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.
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.
CHAPTER XVI.
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.
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.
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.
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.
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.
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.
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 th