FARADAY AND THE FIRST DYNAMO
Michael Faraday, a London newsboy, the son of a blacksmith, became the
inventor of the dynamo, and prepared the way for the wonderful
electrical inventions of the nineteenth century. He began his career as
a book-binder's apprentice, employing his spare moments in reading the
books he was binding. One of these books led him to make some simple
experiments in chemistry. He also made an electrical machine, first with
a glass bottle, and afterward with a glass cylinder.
While an apprentice he wrote to his young friend, Benjamin Abbott: "I
have lately made a few simple galvanic experiments, merely to illustrate
to myself the first principles of the science. I was going to Knight's
to obtain some nickel, and bethought me that they had malleable zinc. I
inquired, and bought some--have you seen any yet? The first portion I
obtained was in the thinnest pieces possible. It was, they informed me,
thin enough for the electric stick. I obtained it for the purpose of
forming disks with which and copper to make a little battery. The first
I completed contained the immense number of seven pairs of plates!!! and
of the immense size of halfpence each!!!!!! I, sir, I my own self, cut
out seven disks of the size of half pennies each! I, sir, covered them
with seven halfpence, and I interposed between them seven, or rather
six, pieces of paper soaked in a solution of muriate of soda (common
salt). But laugh no longer, dear A., rather wonder at the effects this
trivial power produced."
This tiny battery made of half pennies with zinc disks and salt solution
would decompose a certain solution which Faraday tested. A larger
battery made of copper and zinc disks with salt solution would decompose
water from the cistern. When the wires from the larger battery were put
in the cistern-water he saw a dense white cloud descending from the
positive wire, and bubbles rising from the negative wire. This action
continued until all the white substance was taken out of the water.
Because of his interest in science, young Faraday attracted the
attention of a Mr. Dance, a member of the Royal Institution and a
customer of his master, Mr. Riebau. Through the kindness of Mr. Dance he
heard four lectures by Sir Humphry Davy. He took notes on the lectures,
wrote them out carefully, and added drawings of the apparatus. These
notes he sent to Davy with a letter expressing the wish that he might
secure employment at the Royal Institution. In a short time, after a
warning from Sir Humphry that he had better stick to his business of
book-binding, that "Science is a harsh mistress," his wish was granted,
and we find him cleaning and caring for apparatus in the Royal
Institution and assisting Davy in preparing for his lectures.
Count Rumford
Our story now takes us back to the time of the American Revolution. In
America, we find a young man of nineteen, Benjamin Thompson by name,
serving as major in the Second Regiment of New Hampshire. The
appointment of so young a man as major, and his evident hold on the
governor's favor, aroused the jealousy of the older officers. He was
accused of being unfriendly to the cause of liberty. He denied the
charge, and was acquitted by the committee of the people of Concord. A
mob gathered round his house, but he escaped. Driven from his refuge in
his mother's home, he fled to England, leaving his wife and child.
Appointed lieutenant-colonel in the British Army, he returned to America
and fought against his former friends.
The war having ended, he returned to England, thence to the Continent,
intending to take part in an expected war between Austria and Turkey. A
chance meeting with a Bavarian prince, Maximilian, changed the course of
his life. This prince, while commanding on parade, saw Thompson among
the spectators mounted on a fine English horse, and addressed him.
Thompson informed him that he came from serving in the American war. The
prince, pointing to a number of his officers, said: "These gentlemen
were in the same war, but against you. They belonged to the Royal
Regiment of Deux Ponts, that acted in America under the orders of Count
Rochambeau." Thompson dined with the prince and French officers. They
conversed of war and the battles in which they met. The prince,
attracted to the colonel, induced him to pass through Munich, and gave
him a letter to his uncle, the Elector of Bavaria.
It was in Bavaria, the country to which such unexpected turns of fortune
led him, that his greatest work was done. He entered the service of the
Duke of Bavaria as aide-de-camp. It was his aim while in the service of
the Bavarian Government to better the condition of the people. He
introduced reforms in the army, used the soldiers to rid the country of
beggars and robbers, and took steps to provide for the infirm and find
employment for the strong, his motto being that people can best be made
virtuous when first made happy.
