Electricity, Magnetism, and Galvanism mutually convertible.--The
Force co-extensive with Nature.--Uses of Thunder-storms.--Languor
from Want of Electricity.--Frictional and Voltaic
Electricity.--Origin of the Name.--Structure of the Voltaic
Pile.--A simple Example of the Pile.--Nerves of a Frog’s Leg.--The
Electric Shock, and how to produce it.--The Electric Jar and
Battery.--Animal Electricity.--The Torpedo and Electric
Eel.--Structure of the Electric Apparatus.--The Electric Spark
obtained from both Fishes.--Channels of Electricity in the
Body.--The Will and the Muscles.--Electricity the conducting
Agent.--The Human Body permeated by Nerves.--Telegraph Wires and
the Nervous System.--Lightning and the Electric Spark.--The
Electric Light and its Power.--The Fire-fly, the Glow-worm, and the
luminous Inhabitants of the Sea.--Magnetism and Diamagnetism.--The
Electric Telegraph and the Compass.--The Principle identical in
both Instruments.
ELECTRICITY AND MAGNETISM.
It has long been known that Electricity, Galvanism, and Magnetism are
but different manifestations of the same force, and that one can be
converted into the other at will. It is also known that this wonderful
and most important principle lies latent in everything, and only needs
the proper machinery to evoke it.
The few following illustrations are intended to show its prevalence in
Nature, and that human art does not create, but only makes manifest a
power that exists, but lies latent until called forth.
Without going into details, which would occupy the whole of such a
volume as this, I may mention that Electricity saturates all the
material creation, and that even man himself is not only a reservoir of
electricity, but that he feels positively ill if the normal amount be
not supplied.
Take, for example, the hours that precede a thunder-storm. We feel
languid and depressed. We cannot bring our thoughts together. We are
almost incapable even of bodily labour. The reason is, that the portion
of the earth on which we live has parted with some of its electricity,
and has drawn it out of our bodies.
Then comes the welcome thunder-storm; clouds overcharged with
electricity come to restore the balance. The lightning flashes from the
clouds to the earth as soon as they are near enough; the rain falls,
carrying with it stores of silent electricity; and in an hour or two all
seems changed.
The air, which hitherto seemed to afford no nourishment to the lungs, is
bracing and invigorating. The nervous system recovers its tension, and
the brain can act without a painful effect. All Nature seems to put on a
different aspect, and brightness and vigour take the place of dulness
and languor.
[Illustration: GALVANISING A FROG’S LEG.]
[Illustration: VOLTAIC PILE.]
By a strange coincidence, there is just such a lack of electricity as I
am writing, and the barometer has rapidly sunk to such a degree that a
storm seems inevitable.
One of the chief difficulties in dealing with such a subject as this is
to know where to begin. We will, however, do our best to take a general
view of it, without going into details.
Many centuries ago it was well known that amber, if rubbed with a dry
cloth, would first attract, and then repel, various small and light
substances. Indeed, the Greek word for amber, namely, _Elektron_, has
given its name to the modern science of Electricity. Many other
substances, such as glass, sealing-wax, &c., possess the same property.
This frictional electricity is but transient, the electric fluid, if we
may be allowed to use the term, being driven out by main force from the
material in which it was latent, just as fire is procured by the
friction of two dry sticks. There is, however, a form of Electricity
called Galvanism, from its discoverer, Galvani, who, somewhere about
1790, discovered that the limbs of a dead frog might be excited to
action by electricity applied to the nerves.
Afterwards, Volta of Pavia, from whom the Voltaic Pile is named, took up
Galvani’s discoveries, and produced electricity without friction, by the
contact of differently conducting substances.
The right-hand figure represents the Voltaic Pile. It is composed of a
series of plates arranged in the following manner--Zinc, Silver, and
Cloth, the whole being moistened with diluted acid. Copper will answer
the purpose nearly as well as silver, and is not so costly. A very
simple mode of demonstrating the presence of electricity is by taking a
piece of zinc and a silver coin, and placing one below and the other
above the tongue. If the two be then brought together, a very peculiar
taste is perceived, and a sudden flash of light seems to pass across the
eyes.
The illustration represents on the right hand the Voltaic Pile as at
present made, and on the left are the two hind-legs of a frog, with the
upper part of the nerves made bare for the purpose of experimenting. The
dotted lines show the extent of the movements of the leg when the
galvanic current is passed through the nerves.
* * * * *
NOW we come to a plan whereby electricity can be accumulated, or locked
up, so to speak, and be discharged at once with a definite shock instead
of being poured away by degrees. This can be done in many ways, the most
common being that which is known by the name of the Electric Jar. It is
a glass vessel coated within and without with tin-foil, and having a
metal rod passing through the cork in such a way that while the lower
end is in contact with the inner coating of tin-foil, the other end is
guarded by a ball.
Electricity is now poured into the interior of the jar, and, when
contact is made between the inner and outer coatings, a sudden discharge
takes place. If a number of persons hold each other’s hands, and those
who form the two extremities touch the outer coating and the ball which
communicates with the inner coating, a sharp discharge is at once made,
passing through all the bodies, and inflicting a smart shock, especially
at the elbows.
