Edmond About - "The Man With The Broken Ear"

Joseph Jacobs (coll. & ed.) - "Celtic Fairy Tales"

Charles Dudley Warner - "The Complete Writings of Charles Dudley Warner Volume 2"

William S. Sadler - "The Mother and Her Child"

Annual Bibliography of Commonwealth Literature 2007
This paper argues that discourses of love in Ghanaian market literature for youth offer a view into complex negotiations of agency and empowerment. Drawing on Deborah Durham's notion of youth as "social `shifters'" and Francis Nyamnjoh's conception of the "interconnectedness" of agency, I take Ghanaian market literature as one specific case of how African literature for youth foregrounds questions of continuity and change as African societies enter into increasingly complex global relations. In this literature for youth, received notions of love, often constructed out of impressions from American pop and hip hop music, carry new notions of agency that compete with existing "domesticated" forms. Authors like Ike Tandoh and Evelyn Tay employ discourses of love to offer youth alternative avenues for empowerment in a context of socio-economic disenfranchizement. In a creative process of "straddling", this writing both reveals and reproduces the contradictions that obtain in youth configurations of agency.

The Outline of Science, Vol. 1 (of 4)

J >> J. Arthur Thomson >> The Outline of Science, Vol. 1 (of 4)





Sec. 10

What an Electric Current is

The discovery of these two kinds of electricity has, however, enabled us
to understand very fairly what goes on in electrical phenomena. The
outlying electrons, as we saw, may pass from atom to atom, and this, on
a large scale, is the meaning of the electric current. In other words,
we believe an electric current to be a flow of electrons. Let us take,
to begin with, a simple electrical "cell," in which a feeble current is
generated: such a cell as there is in every house to serve its electric
bells.

In the original form this simple sort of "battery" consisted of a plate
of zinc and a plate of copper immersed in a chemical. Long before
anything was known about electrons it was known that, if you put zinc
and copper together, you produce a mild current of electricity. We know
now what this means. Zinc is a metal the atoms of which are particularly
disposed to part with some of their outlying electrons. Why, we do not
know; but the fact is the basis of these small batteries. Electrons from
the atoms of zinc pass to the atoms of copper, and their passage is a
"current." Each atom gives up an electron to its neighbour. It was
further found long ago that if the zinc and copper were immersed in
certain chemicals, which slowly dissolve the zinc, and the two metals
were connected by a copper wire, the current was stronger. In modern
language, there is a brisker flow of electrons. The reason is that
the atoms of zinc which are stolen by the chemical leave their
detachable electrons behind them, and the zinc has therefore more
electrons to pass on to the copper.

[Illustration: DISINTEGRATION OF ATOMS

An atom of Uranium, by ejecting an Alpha particle, becomes Uranium X.
This substance, by ejecting Beta and Gamma rays, becomes Radium. Radium
passes through a number of further changes, as shown in the diagram, and
finally becomes lead. Some radio-active substances disintegrate much
faster than others. Thus Uranium changes very slowly, taking
5,000,000,000 years to reach the same stage of disintegration that
Radium A reaches in 3 minutes. As the disintegration proceeds, the
substances become of lighter and lighter atomic weights. Thus Uranium
has an atomic weight of 238, whereas lead has an atomic weight of only
206. The breaking down of atoms is fully explained in the text.]

[Illustration: _Reproduced by permission from "The Interpretation of
Radium" (John Murray)._

SILK TASSEL ELECTRIFIED

The separate threads of the tassel, being each electrified with the same
kind of electricity, repel one another, and thus the tassel branches out
as in the photograph.]

[Illustration: SILK TASSEL DISCHARGED BY THE RAYS FROM RADIUM

When the radium rays, carrying an opposite electric charge to that on
the tassel, strikes the threads, the threads are neutralised, and hence
fall together again.]

[Illustration: A HUGE ELECTRIC SPARK

This is an actual photograph of an electric spark. It is leaping a
distance of about 10 feet, and is the discharge of a million volts. It
is a graphic illustration of the tremendous energy of electrons.]

[Illustration: _From "Scientific Ideas of To-day_."

ELECTRICAL ATTRACTION BETWEEN COMMON OBJECTS

Take an ordinary flower-vase well dried and energetically rub it with a
silk handkerchief. The vase which thus becomes electrified will attract
any light body, such as a feather, as shown in the above illustration.]

