Falling in Love; With Other Essays on More Exact Branches of Science
Meteors, indeed, might very easily be confounded with lightning, especially by people who already have the full-blown conception of a thunderbolt floating about vaguely in their brains. The meteor leaps upon the earth suddenly with a rushing noise; it is usually red-hot when it falls, by friction against the air; it is mostly composed of native iron and other heavy metallic bodies; and it does its best to bury itself in the ground in the most orthodox and respectable manner. The man who sees this parlous monster come whizzing through the clouds from planetary space, making a fiery track like a great dragon as it moves rapidly across the sky, and finally ploughing its way into the earth in his own back garden, may well be excused for regarding it as a fine specimen of the true antique thunderbolt. The same virtues which belong to the buried stone are in some other places claimed for meteoric iron, small pieces of which are worn as charms, specially useful in protecting the wearer against thunder, lightning, and evil incantations. In many cases miraculous images have been hewn out of the stones that have fallen from heaven; and in others the meteorite itself is carefully preserved or worshipped as the actual representative of god or goddess, saint or madonna. The image that fell down from Jupiter may itself have been a mass of meteoric iron.
Both meteorites and stone hatchets, as well as all other forms of thunderbolt, are in excellent repute as amulets, not only against lightning, but against the evil eye generally. In Italy they protect the owner from thunder, epidemics, and cattle disease, the last two of which are well known to be caused by witchcraft; while Prospero in the 'Tempest' is a surviving proof how thunderstorms, too, can be magically produced. The tongues of sheep-bells ought to be made of meteoric iron or of elf-bolts, in order to insure the animals against foot-and-mouth disease or death by storm. Built into walls or placed on the threshold of stables, thunderbolts are capital preventives of fire or other damage, though not perhaps in this respect quite equal to a rusty horseshoe from a prehistoric battlefield. Thrown into a well they purify the water; and boiled in the drink of diseased sheep they render a cure positively certain. In Cornwall thunderbolts are a sovereign remedy for rheumatism; and in the popular pharmacopœia of Ireland they have been employed with success for ophthalmia, pleurisy, and many other painful diseases. If finely powdered and swallowed piecemeal, they render the person who swallows them invulnerable for the rest of his lifetime. But they cannot conscientiously be recommended for dyspepsia and other forms of indigestion.
As if on purpose to confuse our already very vague ideas about thunderbolts, there is one special kind of lightning which really seems intentionally to simulate a meteorite, and that is the kind known as fireballs or (more scientifically) globular lightning. A fireball generally appears as a sphere of light, sometimes only as big as a Dutch cheese, sometimes as large as three feet in diameter. It moves along very slowly and demurely through the air, remaining visible for a whole minute or two together; and in the end it generally bursts up with great violence, as if it were a London railway station being experimented upon by Irish patriots. At Milan one day a fireball of this description walked down one of the streets so slowly that a small crowd walked after it admiringly, to see where it was going. It made straight for a church steeple, after the common but sacrilegious fashion of all lightning, struck the gilded cross on the topmost pinnacle, and then immediately vanished, like a Virgilian apparition, into thin air.
A few years ago, too, Dr. Tripe was watching a very severe thunderstorm, when he saw a fire-ball come quietly gliding up to him, apparently rising from the earth rather than falling towards it. Instead of running away, like a practical man, the intrepid doctor held his ground quietly and observed the fiery monster with scientific nonchalance. After continuing its course for some time in a peaceful and regular fashion, however, without attempting to assault him, it finally darted off at a tangent in another direction, and turned apparently into forked lightning. A fire-ball, noticed among the Glendowan Mountains in Donegal, behaved even more eccentrically, as might be expected from its Irish antecedents. It first skirted the earth in a leisurely way for several hundred yards like a cannon-ball; then it struck the ground, ricochetted, and once more bounded along for another short spell; after which it disappeared in the boggy soil, as if it were completely finished and done for. But in another moment it rose again, nothing daunted, with Celtic irrepressibility, several yards away, pursued its ghostly course across a running stream (which shows, at least, there could have been no witchcraft in it), and finally ran to earth for good in the opposite bank, leaving a round hole in the sloping peat at the spot where it buried itself. Where it first struck, it cut up the peat as if with a knife, and made a broad deep trench which remained afterwards as a witness of its eccentric conduct. If the person who observed it had been of a superstitious turn of mind we should have had here one of the finest and most terrifying ghost stories on the entire record, which would have made an exceptionally splendid show in the 'Transactions of the Society for Psychical Research.' Unfortunately, however, he was only a man of science, ungifted with the precious dower of poetical imagination; so he stupidly called it a remarkable fire-ball, measured the ground carefully like a common engineer, and sent an account of the phenomenon to that far more prosaic periodical, the 'Quarterly Journal of the Meteorological Society.' Another splendid apparition thrown away recklessly, for ever!
