John Lord.

Beacon Lights of History, Volume 14 The New Era; A Supplementary Volume, by Recent Writers, as Set Forth in the Preface and Table of Contents online

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another circuit containing a galvanometer, - a device for showing the
presence of an electric current and measuring its strength, - but failed
to obtain any result. He looked for such results only when the current
had been fully established in the active circuit. Undismayed by failure,
he reasoned that probably effects were present, but that they were too
small to be observed owing to the feeble inducing current employed. He
therefore increased the strength of the current in the active wire; but
still with no results.

Again and again he interrogates nature, but unsuccessfully. At last he
notices that there is a slight movement of the galvanometer needle at
the moment of making and breaking the circuit. Carefully repeating his
experiments in the light of this observation, he discovers the important
fact that it is only at the moment a current is increasing or decreasing
in strength - at the moment of making or breaking a circuit - that the
active circuit is capable of producing a current in a neighboring
inactive circuit by induction. This was an important discovery, and in
the light of his after-knowledge was correctly regarded as a solution of
the production of electricity from magnetism.

Observing that the galvanometer needle momentarily swings in one
direction on making the circuit, and in the opposite direction on
breaking it, he establishes the fact that the current induced on making
flows in the opposite direction to the inducing current, and that
induced on breaking flows in the same direction as the inducing current.

Having thus established the fact of current induction, he makes the step
of substituting magnets for active circuits; a simple step in the light
of our present knowledge, but a giant stride at that time. Remembering
that current induction, or, as he called it, voltaic current induction,
takes place only while some effect produced by the current is either
increasing or decreasing, he moves coils of insulated wire towards or
from magnet poles, or magnet poles towards or from coils of wire, and
shows that electric currents are generated in the coils while either the
coils or the magnets are in motion, but cease to be produced as soon as
the motion ceases. Moreover, these magnetically induced currents differ
in no respects from other currents, - for example, those produced by the
voltaic pile, - since, like the latter, they produce sparks, magnetize
bars of steel, or deflect the needle of a galvanometer. In this manner
Faraday solved the great problem. He had produced electricity directly
from magnetism!

With, perhaps, the single exception of the discovery by Oersted, in
1820, of the invariable relation existing between an electric current
and magnetism, this discovery of Faraday may be justly regarded as the
greatest in this domain of physical science. These two master minds in
scientific research wonderfully complemented each other. Oersted showed
that an electric current is invariably attended by magnetic effects;
Faraday showed that magnetic changes are invariably attended by electric
currents. Before these discoveries, electricity and magnetism were
necessarily regarded as separate branches of physical science, and were
studied apart as separate phenomena. Now, however, they must be regarded
as co-existing phenomena. The ignorance of the scientific world had
unwittingly divorced what nature had joined together.

In view of the great importance of Faraday's discovery, we shall be
justified in inquiring, though somewhat briefly, into some of the
apparatus employed in this historic research. Note its extreme
simplicity. In one of his first successful experiments he wraps a coil
of insulated wire around the soft iron bar that forms the armature or
keeper of a permanent magnet of the horse-shoe type, and connects the
ends of this coil to a galvanometer. He discovers that whenever the
armature is placed against the magnet poles, and is therefore being
rendered magnetic by contact therewith, the deflection of the needle of
the galvanometer shows that the coiled wire on the armature is traversed
by a current of electricity; that whenever the armature is removed from
the magnet poles, and is therefore losing its magnetism, the needle of
the galvanometer is again deflected, but now in the opposite direction,
showing that an electric current is again flowing through the coiled
wire on the armature, but reversed in direction. He notices, too, that
these effects take place only while changes are going on in the strength
of the magnetism in the armature, or when magnetic flux is passing
through the coils; for, the galvanometer needle comes to rest, and
remains at rest as long as the contact between the armature and the
poles remains unbroken.