A Military Workhouse was opened for the beggars, and a House of Industry
for the poor. A Military Academy was formed with a view to the free
education of young people of talent for the public service. He became
absorbed in the one aim of helping the poor. So thorough was his
devotion to the people, and so deeply did he win their affection, that
when he was dangerously ill a multitude of hundreds went in procession
to the church to make public prayers for his recovery.
He saw that the poor may be helped by teaching them to save, and in
nothing is there greater need of saving than in fuel and heat. In the
kitchens of the Military Academy and the House of Industry he carried
out a series of experiments on the economy of fuel, and succeeded in
greatly reducing the amount of fuel needed for cooking the food. He did
this by using a "closed fireplace," the forerunner of the stove. The
closed fireplace was in reality a brick stove, and was a great
improvement over the open chimney fireplaces then in common use. He
made the covers of the cooking utensils double, to save the heat, for he
had found that heat cannot escape through confined air.
Benjamin Thompson was knighted by George III., and in 1791 he was made a
Count of the Holy Roman Empire, and is known to the world of science as
Count Rumford.
Count Rumford's Experiment with the Cannon
While in the service of the Duke of Bavaria, it became his duty to
organize the field artillery. To provide cannon for this purpose, he
erected a foundry and machine-shops. Being alert for any unusual fact
relating to heat, he observed the very high temperature produced by the
boring of the cannon. He was eager to learn how so much heat could be
produced. For this purpose he took a cannon in the rough, as it came
from the foundry, fixed it in the machine used for boring, and caused
the cannon to be turned by horses while a blunt borer was forced against
the end of the cannon. He first tested the temperature of the metal
itself as it turned. Then he surrounded the end of the cannon with water
in an oblong box fitted water-tight (Fig. 20).
[Illustration: FIG. 20--COUNT RUMFORD'S EXPERIMENT WITH THE CANNON,
MAKING WATER BOIL WITHOUT FIRE
The horses make the water boil by walking around the track; the work
the horses do is changed into heat by the friction of the drill.]
The cannon had been turning but a short time when he found by putting
his hand in the water that heat had been produced. In two hours and
thirty minutes the water actually boiled. Astonishment was expressed in
the faces of the bystanders on seeing so large a quantity of water
heated and actually made to boil without any fire.
"Heat," Count Rumford said; "may thus be produced merely by the strength
of a horse, and, in case of necessity, this heat might be used in
cooking victuals. But no circumstance can be imagined in which there is
any advantage in this method of procuring heat, for more heat might be
obtained by burning the fodder which the horse would eat." The meaning
of this last remark was not understood until the time of Robert Mayer,
about fifty years later. Rumford had found that the work of a horse can
produce heat, and heat, in a steam-engine, can do the work of a horse.
Thus surely, though slowly, men were learning of the forces that move
the world and do man's bidding.
Count Rumford, true to his adopted land, returned to London and became
the founder of the Royal Institution in which Faraday and his successors
have achieved such marvellous results. He believed that the poor can be
helped in no better way than by giving them knowledge, so that they can
better their own condition. For this purpose he founded the Royal
Institution. Here he intended that men skilled in discovery should gain
new knowledge that would add to the comfort and happiness of the people.
Davy
In the English coal-fields many accidents due to the burning of
fire-damp had occurred. Fire-damp is caused by gas issuing from the
coal. On the approach of a flame this gas catches fire, and as it burns
it produces a violent wind, driving the flame before it through the
mine. Miners were scorched to death, suffocated, or buried under ruins
from the roof. Hundreds of miners had been killed. No means of lighting
the mines in safety had been devised. Sir Humphry Davy, Professor of
Chemistry in the Royal Institution, was appealed to. After many
experiments he devised a "safe lamp," which was a common miner's lamp
enclosed in a wire gauze. This proved a perfect protection from
fire-damp, and the Davy safety lamp has been used by miners the world
over for more than a century.
But Davy's best work was with the electric battery. Some of the facts
most familiar to us were discovered by him. Volta had contended that the
contact of the metals in a battery produces a current, that the liquid
merely carries the electricity from one metal plate to the other. But
Davy proved that there can be no current without chemical action.