There is a curious form of electrical discharge, somewhat similar to the fire-ball but on a smaller scale, which may be regarded as the exact opposite of the thunderbolt, inasmuch as it is always quite harmless. This is St. Elmo's fire, a brush of lambent light, which plays around the masts of ships and the tops of trees, when clouds are low and tension great. It is, in fact, the equivalent in nature of the brush discharge from an electric machine. The Greeks and Romans looked upon this lambent display as a sign of the presence of Castor and Pollux, 'fratres Helenæ, lucida sidera,' and held that its appearance was an omen of safety, as everybody who has read the 'Lays of Ancient Rome' must surely remember. The modern name, St. Elmo's fire, is itself a curiously twisted and perversely Christianised reminiscence of the great twin brethren; for St. Elmo is merely a corruption of Helena, made masculine and canonised by the grateful sailors. It was as Helen's brothers that they best knew the Dioscuri in the good old days of the upper empire; and when the new religion forbade them any longer to worship those vain heathen deities, they managed to hand over the flames at the masthead to an imaginary St. Elmo, whose protection stood them in just as good stead as that of the original alternate immortals.
Finally, the effects of lightning itself are sometimes such as to produce upon the mind of an impartial but unscientific beholder the firm idea that a bodily thunderbolt must necessarily have descended from heaven. In sand or rock, where lightning has struck, it often forms long hollow tubes, known to the calmly discriminating geological intelligence as fulgurites, and looking for all the world like gigantic drills such as quarrymen make for putting in a blast. They are produced, of course, by the melting of the rock under the terrific heat of the electric spark; and they grow narrower and narrower as they descend till they finally disappear. But to a casual observer, they irresistibly suggest the notion that a material weapon has struck the ground, and buried itself at the bottom of the hole. The summit of Little Ararat, that weather-beaten and many-fabled peak (where an enterprising journalist not long ago discovered the remains of Noah's Ark), has been riddled through and through by frequent lightnings, till the rock is now a mere honeycombed mass of drills and tubes, like an old target at the end of a long day's constant rifle practice. Pieces of the red trachyte from the summit, a foot long, have been brought to Europe, perforated all over with these natural bullet marks, each of them lined with black glass, due to the fusion of the rock by the passage of the spark. Specimens of such thunder-drilled rock may be seen in most geological museums. On some which Humboldt collected from a peak in Mexico, the fused slag from the wall of the tube has overflowed on to the surrounding surface, thus conclusively proving (if proof were necessary) that the holes are due to melting heat alone, and not to the passage of any solid thunderbolt.