Such cells are now made of zinc and carbon, immersed in sal-ammoniac,
but the principle is the same. The flow of electricity is a flow of
electrons; though we ought to repeat that they do not flow in a body, as
molecules of water do. You may have seen boys place a row of bricks,
each standing on one end, in such order that the first, if it is pushed,
will knock over the second, the second the third, and so on to the last.
There is a flow of _movement_ all along the line, but each brick moves
only a short distance. So an electron merely passes to the next atom,
which sends on an electron to a third atom, and so on. In this case,
however, the movement from atom to atom is so rapid that the ripple of
movement, if we may call it so, may pass along at an enormous speed. We
have seen how swiftly electrons travel.

But how is this turned into power enough even to ring a bell? The actual
mechanical apparatus by which the energy of the electron current is
turned into sound, or heat, or light will be described in a technical
section later in this work. We are concerned here only with the
principle, which is clear. While zinc is very apt to part with
electrons, copper is just as obliging in facilitating their passage
onward. Electrons will travel in this way in most metals, but copper is
one of the best "conductors." So we lengthen the copper wire between the
zinc and the carbon until it goes as far as the front door and the bell,
which are included in the circuit. When you press the button at the
door, two wires are brought together, and the current of electrons
rushes round the circuit; and at the bell its energy is diverted into
the mechanical apparatus which rings the bell.

Copper is a good conductor--six times as good as iron--and is therefore
so common in electrical industries. Some other substances are just as
stubborn as copper is yielding, and we call them "insulators," because
they resist the current instead of letting it flow. Their atoms do not
easily part with electrons. Glass, vulcanite, and porcelain are very
good insulators for this reason.


What the Dynamo does

But even several cells together do not produce the currents needed in
modern industry, and the flow is produced in a different manner. As the
invisible electrons pass along a wire they produce what we call a
magnetic field around the wire, they produce a disturbance in the
surrounding ether. To be exact, it is through the ether surrounding the
wire that the energy originated by the electrons is transmitted. To set
electrons moving on a large scale we use a "dynamo." By means of the
dynamo it is possible to transform mechanical energy into electrical
energy. The modern dynamo, as Professor Soddy puts it, may be looked
upon as an electron pump. We cannot go into the subject deeply here, we
would only say that a large coil of copper wire is caused to turn round
rapidly between the poles of a powerful magnet. That is the essential
construction of the "dynamo," which is used for generating strong
currents. We shall see in a moment how magnetism differs from
electricity, and will say here only that round the poles of a large
magnet there is a field of intense disturbance which will start a flow
of electrons in any copper that is introduced into it. On account of the
speed given to the coil of wire its atoms enter suddenly this magnetic
field, and they give off crowds of electrons in a flash.

It is found that a similar disturbance is caused, though the flow is in
the _opposite_ direction, when the coil of wire leaves the magnetic
field. And as the coil is revolving very rapidly we get a powerful
current of electricity that runs in alternate directions--an
"alternating" current. Electricians have apparatus for converting it
into a continuous current where this is necessary.

A current, therefore, means a steady flow of the electrons from atom to
atom. Sometimes, however, a number of electrons rush violently and
explosively from one body to another, as in the electric spark or the
occasional flash from an electric tram or train. The grandest and most
spectacular display of this phenomenon is the thunderstorm. As we saw
earlier, a portentous furnace like the sun is constantly pouring floods
of electrons from its atoms into space. The earth intercepts great
numbers of these electrons. In the upper regions of the air the stream
of solar electrons has the effect of separating positively-electrified
atoms from negatively-electrified ones, and the water-vapour, which is
constantly rising from the surface of the sea, gathers more freely round
the positively-electrified atoms, and brings them down, as rain, to the
earth. Thus the upper air loses a proportion of positive electricity, or
becomes "negatively electrified." In the thunderstorm we get both kinds
of clouds--some with large excesses of electrons, and some deficient in
electrons--and the tension grows until at last it is relieved by a
sudden and violent discharge of electrons from one cloud to another or
to the earth--an electric spark on a prodigious scale.


