. Fig. 85 shows a steam-turbine run by a jet of steam. In
the water-turbine there are two sets of blades. One set rotates, the
other remains fixed. The use of the fixed blades is to turn the water
and drive it in the right direction against the moving blades. In some
forms of turbine there are more than two sets of blades. The steam, as
it passes through, gives up some of its power to each set of blades
until, after passing the last set, it has given up nearly all its power.
The action of the steam in this turbine is somewhat like that in the
expansion-engine, in which the steam gives up a portion of its power in
each cylinder. Fig. 86 is from a photograph of a modern steam-turbine,
and Fig. 87 is a drawing of the same turbine showing the course of the
steam. Fig. 88 is a turbine that runs a large dynamo.
[Illustration: FIG. 83--AN UNDERSHOT WATER-WHEEL WITH CURVED BLADES]
[Illustration: FIG. 84--AN OVERSHOT WATER-WHEEL]
[Illustration: FIG. 85--DE LAVAL STEAM-TURBINE
Driven by a jet of steam striking the blades.]
[Illustration: FIG. 86--A MODERN STEAM-TURBINE WITH TOP CASING RAISED
SHOWING BLADES]
[Illustration: FIG. 87--DIAGRAM OF TURBINE SHOWN IN FIG. 86
The arrows show the course of the steam.]
[Illustration: FIG. 88--A STEAM-TURBINE THAT RUNS A DYNAMO GENERATING
14,000 ELECTRICAL HORSE-POWER
The steam enters through the large pipe at the left.]
In 1897, as the battle-ships of the British fleet were assembled to
celebrate the Diamond jubilee of Queen Victoria, a little vessel a
hundred feet long darted in and out among the giant ships, defied the
patrol-boats whose duty it was to keep out intruders, and raced down the
lines of battle-ships at the then unheard-of speed of thirty-five knots
an hour. It was the _Turbinia_, fitted with the Parsons turbine. This
event marked the beginning of the modern turbine. It also marked the
beginning of a revolution in steam propulsion.
The Parsons turbine does not use the jet method, but the steam enters
near the centre of the wheel and flows toward the rim, passing over a
number of rows of curved blades. The Parsons turbine is used on the
fastest ocean liners. The _Lusitania_, one of the fastest steamships in
the first decade of the twentieth century, has two sets of high and low
pressure turbines with a total of 68,000 horse-power.
The windmill is a form of turbine driven by the air. As the air rushes
against the blades of the windmill, it forces them to turn. If the
windmill were turned by some mechanical power, it would drive the air
back, and we should have a blower. This is what we have in the electric
fan, a small windmill driven by an electric motor so that it drives the
air instead of being driven by it. The blades of the windmill and the
electric fan are shaped very much like the screw propeller. The screw
propeller, driven by an engine, would drive the water back if the ship
were firmly anchored, just as the fan drives the air. But it cannot
drive the water back without pushing forward on the ship at the same
time, and this forward push propels the ship. It is difficult to attain
what is now regarded as high speed with a single screw. With engines in
pairs and two lines of shafting higher power can be used. The best
steamers, therefore, are fitted with the twin-screw propeller. Some
large steamers have three and some four screws.
The screw propellers of turbine steamships are made of small diameter,
that they may rotate at high speed without undue waste of power. By the
use of turbine engines and twin-screw propellers, the weight of the
machinery has been greatly reduced. The old paddle-wheels, with
low-pressure engines, developed only about two horse-power for each ton
of machinery. The turbine, with the twin-screw propeller, develops from
six to seven horse-power for every ton of machinery. The modern steamer,
with all its machinery and coal for an Atlantic voyage, weighs no more
than the engines of the old paddle-wheel type and coal would weigh for
the same horse-power. The steam-turbine and the twin-screw propeller
have made rapid ocean travel possible.