But it was the introduction and general employment of lightning-rods that dealt a final deathblow to the thunderbolt theory. A lightning-conductor consists essentially of a long piece of metal, pointed at the end whose business it is, not so much (as most people imagine) to carry off the flash of lightning harmlessly, should it happen to strike the house to which the conductor is attached, but rather to prevent the occurrence of a flash at all, by gradually and gently drawing off the electricity as fast as it gathers before it has had time to collect in sufficient force for a destructive discharge. It resembles in effect an overflow pipe which drains off the surplus water of a pond as soon as it runs in, in such a manner as to prevent the possibility of an inundation, which might occur if the water were allowed to collect in force behind a dam or embankment. It is a flood-gate, not a moat: it carries away the electricity of the air quietly to the ground, without allowing it to gather in sufficient amount to produce a flash of lightning. It might thus be better called a lightning-preventer than a lightning-conductor: it conducts electricity, but it prevents lightning. At first, all lightning-rods used to be made with knobs on the top, and then the electricity used to collect at the surface until the electric force was sufficient to cause a spark. In those happy days, you had the pleasure of seeing that the lightning was actually being drawn off from your neighbourhood piecemeal. Knobs, it was held, must be the best things, because you could incontestably see the sparks striking them with your own eyes. But as time went on, electricians discovered that if you fixed a fine metal point to the conductor of an electric machine it was impossible to get up any appreciable charge because the electricity kept always leaking out by means of the point. Then it was seen that if you made your lightning-rods pointed at the end, you would be able in the same way to dissipate your electricity before it ever had time to come to a head in the shape of lightning. From that moment the thunderbolt was safely dead and buried. It was urged, indeed, that the attempt thus to rob Heaven of its thunders was wicked and impious; but the common-sense of mankind refused to believe that absolute omnipotence could be sensibly defied by twenty yards of cylindrical iron tubing. Thenceforth the thunderbolt ceased to exist, save in poetry, country houses, and the most rural circles; even the electric fluid was generally relegated to the provincial press, where it still keeps company harmoniously with caloric, the devouring element, nature's abhorrence of a vacuum, and many other like philosophical fossils: while lightning itself, shorn of its former glories, could no longer wage impious war against cathedral towers, but was compelled to restrict itself to blasting a solitary rider now and again in the open fields, or drilling more holes in the already crumbling summit of Mount Ararat. Yet it will be a thousand years more, in all probability, before the last thunderbolt ceases to be shown as a curiosity here and there to marvelling visitors, and takes its proper place in some village museum as a belemnite, a meteoric stone, or a polished axe-head of our neolithic ancestors. Even then, no doubt, the original bolt will still survive as a recognised property in the stock-in-trade of every well-equipped poet.
HONEY-DEW
Place, the garden. Time, summer. Dramatis personæ, a couple of small brown garden-ants, and a lazy clustering colony of wee green 'plant-lice,' or 'blight,' or aphides. The exact scene is usually on the young and succulent branches of a luxuriant rose-bush, into whose soft shoots the aphides have deeply buried their long trunk-like snouts, in search of the sap off which they live so contentedly through their brief lifetime. To them, enter the two small brown ants, their lawful possessors; for ants, too, though absolutely unrecognised by English law ('de minimis non curat lex,' says the legal aphorism), are nevertheless in their own commonwealth duly seised of many and various goods and chattels; and these same aphides, as everybody has heard, stand to them in pretty much the same position as cows stand to human herdsmen. Throw in for sole spectator a loitering naturalist, and you get the entire mise-en-scène of a quaint little drama that works itself out a dozen times among the wilted rose-trees beneath the latticed cottage windows every summer morning.
It is a delightful sight to watch the two little lilliputian proprietors approaching and milking these their wee green motionless cattle. First of all, the ants quickly scent their way with protruded antennæ (for they are as good as blind, poor things!) up the prickly stem of the rose-bush, guided, no doubt, by the faint perfume exhaled from the nectar above them. Smelling their road cautiously to the ends of the branches, they soon reach their own particular aphides, whose bodies they proceed gently to stroke with their outstretched feelers, and then stand by quietly for a moment in happy anticipation of the coming dinner. Presently, the obedient aphis, conscious of its lawful master's friendly presence, begins slowly to emit from two long horn-like tubes near the centre of its back a couple of limpid drops of a sticky pale yellow fluid. Honey-dew our English rustics still call it, because, when the aphides are not milked often enough by ants, they discharge it awkwardly of their own accord, and then it falls as a sweet clammy dew upon the grass beneath them. The ant, approaching the two tubes with cautious tenderness, removes the sweet drops without injuring in any way his little protégé, and then passes on to the next in order of his tiny cattle, leaving the aphis apparently as much relieved by the process as a cow with a full hanging udder is relieved by the timely attention of the human milkmaid.