Sec. 11

Magnetism

We have seen that an electric current is really a flow of electrons. Now
an electric current exhibits a magnetic effect. The surrounding space is
endowed with energy which we call electro-magnetic energy. A piece of
magnetised iron attracting other pieces of iron to it is the popular
idea of a magnet. If we arrange a wire to pass vertically through a
piece of cardboard and then sprinkle iron filings on the cardboard we
shall find that, on passing an electric current through the wire, the
iron filings arrange themselves in circles round it. The magnetic force,
due to the electric current, seems to exist in circles round the wire,
an ether disturbance being set up. Even a single electron, when in
movement, creates a magnetic "field," as it is called, round its path.
There is no movement of electrons without this attendant field of
energy, and their motion is not stopped until that field of energy
disappears from the ether. The modern theory of magnetism supposes that
all magnetism is produced in this way. All magnetism is supposed to
arise from the small whirling motions of the electrons contained in the
ultimate atoms of matter. We cannot here go into the details of the
theory nor explain why, for instance, iron behaves so differently from
other substances, but it is sufficient to say that here, also, the
electron theory provides the key. This theory is not yet definitely
_proved_, but it furnishes a sufficient theoretical basis for future
research. The earth itself is a gigantic magnet, a fact which makes the
compass possible, and it is well known that the earth's magnetism is
affected by those great outbreaks on the sun called sun-spots. Now it
has been recently shown that a sun-spot is a vast whirlpool of electrons
and that it exerts a strong magnetic action. There is doubtless a
connection between these outbreaks of electronic activity and the
consequent changes in the earth's magnetism. The precise mechanism of
the connection, however, is still a matter that is being investigated.


ETHER AND WAVES

Ether and Waves

The whole material universe is supposed to be embedded in a vast medium
called the ether. It is true that the notion of the ether has been
abandoned by some modern physicists, but, whether or not it is
ultimately dispensed with, the conception of the ether has entered so
deeply into the scientific mind that the science of physics cannot be
understood unless we know something about the properties attributed to
the ether. The ether was invented to explain the phenomena of light, and
to account for the flow of energy across empty space. Light takes time
to travel. We see the sun at any moment by the light that left it 8
minutes before. It has taken that 8 minutes for the light from the
sun to travel that 93,000,000 miles odd which separates it from our
earth. Besides the fact that light takes time to travel, it can be shown
that light travels in the form of waves. We know that sound travels in
waves; sound consists of waves in the air, or water or wood or whatever
medium we hear it through. If an electric bell be put in a glass jar and
the air be pumped out of the jar, the sound of the bell becomes feebler
and feebler until, when enough air has been taken out, we do not hear
the bell at all. Sound cannot travel in a vacuum. We continue to _see_
the bell, however, so that evidently light can travel in a vacuum. The
invisible medium through which the waves of light travel is the ether,
and this ether permeates all space _and all matter_. Between us and the
stars stretch vast regions empty of all matter. But we see the stars;
their light reaches us, even though it may take centuries to do so. We
conceive, then, that it is the universal ether which conveys that light.
All the energy which has reached the earth from the sun and which,
stored for ages in our coal-fields, is now used to propel our trains and
steamships, to heat and light our cities, to perform all the
multifarious tasks of modern life, was conveyed by the ether. Without
that universal carrier of energy we should have nothing but a stagnant,
lifeless world.

[Illustration: _Photo: Leadbeater._

AN ELECTRIC SPARK

An electric spark consists of a rush of electrons across the space
between the two terminals. A state of tension is established in the
ether by the electric charges, and when this tension passes a certain
limit the discharge takes place.]

[Illustration: _From "Scientific Ideas of To-day."_

AN ETHER DISTURBANCE AROUND AN ELECTRON CURRENT

In the left-hand photograph an electric current is passing through the
coil, thus producing a magnetic field and transforming the poker into a
magnet. The poker is then able to support a pair of scissors. As soon as
the electric current is broken off, as in the second photograph, the
ether disturbance ceases. The poker loses its magnetism, and the
scissors fall.]

We have said that light consists of waves. The ether may be considered
as resembling, in some respects, a jelly. It can transmit vibrations.
The waves of light are really excessively small ripples, measuring from
crest to crest. The distance from crest to crest of the ripples in a
pond is sometimes no more than an inch or two. This distance is
enormously great compared to the longest of the wave-lengths that
constitute light. We say the longest, for the waves of light differ in
length; the colour depends upon the length of the light. Red light has
the longest waves and violet the shortest. The longest waves, the waves
of deep-red light, are seven two hundred and fifty thousandths of an
inch in length (7/250,000 inch). This is nearly twice the length of
deep-violet light-waves, which are 1/67,000 inch. But light-waves, the
waves that affect the eye, are not the only waves carried by the ether.
Waves too short to affect the eye can affect the photographic plate, and
we can discover in this way the existence of waves only half the length
of the deep-violet waves. Still shorter waves can be discovered, until
we come to those excessively minute rays, the X-rays.


