CHAPTER XIX.

LUMINOUS SHOWERS.

In many old works, accounts are found of so-called showers of fire, during which the entire heavens seemed filled with gleaming drops, that threatened to burn every living thing, but were in reality harmless; the exhibition being merely another instance of this strange phenomenon of heatless light.

Some years ago a party of peasants were making the ascent of one of the high peaks of the Alps, when they were caught in a rain-storm, which produced a demoralizing effect upon them. As the rain fell, it seemed to become luminous, and drops of fire apparently ran from their clothing and beards. Their attempts at brushing it away, while adding to the startling nature of the phenomenon, showed, however, that it was perfectly harmless.

Dr. Phipson records some interesting instances of this kind of phosphorescence, of which the following may be cited:--

M. de Thielan observed on Jan. 25, 1822, near Freyburg, a most extraordinary spectacle. A heavy snow had been falling during the early part of the evening, and the trees, branches, limbs, and leaves quivered and scintillated with a resplendent bluish light, while the drops of rain upon the grass left golden trains as they dripped to the ground.

[Illustration:

PLATE XXIII.

DEEP SEA ANGLER.

(_Melanocetus johnstoni, Gth._)]

Arrago records similar occurrences: In 1731 a priest named Hallai, who lived at Lessay, near Constance, states that he observed one evening during a severe thunder-storm, rain falling which looked like _drops of red-hot liquid metal_.

Bergman, the eminent Swedish chemist, communicated to the Royal Society of London, in 1761, that late in the afternoon upon two occasions, though hearing no thunder, he had seen rain which glittered as it fell upon the ground, making it look as if covered with waves of fire.

M. Pasumot, on May 3, 1768, was overtaken, while walking near Arnay-le-Duc, on an open plain, by a very heavy storm. The rain collecting on the brim of his hat, he stooped his head to allow it to run off, when to his astonishment, as it encountered that which fell from the clouds, at about twenty inches from the ground, _sparks were emitted_ between the two portions of liquid.

During January, 1822, Lampadius was told by the miners of Freyburg, that they had observed during a storm, _sleet_ which _emitted light_ when it fell upon the ground.

A friend of Howard, the meteorologist, stated to him, that while going from London to Bow on the 19th of May, 1809, there came up a very severe storm; and he observed the rain emit light as it struck the earth.

On the 28th of October, 1772, the Abbé Bertholon, who was travelling to Lyons from Brignai, early in the morning was overtaken by a violent storm of rain and hail. The _rain and hail-stones emitted light_ as they fell upon the metallic mounting of his horse’s trappings.

Luminous hail has often been observed; and when we remember that hail-stones sometimes attain great size, we can imagine the scene occasioned by a fall where each stone is phosphorescent. Ordinary hail-stones are the size of small peas, but they occasionally occur large enough to kill human beings; and I have seen them so large in the Sierra Madre Mountains that any shelter was preferable to exposure to them. In 1707 a hail-storm occurred at the town of Como, Switzerland, doing an incredible amount of damage, some of the stones weighing nearly ten ounces. Darwin describes a storm upon the South American pampas, in which the stones that fell were large enough to kill powerful animals.

Ice has often been observed to emit luminous sparks; and probably one of the grandest spectacles ever witnessed, is the luminous cap of a snow-covered mountain. The glaciers of the Alps have been seen bathed in a soft phosphoric glow, the icy rivers being distinctly marked by the phenomenon, which is so brilliant, at times, that the appearance of a second sunset is occasioned. Not only are the summits of Alpine peaks and the glaciers luminous, but the valleys of Piedmont, Valais, and others have been seen to emit from their covering of snow a soft blue light of singular beauty. So intense is this light about the cap of Mount Blanc, it has been photographed. Luminous vapors or mists may be mentioned in this connection. Several times in the history of this country, luminous mists or fogs have been recorded. Massachusetts was visited by one some years ago, in which the fog was so dense that observers a few feet away were invisible, yet darkness was not an accompaniment; the mist seemed to be light-emitting itself, having a reddish, metallic hue. Others described it as a fiery red or yellow, while to some it appeared to be composed of faintly luminous matter.

In the year 1783 all Europe and a portion of Asia were enveloped in a dense fog of a most remarkable nature. It was termed “dry,” as even at night no dampness was observed. It was first seen at Copenhagen, its coming being heralded by severe storms. A few weeks later it appeared in various parts of France, and rapidly seemed to spread over Europe and portions of Asia. During the day it had a metallic glow, which at night changed to a phosphorescent light, so brilliant that ordinary print could be read by it. Many attempts to explain it were made by the savants of the day, and it was universally supposed to be due to the earthquakes and volcanic eruptions which were of unusual severity that year.