Whenever we put two metals in an acid or other solution that will
dissolve one metal faster than the other, and connect the metals with a
wire, an electric current is produced. If we use water with silver and
gold, there is no current, because water will not dissolve either the
silver or the gold.
Davy discovered the metal, potassium, by means of his electric battery.
Potassium is found in common potash and saltpetre, and, when separated,
is a very soft metal. The newly discovered metal aroused great interest
in other countries. When Napoleon heard of it, he inquired impetuously
how it happened the discovery had not been made in France. On being told
that in France there had not been made an electric battery of sufficient
power, he exclaimed: "Then let one be instantly made without regard to
cost or labor." His command was obeyed, and he was called to witness the
action of the new battery. Before any one could interfere he placed the
ends of the wires under his tongue and received a shock that nearly
deprived him of sensation. On recovering he left the laboratory without
a word, and was never afterward heard to refer to the subject.
Davy made many great discoveries, but the greatest was his discovery of
Faraday.
* * * * *
A journey on the Continent with Davy was an event in the life of
Faraday, who up to that time had never to his own recollection travelled
twelve miles from London. On this journey he met Volta, whom he
describes as "an hale elderly man, very free in conversation." He
visited the Academy del Cimento, in Florence, and wrote: "Here was much
to excite interest; in one place was Galileo's first telescope, that
with which he discovered Jupiter's satellites. It was a simple tube of
wood and paper, about three and a half feet long, with a lens at each
end. There was also the first lens which Galileo made. It was set in a
very pretty frame of brass, with an inscription in Latin on it."
Faraday crossed the Alps and the Apennines, climbed Vesuvius, visited
Rome, and _saw a glow-worm_. The last he thought as wonderful as the
first.
Shortly after his return to London he fell in love. Now, Faraday had
determined that he would not be conquered by the master passion. In
fact, he had written various aspersions on love, of which the following
is a sample:
"What is the pest and plague of human life?
And what the curse that often brings a wife?
'Tis Love.
What is't directs the madman's hot intent,
For which a dunce is fully competent?
What's that the wise man always strives to shun,
Though still it ever o'er the world has run.
'Tis Love."
But he reckoned not with his own heart. It is not long until we find him
writing to Miss Sarah Barnard, a bright girl of twenty-one: "You have
converted me from one erroneous way, let me hope you will attempt to
correct what others are wrong.... Again and again I attempt to say what
I feel, but I cannot. Let me, however, claim not to be the selfish being
that wishes to bend your affections for his own sake only. In whatever
way I can minister to your happiness, either by close attention or by
absence, it shall be done. Do not injure me by withdrawing your
friendship or punish me for aiming to be more than a friend by making me
less."
They were married and lived in rooms at the Royal Institution. No poet
ever loved more tenderly than Faraday. Truly, science does not dry up
the heart's blood. At the age of seventy-one he wrote to his wife while
absent from home for a few days: "Remember me; I think as much of you as
is good for either you or me. We cannot well do without each other. But
we love with a strong hope of love continuing ever."
Faraday's Electrical Discoveries
Now we shall turn to Faraday's electrical discoveries and inventions.
Men had long known that, in houses that have been struck by lightning,
steel objects such as knives and needles are sometimes found to be
magnetized. Ships struck by lightning had found their compass-needles
pointing south instead of north, or wandering in direction and
worthless. Men had wondered how an electrical discharge could magnetize
steel. They had tried the spark of the electrical machine with no
definite result. Franklin, in his experiment of magnetizing a steel
needle by passing an electric spark through it, could not tell before
the spark was passed through the needle which end would be the north
pole. There was no seeming connection between the direction of the
electric discharge and the polarity of the needle. After the discovery
of the electric battery, men tried to discover a relation between the
electric current and magnetism.
Oersted and Electromagnetism
The first success in this direction was achieved by Hans Christian
Oersted, a native of Denmark. Poverty impelled his father to take him
from school at the age of twelve and place him in an apothecary's shop.
The boy, Hans, found delight in the chemical work of the apothecary. His
eagerness to learn and the pressure of poverty led him to neglect the
usual sports of boyhood and devote his leisure time to reading and
study. Again he entered school, and, though paying his way by his own
work, he graduated with honor from the University of Copenhagen. He was
appointed Professor of Physics in this university, and here he made his
first great discovery in electromagnetism.
