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 Plücker 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
conducting circuit on the axis of the disc, and the other end on its
circumference, he succeeded in drawing off a continuous electric current
generated from magnetism, and thus produced the first dynamo. This was
in 1831. Faraday produced many other dynamos besides this simple
disc machine.
Although the disc dynamo in its original form was impracticable as a
commercial machine, yet it was not only the forerunner of the dynamo,
but was, in point of fact, the first machine ever produced that is
entitled to be called a dynamo. He generously left to those who might
come after him the opportunity to avail themselves of his wonderful
discovery. "I have rather, however," he says, "been desirous of
discovering new facts and new relations dependent on magneto-electric
induction than of exalting the force of those already obtained, being
assured that the latter would find their development hereafter." How
profoundly prophetic! Could the illustrious investigator see the
hundreds of thousands of dynamos that are to-day in all parts of the
world engaged in converting millions of horse-power of mechanical energy
into electric energy, he would appreciate how marvellously his
successors have "exalted the force" of some of the effects he had so
ably shown the world how to obtain.
Faraday lived to see his infant dynamo, the first of its kind, developed
into a machine not only sufficiently powerful to maintain electric arc
lights, but also into a form sufficiently practicable to be continuously
engaged in producing such light, in one of the lighthouses on the
English coast. Holmes produced such a machine in 1862, or some years
before Faraday's death. It was installed under the care of the Trinity
House, at the Dungeness Lighthouse, in June, 1862, and continued in use
for about ten years. When this machine was shown to Faraday by its
inventor, the veteran philosopher remarked, "I gave you a baby, and you
bring me a giant."
The alternating-current transformer is another gift of Faraday to the
commercial world. As is well known, this instrument is a device for
raising or lowering electric pressure. The name is derived from the fact
that the instrument is capable of taking in at one pressure the electric
energy supplied to it, and giving it out at another pressure, thus
transforming it. Faraday produced the first transformer during his
investigations on voltaic-current induction. The modern
alternating-current transformer, though differing markedly in minor
details from Faraday's primitive instrument, yet in general details is
essentially identical with it. The enormous use of both step-up and
step-down transformers--transformers which respectively induce currents
of higher and of lower electromotive forces in their secondary coils
than are passed through their primaries--shows the great practical value
of this invention. The wonderful growth of the commercial applications
of alternating currents during the past few decades would have been
impossible without the use of the alternating-current transformer.
It is an interesting fact that it was not in the form of the step-down
alternating-current transformer that Faraday's discovery of
voltaic-current induction was first utilized, but in the form of a
step-up transformer, or what was then ordinarily called an induction
coil. As early as 1842, Masson and Bréguet constructed an induction
coil by means of which minute sparks could be obtained from the
secondary, in vacuo. In 1851, Ruhmkorff constructed an induction coil so
greatly improved, by the careful insulation of its secondary circuit,
that he could obtain from it torrents of long sparks in ordinary air.
The Ruhmkorff induction coil has in late years been greatly improved
both by Tesla and Elihu Thomson, who, separately and independently of
each other, have produced excellent forms of high-frequency
induction coils.
Induction coils have long been in use for purposes of research, and in
later years have been employed in the production both of the Röntgen
rays used in the photography of the invisible, and the electro-magnetic
waves used in wireless telegraphy.
Röntgen's discovery was published in 1895. It was rendered possible by
the prior work of Geissler and Crookes on the luminous phenomena
produced by the passage of electric discharges through high vacua in
glass tubes. Röntgen discovered that the invisible rays, or radiation,
emitted from certain parts of a high-vacuum tube, when high-tension
discharges from induction coils were passing, possessed the curious
property of traversing certain opaque substances as readily as light
does glass or water. He also discovered that these rays were capable of
exciting fluorescence in some substances,--that is, of causing them to
emit light and become luminous,--and that these rays, like the rays of
light, were capable of affecting a photographic plate. From these
properties two curious possibilities arose; namely, to see through
opaque bodies, and to photograph the invisible. Röntgen called these
rays X, or unknown rays. They are now almost invariably called by the
name of their distinguished discoverer.
Let us briefly investigate how it is possible both to see and to
photograph the invisible. Shortly after Röntgen's discovery, Edison,
with that wonderful power of finding practical applications for nearly
all discoveries, had invented the fluoroscope,--a screen covered with a
peculiar chemical substance that becomes luminous when exposed to the
Röntgen rays. Suppose, now, between the rays and such a screen be
interposed a substance opaque to ordinary light, as, for example, the
human hand. The tissues of the hand, such as the flesh and the blood,
permit the rays to readily pass through them, but the bones are opaque
to the rays, and, therefore, oppose their passage; consequently, the
screen; instead of being uniformly illumined, will show shadows of the
bones, so that, to an eye examining the screen, it will seem as though
it were looking through the flesh and blood directly at the bones. In a
similar manner, if a photographic plate be employed instead of the
screen, a distinct photographic picture will be obtained.
Both the fluoroscope and the photographic camera have proved an
invaluable aid to the surgeon, who can now look directly through the
human body and examine its internal organs, and so be able to locate
such foreign bodies as bullets and needles in its various parts, or make
correct diagnoses of fractures or dislocations of the bones, or even
examine the action of such organs as the liver and heart.
