TILLAGE.--DRAINAGE.--SPIRAL PRINCIPLE.--CENTRIFUGAL FORCE.
Systems of cultivating Ground.--The Fallow System.--Manuring the
Ground.--Custom of China.--Nature’s Abhorrence of Waste.--What
becomes of Dead Animals.--Burying-beetles.--The Scarabæus-beetles
and their Work.--Drainage _versus_ Sewage.--Clay Soils and
Drains.--The Mole, the Earth-worm, Rats, Mice, and Rabbits.--The
Flexible Drain and the Lobster’s Tail.--The Turbine Pump and the
Ascidian.--The Spiral Principle.--The Smoke-jack, Kite, and Wings
of Birds.--Centrifugal Force.--Revolution of Planets.--The
“Governor” of the Steam-engine.--The Sling, Amentum, and Mop.--The
Gyroscope, the Bicycle, and the Hoop.
Several times, in the course of this work, we have touched upon man’s
dealings with the earth, such as mining and tunnelling. We will now take
another side of the same question, and, in connection with Tillage,
consider Drainage, whereby superabundant moisture is removed from the
earth, and Manuring, whereby the exhausted soil is renovated.
We will take this subject first.
It has long been known that it is impossible to get more out of the
ground than exists in it, and that when the soil has been so worked as
to become unproductive, there are only two remedies. The one is to allow
the ground to remain uncultivated for a time. It must be ploughed in
deeply, as if it were to be sown with a crop, and must be left to
recruit itself from the air. This is the now abandoned “fallow” system,
which used to be in full operation when I was a child.
As, however, population increased, and with it the perpetually
increasing demand for food, land was found to be too precious to be
allowed to lie fallow and idle. Then came the system of rotation of
crops, potato following wheat, clover following potato, &c. But, above
all, agriculturists learned that in the long-run there is nothing so
cheap as manure, i.e. the return to the soil by animals of the elements
which these animals took out of it.
On the right hand of the illustration (page 495) is shown the simplest
mode of enriching the soil, namely, by spreading the manure on the
surface of the earth, and then digging it in. Any mode of thus enriching
the earth is a proof of civilisation. No savage ever dreamed of such a
thing, and I doubt whether barbarians recognised the principle at any
time.
Nowadays we have recognised the necessity of returning to the soil in
one form the elements which we have taken from it in another. As usual
in such arts of civilisation, the Chinese have long preceded us. They
waste nothing, carrying, perhaps, its principles to an extent which
scarcely suits our European ideas.
They even utilise the little clippings of hair, to which every Chinaman
is almost daily subject, if he wishes to keep up his self-respect in
public. The barbers carefully preserve these clippings, and sell them to
gardeners. They are too precious to be used in general agriculture, but
the flower artist, when he plants the seed, puts in the same hole a
little pinch of human hair, knowing it to be a strong stimulant to
growth.
* * * * *
WITHOUT multiplying examples of artificial manuring, most of which are
too familiar to need description, we will proceed to the methods by
which Nature has for countless centuries achieved the same work that Man
has lately learned to undertake.
Nature abhors waste, and in the long-run will prove it, however wasteful
may be the ways of her servants. Take, for example, the case of an
ordinary tree, such as an elm, an oak, or a birch. In the autumn the
leaves fall. In the next summer scarcely a dead leaf can be found. They
have been decomposed by rain, dews, and gases, and have thus returned to
the earth more than the nutriment which they took out of it.
Here man is apt to interfere. Knowing the invaluable productive powers
of decayed leaves, he removes them as they fall, and stores them in
heaps so as to form the costly, but almost indispensable, “leaf mould.”
In so doing, however, he deprives the trees of their natural nutriment,
and by degrees they dwindle and die.
Nature, in this case, shows her superiority over Art.
Then we have the remarkable fact that millions of animated beings die
annually, and no vestige of their remains is found. Hyænas and vultures
might account for a few bodies, the remnants of which have been found in
ancient caverns. But there is no hyæna which could crush the leg bones
of an adult elephant; and yet I suppose that neither in Africa nor Asia
has any one discovered the body of an elephant or rhinoceros that had
died a natural death.
In the first place, there is the curious point, which I have already
mentioned, and which is shared by nearly every race of human savages,
that when an animal feels that it has received its death-stroke, it
accepts the conditions, withdraws itself from those who yet have life in
them, and yields up its life as calmly as if it were but sleeping.
But what becomes of the body? As to such enormous beings as elephants,
the various species of rhinoceros, and whales, which are as large as
several elephants, rhinoceros, and hippopotamus put together, I cannot
say from practical knowledge.
