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- Wonders of Creation - 4/15 -
between six and seven feet in height, there is an oval basin, measuring about fifty-six feet in one direction, and about forty- six in the other; its average depth is about three feet. In the centre of this basin is a round hole, about ten feet in diameter, out of which the water springs. This hole is the mouth of a circular well, between seventy and eighty feet in depth. It is down this well that the jet retires on its disappearance; and it drags along with it all the water out of the basin, leaving both basin and well quite empty, without even a puff of steam coming out of the hole. In this state of emptiness the basin and well remain for several hours. Suddenly the water begins to rise in the well, overflowing till it fills the basin. Loud explosions are heard from below, and the ground trembles. Then, with amazing violence, up springs a vast column of boiling water, surmounted by clouds of steam, which obscure the air. This first jet is followed by several others in rapid succession, to the number of sixteen or eighteen; the last jet being usually the greatest of all, and attaining a height of nearly a hundred feet. In some instances it has risen to a height of a hundred and fifty feet; and one particular jet was measured which rose to the amazing height of two hundred and twelve feet.
The action of the fountain seldom continues more than about five minutes at a time, and then a repose of several hours ensues. If left to itself, the periods of the fountain's activity, though not quite regular, generally recur at intervals of six or seven hours. But they may be hastened by throwing big stones down the well. This not only hurries the eruption of the jet, but increases its energy, and the stones are thrown out with great force by the column of boiling water; the loudness of the explosions being also considerably augmented.
There are several other geysers in the island besides this big one. Their jets are smaller, but to compensate this deficiency, they are more frequent in their ascent; so that travellers who are too impatient to await the eruptions of the Great Geyser, content themselves with visiting the little ones.
Would it not be very convenient to live near a geyser? We might have our victuals cooked by it, and have pipes led from it all round our house, to keep us comfortable in winter; and we might have nice hot baths in our dressing-rooms, arid even a little steam-engine to roast our meat and grind our coffee. But perhaps you may think it might not be altogether pleasant to be kept so continually in hot water.
Were any of the water from the geyser to fall on your hands, you would doubtless feel it rather sore; still more so, were you to be so rash as to thrust your hand fairly into the jet of boiling water, as it ascends into the air. Nevertheless, strange as it may seem, it would be possible for you, without feeling any pain or sustaining any injury, to thrust your hand right into the glowing lava as it flows from the crater of Hecla. The only precaution needful to be observed, is first to plunge the hand into cold water, and then dry it gently with a soft towel, but so as to leave it still a little moist. This discovery was made by a French philosopher, M. Boutigny, and has been practically proved both by him and M. Houdin, the celebrated conjuror, by thrusting their hands into molten iron, as it flowed from the furnace. The latter describes the sensation as like what one might imagine to be felt on putting the hand into liquid velvet. The reason why this experiment proves so harmless is that between the skin and the glowing substance there is formed a film of vapour, which acts as a complete protection. It is this elastic cushion of vapour which imparts that feeling of softness described by M. Houdin; for it is with it alone that the hand comes into contact.
[1. Houdin's Autobiography, ii 270]
Geysers have been recently discovered in California; but the jets do not rise higher than twenty or thirty feet. They are, however, very numerous, there being upwards of a hundred openings within a space of half a mile square. The vapour from the whole group rises to upwards of a hundred and fifty feet into the air. The boiling water issues from conical mounds, with great noise. The whole ground around them is a mere crust, and when it is penetrated the boiling water is seen underneath. The Californian geysers, however, are impregnated, not with silica, like those of Iceland, but with sulphur, of which they form large deposits. The sulphurous vapours from the water corrode the rocks near the fountains; nevertheless trees grow, without injury to their health, at a distance from them of not more than fifty feet.
Besides obsidian, already mentioned as a product of its volcanoes, Iceland is famed for another mineral of great scientific value. It is that fine variety of carbonate of lime named Iceland-spar. Transparent and colourless, like glass, this mineral possesses the property of double refraction--any small object viewed through it in a particular direction appearing double. It is much used for optical purposes--especially for obtaining polarized light.
There is another volcano lying far to the northward of Iceland. It is in the island of Jan Mayen, off the coast of Greenland, and has on its summit a vast crater, 2000 feet in diameter, and 500 in depth.
Mount Vesuvius--Origin of Name--Former Condition--Eruption of A D 79--Death of Pliny--Destruction of Pompeii and Herculaneum-- Appearance of the Mountain before and after Eruption--Formation of Monte Nuovo--Eruption of Boiling Water--Coloured Vapours--Cascade of Lava--Discovery of Remains of Herculaneum and Pompeii--The Buildings of Pompeii--Street of Tombs--Skeletons--Sundry Shops-- Ascents of Vesuvius--Crater--Temple of Serapis.