Evidently, this is a case of mutual accommodation in the political economy of the ants and aphides: a free interchange of services between the ant as consumer and the aphis as producer. Why the aphides should have acquired the curious necessity for getting rid of this sweet, sticky, and nutritious secretion nobody knows with certainty; but it is at least quite clear that the liquid is a considerable nuisance to them in their very sedentary and monotonous existence—a waste product of which they are anxious to disembarrass themselves as easily as possible—and that while they themselves stand to the ants in the relation of purveyors of food supply, the ants in return stand to them in the relation of scavengers, or contractors for the removal of useless accumulations.
Everybody knows the aphides well by sight, in one of their forms at least, the familiar rose aphis; but probably few people ever look at them closely and critically enough to observe how very beautiful and wonderful is the organisation of their tiny limbs in all its exquisite detail. If you pick off one good-sized wingless insect, however, from a blighted rose-leaf, and put him on a glass slide under a low power of the microscope, you will most likely be quite surprised to find what a lovely little creature it is that you have been poisoning wholesale all your life long with diluted tobacco-juice. His body is so transparent that you can see through it by transmitted light: a dainty glass globe, you would say, of emerald green, set upon six tapering, jointed, hairy legs, and provided in front with two large black eyes of many facets, and a pair of long and very flexible antennæ, easily moved in any direction, but usually bent backward when the creature is at rest so as to reach nearly to his tail as he stands at ease upon his native rose-leaf. There are, however, two other features about him which specially attract attention, as being very characteristic of the aphides and their allies among all other insects. In the first place, his mouth is provided with a very long snout or proboscis, classically described as a rostrum, with which he pierces the outer skin of the rose-shoot where he lives, and sucks up incessantly its sweet juices. This organ is common to the aphis with all the other bugs and plant-lice. In the second place, he has half-way down his back (or a little more) a pair of very peculiar hollow organs, the honey tubes, from which exudes that singular secretion, the honey-dew. These tubes are not found in quite all species of aphides, but they are very common among the class, and they form by far the most conspicuous and interesting organs in all those aphides which do possess them.
The life-history of the rose-aphis, small and familiar as is the insect itself, forms one of the most marvellous and extraordinary chapters in all the fairy tales of modern science. Nobody need wonder why the blight attacks his roses so persistently when once he has learnt the unusual provision for exceptional fertility in the reproduction of these insect plagues. The whole story is too long to give at full length, but here is a brief recapitulation of a year's generations of common aphides.
In the spring, the eggs of last year's crop, which have been laid by the mothers in nooks and crannies out of reach of the frost, are quickened into life by the first return of warm weather, and hatch out their brood of insects. All this brood consists of imperfect females, without a single male among them; and they all fasten at once upon the young buds of their native bush, where they pass a sluggish and uneventful existence in sucking up the juice from the veins on the one hand, and secreting honey-dew upon the other. Four times they moult their skins, these moults being in some respects analogous to the metamorphosis of the caterpillar into chrysalis and butterfly. After the fourth moult, the young aphides attain maturity; and then they give origin, parthenogenetically, to a second brood, also of imperfect females, all produced without any fathers. This second brood brings forth in like manner a third generation, asexual, as before; and the same process is repeated without intermission as long as the warm weather lasts. In each case, the young simply bud out from the ovaries of the mothers, exactly as new crops of leaves bud out from the rose-branch on which they grow. Eleven generations have thus been observed to follow one another rapidly in a single summer; and indeed, by keeping the aphides in a warm room, one may even make them continue their reproduction in this purely vegetative fashion for as many as four years running. But as soon as the cold weather begins to set in, perfect male and female insects are produced by the last swarm of parthenogenetic mothers; and these true females, after being fertilised, lay the eggs which remain through the winter, and from which the next summer's broods have to begin afresh the wonderful cycle. Thus, only one generation of aphides, out of ten or eleven, consists of true males and females: all the rest are false females, producing young by a process of budding.