About 1886, Hertz discovered that if a small Leyden jar is discharged
through a short and simple circuit, provided with a spark-gap of
suitable length, a series of electro-magnetic waves are set up, which,
moving through space in all directions, are capable of exciting in a
similar circuit effects that can be readily recognized, although the two
circuits are at fairly considerable distances apart. Here we have a
simple basic experiment in wireless telegraphy, which, briefly
considered, consists of means whereby oscillations or waves, set up in
free space by means of disruptive discharges, are caused to traverse
space and produce various effects in suitably constructed receptive
devices that are operated by the waves as they impinge on them.
At first a doubt was expressed by eminent scientific men as to the
practicability of successfully transmitting wireless messages through
long distances, since these waves, travelling in all directions, would
soon become too attenuated to produce intelligible signals; but when it
was shown, from theoretical considerations, that these waves when
traversing great distances are practically confined to the space between
the earth's surface and the upper rarified strata of the atmosphere, the
possibility of long-distance wireless telegraphic transmission was
recognized. To increase the distance, it was only necessary either to
increase the energy of the waves at the transmitting station, or to
increase the delicacy of the receiving instruments, or both.
It has been but a short time since both the scientific and the financial
worlds were astounded by the actual transmission of intelligible
wireless signals across the Atlantic, and the name of Marconi will go
down to posterity as the one who first accomplished this great feat.
The principal limit to the distance of transmission lies in the delicacy
of the receiving instruments. The most sensitive are those in which a
telephone receiver forms a part of the receiving apparatus. The almost
incredibly small amount of electric energy required to produce
intelligible speech in an ordinary Bell telephone receiver nearly passes
belief. The work done in lifting such an instrument from its hook to the
ear of the listener, would, if converted into electric energy, be
sufficient to maintain an audible sound in a telephone for 240,000
years! Even extremely attenuated waves may therefore produce audible
signals in such a receiver.
The electric motor was another gift of Faraday to commercial science,
although in this case there are others who can, perhaps, justly claim to
share the honor with him. Faraday's early electric motor consisted
essentially in a device whereby a movable conductor, suspended so as to
be capable of rotation around a magnet pole, was caused to rotate by the
mutual interaction of the magnetic fields of the active conductor and
the magnet. The magnet, which consisted of a bar of hardened steel, was
fixed in a cork stopper, which completely closed the end of an upright
glass tube. A small quantity of mercury was placed in the lower end of
the tube, so as to form a liquid contact for the lower end of a movable
wire, suspended so as to be capable of rotating at its lower extremity
about the axis of the tube. On the passage of an electric current
through the wire, a continuous rotary motion was produced in it, the
direction of which depends both on the direction of the current, and on
the polarity of the end of the magnet around which the rotation occurs.
The great value of the electric motor to the world is too evident to
need any proof. The number of purposes for which electric motors are now
employed is so great that the actual number of motors in daily use is
almost incredible, and every year sees this number rapidly increasing.
The above are the more important machines or devices that have been
directly derived from Faraday's great investigation as to the production
of electricity from magnetism. Let us now inquire briefly as to what
useful processes or industries have been rendered possible by the
existence of these machines.
Apparently one of the most marked requirements of our twentieth-century
civilization is that man shall be readily able to extend the day far
into the night. He can no longer go to sleep when the sun sets, and keep
abreast with his competitors. Of all artificial illuminants yet
employed, the arc and the incandescent electric lights are
unquestionably the best, whether from a sanitary, aesthetic, or truest
economical standpoint. Now, while it is a well-known matter of record
that both arc and incandescent lights were invented long before
Faraday's time, yet it was not until a source of electricity was
invented, superior both in economy and convenience to the voltaic
battery, that either of these lights became commercial possibilities.
Such an electric source was given to the world by Faraday through his
invention of the dynamo-electric machine, and it was not until this
machine was sufficiently developed and improved that commercial electric
lighting became possible. The energy of burning coal, through the
steam-engine, working the dynamo, is far cheaper and more efficient for
producing electricity than the consumption of metals through the
voltaic pile.
It is characteristic of the modesty of Faraday that when, in
after-life, he heard inventors speaking of their electric lights, he
refrained from claiming the electric light as his own, although, without
the machine he taught the world how to construct, commercial lighting
would have been an impossibility.
The marvellous activity in the electric arts and sciences, which
followed as a natural result of Faraday giving to the world in the
dynamo-electric machine a cheap electric source, naturally leads to the
inquiry as to whether at a somewhat later day a yet greater revolution
may not follow the production of a still cheaper electric source. In
point of fact such a discovery is by no means an impossibility. When a
dynamo-electric machine is caused to produce an electric current by the
intervention of a steam-engine, the transformation of energy which takes
place from the energy of the coal to electric energy is an extremely
wasteful one. Could some practical method be discovered by means of
which the burning of coal liberates electric energy, instead of heat
energy, an electric source would be discovered that would far exceed in
economy the best dynamo in existence. With such a discovery what the
results would be no one can say; this much is certain, that it would,
among other things, relegate the steam-engine to the scrap-heap, and
solve the problem of aerial navigation.