Mount Vesuvius is the only active volcano on the continent of Europe, and it is highly interesting both from its historical associations and the frequency of its eruptions. It is situated on the coast of the Bay of Naples, about six miles to the eastward of the city and at a short distance from the shore. It forms a conspicuous feature in the beautiful landscape presented by that bay, when viewed from the sea, with the city in the foreground.
Mount Vesuvius was in ancient times held sacred to the deified hero Hercules, and the town of Herculaneum, built at its base, was named after him. So also, it is said, was the mountain itself, though in a more round-about way. Hercules, as you will doubtless learn, was feigned to have been the son of the heathen god Zeus and Alcmena, a Theban lady. Now one of the appellations of Zeus was Ves, which was applied to him as being the god of rains and dews--the wet divinity. Thus Hercules was Vesouuios, the son of Ves. How this name should have become corrupted into "Vesuvius," you can be at no loss to perceive.
Vesuvius was not always a volcano. It was for many ages a very peaceable and well-behaved mountain. Ancient writers describe it as having been covered with gardens and vineyards, except at the top which was craggy. Within a large circle of nearly perpendicular cliffs, was a flat space sufficient for the encampment of an army. This was doubtless an ancient crater; but nobody in those times knew anything of its history. So little was the volcanic nature of the mountain suspected, that the Roman towns of Stabiae, Pompeii, and Herculaneum had been erected at its base, and their inhabitants dwelt in fancied security.
In the year A.D. 63, however, the dwellers in the cities got a great fright; for the mountain shook violently, and a good many houses were thrown down. But soon all became quiet again, and the people set about rebuilding the houses that had fallen. They continued to live in apparent safety for some time longer. They danced, they sung, they feasted; they married, and were altogether as merry a set of citizens as any in southern Italy. But the 24th of August A.D. 79 at length arrived. Then, woe to Stabiae! woe to Pompeii! woe to Herculaneum!
Pliny the elder was that day in command of the Roman fleet at Misenum, which was not far off. His family were with him, and, among others, his nephew, Pliny the younger, who has left an interesting account of what happened on the occasion. He observed an extraordinary dense cloud ascending in the direction of Vesuvius, of which he says:--"I cannot give you a more exact description of its figure, than by resembling it to that of a pine tree; for it shot up to a great height in the form of a tall trunk, which spread out at the top into a sort of branches. It appeared sometimes bright, and sometimes dark and spotted, as it was either more or less impregnated with earth and cinders"
On seeing this remarkable appearance, the elder Pliny, who was a great naturalist and a man of inquiring mind, resolved to go ashore and inspect more narrowly what was going on. But a rash resolve it proved. Steering towards Retina (now Resina), a port at the foot of the mountain, he was met, on his approach, by thick showers of hot cinders, which grew thicker and hotter as he advanced--falling on the ships along with lumps of pumice and pieces of rock, black but burning hot. Vast fragments came rolling down the mountain and gathered in heaps upon the shore. Then the sea began suddenly to retreat, so that landing at this point became impracticable. He therefore steered for Stabiae, where he landed, and took up his abode with Pomponianus--an intimate friend.
Meanwhile, flames appeared to issue from several parts of the mountain with great violence--the darkness of the night heightening their glare. Pliny nevertheless went to sleep. Soon, however, the court leading to his chamber became almost filled with stones and ashes; so his servants awoke him, and he joined Pomponianus and his household. The house now began to rock violently to and fro; while outside, stones and cinders were falling in showers. They, notwithstanding, thought it safer to make their way out from the tottering mansion; so, tying pillows upon their heads with napkins, they sallied forth. Although it was now day, the darkness was deeper than that of the blackest night. By the aid of torches and lanterns, however, they groped their way towards the beach, with a view to escape by sea; but they found the waves too high and tumultuous. Here Pliny, having drunk some cold water, lay down upon a sailcloth which was spread for him; when almost immediately flames, preceded by a strong smell of sulphur, issuing from the ground, scattered the company and forced him to rise. With the help of two of his servants he succeeded in raising himself; but, choked by some noxious vapour, he instantly fell down dead.
[Illustration: Vesuvius Before the Eruption of A.D. 79.]
Nor was he alone in his death; for although many of the inhabitants of the devoted cities were able to effect their escape; yet, so suddenly did the overwhelming shower of ashes, cinders, and stones
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