Setting aside for the present certain special modifications of this strange cycle which have been lately described by M. Jules Lichtenstein, let us consider for a moment what can be the origin and meaning of such an unusual and curious mode of reproduction.
The aphides are on the whole the most purely inactive and vegetative of all insects, unless indeed we except a few very debased and degraded parasites. They fasten themselves early in life on to a particular shoot of a particular plant; they drink in its juices, digest them, grow, and undergo their incomplete metamorphoses; they produce new generations with extraordinary rapidity; and they vegetate, in fact, almost as much as the plant itself upon which they are living. Their existence is duller than that of the very dullest cathedral city. They are thus essentially degenerate creatures: they have found the conditions of life too easy for them, and they have reverted to something so low and simple that they are almost plant-like in some of their habits and peculiarities.
The ancestors of the aphides were free winged insects; and, in certain stages of their existence, most living species of aphides possess at least some winged members. On the rose-bush, you can generally pick off a few such larger winged forms, side by side with the wee green wingless insects. But creatures which have taken to passing most of their life upon a single spot on a single plant hardly need the luxury of wings; and so, in nine cases out of ten, natural selection has dispensed with those needless encumbrances. Even the legs are comparatively little wanted by our modern aphides, which only require them to walk away in a stately sleepy manner when rudely disturbed by man, lady-birds, or other enemies; and indeed the legs are now very weak and feeble, and incapable of walking for more than a short distance at a time under exceptional provocation. The eyes remain, it is true; but only the big ones: the little ocelli at the top of the head, found amongst so many of their allies, are quite wanting in all the aphides. In short, the plant-lice have degenerated into mere mouths and sacks for sucking and storing food from the tissues of plants, provided with large honey-tubes for getting rid of the waste sugar.
Now, the greater the amount of food any animal gets, and the less the amount of expenditure it performs in muscular action, the greater will be the surplus it has left over for the purposes of reproduction. Eggs or young, in fact, represent the amount thus left over after all the wants of the body have been provided for. But in the rose-aphis the wants of the body, when once the insect has reached its full growth, are absolutely nothing; and it therefore then begins to bud out new generations in rapid succession as fast as ever it can produce them. This is strictly analogous to what we see every day taking place in all the plants around us. New leaves are produced one after another, as fast as material can be supplied for their nutrition, and each of these new leaves is known to be a separate individual, just as much as the individual aphis. At last, however, a time comes when the reproductive power of the plant begins to fail, and then it produces flowers, that is to say stamens (male) and pistils (female), whose union results in fertilisation and the subsequent outgrowth of fruit and seeds. Thus a year's cycle of the plant-lice exactly answers to the life-history of an ordinary annual. The eggs correspond to the seeds; the various generations of aphides budding out from one another by parthenogenesis correspond to the leaves budded out by one another throughout the summer; and the final brood of perfect males and females answers to the flower with its stamen and pistils, producing the seeds, as they produce the eggs, for setting up afresh the next year's cycle.
This consideration, I fancy, suggests to us the most probable explanation of the honey-tubes and honey-dew. Creatures that eat so much and reproduce so fast as the aphides are rapidly sucking up juices all the time from the plant on which they fasten, and converting most of the nutriment so absorbed into material for fresh generations. That is how they swarm so fast over all our shrubs and flowers. But if there is any one kind of material in their food in excess of their needs, they would naturally have to secrete it by a special organ developed or enlarged for the purpose. I don't mean that the organ would or could be developed all at once, by a sudden effort, but that as the habit of fixing themselves upon plants and sucking their juices grew from generation to generation with these descendants of originally winged insects, an organ for permitting the waste product to exude must necessarily have grown side by side with it. Sugar seems to have been such a waste product, contained in the juices of the plant to an extent beyond what the aphides could assimilate or use up in the production of new broods; and this sugar is therefore secreted by special organs, the honey-tubes. One can readily imagine that it may at first have escaped in small quantities, and that two pores on their last segment but two may have been gradually specialised into regular secreting organs, perhaps under the peculiar agency of the ants, who have regularly appropriated so many kinds of aphides as miniature milch cows.