Similar effects can be produced with the Voltaic Battery, but, as that
instrument has already been figured, the Electric Jar has been selected.
Of course any number of such jars can be connected together, and the
shock will be proportionately increased in intensity.
* * * * *
IN Nature we have several-parallels. Putting aside the obvious one of a
lightning-flash, which has already been mentioned, we pass to two
remarkable examples of the capability of animal structure to produce
electricity, to store it up, so to speak, and discharge it at will. Both
these creatures are fishes, one belonging to the Skates or Rays, and the
other to the Eels.
[Illustration:
TORPEDO.
ELECTRIC EEL.
ELECTRIC BATTERY.]
The upper figure on the left-hand side of the illustration represents
the Torpedo, sometimes called the Cramp-fish, Numb-fish, or Electric
Ray. Fortunately for us, it is but seldom found on our coasts, but it is
tolerably common in the warmer parts of the world.
The electric organ in this fish is double, and so large that its shape
can easily be recognised even through the skin. It is made up of a vast
number of discs arranged upon each other in columns like the metallic
portions of the Voltaic Pile, and separated from each other by delicate
membranes, which take the place of the cloth. When I mention that more
than eleven hundred columns have been found in a single Torpedo, and
that each column contains several hundred discs, it may be imagined that
the shock which such a creature can give must be a very powerful one.
The object of this power seems to be analogous to that of the venomous
serpent, _i.e._ to enable the creature to secure its prey by either
killing it or rendering it temporarily insensible by an electric shock.
As if to show that the delivery of the shock is achieved by an exertion
of will, observers have noticed that just before the shock is delivered,
the eyes are depressed in the head like those of a toad when swallowing
a large insect.
* * * * *
A STILL more powerfully electric animal is the Electric Eel of Southern
America. It sometimes attains a length of six feet, and its electric
organs are four times as proportionately large as those of the torpedo.
There is no doubt as to the object of the electric power of this eel, as
I have often seen it kill fish, and then eat them.
When about to deliver its shock, it curves its body towards the intended
victim, stiffens itself, and with a sort of shudder the electric fluid
is emitted. The fish at which it is aimed never seems to escape, but,
simultaneously with the shudder on the part of the Electric Eel, turns
on its back and lies motionless until it is picked up by its destroyer.
Neither the Torpedo nor the Electric Eel has unlimited stores of
electricity. If irritated into delivering repeated shocks, each
discharge is less powerful than its predecessor, until at last the
creature is almost wholly powerless, and must rest and recruit itself
before it can lay up fresh stores of the electric fluid.
I may add that the electric spark has been obtained from both these
fishes. It was only a small spark, but in such experiments a small spark
is as satisfactory as a large one.
* * * * *
WHAT are the channels by which the electric fluid is transmitted through
our bodies?
They are the nerves, which convey from and to the brain a subtle fluid,
if it may be so called, just as the arteries and veins convey blood to
and from the heart. If any of these nerves be electrified, even after
the death of the animal, or after the separation of a limb from the
body, muscular movements are induced, and the limb moves as if instinct
with life.
Without these nerves we should be unable to feel the severest shock, but
they permeate the body so completely, that not a part of the skin can be
pricked without a nerve being wounded.
It is by means of these conductors that the will is made to act upon the
limbs. The mind, for example, desires the legs to walk, and they do so,
the order being transmitted to them through the nerves.
As a rule, we are unconscious of this process. But, when paralysis takes
place, and the nerves refuse to perform their functions, the will is
absolutely useless, and, however desirous a man may be of walking, he
cannot move a step if the nerves of his legs are paralyzed. In cases
where the paralysis comes on slowly and in detail, the patient mostly
becomes conscious of the part played by the nerves, and feels that his
will can to a certain degree rouse the expiring powers of the nerve
fluid.
This in its turn is but the conductor for another and infinitely more
subtle fluid, of which our space will not allow us to treat, but which
forms the connecting link between body and spirit. Perhaps some of my
readers may have seen those curious preparations of the human form, when
the arteries have been injected with red wax, and the veins with blue
wax, and then the fleshy portions dissolved away by chemical means.
The result is a perfect human form, and even to the very tips of the
fingers and toes the blood-vessels follow the contour of the body. Did
we have means of injecting the nervous system, we should arrive at
similar results, except that the nerves would be found infinitely more
intricate than the veins and arteries. Thus a human being is a series of
human forms, interwoven with each other, and mutually dependent on each
other.
* * * * *
IT is curious to see how the great discoveries of modern days have but
copied Nature.
Take, for example, the network of telegraphic wires which is day by day
spreading itself over the surface of the earth, and the parallel will
at once be visible. Just as the brain transmits its message to the limbs
by means of the nerves, so does the same brain transmit its message
through thousands of miles, by utilising the wires which are but the
rough and coarse imitations of the wonderful nervous system of the human
frame.
