SCIENCE FROM AN EASY CHAIR.

Press, Volume XLIX, Issue 14854, 20 December 1913, Page 9

SCIENCE FROM AN EASY CHAIR.

VESUVIUS IN ERTT-T-ON.—II. (Br Sib Ray Lankebter, X.C.8., F.R.6.) (Special rights secured by "The Press." 1 ) Not long before I went, in 1871, to Naples, I had spent some weeks in visiting tho extinct volcanoes of the Auvergno and of the Eiffel, and I was eager to examine the still living Vesuvius. In the first week of October I made an excursion to the crater of Vesuvius in company with the son of a Russian admiral, whose name, "Popoff," was under the circumstances, unpleasantly suggestive. We examined some black slag-like masses of old lavastreams, and struggled up the loose sandy ash-cone (there was no "funicular" in those days), and prodded with our -ticks the few yards of molten lava which emerged from the. side of the cone about 100 ft from the summit. On November Ist my friend Anton Dobru (who was then negotiating with the Naples Muncipality for a site in the Villa Nazionale on which to erect the great Zoological Station and Aquarium, now so well known), was with mc, and some Neapolitan acquaintances looking at Vesuvius across the bay from PousUippo, where we had established ourselves,, when we noticed that a long line of steam was rising from the lower . part of the ash-cone, and that puffs of steam were issuing at intervals from the crater. "Dio mio! Dio di Dio! cried the Neapolitans in terror, _and expressed their intention of leaving Naples withou an hour's delay. As night fell a new glowing line of fire appeared far down near the base of tie ash-cone, whilst what looked in tho distance like sparks from a furnace, out were really red-hot stones, were thrown every two or three minutes from tho crater.

We hired a carriage, drove to Resina (built above buried Herculaneum). and walked up towards the observatory in order to spend the night on the buriusg mountain. We found thai two whitehot streams each about twenty yards Broad, were issuing from the base of the cone. The glowing stones thrown up by the crater were now separately visible; a loud roar accompanied each spasmodic ejection. The nighty was very clear, and a white firmly-cut cioud, due to the steam ejected by it, hung above the crater. At intervals we heard a milder detonation, whilst lightning phved in tho cloud, giving it a greenish illumination by contrasT with the red Same colour reflected on to it >v. recT-hot material within the crater. The flames attributed to volcanoes are generally of this nature, but actual flames do sometimes occur in volcanic eruptions by the ignition of combustible gases. The puffs of steam from the crater were separated by intervals of about three minutes. WTien an eruption becomes violent they succeed one another at the rate of many in a second, and the force of the steam jet is gigantic,-driving a column of transpar-

ent super-heated steam with such vigour that as it cools into the condition of 'cloud" an appearance like that of a gigantic pine-tree seven miles higu (in the caso of Vesuvius) ia produced.

We made our way to the advancing end of one of the lava streams (like the "snout" of a glacier) which was 20ft high and moved forwards but slowly in successive jerks. Two hundred yards further up, where it issued from tho sandy ashes, the lava was white-hot and running like water, but it was not in very great quantity and rapidly cooled on tbo surface and become ' sticky." A cooled skin of slag was formed in this way, which arrested the .advancing stream of lava. At intervals this cooled crust was broken into innumerable clinkers by the pressure of the stream, and there was a noise like tlio smashing of a gigantic store of crockery ware as the pieces or "clinkers" fell over one another down the nearly vertical "snout" of the lava stream, whilst the red-hot molten material burst forward for a few feet, but immediately became again "crusted over" and stopped in its progress. We watched the corning together and fusion of the two streams and the overwhelming and burning up of several trees by tho steadily, though slowly, advancing river of fire. Then we climbed up the ash-cone, getting nearer and nearer to the rim of the crater, from which showers of glowing stones were being shot. The deep roar of the mountain at each effort was echoed from tho cliffs of the ancient mother-crater. Monte Somroa, and the ground shook under our feet as does a ship at sea. when struck by a wave. The night was very still in the intervals. The moon was shining, and a weird melancholy '"ritornelle sung by peasantfar off in somo village below us came to our ears with strange distinctness. It might have been the chorus of tho imprisonmed giants of Vulcan's forge as they blew the sparks with their bellows and shook the mountain with the heavy blows of their hammers.