After working for seven years to discover a relation between current
electricity and magnetism, he made a discovery which proved to be the
first step in the invention of the dynamo. He was using a magnetic
compass, which is a small magnetic needle balanced on a steel point. The
needle points nearly north and south unless disturbed by a magnet
brought near it. He had tried to find if a wire through which a current
is flowing would disturb the compass as a magnet does. He had tried
placing the wire east and west, thinking the compass-needle would follow
the wire as it does a magnet. One day, while lecturing to his students,
it occurred to him for the first time to place the wire north and south
over the compass-needle. He was surprised and perplexed as he did so to
see the needle swing round and point nearly east and west (Fig. 21). On
reversing the current the needle swung in the opposite direction. He had
discovered the magnetic action of an electric current. It was learned
soon afterward that a coil of wire with an electric current flowing
through it acts like a magnet, and that a current flowing around a bar
of soft iron makes the iron a magnet (Figs. 22 and 23).
[Illustration: FIG. 21--OERSTED'S EXPERIMENT
An electric current flowing over the compass-needle toward the north
causes the needle to turn until it points nearly west.
By permission of Joseph G. Branch.]
[Illustration: FIG. 22.--A COIL WITH A CURRENT FLOWING THROUGH IT ACTS
LIKE A MAGNET
The coil is picking up iron filings.]
[Illustration: FIG. 23--A BAR OF SOFT IRON WITH A CURRENT FLOWING AROUND
IT BECOMES A MAGNET]
Ampère
The news of Oersted's discovery aroused great interest throughout
Europe. Soon after its announcement in France, André Marie Ampère made a
discovery of equal importance. Oersted had discovered electromagnetism.
Ampère discovered electrical power or motion produced by an electrical
current.
The youth of Ampère was passed amid the stormy scenes of the French
Revolution. His father had moved from his country home to Lyons and
become a justice of the peace. In the destruction of the city of Lyons
during the Reign of Terror he lost his head under the guillotine.
The blow was too great for Ampère, then a youth of eighteen. He had been
a precocious child, advanced beyond his years in all the studies of the
schools. But now his strong mind failed. For a year he wandered about
mechanically piling up heaps of sand or gazing upon the sky. Then his
mental power returned, and he took up with eagerness the study of botany
and poetry.
He became a professor in the Polytechnic School in Paris, and it was
while teaching in this school that he made his great discoveries. He
found that two coils of wire can be made to attract or repel each other
by an electric current. If the current flows through the two coils in
the same direction, they attract each other (Fig. 24). If the current
flows in opposite directions through the coils, they repel each other
(Fig. 25). This is not very strange to us, for we know that a coil with
a current flowing through it acts just like a magnet. Each coil then has
a north pole and a south pole. If the coils are placed so that the two
north poles or the two south poles are together, they will repel each
other. If the north pole of one coil is near the south pole of the
other, they will attract each other.
[Illustration: FIG. 24--TWO COILS WITH CURRENTS FLOWING IN SAME
DIRECTION ATTRACT EACH OTHER]
[Illustration: FIG. 25--TWO COILS WITH CURRENTS FLOWING IN OPPOSITE
DIRECTIONS REPEL EACH OTHER]
Ampère believed that electric currents are flowing around within the
earth, and that the earth has a north and a south magnetic pole for the
same reason that a coil of wire has magnetic poles; that these poles are
caused by the currents flowing around in the earth just as the poles of
the coil are caused by the current flowing around in the coil.
We do honor to the name of Ampère whenever we measure an electric
current, for electric currents are measured in "amperes."
Arago
Another important discovery was made by a young Frenchman, François
Arago, within a year of the time when Oersted and Ampère made their
discoveries. The three great discoveries of these men were made in the
years 1819 and 1820. The youth of Arago was full of adventure. He had
assisted in making a survey in the Pyrenees, the haunt of daring
robber-bands. Twice in his cabin he was visited by a chief of a
robber-band who claimed to be a custom-house guard. On the second visit
he said to the robber: "Your position is perfectly known to me. I know
that you are not a custom-house guard. I have learned that you are the
chief of the robbers of the country. Tell me whether I have anything to
fear from your confederates." The robber replied: "The idea of robbing
you did occur to us; but, on the day that we molested an envoy from the
French, they would direct against us several regiments of soldiers, and
we are not so strong as they. Allow me to add that the gratitude which I
owe you for the night's shelter is your surest guarantee."