A somewhat similar fog appeared in the United States, a portion of Europe, and Africa in August, 1831. The daylight was perceptibly diminished, while at night a conspicuous phosphorescent light was emitted. A remarkable luminous fog occurred in Switzerland in 1859. M. L. F. Wartmann of Geneva states that the strange light was observed on five successive nights, and apparently proceeded from a heavy dry fog that hung over Geneva during the time. The light was so brilliant that this gentleman distinguished the smallest objects upon his table with perfect ease, no other light being in the apartment. The light caused general comment in the places in which it appeared, and a traveller between Geneva and Annemassi stated that he readily found the road by its means. Dr. Verdeil of Lausanne describes a fog which diffused so much light that distant objects were perfectly visible at night.

Among the phenomena which attended the eruption of Vesuvius in 1794 was one which did not tend to allay the fears of the people. During the day a fine dust filled the air about Naples, which was not particularly noticeable; but as night came on, it emitted a pale though distinct phosphorescent light. An English gentleman sailing near Torre del Greco noticed that where the dust collected upon his hat it was luminous, and no little consternation was caused among the superstitious sailors by the occurrence.

Luminous dust-showers have been noticed in several localities; and the peculiar glows that were seen in this country a few years ago were accredited by many to them, the supposition being that dust, perhaps from volcanic eruptions, was floating about in the upper strata of the atmosphere. Many other explanations were given, and the literature upon the subject is extremely voluminous and interesting.

The amount of material floating about in the upper regions of the air is perhaps little realized by my young readers, and some reference to the phenomenon may be of interest.

Professor Nordenskjöld has for many years been a close observer of dust of all kinds that has fallen upon the earth in rain or snow; and it was his good fortune, during the expedition of the “Vega,” to prove beyond a doubt the presence of cosmic dust. For many years we have been assured by astronomers that the earth was being bombarded, as it were, continually, by innumerable meteors. The moment they enter our domain, we observe the spectacle of their ignition. In a moment they are reduced to ashes, and the fine impalpable dust drops slowly, an invisible shower, upon the earth. When such showers are intensified, it is not impossible that some outward and visible phenomena may be the result.

In the search for this cosmic dust, the far North, where the surface is covered by an almost continuous coating of snow and ice, offers a wide and promising field for investigation. Here no other dust prevails. Professor Nordenskjöld first found cosmic dust in the North at Spitzbergen. The second discovery, off the Taimar coast, seemed to be in the form of yellow specks lying on the snow. They were at first supposed to be diatomaceous ooze;[49] but when placed in the hands of Dr. Kjellman, he pronounced them to be pale yellow crystals, and, curious enough, formed of carbonate of lime. “The original composition and origin of this substance,” says Professor Nordenskjöld, “appears to me exceedingly enigmatical. It was not carbonate of lime, for the crystals were rhomboidal, and did not show the cleavage of calcite. Nor can there be a question of its being arragonite, because this mineral might indeed fall asunder of itself; but in that case the newly formed powder ought to be crystalline. Have the crystals originally been a new hydrated carbonate of lime formed by crystallizing out at a temperature of ten or twenty degrees above the freezing point? In such case they ought not to have been found on the surface of the _snow_, but lower, on the surface of the _ice_. Or have they fallen down from the inter-planetary spaces to the surface of the earth, and before crumbling down have had a composition differing from terrestrial substances, in the same way as various chemical compounds found in recent times in meteoric stones? The occurrence of the crystals in the uppermost layer of snow, and their falling asunder in the air, tell in favor of this view. Unfortunately there is no possibility of settling these questions; but at all events this discovery is a further incitement to those who travel in the high North, to collect with extreme care, from snow-fields lying far from the ordinary routes of communication, all foreign substances, though apparently of trifling importance.”

The investigations of the Swedish naturalist in this field are of exceeding interest. His first attempt to obtain meteoric dust was at Stockholm, where, in December, 1871, there was a great fall of snow, the heaviest ever known. On the last days of the storm, after the atmosphere had been presumably purified of extraneous substances, he collected a cubic metre of snow, melted it over a fire, and found that after the water had evaporated a residue of black powder remained, in which were many grains of metallic iron, that were attracted by a magnet. In 1872 his brother made a similar examination of the snow, in a quiet locality near the remote village of Evois, Finland. The snow upon being melted also gave the same black powder and metallic iron.

