The Rain Cloud Part 5

Thus it will be seen, that the primary bow is produced by two refractions, and one intermediate reflection of the rays that fall on the upper sides of the drops of rain. It is different with the rays which enter the drops below. The red and violet rays will be bent or refracted in different directions; and, after being twice reflected, will be again bent towards the eye of the observer at E; but in this case the violet forms the upper part, and the red the under part of the spectrum. The inclination of these rays to the sun's rays at S, is 50 58' for the red ray, and 54 10' for the violet ray; so that the breadth of the bow is 3 10', and the distance between the primary and secondary bows is 8 15'.

Hence the secondary is formed in the outside of the primary bow, with its colours reversed, in consequence of their being produced by two reflexions and two refractions. The colours of the secondary bow are much fainter than those of the primary, because they undergo two reflexions instead of one.

There is something very wonderful in the rapidity and perfection with which these natural prisms, the falling drops of rain, produce these effects. In the inconceivably short s.p.a.ce of time occupied by a drop falling through those parts of the sky which form the proper angles with the sun's rays and the eye of the observer, the light enters the surface of the drop, undergoes within it one or two reflexions, two refractions and decompositions, and has reached the eye; and all this is done in a portion of time too small for the drop to have fallen through a s.p.a.ce which we have the means of measuring.

It will be understood, that since the eyes of different observers cannot be in precisely the same place at the same time, no two observers can see the _same_ rainbow; that is to say, the bow produced by one set of drops to the eye of one observer is produced by another set of drops to the eye of another observer.

A rainbow can never be greater than a semicircle, unless the spectator is on elevated ground; for if it were greater than a semicircle the centre of the bow would be above the horizon, while the sun, which must be in a line drawn through that centre and the eye of the observer, would be below the horizon: but in such a case, the sun could not shine on the drops of rain, and consequently there could be no rainbow.

When the rain cloud is of small extent only a portion of a bow is visible; when the cloud overspreads a large part of the sky a perfect bow appears. Sometimes the bow may be traced across a portion of blue sky, or it may appear to rest on the ground. In the former case, there are vapours in the air too thin to be seen, but sufficient to refract and reflect the rays of light; in the latter, the drops of rain, adhering to the gra.s.s and foliage, produce the same effect. A coloured bow, similar to that produced by rain, is sometimes seen in the spray of a fountain or of a water-fall, and also in mists that lie low upon the ground.

In mountainous and stormy regions rainbows are often seen to great advantage. In the islands off the Irish coast the author of "Letters from the Irish Islands," describes the rainbow of winter "as gradually advancing before the lowering clouds, sweeping with majestic stride across the troubled ocean, then, as it gained the beach, and seemed almost within one's grasp, vanishing amid the storm of which it had been the lovely but treacherous forerunner. It is, I suppose, a consequence of our situation, and the close connexion between sea and mountain, that the rainbows here are so frequent and so peculiarly beautiful. Of an amazing breadth, and of colours vivid beyond description, I know not whether most to admire this aerial phenomenon, when suspended in the western sky, one end of the bow sinks behind the Island of Boffin, while at the distance of several leagues the other rests upon the misty hills of Ennis Turc; or when, at a later hour of the day, it has appeared stretched across the ample sides of Mulbrea, penetrating far into the deep blue waters that flow at its base. With feelings of grateful recollection, too, we may hail the repeated visits of this heavenly messenger, occasionally as often as five or six times in the course of the same day, in a country exposed to such astonishing, and, at times, almost incessant floods of rain."

The beauty of the rainbow is not the only reason why we should regard it with interest. The rainbow was appointed by G.o.d himself as a sign of the covenant of mercy, made with Noah and with all mankind, after the flood.

The words in which this declaration was made to mankind, are recorded in the Book of Genesis, chap. ix. ver. 11 to 16.