Still, as size is only comparative, the rule that holds good with a
small animal may hold equally good with a large one. It is my lot to
walk very often upon the banks of the Thames. It is a charming walk at
high water, but at low water there is too much odoriferous mud, and
there are too many dead dogs and cats to make it an agreeable resort,
except for enthusiastic entomologists, who seem to swarm in this
neighbourhood.
Scarcely has such a carcass been stranded than it is beset by
Burying-beetles of various kinds. Hundreds upon hundreds can be shaken
out of the corpse of a dog or cat, and, before the next tide has come
up, there is scarcely any flesh left on the bones, it having been dug
into the earth by the Burying-beetles.
* * * * *
THEN there is that wonderful family of Scarabæus-beetles, which do us
invaluable service as scavengers and agriculturists. They follow the
path of the caravans, and effectively cleanse the course which has been
traversed. Even man is obliged to utilise as fuel the droppings of the
horses, cows, and camels; but the Scarabæus goes further, collecting all
that man does not need, and burying it in the earth.
The instinct of the female Scarabæus urges it to gather together the
rejecta, to form them into balls, placing an egg in the middle of each
ball, and to bury them in the ground. Thus a double object is attained,
the offensive substances being removed from the surface of the ground,
where they do harm, and being transferred below the surface, where they
do good.
Even the curious instinct of the dog, which leads it to bury bones, &c.,
which it cannot consume, and which it often forgets, if well fed, leaves
them to be consumed by the all-absorbing earth.
[Illustration: SCARABÆUS-BEETLES.]
[Illustration: MEN MANURING GROUND.]
It is evident that, in the end, the earth _must_ receive back again that
which has been taken from it. If, for example, we follow the present
most wasteful plan of drainage, and fling into rivers everything which
ought to be utilised on land, it only gets into the sea in the end, and
in the course of years is decomposed, and returns to the earth in the
form of gases. Meanwhile, however, we have robbed the locality, deprived
it of the nourishment which it required, and forced ourselves to supply
it elsewhere at a costly rate.
So runs the cycle of creation. Sooner or later, Nature will have her
way, and the more we help her, the better it will be for us.
* * * * *
OF course I do not mean to condemn Drainage, which is an absolute
necessity in agriculture, and a matter of life and death in households.
But, when rightly conducted, it only signifies that water is removed
from a spot which is overstocked with moisture to one where it is
needed. Wet clay lands, for example, which were unproductive in point of
crops, and injurious in point of human health, have been converted by
judicious drainage into fertile and healthy grounds.
This, as it will be seen, is a very different business from removing
from the soil the elements which rightly belong to it, and which sooner
or later, in some form or another, it will claim and recapture.
Still, it is evident that in the progress of civilisation there must be
accumulations of all kinds of refuse, which savages utterly disregard.
Then we come to the question of the Drain combined with the Sewer, and
are enabled to see how the hand of man, if properly directed, only
follows the course of Nature.
[Illustration: TUNNEL OF MOLE.]
[Illustration: SEWER.]
So we undermine our towns with a complex system of drains which are
understood by only a very few people. For example, just as a tree is
only half visible, the roots being about equivalent to the branches,
London is only half visible, the subterranean architecture being little,
if at all, inferior to that of the surface.
Here, again, we are met by Nature. Very few of us can appreciate the
extensive subterranean works which underlie us, even where the hand of
man has never been placed. Putting aside a multitude of tiny creatures,
there are, in our own country, the earth-worms which pierce the ground
in all directions, at the same time draining and manuring it. They
penetrate it with their little burrows, thus admitting the air, which
the earth needs as much as we do, and allowing moisture to take its
right place. Then there are the moles, that are perpetually travelling
after the earth-worms, and making drainage galleries of wonderful
extent. Then there are the numerous other burrowers, such as rabbits,
mice, and rats, which are common everywhere, besides the less plentiful
foxes, badgers, and various burrowing birds, all of which assist more or
less in the drainage of the earth.
Even bees and wasps of different kinds assist in this work, the hardest
soil yielding to their small, though powerful, jaws and feet, and so
being made, if only temporarily, able to carry off the superabundant
moisture.
* * * * *
[Illustration: TAIL OF LOBSTER.]
[Illustration: FLEXIBLE WATER MAIN.]
One of the most ingenious modes of Drainage was that which was invented
by Watts, and was avowedly based on Nature. He had engaged himself to
carry a drain tube through, or rather over, an extremely irregular bed
of a river, where the pipes must accommodate themselves to existing
conditions. The modern system of pipes not having been brought into
existence, Watts had to adapt himself to circumstances, and did so by
making his pipe on the model of a Lobster’s tail, as shown in the
illustration.
We have already seen how the same object has been utilised in warfare as
a pattern for armour, but it does seem rather strange that it should be
employed in the tranquil arts of peace.