The investigations of Nordenskjöld himself, conducted in Spitzbergen, as previously mentioned, were the most satisfactory. The observations were made in 80° north latitude, and 13° to 150° east longitude, in the layer of snow that covered the ice. An imaginary section was as follows: (1), new fallen snow; (2), a layer of hardened old snow, eight millimetres in thickness; (3), a layer of snow, conglomerated to a crystalline granular mass; and (4), common granular hardened snow. Layer three was full of small black grains, among which were found numerous metallic particles, that were attracted by the magnet, and found to contain iron, cobalt, and possibly nickel also.

In his visit to Greenland in 1870, Nordenskjöld found in the dust that lay on the inland ice, grains of metallic iron and cobalt. “The main mass,” he says, “consisted of a crystalline, double refracting silicate, drenched through with an ill-smelling organic substance. The dust was found in large quantities at the bottom of innumerable small holes in the surface of the inland ice. This dust could scarcely be of volcanic origin, because by its crystalline structure it differs completely from the glass dust that is commonly thrown out of volcanoes, and is often carried by the wind to very remote regions; as also from the dust which, in March, 1875, fell at many places in the middle of Scandinavia, and which was proved to have been thrown out by volcanoes in Iceland.” Professor Nordenskjöld’s estimate of the quantity of dust shows that it has been in past ages a not unimportant factor, perhaps, in its addition to the crust. He says, “I estimate the quantity of the dust that was found on the ice north of Spitzbergen, at from .01 to 1 milligram per square metre; and probably the whole fall of dust for the year far exceeded the latter figure. But a milligram on every square metre of the surface of the earth amounts for the globe to five hundred million kilograms (say half a million tons). Such a mass, collected year by year during the geological ages, of a duration probably incomprehensible by us, becomes a consideration too important to be neglected, when the fundamental facts of the geological history of our planet are enumerated. A continuation of these investigations will perhaps show that our globe has increased gradually from a small beginning to the dimensions it now possesses; that a considerable quantity of the constituents of our sedimentary strata, especially of those that have been deposited in the open sea far from land, are of cosmic origin; and will throw an unexpected light on the origin of the fire-hearths of the volcanoes, and afford a simple explanation of the remarkable resemblance which unmistakably exists between plutonic rocks and meteoric stones.”

Such enormous masses of material could well explain the rosy and other curious lights that are from time to time observed. But cosmic dust is not the only matter in the air that could occasion the phenomena; the atmosphere is constantly filled with innumerable forms caught up by currents and carried to inconceivable heights, and thus to great distances, to be precipitated to the earth in hail, snow, or rain.

Near St. Domingo, Darwin tells us, the atmosphere became thick and hazy from the impalpable fine dust that actually injured their astronomical instruments. “The morning before we anchored at Porto Praya,” he says, “I collected a little packet of this brown-colored dust, which appeared to have been filtered from the wind by the gauze of the vane at the masthead. Mr. Lyell has also given me four packets of dust which fell on a vessel a few hundred miles northward of these islands. Professor Ehrenberg finds that this dust consists in great part of _infusoria_ with siliceous shields, and of the siliceous tissue of plants. In five little packets which I sent him, he has ascertained no less than sixty-seven different organic forms. The _infusoria_, with the exception of two marine species, are all inhabitants of fresh water. I have found no less than fifteen different accounts of dust having fallen on vessels when far out in the Atlantic. From the direction of the wind whenever it has fallen, and from its having always fallen during those months when the harmattan is known to raise clouds of dust high into the atmosphere, we may feel sure that it all comes from Africa. It is, however, a very singular fact, that, although Professor Ehrenberg knows many species of _infusoria_ peculiar to Africa, he finds none of them in the dust which I sent him; on the other hand, he finds in it two species which hitherto he knows as living only in South America. The dust falls in such quantities as to dirty every thing on board, and to hurt people’s eyes; vessels even have run ashore, owing to the obscurity of the atmosphere. It has often fallen on ships when more than a thousand miles from the coast of Africa, and at points sixteen hundred miles distant in a north and south direction. In some dust which was collected on a vessel three hundred miles from the land, I found particles of stone, above the thousandth of an inch square, mixed with finer matter. After this fact, one need not be surprised at the diffusion of the far lighter and smaller sporules of cryptogamic plants.”