Burnet, in his "Sacred Theory of the Earth," has some remarks on the first appearance of the rainbow to the inhabitants of the earth after the deluge. He says, "How proper and how apposite a sign would this be for Providence to pitch upon, to confirm the promise made to Noah and his posterity, that the world should be no more destroyed by water! It had a secret connexion with the effect itself, and was so far a natural sign; but, however, appearing first after the deluge, and in a watery cloud, there was, methinks, a great easiness and propriety of application for such a purpose. And if we suppose, that while G.o.d Almighty was declaring his promise to Noah, and the sign of it, there appeared at the same time in the clouds a fair rainbow, that marvellous and beautiful meteor which Noah had never seen before; it could not but make a most lively impression upon him, quickening his faith, and giving him comfort and a.s.surance that G.o.d would be stedfast to his promise."

A rainbow is sometimes formed by the rays of the moon falling upon drops of rain, in the same manner as the solar rays, and refracted and reflected by the drops; but the colours are faint in consequence of the feeble light of the moon compared with that of the sun. A lunar rainbow has been thus described by an observer:-"The moon was truly 'walking in brightness,' brilliant as she could be, not a cloud was to be seen near her; and over against her, toward the north-west, or perhaps rather more to the north, was a rainbow, a vast arch, perfect in all its parts, not interrupted or broken as rainbows frequently are, but unremittedly visible from one horizon to the other. In order to give some idea of its extent, it is necessary to say, that, as I stood toward the western extremity of the parish of Stoke Newington, it seemed to take its rise from the west of Hampstead, and to end perhaps in the river Lea, the eastern boundary of Tottenham. Its colour was white, cloudy, or greyish, but a part of its western limb seemed to exhibit tints of a faint sickly green. After some time the moon became darkened by clouds, and the rainbow of course vanished."

[Picture: Lunar Rainbow]

The brilliant colours of the solar rainbow are frequently produced by the clouds without any prismatic arrangement. The light of the sun is decomposed by a process called absorption: for example, white light is composed of red, yellow, and blue rays, in certain proportions; now, if in pa.s.sing through, or falling upon any substance whatever, the red rays are stifled or absorbed, while the yellow and blue are allowed to pa.s.s or to be reflected, it is obvious that such a substance cannot appear white, because one of the elements of white light, namely, the red, is wanting; it must therefore appear of such a colour as results from the combination of yellow and blue; the substance will therefore appear green. So, also, when white light falls upon what we call a _red_ surface, the yellow and blue rays are stifled or absorbed, leaving the red only to be reflected.

Now, when we consider the various ways in which this absorption may take place; one or two, or all of the coloured rays being absorbed in every possible proportion, it is easy to form some idea of the manner by which the innumerable tints of the sky are produced.

It has been calculated, that, of the horizontal sunbeams which pa.s.s through two hundred miles of air, scarcely a two thousandth part reaches the earth. A densely formed cloud must therefore detain a much larger share; and those dark and sombre forms, which sometimes make the sky so gloomy, can only result from the abundant absorption of the solar light.

The brilliant whiteness which their edges occasionally exhibit, must result from the more copious transmission of light, so that the depths of shade in a cloud may be regarded as comparative measures of the varied thickness of its ma.s.s.

Sometimes the clouds absorb equally all the solar rays, in which case the sun and moon appear through them perfectly white. Instances are recorded in which the sun appeared of a pale blue. It has also been observed to be orange at its upper part, while the lower was of a brilliant red.

The position from which clouds are seen, has much to do with their colours; and it seems difficult sometimes to believe that the clouds, which in the evening are seen drenched with crimson and gold, are the same we beheld absolutely colourless in the middle of the day.

In the immediate neighbourhood of the sun the most brilliant colours may be disclosed; and their vividness and intensity diminish, and at last disappear at some distance from it. Parry noticed some white fleecy clouds, which, at the distance of fifteen or twenty degrees from the sun, reflected from their edges the most soft and tender tints of yellow, bluish green, and lake; and as the clouds advanced the colours increased gradually, until they reached a sort of limit two degrees below the solar orb. As the current continued to transport them, the vividness of colour became weakened by almost insensible degrees until the whole a.s.semblage of tints vanished.

"Who can venture to imitate, by the pencil, the endless varieties of red and orange and yellow which the setting sun discloses, and the magical illusions which all the day diversify the vast and varied s.p.a.ce the eye travels over in rising gradually from the horizon to the upper sky?