At a later time, when war between Spain and France was threatened, he
was accused of being a spy, and a mob was formed to put him out of the
way. He escaped in disguise through the midst of the mob and boarded a
Spanish ship. He was carried to Morocco, ran the gantlet of bloodthirsty
Mussulmans in Algiers, escaped death by a hair's-breadth, and through it
all clung to the papers which recorded the results of the survey in the
mountains, and delivered them in safety to the office of the Bureau of
Longitude in Paris.
Arago made a discovery which, with those of Oersted and Ampère, prepared
the way for Faraday's great electrical discoveries and the invention of
the dynamo. He found that a plate of copper whirling above or below a
magnetic needle will draw the needle after it (Fig. 26). He could make
the speed of the whirling copper plate so great that the needle would
whirl rapidly, following the copper plate. Faraday was the first to
explain Arago's experiment.
[Illustration: FIG. 26--ARAGO'S EXPERIMENT
When the copper plate whirls the magnet whirls also, though it does
not touch the copper plate.]
Faraday's First Electric Motor
Faraday's first electrical discovery was made soon after that of Arago.
Oersted had proven that an electric current acts on a magnet. The magnet
turns at right angles to the wire. Faraday saw that this is because the
north pole of the magnet tries to go round the wire in one direction,
and the south pole tries to go round in the opposite direction. He
placed a magnet on end in a dish of mercury, with one pole of the magnet
above the mercury, and found that the magnet would spin round a wire
carrying a current. When the current acts on one pole of the magnet
only, the magnet spins round the wire (Fig. 27). So Faraday's first
electrical discovery prepared the way for the electric motor.
[Illustration: FIG. 27--ONE POLE OF A MAGNET SPINS ROUND A WIRE THROUGH
WHICH AN ELECTRIC CURRENT FLOWS]
An Electric Current Produced by a Magnet
He had written in his note-book: "Convert magnetism into electricity."
An electric current would magnetize iron. Would not a magnet produce an
electric current? This was his problem.
He connected a coil of wire to an instrument that would tell when a
current was flowing, and placed a magnet in the coil. Others had
claimed, and Faraday at first believed, that a current would flow while
the magnet lay quiet within the coil. But Faraday was alert for the
unexpected, and the unexpected happened. For an instant, as he thrust
the magnet into the coil, his instrument showed that a current was
flowing. Again, as he drew the magnet quickly from the coil, a current
flowed, but in the opposite direction (Fig. 28). From this simple
experiment has grown the alternating-current machinery by which the
power of Niagara is made to light cities and drive electric cars at a
distance of many miles.
[Illustration: FIG. 28--WHEN A MAGNET IS THRUST INTO A COIL OF WIRE IT
CAUSES A CURRENT TO FLOW IN THE COIL, BUT THE CURRENT FLOWS ONLY WHILE
THE MAGNET IS MOVING
Drawing reproduced by permission of Joseph G. Branch.]
A friend of Faraday, on learning of this discovery, wrote the following
impromptu lines:
"Around the magnet Faraday
Was sure that Volta's lightnings play.
But how to draw them from the wire?
He took a lesson from the heart:
'Tis when we meet, 'tis when we part,
Breaks forth the electric fire."
A magnet will produce an electric current in a wire, but only when the
magnet or the wire is in motion.
Detecting and Measuring an Electric Current
The instrument which Faraday used to detect a current was derived from
Oersted's experiment. When a current flows in a north-and-south
direction over a compass-needle, the needle swings round. When the
current stops flowing the needle swings back to the north-and-south
position. The effect on the needle is stronger if the current flows
through a coil of wire and the coil is placed in a north-and-south
position around the needle (Fig. 29). The stronger the current flowing
through the coil the farther the needle will turn from the
north-and-south position.
[Illustration: FIG. 29--A COIL OF WIRE AROUND A COMPASS-NEEDLE
The needle tells when a current is flowing, and how strong the current
is.]