The extent to which dust and ashes can be taken up and held by air currents is shown in volcanoes. In 1810 the ashes from a volcano at St. Vincent were wafted to Barbados, nearly a hundred miles; and in 1835 the material thrown from a volcano in Guatemala to Jamaica, eight hundred miles. As intimated, these showers are not all inorganic, but are often living or fossil animals or plants that are floating about. Such are the reddish or gray showers that are frequently met with off the African coast, and when in the snow they are called “blood-rains.” The one in 1755, near Lago Maggiore, covered over two hundred square leagues, causing a panic among the inhabitants. For a distance of nine feet below the surface, the snow was blood red, the atmosphere appeared red and fiery, while at sunrise and sunset a rosy hue pervaded every thing. When this shower fell and there was no snow, the earthy deposit accumulated an inch deep; and it has been estimated that, supposing it to average two lines in depth, there would be for each square mile an amount equal to nearly three thousand cubic feet. A similar panic was caused some years ago by a swarm of butterflies. Everywhere they left a drop of blood-colored fluid, so that the fences, houses, and cattle were covered with it. The insects were so numerous that they obstructed the vision.

In the “blood-rains” of Italy, and generally in such instances, the red hue comes from red oxide of iron. At a single shower in Lyons in 1846, Ehrenberg estimated that seven hundred and twenty thousand pounds of material fell, ninety thousand pounds of which were microscopic organisms, including thirty-nine species of siliceous diatoms, and many others of great beauty of form and shape.

Ehrenberg enumerates a very large number of these showers, referring to Homer’s “Iliad” for one of the earliest known; and asks, with such facts before us, how many thousand millions of hundred-weight of microscopic organism have reached the earth since Homer’s time? The whole number of species made out is over three hundred. The species, as far as ascertained, are not African; fifteen are North American. But the origin of the dust is yet unknown. The zone in which these showers occur covers Southern Europe and Northern Africa, with the adjoining portion of the Atlantic, and the corresponding latitudes in Western and middle Asia.

When blown along by the wind, these showers perform another office besides affecting, perhaps, the color or tint of the atmosphere; they wear away rock, and polish and furrow it. Such work can be seen in the granite rocks at the San Bernardino Pass in California. Quartz is polished, and hard gems left weathered out; while at Cape Cod ordinary sand has been known to wear holes through glass windows by continually blowing against them.

[Illustration:

PLATE XXIV.

PELICAN FISH.

(_Eyrypharyx pelecanoides._)]

An ingenious instrument has been invented to capture these flying objects of the air. It is called by the inventor, Doctor Miguel, the æroscope, and is really a net for animals invisible to the naked eye.

Many objects are phosphorescent when struck, or when divided into thin laminæ. Some simple materials for such experiments are chlorate of potash, fluor-spar, feld-spar, sugar, etc. By placing any of these in a mortar, and grinding them in the dark, flashes of light will be seen, powdered sugar often making a striking display. A beautiful and effective exhibition can be produced by placing a small amount of phosphuret of calcium in water; decomposition follows, and phosphuretted gas is evolved. As the bubbles of gas rise and come in contact with the atmosphere, they seem to take fire. If in a dark room, luminous rings are seen rising, and they can be made to take various shapes by using a fan. A trick often performed by magicians is to hand around a marble, and then pretend to render it luminous by blowing upon it. This trick consists in having small balls at hand, of a material that can readily be rendered luminous by the application of heat. These substances can be easily made.

A fine light is produced by taking,--

Barium sulphate (C P.) 32 parts Magnesium carbonate (C P.) 1 part Sulphur (C P.) 1 part Gum tragacanth q. s.

This should be made into balls of a convenient size, dried at a moderate temperature, and kept in a crucible at a red heat for about an hour. Allow them to cool slowly, and then place in a glass-stoppered bottle before their heat has disappeared. When required for use, expose them to the sun or any strong light, and they will become luminous, and continue so for many hours.

Another formula is:--

Strontium sulphate (C P.) 22 parts Sulphur (C P.) 1 part Gum tragacanth q. s.

This should be heated as above described.

A most interesting experiment is to make a selection of artificial flowers, and, having brushed them over with glue or mucilage, dust them with the powder from one of the balls made as described. If the flowers are exposed to the sun a short time, they will emit a phosphorescent light, each flower standing out in the darkness with extreme brilliancy,--a striking and remarkable spectacle.

Canton’s phosphorus is easily made by calcining clean oyster-shells, until they are perfectly white, in a crucible. The clearer and finer portions should then be reduced to powder, and placed in layers with alternate layers of flowers of sulphur in a crucible. Cover, and heat to a dull redness for about half an hour, then allow to cool slowly.