Those who have paid any attention to colours, must be aware of the difficulty of describing the various tints and shades that appear, and which are known to amount to many thousands."

The rapid changes of colour which the clouds undergo, seem to depend on something more than change of position either in the cloud or in the sun.

Forster mentions an instance of some detached cirro-c.u.muli being of a fine golden yellow, but in a single minute becoming deep red. On another occasion he saw the exact counterpart in a cirro-stratus, by its instantly changing from a beautiful red to a bright golden yellow.

"What, indeed, can be more interesting, than when by the breaking out of the sun in gleams, a cloud which a moment before seemed only an unshapened ma.s.s devoid of all interest and beauty, is suddenly pierced by cataracts of light, and imbued with the most splendid colours, varying every instant in intensity? Numerous examples occur of this beautiful play of colour, which cannot but remind us of the phenomena displayed by the pigeon's neck and the peac.o.c.k's tail, by opal and pearl.

"After the sun is set, the mild glow of his rays is still diffused over every part; and it has been remarked, that the clouds a.s.sume their brightest and most splendid colours a few minutes after it is below the horizon. It is in the finest weather that the colouring of the sky presents the most perfect examples of harmony, in tempestuous weather it being almost always inharmonious. At the time of a warm sun-setting, the whole hemisphere is influenced by the prevailing colour of the light.

The snowy summits of the Alps appear about sunset of a most beautiful violet colour, approaching to light crimson or pink. It is remarkable, also, as an example of that general harmony which prevails in the material world, that the most glowing and magnificent skies occur when terrestrial objects put on their deepest and most splendid hues. It has also been observed, that it is not the change of vegetation only, which gives to the decaying charms of autumn their finest and most golden hues, but also the atmosphere and the peculiar lights and shadows which then prevail; and there can be no doubt, on the other hand, that our perception of beauty in the sky is very much influenced by the surrounding scenery. In autumn all is matured; and the rich hues of the ripened fruits and the changing foliage are rendered still more lovely by the warm haze which a fine day at that season presents. So, also, the earlier hues of spring have a transparency, and a thousand quivering lights, which in their turn harmonize with the light and flitting clouds and uncertain shadows which then prevail." {155}

[Picture: Decorative picture of lady by river]

[Picture: Foot-print of a bird, and impression of rain-drops sand-stone]

CHAPTER VII.

REMARKABLE SHOWERS-SHOWERS OF SAND-OF MUD-SHOWERS OF SULPHUR, OR YELLOW RAIN-LUMINOUS RAIN-RED RAIN, OR SHOWERS OF BLOOD-SUPERSt.i.tIONS CONNECTED THEREWITH-EXPLANATION OF THE CAUSE-SHOWERS OF FISH-SHOWERS OF RATS-SHOWERS OF FROGS-INSECT SHOWER-SHOWERS OF VEGETABLE SUBSTANCES-MANNA-WHEAT-SHOWERS OF STONES-METEORIC STONES, OR AEROLITES-METEORIC IRON-SUPPOSITIONS RESPECTING THEM-FOSSIL RAIN.

Water, in the state of rain, hail, snow, or dew, is generally the only substance which falls from the atmosphere upon the earth. There are, however, many well authenticated instances of various substances being showered down upon the land, to the great alarm of persons who were ignorant that the powerful action of the wind was, perhaps, the chief cause of the strange visitations to which we allude.

We read of showers of sand, mud, sulphur, blood, fishes, frogs, insects, and stones; and it may be useful, as well as interesting, to quote a few examples of each description of shower.

On the west coast of Africa, between Cape Bojador and Cape Verd, and thence outwards, the land, during the dry season, consists of little else but dust or sand, which, on account of its extreme fineness, is raised into the atmosphere by the slightest current of air; while a moderate wind will convey it to so considerable a distance as even to annoy ships crossing the Atlantic. On the 14th and 15th January, 1839, the Prussian ship, _Princess Louisa_, being in N. lat. 24 20', and W. long. 26 42', had her sails made quite yellow by the fine sand which covered them.