Below the Limits of Visibility

But we can extend our investigations in the other direction; we find
that the ether carries many waves longer than light-waves. Special
photographic emulsions can reveal the existence of waves five times
longer than violet-light waves. Extending below the limits of visibility
are waves we detect as heat-waves. Radiant heat, like the heat from a
fire, is also a form of wave-motion in the ether, but the waves our
senses recognise as heat are longer than light-waves. There are longer
waves still, but our senses do not recognise them. But we can detect
them by our instruments. These are the waves used in wireless
telegraphy, and their length may be, in some cases, measured in miles.
These waves are the so-called electro-magnetic waves. Light, radiant
heat, and electro-magnetic waves are all of the same nature; they differ
only as regards their wave-lengths.


LIGHT--VISIBLE AND INVISIBLE

If Light, then, consists of waves transmitted through the ether, what
gives rise to the waves? Whatever sets up such wonderfully rapid series
of waves must be something with an enormous vibration. We come back to
the electron: all atoms of matter, as we have seen, are made up of
electrons revolving in a regular orbit round a nucleus. These electrons
may be affected by out-side influences, they may be agitated and their
speed or vibration increased.


Electrons and Light

The particles even of a piece of cold iron are in a state of vibration.
No nerves of ours are able to feel and register the waves they emit, but
your cold poker is really radiating, or sending out a series of
wave-movements, on every side. After what we saw about the nature of
matter, this will surprise none. Put your poker in the fire for a time.
The particles of the glowing coal, which are violently agitated,
communicate some of their energy to the particles of iron in the poker.
They move to and fro more rapidly, and the waves which they create are
now able to affect your nerves and cause a sensation of heat. Put the
poker again in the fire, until its temperature rises to 500 deg. C. It
begins to glow with a dull red. Its particles are now moving very
violently, and the waves they send out are so short and rapid that they
can be picked up by the eye--we have _visible_ light. They would still
not affect a photographic plate. Heat the iron further, and the crowds
of electrons now send out waves of various lengths which blend into
white light. What is happening is the agitated electrons flying round in
their orbits at a speed of trillions of times a second. Make the iron
"blue hot," and it pours out, in addition to light, the _invisible_
waves which alter the film on the photographic plate. And beyond these
there is a long range of still shorter waves, culminating in the X-rays,
which will pass between the atoms of flesh or stone.

Nearly two hundred and fifty years ago it was proved that light
travelled at least 600,000 times faster than sound. Jupiter, as we saw,
has moons, which circle round it. They pass behind the body of the
planet, and reappear at the other side. But it was noticed that, when
Jupiter is at its greatest distance from us, the reappearance of the
moon from behind it is 16 minutes and 36 seconds later than when the
planet is nearest to us. Plainly this was because light took so long to
cover the additional distance. The distance was then imperfectly known,
and the speed of light was underrated. We now know the distance, and we
easily get the velocity of light.

No doubt it seems far more wonderful to discover this within the walls
of a laboratory, but it was done as long ago as 1850. A cogged wheel is
so mounted that a ray of light passes between two of the teeth and is
reflected back from a mirror. Now, slight as is the fraction of a second
which light takes to travel that distance, it is possible to give such
speed to the wheel that the next tooth catches the ray of light on its
return and cuts it off. The speed is increased still further until the
ray of light returns to the eye of the observer through the notch _next_
to the one by which it had passed to the mirror! The speed of the wheel
was known, and it was thus possible again to gather the velocity of
light. If the shortest waves are 1/67,000 of an inch in length, and
light travels at 186,000 miles a second, any person can work out that
about 800 trillion waves enter the eye in a second when we see "violet."


Sorting out Light-waves

The waves sent out on every side by the energetic electrons become
faintly visible to us when they reach about 1/35,000 of an inch. As they
become shorter and more rapid, as the electrons increase their speed, we
get, in succession, the colours red, orange, yellow, green, blue,
indigo, and violet. Each distinct sensation of colour means a wave of
different length. When they are all mingled together, as in the light of
the sun, we get white light. When this white light passes through glass,
the speed of the waves is lessened; and, if the ray of light falls
obliquely on a triangular piece of glass, the waves of different lengths
part company as they travel through it, and the light is spread out in a
band of rainbow-colour. The waves are sorted out according to their
lengths in the "obstacle race" through the glass. Anyone may see this
for himself by holding up a wedge-shaped piece of crystal between the
sunlight and the eye; the prism separates the sunlight into its
constituent colours, and these various colours will be seen quite
readily. Or the thing may be realised in another way. If the seven
colours are painted on a wheel as shown opposite page 280 (in the
proportion shown), and the wheel rapidly revolved on a pivot, the wheel
will appear a dull white, the several colours will not be seen. But
_omit_ one of the colours, then the wheel, when revolved, will not
appear white, but will give the impression of one colour, corresponding
to what the union of six colours gives. Another experiment will show
that some bodies held up between the eye and a white light will not
permit all the rays to pass through, but will intercept some; a body
that intercepts all the seven rays except red will give the impression
of red, or if all the rays except violet, then violet will be the colour
seen.