In another experiment he employs a simple hollow coil, or helix, of
insulated wire whose ends are connected with a galvanometer. On suddenly
thrusting one end of a straight cylindrical magnet into the axis of the
helix, the deflection of the galvanometer needle showed the presence of
an electric current in the helix. The magnet being left in the helix,
the galvanometer needle came to rest, thus showing the absence of
current. When the bar magnet was suddenly withdrawn from the helix, the
galvanometer needle was again deflected, but now in the opposite
direction, showing that the direction of the current in the helix had
been reversed.

The preceding are but some of the results that Faraday obtained by
means of his experimental researches in the direct production of
electricity from magnetism. Let us now briefly examine just what he was
doing, and the means whereby he obtained electric currents from
magnetism. We will consider this question from the views of the present
time, rather than from those of Faraday, although the difference between
the two are in most respects immaterial.

Faraday knew that the space or region around a magnet is permeated or
traversed by what he called magnetic curves, or lines of magnetic force.
These lines are still called "lines of magnetic force," or by some
"magnetic streamings" "magnetic flux," or simply "magnetism." They are
invisible, though their presence is readily manifested by means of iron
filings. They are present in every magnet, and although we do not know
in what direction they move, yet in order to speak definitely about
them, it is agreed to assume that they pass out of every magnet at its
north-seeking pole (or the pole which would point to the magnetic north,
were the magnet free to move as a needle), and, after having traversed
the space surrounding the magnet, reenter at its south-seeking pole,
thus completing what is called the magnetic circuit. Any space traversed
by lines of magnetic force is called a magnetic field.

But it is not only a magnet that is thus surrounded by lines of
magnetic force, or by ether streamings. The same is true of any
conductor through which an electric current is flowing, and their
presence may be shown by means of iron filings. If an active
conductor - a conductor conveying an electric current, as, for example, a
copper wire - be passed vertically through a piece of card-board, or a
glass plate, iron filings dusted on the card or plate will arrange
themselves in concentric circles around the axis of the wire. It
requires an expenditure of energy both to set up and to maintain these
lines of force. It is the interaction of their lines of force that
causes the attractions and repulsions in active movable conductors.
These lines of magnetic force act on magnetic needles like other lines
of magnetic force and tend to set movable magnetic needles at right
angles to the conducting wire.

The setting up of an electric current in a conducting wire is,
therefore, equivalent to the setting up of concentric magnetic whirls
around the axis of the wire, and anything that can do this will produce
an electric current. For example, if an inactive conducting wire is
moved through a magnetic field; it will have concentric circular whirls
set up around it; or, in other words, it will have a current generated
in it as a result of such motion. But to set up these whirls it is not
enough that the conducting wire be moved along the lines of force in the
field. In such a case no whirls are produced around the conductor. The
conductor must be moved so as to cut or pass through the lines of
magnetic force. Just what the mechanism is by means of which the cutting
of the lines of force by the conductor produces the circular magnetic
whirls around it, no man knows any more than he knows just what
electricity is; but this much we do know, - that to produce the circular
whirls or currents in a previously inactive conductor, the lines of
force of some already existing magnetic field must be caused to pass
through the conductor, and that the strength of the current so produced
is proportional to the number of lines of magnetic force cut in a given
time, say, per second; or, in other words, is directly proportional to
the strength of the magnetic field, and to the velocity and length of
the moving conductor.

Or, briefly recapitulating: Oersted showed that an electric current,
passed through a conducting circuit, sets up concentric circular whirls
around its axis; that is, an electric current invariably produces
magnetism; Faraday showed, that if the lines of magnetic force, or
magnetism, be caused to cut or pass through an inactive conductor,
concentric circular whirls will be set up around the conductor; that is,
lines of magnetic force passed across a conductor invariably set up an
electric current in that conductor.