* * * * *
ANOTHER method of removing superfluous water is by the TURBINE PUMP, by
which the water, instead of being cast up in successive jets, was flung
out in a continuous torrent. Some of my readers may remember the
sensation which was created at the first Exhibition of 1852 by the then
extraordinary powers of the Turbine Pump.
Yet this is, after all, nothing but an imperfect copy of the now
celebrated being to which human beings have been supposed to owe their
origin, namely, the Ascidian, popularly known by the name of the
Sea-squirt, and with very good reasons.
As a rule, it keeps up a rotation of tentacles, such as is shown in the
illustration, acting exactly on the principle of the Turbine Pump, and
drawing in and discharging water with a power that is perfectly
astonishing in so small a being. Beside this, it has the power of
flinging out at once the whole of its watery contents, and any one who
has incautiously handled a mass of Ascidians, and been drenched by them,
can answer with more truth than satisfaction as to the water-absorbing
power of the Turbine.
[Illustration: ASCIDIAN.]
[Illustration: TURBINE PUMP.]
Then the Ascidian can do what the Turbine cannot do. In the Turbine the
water which is taken in must necessarily be ejected in equal
proportions. With the Ascidian the same thing takes place, but with the
additional power of ejecting all the contained water, and then beginning
afresh.
There is now no doubt that the Circular or the Turbine Pump is the most
powerful in such cases as emptying mines of the water which, in spite of
all precautions, will make its way in, and destroy the labours of the
miners. But I merely wish to carry out the object of this work by
remarking that the invaluable Turbine Pump is only a very inferior copy
of a natural pump, which existed, as far as we know, centuries before
Man could find his place upon this earth.
THE SPIRAL.
In an early portion of this work the Spiral or Screw was touched upon,
mostly in connection with the propulsion of vessels. We will now extend
it a little further, and see how it is modified so as to perform other
offices than those which have been described.
Allusion has already been made to the Spiral or Wedge principle, but
some of the illustrations were accidentally omitted. I therefore
introduce them here, this being a chapter of miscellanea.
The Windmill has previously been described, as has also the ship’s
Screw, another form of which is here given.
[Illustration: BIRDS’ WINGS AND TAILS.]
[Illustration: SMOKE-JACK. SHIP’S SCREW. WINDMILL. KITE.]
In the centre is shown the mechanism popularly known as the Smoke-jack,
though it really works by means of hot air, and only becomes gradually
choked by the soot which the smoke by degrees deposits upon it. It is,
in fact, nothing but a windmill working horizontally instead of
vertically, the vanes being moved by the rapidly ascending heated air.
So powerful is the spiral pressure of this air, that in my old college
days at least a dozen rows of heavily laden spits were perpetually
turned by a single Smoke-jack. It is many years since I visited my old
college, and I cannot say whether the Smoke-jack still exists, but, as
it did its work well so long ago, I presume that it does so now.
Then there is the well-known spiral ventilator set in the windows of
workshops. Perhaps its revolution may not assist the air-current, but it
does, at all events, show how much exhausted air has to be expelled from
the room, and consequently how much fresh air needs to be brought into
it.
* * * * *
PERHAPS the reader may be surprised to see that the Wings and Tail of a
bird and a boy’s Kite are placed among the examples of the Spiral
principle. Yet such is the fact. If the reader will move up and down the
wings of any bird which will not bite him, he will find that there is in
them a peculiar screwing motion, difficult of description, but very
observable.
It is mostly for want of this movement that all our attempts at fitting
wings to human beings have been such utter failures. We can make the
wings work up and down well enough, but we cannot as yet impart to them
the all-important spiral movement.
* * * * *
THAT very well-known toy, the Kite, is another example of the same
principle which drives the screw steamer. Its “tail,” which need be
nothing but a piece of string with a proportionate weight at the end,
keeps the Kite in a slanting position, providing that the “belly-band”
be properly arranged. The consequence is that the pressure of the wind
acts on it as on a wedge, and so drives it upwards until the combined
weight of itself and the string counterbalance the upward pressure.
Indeed, the only object of the string is to keep the Kite at a proper
inclination; and, if that object could be attained by the force of
gravity alone, the Kite would ascend to a height nearly double that to
which it can at present attain.
CENTRIFUGAL FORCE.
Closely connected with the spiral principle is Centrifugal Force, that
marvellous power which gives to our whole solar system its ceaseless
movements, and may extend, as far as we know, to other and vaster
systems yet unknown.
Tie a ball to a string, and swing it round, and it will be an exact,
though rough, representation of the double power by which the movements
of the heavenly bodies are governed, our earth being included among
them.