* * * * *
THE illustration shows the parallelism as well as can be done by a mere
chart.
[Illustration: NERVES.]
[Illustration: TELEGRAPHIC WIRES.]
On the left-hand side is shown the manner in which a nerve-group is
distributed to different parts of the body. On the right the railway
telegraph wires are seen, and, as the reader will probably remember,
branch wires are carried into the signal boxes, just as branch nerves
are carried to the most distant parts of the body.
* * * * *
I HAVE already mentioned the Electric Spark, and that it is, in fact, a
miniature lightning-flash, the little crackling report being a miniature
thunder-clap. It can be produced by frictional electricity, or by the
voltaic pile in its many variations, or by animal substances alone, as
in the case of the torpedo and electric eel.
We now come to a modification of the spark, whereby a continuous current
of electricity is sent through two charcoal points, and inflames them
with such intensity that the eye cannot look upon its dazzling
whiteness. There is none of the yellowness about it which is so great a
drawback to our artificial lights, whether they be gas, candle, or lamp,
and which makes ladies’ dresses that are really beautiful by day look
dull and almost ugly by night.
It is wonderful to see how the Electric Light kills all other lights.
The brightest gas becomes dull, and its shadow is thrown on the wall
which it formerly illuminated, and the most delicate tints of silks and
satins suddenly display themselves in the blinding whiteness of the
Electric Light.
At present it is too costly to be brought into common use, but its
intensity is so great that serious ideas have been formed of dispensing
with street lamps altogether, and illuminating towns with a few electric
lamps placed at a considerable height, and having their beams reflected
downwards.
[Illustration:
LIGHTNING.
FIRE-FLY.
GLOW-WORM.
ELECTRIC LIGHT.]
London is thought to be a specially fit subject for this mode of
lighting, as the electric beams can pierce the fogs which the gas-lamp
only augments, and give the traveller some hope of finding his way
through the most familiar streets.
* * * * *
IN the illustration the right-hand figure represents the Electric Light
as at present in use. The upper portion of the left-hand side represents
the forked lightning, whose dazzling whiteness is so familiar to us,
even in the noon of a summer’s day.
Below are shown the Fire-fly of warm climates, and the Glow-worm, which,
in our comparatively cool country, cheers the summer evenings with its
pale lamp. As to the source of this mysterious light, which burns
without producing heat sufficient to be recognised by our most delicate
instruments, we know but little.
There are instruments so infinitely more sensitive than the best
thermometer, that they will record instantaneously an increase of heat
if a human being passes in front of them, though at several yards’
distance. Yet no effect is produced on them by any of the Fire-flies or
the Glow-worm. The spectroscope itself gives little or no information,
the spectrum of the light being without bands or bars, and being what is
technically called a “continuous” spectrum.
Last year I tried numbers of Glow-worms with the spectroscope, and
always with the same result. I never saw the Fire-flies alive, but, no
matter what may be the colour of the light, the spectrum, whether of the
Glow-worm or any of the Fire-flies, seems to be always continuous, and
so to give but little information as to its source.
There appears, however, to be little doubt that animal electricity is
the real cause of this curious phenomenon, and that the force which is
expended in the torpedo and electric eel, in giving shocks accompanied
by slight electric sparks, may develop itself in these insects by
producing a continuous light. And just as the electric fishes can emit
or withhold the shock as they please, so can the Fire-flies and
Glow-worms give out or retain the light by which they are so well known.
Then we come to the multitudinous luminous inhabitants of the sea,
which, as many of my readers have probably seen, convert the waves into
rolling masses of living fire.
MAGNETISM.
Now we come to another condition of electrical force, called MAGNETISM.
One form of it is strongly developed in the Loadstone, an ore of iron.
This ore has the property of turning east and west when suspended
freely, it attracts any object made of iron, and can communicate its
powers to iron by merely stroking it. There is in the Museum at Oxford a
splendid specimen of the Loadstone, which has imparted its virtues to
thousands of iron magnets, and has lost none of its virtues by so doing.
All bodies are now known to be magnetic in some way or other. Several,
such as iron, nickel, and one or two other metals, turn north and south
when suspended on a pivot, but the great bulk of other bodies turn east
and west, and are called Diamagnetics.
As we all know, the property of turning north and south has been
utilised in the Compass, without which modern science would be
paralyzed, and travel rendered impossible.
[Illustration: LOADSTONE.]
[Illustration: COMPASS.]
It is worthy of notice that although the magnetic needle of the compass
turns to the north, it does not do so because it is attracted by the
north pole, but because it is repelled from the east and west.
We have long known that if a current of electricity be sent round a
magnetic needle, the latter at once turns at right angles to it. On this
principle depends the Electric Telegraph. When communication is made by
using the handles, a current of electricity is sent round the needles,
and causes them to turn at right angles until stopped by a little ivory
pin, which prevents them from overshooting themselves.
There is a perpetual stream of electricity passing over the earth from
east to west, and in consequence all magnetic bodies are forced to turn
at right angles, just as is the case with the magnetic needle.
USEFUL ARTS.