The coil and the needle together are called a galvanometer, and may be
used to tell when a current is flowing, and also to indicate the
strength of the current.
An Electric Current Produced by the Magnetic Field of Another Current
Faraday had found that a current flowing around a piece of iron will
make the iron a magnet, and that a magnet in motion will cause a current
to flow in a wire. It seemed to him that a second wire placed near the
first should have a current produced in it without the presence of iron.
He wound two coils of copper wire upon the same wooden spool. The wire
of the two coils he separated with twine and calico. One coil was
connected with a galvanometer, the other with a battery of ten cells,
yet not the slightest turning of the needle could be observed. But he
was not deterred by one failure. He raised his battery from ten cells to
one hundred cells, but without avail. The current flowed calmly through
the battery wire without producing, during its flow, any effect upon the
galvanometer. During its flow was the time when an effect was expected.
Again the unexpected happened. At the instant of making contact with the
battery there was a slight movement of the needle. When the contact was
broken, another slight movement, but in the opposite direction to the
first (Fig. 30). The current in one wire caused a current to flow in the
other, but the current in the second wire continued for an instant only
at the making and breaking of the contact with the battery. This was the
beginning of the induction-coil used to-day in wireless telegraphy.
[Illustration: FIG. 30--FARADAY'S INDUCTION-COIL
Starting and stopping the battery current in the primary coil causes a
changing magnetic field, and this causes a current to flow in the
secondary coil.
Drawing reproduced by permission of Joseph G. Branch.]
What was the secret of it? Simply this: that a current in one wire will
cause a current to flow in another wire near it, but only while the
current in the first wire is changing. That is, at the instant when the
first wire is connected to the battery, or its connection broken, a
current is induced in the second wire. There is no battery or other
source of current connected to the second wire; but a current flows in
this wire because it is near a wire in which a current is rapidly
starting and stopping. When these two wires are wound in coils, together
they form an induction-coil. The wire which we have called the first
wire forms the "primary" coil, and the one we have called the second
wire forms the "secondary" coil. By repeatedly making and breaking the
circuit in the primary coil we get an alternating current in the
secondary coil. Fig. 31 is from a photograph of some of the coils
actually used by Faraday.
[Illustration: FIG. 31--HISTORICAL APPARATUS OF FARADAY IN THE ROYAL
INSTITUTION
Some of Faraday's transformer coils are shown here. The instrument on
the left in a glass case is his galvanometer.]
Faraday's Dynamo
To invent a new electrical machine was Faraday's next aim. Arago's disk
of copper whirling near a magnet had a current induced in it, so Faraday
thought. It was the action of this induced current which caused the
magnet to follow the whirling disk. Could the current in Arago's disk be
collected and caused to flow through a wire? He placed a copper disk
between the poles of a magnet. One galvanometer wire passed around the
axis of the disk, the other he held in contact with the edge. He whirled
the disk. The galvanometer needle moved. A current was flowing in the
disk as it whirled. The current from the whirling disk flowed through
the galvanometer. Faraday had discovered the dynamo (Fig. 32).
[Illustration: FIG. 32--FARADAY'S FIRST DYNAMO
A current flows in the copper disk as it whirls between the poles of
the magnet.
By permission of Joseph G. Branch.]
All this work occupied but ten days in the autumn of 1831, though years
of preparation had gone before. In these ten days the foundation was
laid for the induction-coil, modern dynamo-electric machinery, and
electric lighting. Fig. 33 shows the laboratory in which Faraday did
this work.
[Illustration: FIG. 33--FARADAY'S LABORATORY, WHERE THE FIRST DYNAMO WAS
MADE
From the water-color drawing by Miss Harriet Moore.]
Faraday continued to explore the field opened up before him. In one
experiment two small pencils of charcoal lightly touching were connected
to the ends of a secondary coil. A spark passed between the charcoal
points when the primary circuit was closed. This was the first
transformer producing a tiny electric light (Fig. 34).