The wonderful completeness of Faraday's researches into the production
of electricity from magnetism may be inferred from the fact that all
the forms of magneto-electric induction known to-day - namely,
self-induction, or the induction of an active circuit on itself; mutual
induction, or the induction of an active circuit on a neighboring
circuit; and electro-magnetic induction, and magneto-electric induction,
or the induction produced in conductors through which the magnetic flux
from electro and permanent magnets respectively is caused to pass - were
discovered and investigated by him. Nor were these investigations
carried on in the haphazard, blundering, groping manner that
unfortunately too often characterizes the explorer in a strange country;
on the contrary, they were singularly clear and direct, showing how
complete the mastery the great investigator had over the subject he was
studying. It is true that repeated failures frequently met him, but
despite discouragements and disappointments he continued until he had
entirely traversed the length and breadth of the unknown region he was
the first to explore.

Let us now briefly examine Faraday's many remaining discoveries and
inventions. Though none of these were equal to his great discovery, yet
many were exceedingly valuable. Some were almost immediately utilized;
some waited many years for utilization; and some have never yet been
utilized. We must avoid, however, falling into the common mistake of
holding in little esteem those parts of Faraday's work that did not
immediately result either in the production of practical apparatus, or
in valuable applications in the arts and sciences, or those which have
not even yet proved fruitful. Some discoveries and devices are so far
ahead of the times in which they are produced that several lifetimes
often pass before the world is ready to utilize them. Like immature or
unripe fruit, they are apt to die an untimely death, and it sometimes
curiously happens that, several generations after their birth, a
subsequent inventor or discoverer, in honest ignorance of their prior
existence, offers them to the world as absolutely new. The times being
ripe, they pass into immediate and extended public use, so that the
later inventor is given all the credit of an original discovery, and the
true first and original inventor remains unrecognized.

We will first examine Faraday's discovery of the relations existing
between light and magnetism. Though the discovery has not as yet borne
fruit in any direct practical application, yet it has proved of immense
value from a theoretical standpoint. In this investigation Faraday
proved that light-vibrations are rotated by the action of a magnetic
field. He employed the light of an ordinary Argand lamp, and polarized
it by reflection from a glass surface. He caused this polarized light to
pass through a plate of heavy glass made from a boro-silicate of lead.
Under ordinary circumstances this substance exerted no unusual action on
light, but when it was placed between the poles of a powerful
electro-magnet, and the light was passed through it in the same
direction as the magnetic flux, the plane of polarization of the light
was rotated in a certain direction.

Faraday discovered that other solid substances besides glass exert a
similar action on a beam of polarized light. Even opaque solids like
iron possess this property. Kerr has proved that a beam of light passed
through an extremely thin plate of highly magnetic iron has its plane of
polarization slightly rotated. Faraday showed that the power of rotating
a beam of polarized light is also possessed by some liquids. But what is
most interesting, in both solids and liquids, is that the direction of
the rotation of the light depends on the direction in which the
magnetism is passing, and can, therefore, be changed by changing the
polarity of the electro-magnet.

Faraday did not seem to thoroughly understand this phenomenon. He spoke
as if he thought the lines of magnetic force had been rendered luminous
by the light rays; for, he announced his discovery in a paper entitled,
"Magnetization of Light and the Illumination of the Lines of Magnetic
Force." Indeed, this discovery was so far ahead of the times that it was
not until a later date that the results were more fully developed,
first by Kelvin, and subsequently by Clerk Maxwell. In 1865, two years
before Faraday's death, Maxwell proposed the electro-magnetic theory of
light, showing that light is an electro-magnetic disturbance. He pointed
out that optical as well as electro-magnetic phenomena required a medium
for their propagation, and that the properties of this medium appeared
to be the same for both. Moreover, the rate at which light travels is
known by actual measurement; the rate at which electro-magnetic waves
are propagated can be calculated from electrical measurements, and these
two velocities exactly agree. Faraday's original experiment as to the
relation between light and magnetism is thus again experimentally
demonstrated; and, Maxwell's electro-magnetic theory of light now
resting on experimental fact, optics becomes a branch of electricity. A
curious consequence was pointed out by Maxwell as a result of his
theory; namely, that a necessary relation exists between opacity and
conductivity, since, as he showed, electro-magnetic disturbances could
not be propagated in substances which are conductors of electricity. In
other words, if light is an electro-magnetic disturbance, all conducting
substances must be opaque, and all good insulators transparent. This we
know to be the fact: metallic substances, the best of conductors, are
opaque, while glass and crystals are transparent. Even such apparent
exceptions as vulcanite, an excellent insulator, fall into the law,
since, as Graham Bell has recently shown, this substance is remarkably
transparent to certain kinds of radiant energy.