The string represents the force of attraction, which binds all our
planets to the sun, and their satellites to the planets, while the force
that is employed in swinging the ball represents the mysterious power
that issues from the sun, and gives motion to the planets. The metaphor
is a very homely one, but it is nevertheless correct.
* * * * *
IN the accompanying illustration are several examples of Centrifugal
Force as found both in Nature and Art. On the left hand we have diagrams
of some of the heavenly bodies, showing the revolution of their
offspring, so to call them, while on the right are seen examples of
Centrifugal Force as applied to human use. For convenience’ sake, the
illustrations have been separated into two portions.
[Illustration: CENTRIFUGAL FORCE OF HEAVENLY BODIES.]
[Illustration: CENTRIFUGAL FORCE OF “GOVERNORS” OF ENGINE. SLING.
AMENTUM AND MOP.]
In the first of these illustrations we have the “Governor” of the
steam-engine, that wonderfully ingenious and simple piece of mechanism
which controls the force of the steam, and, without the superintendence
of man, acts almost as a living being might.
It is composed of two heavy metal balls, hinged, as shown in the
illustration, to a movable collar which slides up and down the central
rod. When the engine is at work the Governor revolves, and the harder it
works, the more rapid is the revolution. Consequently, as it revolves,
the balls diverge and draw the sliding collar up the rod.
Here lies the whole beauty of the invention. The sliding collar is
connected with the safety-valve. Thus, if the engine should be working
beyond its proper powers, the Governor draws up the collar, and releases
sufficient steam to take the undue pressure off the boiler. Thus the
engine may be left, so to speak, to manage itself.
* * * * *
NEXT are shown two examples of Centrifugal Force as applied in ancient
warfare, namely, the Sling, which is now retained merely as a boy’s toy,
and the Amentum, which was practically a sling attached to a spear. Both
weapons have been superseded by the modern firearms, but the Sling is
really a more formidable offensive weapon, in skilful hands, than is
generally suspected.
A good slinger is as sure of his aim as a good rifleman, and can send
his missile to a wonderful distance. Were I to be armed with the best
pistol hitherto invented, I should be sorry to fight an accomplished
slinger, unless under cover.
The really tremendous power of the Sling is obtained by Centrifugal
Force, the weapon, with its missile, being whirled in the air, and then
one string being loosed with a peculiar knack something like the “loose”
of a good archer. In consequence, the centrifugal force is converted
into direct force, and the missile flies directly forwards.
The Amentum is simply a cord tied to a javelin, so that the thrower has
the advantage of a lever, which, after all, is only the conversion of
centrifugal force.
The very familiar Mop, flinging off its moisture to a considerable
distance, needs no description; but I have introduced it to show the
action of centrifugal force in small as well as in great things.
* * * * *
THE next illustration shows how this very same power acts upon the
greatest as well as the least of objects, and enables them to maintain
positions which otherwise they must of necessity fail to do. Take, for
example, our own Earth, and its peculiar position of being tilted on one
side, so as to give us the alternative seasons as it flies on its annual
course.
This is simply due to its own rapid revolution, which, on the same
principle that keeps the arrow and the rifle-ball straight on their
course, prevents it from altering its position.
The very same principle acts on the boys’ Tops, and is shown in a really
remarkable manner by the professional Japanese top-spinners, who will
place several tops upon each other, as shown in the illustration, and
make them sway backwards and forwards in the most extraordinary manner,
sometimes being all upright, and sometimes leaning almost at right
angles to each other.
A favourite mode of illustrating this power of Centrifugal Force is by
the Gyroscope, a figure of which is given on the right hand of the
illustration. The interior wheel is made to revolve rapidly, and the
effect of the revolution is to enable the instrument to maintain a
horizontal position, even when suspended on one side, as shown in the
engraving.
[Illustration: REVOLUTION OF EARTH.]
[Illustration: JAPANESE TOPS.]
[Illustration: GYROSCOPE.]
The power of this revolution is quite wonderful, even in a small
Gyroscope which can be purchased for a few shillings. It almost seems to
be alive, and to insist on retaining its position, in spite of all
efforts to the contrary.
This principle is used in the swinging cabin of the Bessemer ship, and
is also employed by quoit-players in keeping their missile steady as it
flies towards the mark. Even the now fashionable Bicycle is managed on
the same principle.
As is well known to all bicycle riders, it is comparatively easy to
maintain the balance when the pace is rapid and the wheels revolving
quickly. The difficulty is, to do so when the pace is slow, and the
rider is deprived of the centrifugal force which keeps him on his
balance almost in spite of himself. It is just the same with a child’s
hoop, which runs straight and upright when it is driven rapidly, or
when, for example, it runs downhill. But, as soon as the centrifugal
force is expended, it begins to waver, loses its direction, and soon
falls to the ground.
USEFUL ARTS.