[Illustration: FIG. 34--THE FIRST TRANSFORMER]
Faraday discovered the induction-coil, the dynamo, and the transformer,
and he showed that, in each of these, it is magnetism which produces the
electric current. He had discovered the secret when he obtained a
current by thrusting a magnet into a coil of wire. The space about a
magnet in which the magnet will attract iron he called the "magnetic
field" (Figs. 35 and 36). In every case of magnetism causing an electric
current to flow in a coil of wire, the coil is in a magnetic field, and
the magnetic field is changing--that is, the magnetic field is made
alternately stronger and weaker, or the coil moves across the magnetic
field. The point is that magnetism at rest will not produce an electric
current. There must be a changing magnetic field or motion. In Faraday's
dynamo a copper disk whirled between the poles of a magnet and the
whirling of the disk in the magnetic field caused an electric current.
In the modern dynamo it is the whirling of a coil of wire in a magnetic
field that causes a current to flow. In the induction-coil it is the
change in the magnetic field that causes a current to flow in the
secondary coil. A coil of wire with an electric current flowing through
it will attract iron like a magnet. The primary coil with a current from
a battery flowing through it acts in all respects like a magnet; but as
soon as the current ceases to flow the magnetic field disappears--the
coil is no longer a magnet. When we make and break the connection
between the primary coil and the battery, then, we repeatedly make and
destroy the magnetic field, and this changing magnetic field causes a
current to flow in the secondary coil. The induction-coil is one form of
transformer. We shall see later how the dynamo and the transformer
developed in the nineteenth century.
[Illustration: FIG. 35--THE "MAGNETIC FIELD" IS THE SPACE AROUND A
MAGNET IN WHICH IT WILL ATTRACT IRON
The iron filings over the magnet arrange themselves along the "lines of
force."]
[Illustration: FIG. 36--MAGNETIC FIELD OF A HORSESHOE MAGNET]
When a boy, Faraday had passed the current from his little battery
through a jar of cistern-water, and saw in the water a "dense white
cloud" descending from the positive wire, and bubbles arising from the
negative wire. Something was being taken out of the water by the
electric current. When he tried the experiment later in his laboratory,
he found that, whenever an electric current is passed through water,
bubbles of two gases, oxygen and hydrogen, rise through the water. He
found that if the current is made stronger the bubbles are formed
faster. The water in time disappears, for it has been changed or
"decomposed" into the two gases.
It was the current from a battery that would decompose water. The
electricity from the electrical machine would do other things that he
had never seen a battery current do. "Do the battery and the electrical
machine produce different kinds of electricity, or is electricity one
and the same in whatever way it is produced?" This was the query that
troubled him. The answer to this question had been so uncertain that the
effect of the voltaic battery had been termed "galvanism," while that of
the friction machine retained the name "electricity."
Faraday tried many experiments in searching for an answer to this
question. He found that the electricity of the machine will produce the
same effect as that of a battery if the machine is compelled to
discharge slowly. An electrical machine or a battery of Leyden jars can
be made to give out an electric current, and this current will affect a
magnetic needle in the same way that a battery current will. It will
magnetize steel. If passed through water, it will decompose the water
into the two gases oxygen and hydrogen. In short, a current from an
electrical machine or a Leyden jar will do everything that a current
from an electric battery will do. Faraday caused the Leyden jar to give
a current instead of a spark by connecting the two metal coatings with a
wet string. On the other hand, the discharge from a powerful electric
battery will produce a spark and affect the human nerves in the same way
as the discharge from the electrical machine. The same effects may be
obtained from one as from the other.
In the discharge from the machine, a small quantity of electricity is
discharged under high pressure, as water may be forced through a small
opening by very high pressure. The voltaic cell, on the other hand,
furnishes a large quantity of electricity at low pressure, as a street
may be flooded by a broken water-main though the pressure is low. In
fact, the quantity of electricity required to decompose a grain of water
is equal to that discharged in a stroke of lightning, while the action
of a dilute acid on the one-hundredth part of an ounce of zinc in a
battery yields electricity sufficient for a powerful thunder-storm.
Many tests were made, and the result was a convincing proof that
electricity is the same whatever its source, the different effects being
due to difference in pressure and quantity. "But in no case," said
Faraday, "not even in those of the electric eel and torpedo, is there a
production of electric power without something being used up to supply
it."