This effect was produced when the distance from land was as much as from 12 to 20. About a fortnight after the time when this ship crossed these parts of the Atlantic, a similar effect was produced on board the English ship _Roxburgh_. One of the pa.s.sengers, the Rev. W. B. Clarke, says:-"The sky was overcast, and the weather thick and insufferably oppressive, though the thermometer was only 72. At 3 P.M. Feb. 4, the wind suddenly lulled into a calm; then rose from the SW. accompanied by rain, and the air appeared to be filled with dust, which affected the eyes of the pa.s.sengers and crew. The weather was clear and fine, and the powder which covered the sails was of a reddish-brown colour, resembling the ashes ejected from Vesuvius; and Mr. Clarke thinks that this dust may have proceeded from the volcanic island of Fogo, one of the Cape de Verds, about forty-five miles from the place where the ship then was.

In countries which are subject to long-continued droughts the soil is frequently converted into dust, which, being carried away by the winds, leaves the land barren. The climate of Buenos Ayres, in South America, has of late years been subject to such droughts, as to disappoint the hopes of the husbandman and the breeder of cattle. In the early part of 1832, the drought had reached to such a height as to convert the whole province into one continued bleak and dreary desert. The clouds of dust raised by the winds were so dense as completely to obscure the sun at mid-day, and envelope the inhabitants in almost total darkness. When the rains at length commenced, in March, the water, in its pa.s.sage through the air, intermingled so completely with the dust suspended in it, as to descend in the form of showers of mud; and, on some occasions, gave to the whole exterior of the houses the appearance of having been plastered over with earth. Many flocks of sheep were smothered on these occasions, in a similar manner as in the snow-storms which occur in the mountainous districts of Scotland.

Showers of sulphur, or yellow rain, have fallen at different times in various parts of Europe; and sometimes, when falling by night, they have appeared luminous, to the great alarm of the observers. Yellow rain has been accounted for in the following way:-The pollen, or impregnating seed-dust of the flowers of the fir, birch, juniper, and other trees, is of a yellow colour, and this pollen, by the action of the wind, is carried to a considerable distance, and descends with falling rain. This yellow rain has also been found impregnated with sulphur; and during a shower of this kind which once fell in Germany, matches were made by being dipped in it.

Many examples of luminous rain are recorded on good authority. One of the latest instances is mentioned by Dr. Morel Deville, of Paris, who on the 1st of November, 1844, at half-past eight o'clock in the evening, during a heavy fall of rain, noticed, as he was crossing the court of the College Louis-le-Grand, that the drops, on coming in contact with the ground, emitted sparks and tufts (_aigrettes_) of light, accompanied by a rustling and crackling noise; a smell of phosphorus having been immediately after perceptible. The phenomenon was seen three times. At the same hour a remarkable brightness was seen in the northern sky.

An officer of the Algerian army states, that during a violent storm on the 20th September, 1840, the drops of rain that fell on the beards and mustachios of the men were luminous. When the hair was wiped the appearance ceased; but was renewed the moment any fresh drops fell on it.

But of all these remarkable showers, the greatest alarm has been occasioned by _red rain_, or showers of blood as they have been ignorantly called. In the year 1608, considerable alarm was excited in the city of Aix and its vicinity by the appearance of large red drops upon the walls of the cemetery of the greater church, which is near the walls of the city, upon the walls of the city itself, and also upon the walls of villas, hamlets, and towns, for some miles round the city. The husbandmen are said to have been so alarmed, that they left their labour in the fields and fled for safety into the neighbouring houses; and a report was set on foot, that the appearance was produced by demons or witches shedding the blood of innocent babes. M. Peiresc, thinking this story of a b.l.o.o.d.y shower to be scarcely reconcileable with the goodness and providence of G.o.d, accidentally discovered, as he thought, the true cause of the phenomenon. He had found, some months before, a chrysalis of remarkable size and form, which he had enclosed in a box; he thought no more of it, until hearing a buzz within the box, he opened it, and perceived that the chrysalis had been changed into a beautiful b.u.t.terfly, which immediately flew away, leaving at the bottom of the box a red drop of the size of a shilling. As this happened about the time when the shower was supposed to have fallen, and when mult.i.tudes of those insects were observed fluttering through the air in every direction, he concluded that the drops in question were emitted by them when they alighted upon the walls. He, therefore, examined the drops again, and remarked that they were not upon the upper surfaces of stones and buildings, as they would have been if a shower of blood had fallen from the sky, but rather in cavities and holes where insects might nestle. He also noticed that they were to be seen upon the walls of those houses only which were near the fields; and not upon the more elevated parts of them, but only up to the same moderate height at which b.u.t.terflies were accustomed to flutter.

