f 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 bo

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 ea

nd 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

ok 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 Si

t Ru

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 gat

tors 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 ac

. 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

ng 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

xperiments 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

1791 he was made a Count of the Holy Roman Empire, a

s Experiment w

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

ERIMENT WITH THE CANNON, MA

ound the track; the work the horses do is ch

n produced. In two hours and thirty minutes the water actually boiled. Astonishment was expressed in the face

ge 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 la

vellous 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

a

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,

rely 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 met

sly 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 w

veries, but the greatest w

rly 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.

mbed Vesuvius, visited Rome, and saw a glow-wor

rmined that he would not be conquered by the master passion. In fact, he

est and plague

urse that ofte

s L

cts the madman

dunce is ful

wise man always

t ever o'er th

s L

orrect 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 whateve

y 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 m

Electrical

h, 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

nd Electr

ound 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,

hrough 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

ERSTED'S

ass-needle toward the north causes the ne

on of Josep

CURRENT FLOWING THROU

picking up i

N WITH A CURRENT FLOWING

pè

ement in France, André Marie Ampère made a discovery of equal importance. Oersted had discovered

had moved from his country home to Lyons and become a justice of the peace. In the destru

ll the studies of the schools. But now his strong mind failed. For a year he wandered about mechanically piling up heaps of

o 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

RRENTS FLOWING IN SAME DI

RENTS FLOWING IN OPPOSITE

th magnetic pole for the same reason that a coil of wire has magnetic poles; that these poles are caused by the curr

r we measure an electric current, for ele

r

er-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

ugh 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

ynamo. 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 t

ARAGO'S

e magnet whirls also, though it

First Elec

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 t

SPINS ROUND A WIRE THROUGH WH

urrent Produc

ctricity." An electric current would magnetize iron. Would n

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

IRE IT CAUSES A CURRENT TO FLOW IN THE COIL, BUT

d by permission o

ing of this discovery, wrote

the magn

t Volta's li

draw them f

lesson fro

meet, 'tis

th the ele

current in a wire, but only when t

Measuring an E

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 coi

OF WIRE AROUND

current is flowing, and

meter, and may be used to tell when a current is flow

duced by the Magnetic F

. 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 n

t 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 co

RADAY'S IN

rimary coil causes a changing magnetic field, and

d by permission o

econd 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 call

PARATUS OF FARADAY IN

e shown here. The instrument on the le

ay's

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 c

RADAY'S FI

per disk as it whirls betw

on of Josep

before. In these ten days the foundation was laid for the induction-coil, modern dynamo-electr

BORATORY, WHERE THE

lor drawing by Mi

lightly touching were connected to the ends of a secondary coil. A spark passed between the charcoal points w

HE FIRST

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

IS THE SPACE AROUND A MAGNET

magnet arrange themselves

IC FIELD OF A

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 gas

attery 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. Th

ffect 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 L

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 wa

ferent effects being due to difference in pressure and quantity. "But in no case," said Faraday, "not even in those o

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 bod

. He saw the beauty of electricity, which he said lies not in its mystery, but

ful Law

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 b

eat out of nothing, but consumes fuel. The fuel is consumed in the blood, and there the heat is produced. In the

he iron and the heat produced in his body are together equal to the heat of the fuel consumed in his bloo

ces 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 engin

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 nothi

. Neither can man create energy; he can only direct its changes as the engineer, by the motion of his finger in openin

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

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 cann