Faraday's professional work would have made him wealthy. In one year he
made £1000 ($5000), and the amount would have increased had he sold his
services at their market value. But then there would have been no
Faraday the discoverer. The world would have had to wait, no one knows
how long, for the laying of the foundations of electrical industries. He
chose to give up wealth for the sake of discovery. He gave up
professional work with the exception of scientific adviser to Trinity
House, the body which has charge of Great Britain's lighthouse service.
Nor did he carry his discoveries to the point of practical application.
As soon as he discovered one principle, he set out in pursuit of others,
leaving the practical application to the future.
Faraday loved the beauty of nature. The sunset he called the scenery of
heaven. He saw the beauty of electricity, which he said lies not in its
mystery, but in the fact that it is under law and within the control of
the human intellect.
A Wonderful Law of Nature
Not long after Faraday made his first dynamo, Robert Mayer, a physician
from Germany, was making a voyage to the East Indies which proved to be
a voyage of discovery. He had sailed as the ship's physician, and after
some months an epidemic broke out among the ship's company. In his
treatment he drew blood from the veins of the arms. He was startled to
see bright-red blood issue from the veins. He might almost have believed
that he had opened an artery by mistake. It was soon explained to him by
a physician who had lived long in the tropics that the blood in the
veins of the natives, and of foreigners as well, in the tropics is of
nearly the same color as arterial blood. In colder climates the venous
blood is much darker than the arterial.
He reasoned upon this curious fact for some time, and came to the
conclusion that the human body does not make heat out of nothing, but
consumes fuel. The fuel is consumed in the blood, and there the heat is
produced. In the tropics less heat is needed, less fuel is consumed, and
therefore there is less change in the color of the blood.
When a man works he uses up fuel. If a blacksmith heats a piece of iron
by hammering, the heat given to the iron and the heat produced in his
body are together equal to the heat of the fuel consumed in his blood.
The work a man does, as well as the heat of his body, comes from the
burning of the fuel in his blood.
What is true of a man is true of an engine. The work the engine does, as
well as the heat it produces, comes from the heat of the fuel in the
furnace. Mayer found that one hundred pounds of coal in a good working
engine produces the same amount of heat as ninety-five pounds in an
engine that is not working. In the working engine the heat of the five
pounds of coal is used up in the work of running the engine, and
therefore does not heat the engine. Heat that is used in running the
engine is no longer heat, but work. So Mayer said the heat is not
destroyed, but only changed into work. He said, further, that the work
of running the engine may be changed again into heat.
Mayer's theory was opposed by many scientific men of Europe. One great
scientist said to him that if his theory were correct water could be
warmed by shaking. He remembered what the helmsman had remarked to him
on the voyage to Java, that water beaten about by a storm is warmer than
quiet sea-water; but he said nothing. He went to his laboratory, tried
the experiment, and some weeks later returned, exclaiming: "It is so! It
is so!" He had warmed water simply by shaking it.
These results mean that work or energy cannot be destroyed. Though it
changes form in many ways, it is never destroyed. Neither can man create
energy; he can only direct its changes as the engineer, by the motion of
his finger in opening a valve, sets the locomotive in motion. He does
not move the locomotive. He directs the energy already in the steam.
Since the time of Galileo, men had caught now and then a glimpse of this
great law. Galileo had stated his law of machines; that, when a machine
does work, a man or a horse or some other power does an equal amount of
work upon the machine. Count Rumford had performed his experiment with
the cannon, showing that heat is produced by the work of a horse. Davy
had proved that, in the voltaic battery, something must be used up to
produce the current--the mere contact of the metals is not sufficient.
Faraday had said that in no case is there a production of electrical
power without something being used up to supply it. Mayer stated clearly
this law of energy when he said that energy cannot be created or
destroyed, but only changed from one form to another.
And yet inventors have not learned the meaning of this law. They
continue trying to invent perpetual-motion machines--machines that will
produce work from nothing. This is what a perpetual-motion machine would
be if such a machine were possible. For a machine without friction is
impossible, and friction means wasted work--work changed into heat. A
machine to keep itself running and supply the work wasted in friction
must produce work from nothing. The great law of nature is that you
cannot get something for nothing. Whether you get work, heat,
electricity, or light, something must be used up to produce it. For
whatever you get out of a machine you must give an equivalent. This law
cannot be evaded, and from it there is no appeal.