This was, no doubt, the correct explanation of the phenomenon in question; for it is a curious and well-ascertained fact, that when insects are evolved from the pupa state, they always discharge some substance, which, in many b.u.t.terflies, is of a red colour, resembling blood, while in several moths it is orange or whitish.

It appears, however, from the researches of M. Ehrenberg, a distinguished microscopic observer, that the appearances of blood which have at different times been observed in Arabia, Siberia, and other places, are not to be attributed to one, but to various causes. From his account, it appears that rivers have flowed suddenly with red or b.l.o.o.d.y water, without any previous rain of that colour having fallen; that lakes or stagnant-waters were suddenly or gradually coloured without previous blood-rain; that dew, rain, snow, hail, and shot-stars, occasionally fall from the air red-coloured, as blood-dew, blood-rain, and clotted blood; and, lastly, that the atmosphere is occasionally loaded with red dust, by which the rain accidentally a.s.sumes the appearance of blood-rain, in consequence of which rivers and stagnant waters a.s.sume a red colour.

The blood-red colour sometimes exhibited by pools, was first satisfactorily explained at the close of the last century. Girod Chantran, observing the water of a pond to be of a brilliant red colour, examined it with the microscope, and found that the sanguine hue resulted from the presence of innumerable animalculae, not visible to the naked eye. But, before this investigation, Linnaeus and other naturalists had shown that red infusoria were capable of giving that colour to water which, in early times, and still, we fear, in remote districts, was supposed to forebode great calamities. In the year 1815 an instance of this superst.i.tious dread occurred in the south of Prussia. A number of red, violet, or gra.s.s-green spots were observed in a lake near Lubotin, about the end of harvest. In winter the ice was coloured in the same manner at the surface, while beneath it was colourless. The inhabitants, in great dismay, antic.i.p.ated a variety of disasters from the appearance; but it fortunately happened that the celebrated chemist Klaproth, hearing of the circ.u.mstance, undertook an examination of the waters of the lake.

He found them to contain an alb.u.minous vegetable matter, with a particular colouring matter similar to indigo, produced, probably, by the decomposition of vegetables in harvest; while the change of colour from green to violet and red, he explained by the absorption of more or less oxygen. A few years ago the blood-red waters of a Siberian lake were carefully examined by M. Ehrenberg, and found to contain mult.i.tudes of infusoria, by the presence of which this remarkable appearance was accounted for. Thus it appears that both animals and vegetables are concerned in giving a peculiar tint to water. It has also been ascertained that red snow is chiefly occasioned by the presence of red animalculae.

Showers of fish and frogs are by no means uncommon, especially in India.

One of these showers, which fell about twenty miles south of Calcutta, is thus noticed by an observer:-"About two o'clock, P.M., of the 20th inst., (Sept. 1839,) we had a very smart shower of rain, and with it descended a quant.i.ty of live fish, about three inches in length, and all of one kind only. They fell in a straight line on the road from my house to the tank which is about forty or fifty yards distant. Those which fell on the hard ground were, as a matter of course, killed from the fall, but those which fell where there was gra.s.s sustained no injury; and I picked up a large quant.i.ty of them, 'alive and kicking,' and let them go into my tank. The most strange thing that ever struck me in connexion with this event, was, that the fish did not fall helter skelter, everywhere, or 'here and there;' but they fell in a straight line, not more than a cubit in breadth." Another shower is said to have taken place at a village near Allahabad, in the month of May. About noon, the wind being in the west, and a few distant clouds visible, a blast of high wind came on, accompanied with so much dust as to change the tint of the atmosphere to a reddish hue. The blast appeared to extend in breadth four hundred yards, and was so violent that many large trees were blown down. When the storm had pa.s.sed over, the ground, south of the village, was found to be covered with fish, not less than three or four thousand in number.