In 1778, Brugmans of Leyden noticed that if a piece of bismuth was held
near either pole of a strong magnet, repulsion occurred. Other observers
noticed the same effect in the case of antimony. These facts appear to
have been unknown to Faraday, who, in 1845, by employing powerful
electro-magnets rediscovered them, and in addition showed that
practically all substances possess the power of being attracted or
repelled, when placed between the poles of sufficiently powerful
magnets. By placing slender needles of the substances experimented on
between the poles of powerful horse-shoe magnets, he found that they were
all either attracted like iron, coming to rest with their greatest
length extending between the poles; or, like bismuth, were apparently
repelled by the poles, coming to rest at right angles to the position
assumed by iron. He regarded the first class of substances as attracted,
and the second class as repelled, and called them respectively
paramagnetic and diamagnetic substances. In other words, paramagnetic
substances, like iron, came to rest axially (extending from pole to
pole), and diamagnetic substances, like bismuth, equatorially (extending
transversely between the poles). He reserved the term magnetic
substances to cover the phenomena of both para and dia-magnetism. He
communicated the results of this investigation to the Royal Society in a
paper on the "Magnetic Condition of All Matter," on Dec. 18, 1845.

The properties of paramagnetism and diamagnetism are not possessed by
solids only, but exist also in liquids and gases. When experimenting
with liquids, they were placed in suitable glass vessels, such as watch
crystals, supported on pole pieces properly shaped to receive them.
Under these circumstances paramagnetic liquids, such as salts of iron or
cobalt dissolved in water, underwent curious contortions in shape, the
tendency being to arrange the greater part of their mass in the
direction in which the flux passed; namely, directly between the poles.
Diamagnetic liquids, such as solutions of salts of bismuth and antimony,
in a similar manner, arranged the greater part of their mass in
positions at right angles to this direction, or equatorially.

At first Faraday attributed the repulsion of diamagnetic substances to a
polarity, separate and distinct from ordinary magnetic polarity, for
which he proposed the name, diamagnetic polarity. He believed that when
a diamagnetic substance is brought near to the north pole of a magnet, a
north pole was developed in its approached end, and that therefore
repulsion occurred. He afterwards rejected this view, though it has
been subsequently adopted by Weber and Tyndall, the latter of whom
conducted an extended series of experiments on the subject. The majority
of physicists, however, at the present time, do not believe in the
existence of a diamagnetic polarity. They point out that the apparent
repulsion of diamagnetic substances is due to the fact that they are
less paramagnetic than the oxygen of the air in which they are
suspended.

During this investigation Faraday observed some phenomena that led him
to a belief in the existence of another form of force, distinct from
either paramagnetic or diamagnetic force, which he called the
magne-crystallic force. He had been experimenting with some slender
needles of bismuth, suspending them horizontally between the poles of an
electro-magnet. Taking a few of these cylinders at random from a greater
number, he was much perplexed to find that they did not all come to rest
equatorially, as well-behaved bars of diamagnetic bismuth should do,
though, if subjected to the action of a single magnetic pole, they did
show this diamagnetic character by their marked repulsion. After much
experimentation, he ascribed this phenomenon to the crystalline
condition of the cylinder. By experimenting with carefully selected
groups of crystals of bismuth, he believed he could trace the cause of
the phenomenon to the action of a force which he called the
magne-crystallic force.

Extended experiments carried on by Pl├╝cker on the influence of
magnetism on crystalline substances led him to believe that a close
relation exists between the ultimate forms of the particles of matter
and their magnetic behavior. This subject is as yet far from being fully
understood.