[Illustration: _Photo: H. J. Shepstone._

LIGHTNING

In a thunderstorm we have the most spectacular display in lightning of a
violent and explosive rush of electrons (electricity) from one body to
another, from cloud to cloud, or to the earth. In this wonderful
photograph of an electrical storm note the long branched and undulating
flashes of lightning. Each flash lasts no longer than the one
hundred-thousandth part of a second of time.]

[Illustration: LIGHT WAVES

Light consists of waves transmitted through the ether. Waves of light
differ in length. The colour of the light depends on the wave-length.
Deep-red waves (the longest) are 7/250000 inch and deep-violet waves
1/67000 inch. The diagram shows two wave-motions of different
wave-lengths. From crest to crest, or from trough to trough, is the
length of the wave.]

[Illustration: THE MAGNETIC CIRCUIT OF AN ELECTRIC CURRENT

The electric current passing in the direction of the arrow round the
electric circuit generates in the surrounding space circular magnetic
circuits as shown in the diagram. It is this property which lies at the
base of the electro-magnet and of the electric dynamo.]

[Illustration: THE MAGNET

The illustration shows the lines of force between two magnets. The lines
of force proceed from the north pole of one magnet to the south pole of
the other. They also proceed from the north to the south poles of the
same magnet. These facts are shown clearly in the diagram. The north
pole of a magnet is that end of it which turns to the north when the
magnet is freely suspended.]


The Fate of the World

Professor Soddy has given an interesting picture of what might happen
when the sun's light and heat is no longer what it is. The human eye
"has adapted itself through the ages to the peculiarities of the sun's
light, so as to make the most of that wave-length of which there is
most.... Let us indulge for a moment in these gloomy prognostications,
as to the consequences to this earth of the cooling of the sun with the
lapse of ages, which used to be in vogue, but which radio-activity has
so rudely shaken. Picture the fate of the world when the sun has become
a dull red-hot ball, or even when it has cooled so far that it would no
longer emit light to us. That does not all mean that the world would be
in inky darkness, and that the sun would not emit light to the people
then inhabiting this world, if any had survived and could keep
themselves from freezing. To such, if the eye continued to adapt itself
to the changing conditions, our blues and violets would be ultra-violet
and invisible, but our dark heat would be light and hot bodies would be
luminous to them which would be dark to us."


Sec. 12

What the Blue "Sky" means

We saw in a previous chapter how the spectroscope splits up light-waves
into their colours. But nature is constantly splitting the light into
its different-lengthed waves, its colours. The rainbow, where dense
moisture in the air acts as a spectroscope, is the most familiar
example. A piece of mother-of-pearl, or even a film of oil on the street
or on water, has the same effect, owing to the fine inequalities in its
surface. The atmosphere all day long is sorting out the waves. The blue
"sky" overhead means that the fine particles in the upper atmosphere
catch the shorter waves, the blue waves, and scatter them. We can make a
tubeful of blue sky in the laboratory at any time. The beautiful
pink-flush on the Alps at sunrise, the red glory that lingers in the
west at sunset, mean that, as the sun's rays must struggle through
denser masses of air when it is low on the horizon, the long red waves
are sifted out from the other shafts.

Then there is the varied face of nature which, by absorbing some waves
and reflecting others, weaves its own beautiful robe of colour. Here and
there is a black patch, which _absorbs_ all the light. White surfaces
_reflect_ the whole of it. What is reflected depends on the period of
vibration of the electrons in the particular kind of matter. Generally,
as the electrons receive the flood of trillions of waves, they absorb
either the long or the medium or the short, and they give us the
wonderful colour-scheme of nature. In some cases the electrons continue
to radiate long after the sunlight has ceased to fall upon them. We get
from them "black" or invisible light, and we can take photographs by it.
Other bodies, like glass, vibrate in unison with the period of the
light-waves and let them stream through.

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