They all belonged to a species well known in India, and were about a span in length. They were all dead and dry.

It would be easy to multiply these examples to almost any extent, although they are not so frequent in Great Britain. It is related in Hasted's History of Kent, that about Easter, 1666, in the parish of Stanstead, which is a considerable distance from the sea, and a place where there are no fishponds, and rather a scarcity of water, a pasture field was scattered all over with small fish, supposed to have been rained down during a thunder-storm. Several of these fish were sold publicly at Maidstone and Dartford. In the year 1830, the inhabitants of the island of Ula, in Argyleshire, after a day of very hard rain, which occurred on the 9th March, were surprised to find numbers of small herrings strewed over the fields, perfectly fresh and some of them alive.

Some years ago, during a strong gale, herrings and other fish were carried from the Frith of Forth so far as Loch-Leven.

In some countries rats migrate in vast numbers from the high to the low countries; and it is recorded in the history of Norway, that a shower of these, transported by the wind, fell in an adjacent valley.

Several notices have, from time to time, been brought before the French Academy, of showers of frogs having fallen in different parts of France.

Professor Pontus, of Cahors, states, that in August, 1804, while distant three leagues from Toulouse, the sky being clear, suddenly a very thick cloud covered the horizon, and thunder and lightning came on. The cloud burst over the road about sixty toises (383 feet) from the place where M.

Pontus was. Two gentlemen, returning from Toulouse, were surprised by being exposed not only to a storm, but to a shower of frogs. Pontus states that he saw the young frogs on their cloaks. When the diligence in which he was travelling, arrived at the place where the storm burst, the road, and the fields alongside of it, were observed full of frogs, in three or four layers placed one above the other. The feet of the horses and the wheels of the carriage killed thousands. The diligence travelled for a quarter of an hour, at least, along this living road, the horses being at a trot.

In the "Journal de St. Petersburg," is given an account of the fall of a shower of insects during a snow-storm in Russia. "On the 17th October, 1827, there fell in the district of Rjev, in the government of Tver, a heavy shower of snow, in the s.p.a.ce of about ten versts (nearly seven English miles), which contained the village of Pakroff and its environs.

It was accompanied in its fall by a prodigious quant.i.ty of worms of a black colour, ringed, and in length about an inch and a quarter. The head of these insects was flat and shining, furnished with antennae, and the hair in the form of whiskers; while the body, from the head to about one-third of their length, resembled a band of black velvet. They had on each side three feet, by means of which they appeared to crawl very fast upon the snow, and a.s.sembled in groups about the plants and the holes in trees and buildings. Several having been exposed to the air in a vessel filled with snow, lived there till the 26th October; although, in that interval, the thermometer had fallen to eight degrees below zero. Some others which had been frozen continued alive equally long; for they were not found exactly encrusted with the ice, but they had formed round their bodies a s.p.a.ce similar to the hollow of a tree. When they were plunged into water they swam about as if they had received no injury; but those which were carried into a warm place perished in a few minutes."

All these remarkable showers may be accounted for, when we consider the mighty power of the wind; especially that form of it which is popularly called the whirlwind. It is now pretty well ascertained, that in all, or most of the great storms which agitate the atmosphere, the wind has a circular or rotatory movement; and the same is probably the case in many of the lesser storms, in which the air is whirled upwards in a spiral curve with great velocity, carrying up any small bodies which may come within the circuit. When such a storm happens at sea, the water-spout is produced. In the deserts of Arabia, pillars of sand are formed; and, in other places various light bodies are caught up; fishponds have been entirely emptied in an instant, and the moving column, whether of water, sand, or air, travels with the wind with great swiftness. When, however, the storm has subsided, the various substances thus caught up and sustained in the air, are deposited at great distances from the place where they were first found, and thus produce these remarkable showers.

In some cases, however, the direct force of the wind has actually blown small fish out of the water, and conveyed them several miles inland.

Showers of nutritious substances have been recorded on good authority.