There was another series of investigations made by Faraday between the
years 1831 and 1840, that has been wonderfully utilized, and may
properly be ranked among his great discoveries. We allude to his
researches on the laws which govern the chemical decomposition of
compound substances by electricity. The fact that the electric current
possesses the power of decomposing compound substances was known as
early as 1800, when Carlisle and Nicholson separated water into its
constituent elements, by the passage of a voltaic current. Davy, too, in
1806, had delivered his celebrated discourse "On Some Chemical Agencies
of Electricity," and in 1807, had announced his great discovery of the
decomposition of the fixed alkalies.

Faraday showed that the amount of chemical action produced by
electricity is fixed and definite. In order to be able to measure the
amount of this action, he invented an instrument which he called a
voltameter, or a volta-electrometer. It consisted of a simple device for
measuring the amount of hydrogen and oxygen gases liberated by the
passage of an electric current through water acidulated with sulphuric
acid. He showed, by numerous experiments, that the decomposition
effected is invariably proportional to the amount of electricity
passing; that variations in the size of the electrodes, in the pressure,
or in the degree of dilution of the electrolyte, had nothing to do with
the result, and that therefore a voltameter could be employed to
determine the amount of electricity passing in a given circuit. He also
demonstrated that when a current is passed through different
electrolytes (compound substances decomposed by the passage of
electricity), the amount of the decompositions are chemically equivalent
to each other.

The extent of Faraday's work in the electro-chemical field may be judged
by considering some of the terms he proposed for its phenomena, most of
which, with some trifling exceptions, are still in use. It was he who
gave the name electrolysis to decomposition by the electric current; he
also proposed to call the wires, or conductors connected with the
battery, or other electric source, the electrodes, naming that one which
was connected with the positive terminal, the anode, and that one
connected with the negative terminal, the cathode. He called the
separate atoms or groups of atoms into which bodies undergoing
electrolysis are separated, the radicals, or ions, and named the
electro-positive ions, which appear at the cathode, the kathions, and
the electro-negative radicals which appear at the anode, the anions.

There were many other researches made by Faraday, such as his
experiments on disruptive electric discharges, his investigations on the
electric eel, his many researches on the phenomena both of frictional
electricity and of the voltaic pile, his investigations on the contact
and chemical theories of the voltaic pile, and those on chemical
decomposition by frictional electricity; these are but some of the mere
important of them. Those we have already discussed will, however, amply
suffice to show the value of his work. Rather than take up any others,
let us inquire what influence, if any, the various groups of discoveries
we have already discussed have exerted on the electric arts and sciences
in our present time. What practical results have attended these
discoveries? What actual, useful, commercial machines have been based on
them? What useful processes or industries have grown out of them?

And, first, as to actual commercial machines. These researches not only
led to the production of dynamo-electric machines, but, in point of
fact, Faraday actually produced the first dynamo. A dynamo-electric
machine, as is well known, is a machine by means of which mechanical
energy is converted into electrical energy, by causing conductors to cut
through, or be cut through by, lines of magnetic force; or, briefly, it
is a machine by means of which electricity is readily obtained from
magnetism.

Faraday's invention of the first dynamo is interesting because at the
same time he made the invention he solved a problem which up to his time
had been the despair of the ablest physicists and mathematicians. This
was the phenomenon of Arago's rotating disc. It was briefly as follows:
If a copper disc be rotated above a magnet, the needle tends to follow
the plate in its rotation; or, if a copper plate be placed at rest above
or below an oscillating magnet, it tends to check its oscillations and
bring the needle quickly to rest. Faraday investigated these phenomena
and soon discovered that a copper disc rotated below two magnet poles
had electric currents generated in it, which flowed radially through the
disc between its circumference and centre. By placing one end of a


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Online LibraryJohn LordBeacon Lights of History, Volume 14 The New Era; A Supplementary Volume, by Recent Writers, as Set Forth in the Preface and Table of Contents → online text (page 22 of 26)