Luminous “ink” or liquid can be made by placing a small piece of phosphorus about as large as a pea in a test-tube with a small quantity of olive oil; hold the tube in a water-bath until the oil becomes heated, and the phosphorus liquefies; then shake it until the oil will take up no more phosphorus, and, when it becomes clear, pour into a bottle with a glass stopper. When it is to be used, take out the stopper, and admit the air. The oil can be used with a brush, and in the dark will appear luminous.

Water may be rendered phosphorescent by dissolving a small piece of phosphorus in ether for several days in a glass-stoppered bottle; then by immersing a piece of sugar in the solution, and placing it in water, the latter becomes vividly phosphorescent. It should be remembered that phosphorus and ether are both extremely dangerous, and experiments with them should be conducted with care and judgment.

While this is a mere toy, luminous paint is of great value. It is easily made, and can be applied to many purposes.

Schade of Dresden has quite recently patented an invention, which enables him to produce paints that are luminous without affecting the tint by day. This is accomplished, according to the inventor, as follows:--

Zanzibar or Kauri copal is melted over a charcoal fire. Fifteen parts of the melt are dissolved in 60 parts of French oil of turpentine, and the filtered solution is mixed with 25 parts, previously heated and cooled, pure linseed-oil. The varnish which is thus obtained, is used in the following methods, in the manufacture of luminous paints, by grinding between granite rolls in a paint-mill. Iron rolls should be avoided, because particles of iron, which are liable to be detached, would injure the luminous properties.

Varnishes, as they occur in commerce, generally contain lead or manganese, which would destroy the phosphorescence of calcium sulphide. _A pure white luminous paint_ is prepared by mixing 40 parts of the varnish obtained in the abovedescribed process with 6 parts prepared barium sulphate, 6 parts prepared calcium carbonate, 12 parts prepared white zinc sulphide, and 36 parts good luminous calcium sulphide in a proper vessel, to an emulsion, and then grinding it very fine in a color-mill. For _red luminous paint_, 60 parts varnish are mixed with 8 parts prepared barium sulphate, 2 parts prepared madder lake, 6 parts prepared realgar (red arsenic sulphide), and 30 parts luminous calcium sulphide, and treated the same as for white paint. For _orange luminous paint_, 46 parts varnish are mixed with 17.5 parts prepared barium sulphate, 1 part prepared Indian yellow, 1.5 parts prepared madder lake, and 38 parts luminous calcium sulphide. For _yellow luminous paint_, 48 parts varnish are mixed with 10 parts prepared barium sulphate, 8 parts barium chromate, and 34 parts luminous calcium sulphide. For _green luminous paint_, 48 parts varnish are mixed with 10 parts prepared barium sulphate, 8 parts chromium oxide green, and 34 parts luminous calcium sulphide.

_A blue luminous paint_ is prepared from 42 parts varnish, 10.2 parts prepared barium sulphate, 6.4 parts ultramarine blue, 5.4 parts cobalt blue, and 46 parts luminous calcium sulphide.

_A violet luminous paint_ is made from 42 parts varnish, 10.2 parts prepared barium sulphate, 2.8 parts ultramarine violet, 9 parts cobaltous arsenate, and 36 parts luminous calcium sulphide.

_For gray luminous paint_, 45 parts of the varnish are mixed with 6 parts prepared barium sulphate, 6 parts prepared calcium carbonate, O.5 parts ultramarine blue, 6.5 parts gray zinc sulphide.

_A yellowish-brown luminous paint_ is obtained from 48 parts varnish, 10 parts precipitated barium sulphate, 8 parts auri pigment, and 34 parts luminous calcium sulphide.

_Luminous colors for artists’_ use are prepared by using East India poppy oil in the same quantity, instead of the varnish, and taking particular pains to grind the materials as fine as possible.

_For luminous oil-color paints_, equal quantities of pure linseed oil are used in place of the varnish. The linseed oil must be cold-pressed, and thickened by heat. All the above luminous paints can be used in the manufacture of colored papers, etc., if the varnish is altogether omitted, and the dry mixtures are ground to a paste with water.

The luminous paints can also be used as _wax colors for painting on glass_ and similar objects, by adding, instead of the varnish, ten per cent more of Japanese wax, and one-fourth the quantity of the latter of olive oil. The wax colors prepared in this way may also be used for painting upon porcelain, and are then carefully burned without access of air. Paintings of this kind can also be treated with water-glass.