As wo ascended the upoer part of the cone the red-hot stones were falling to our left, and we determined to risk a rapid climb to the edge of tho crater on the right or southern side, and to look into it. We did so, and as Aye peered into the great steaming pit a terrific roar, accompanied by a shuddering of the whole mountain, burst from it, hundreds of red-hot stones rose in the air to a height of 400 ft, and fell, happily, to our left. \\e ran quickly down the sandy side of the cone to a safe position, about 300 ft below the crater's lip. and having lit our pipes from one of the red-hot "bombs," rested for a while, and waited for tho sunrise. A vast horizontal layer of cloud had now formed below us. and Vesuvius and tho hills around Naples appeared as islands emerging from a sea.. The brilliant sunlight was reassuring after this night of strange experiences. The fields and lanes were deserted in the early morn as do descended to the sea-level. Suddenly we met a procession of figures f[ ad , in long white robes, enveloping the head closely, but leaving apertures for the eyes. They were a party of the lay-brothers of tho Misericordia carrying a dead man to his grave. Then wo found our carriage, and drove quickly back to Naples and sleep I

In the following March I acted as guide to my friend Professor Huxley in expeditions to Vesuvius, now quiescent, and to the Solfatara. Then suddenly, in April, the great eruption of 1872 burst upon us. On tho first day of the outbreak some imprudent visitors were killed by steam and gas ejected by the lava stream. By the next day the violence of the eruption was too great for anyone to venture near it. The crater sent forth no intermittent "puffs" as in the preceding November, but a continuously throbbing jet which produced a cloud for miles high, like an enormous cauliflower in shape, suspended above the mountain and making it look by comparison like a molehill. Showers of fine ashes, as in the days of Pompeii, fell thickly around, accumulating to the depth of an Inch in a few hours even at my house in Posilippo, nine miles distant across tho bay. I was recovering at tho time from an attack of typhoid fevor, and lay in bed, listening to the deep humming sound and wondering at the darkness until my doctor came and told mc of the eruption. I was able to get up and see from the window the great cauliflower _ike cloud and tho vacant place where the ash-cone was, but whence it had now been scattered into tho sky. (It has been gradually re-formed by later eruptions, of which tho last of any size was in 1906.) I could also see steam rising like smoke from a long lino reaching six miles down the mountain into the flat country below —tho great lava stream which had destroyed two prosperous villages in its course.

After ten days I was able to get about, and drove over to one of these villages and along its main street, which was closely blocked at the end by what looked like a railway embankment some 40ft hirfi. It was the side of the great lava-stream now cooled and hardened on the surface. It had sharply cut the houses on each side of the street in half without setting them on-fire, so that the various rooms were exposed in section —pictures hanging on the walls, and even chairs and other furniture remaining in place on the remaining portion of the floor. The villagers had provided ladders by which I ascended the steep side of tne em-bankment-like mass at the end of the street, and there a wonderful sight revealed itself. One looked out on a great p river seven miles long, narrow where it started from the broken-down crater, but widening to three mdes where I stood, and wider still further on as it descended. This river, with all its waves and ripples, was turned to stone, and resembled some of the Swiss glaciers. A foot below the surface it was still red-hot, and a stick pushed into a crevice caught fire. It was not 6afe to venture far on to the pje-crust surface. A couple of miles away the campanile of the church of » village called Massa di Somma stood out, leaning like that of Pisa, from the petrified mass, and tho rest of the village was overwhelmed and covered in by tho great stream.

A curious resemblance of the lavastream to a glacier arose from the fact that it was almost completely covered by a white snow-like powder. This snow-like powder, which often appears on freshly-run lava, is salt—common sea salt and other mineral salts dissolved in the water ejected as steam mixed with the lava. The steam condenses as the lava cools into water and evaporates slowly, leaving the salt as crystals. Often theso are not white, but contain iron salt, mixed with the white sodium, potassium, and ammonium chlorides, which gives them a yellow or orange colour. Salts coloured in this way have the appearance, of sulphur, and are often mistaken for it. The whole of the interior of the crater of Vesuvius when I revisited it in 1875 was thus coloured yellow, and I v have a carefully made wat<y--colour sketch of the scene. As a matter of fact, though small quantities of the choking gas called "sulphurous Mid are among the vapours given off by Vesuvius, there is no deposit of sulphur there. ' Some large volcanoes (in Mexico and Japan) have made deposits of sulphur; which is dug for commercial purposes; but the sulphur of Sicily is not, and has not been, thrown out or volatilised by Etna. It occurs in rough masses and in splendid crystals in a tertiary calcareous marine deposit, and was probably due to a chemical decomposition of constituents of the sea water brought about by minute plants, known as sulphur bacteria. Whether the neighbouring great volcano had any share m the process seems to be doubtful.

It is generally recognised that sea water makes its way m large quantity through fissures connected with volcanic

channels, and is one of the agents of the explosions caused by tho subterreanean molten matter. Gaseous water, hydrochloric acid, carbonic acid, hydrofluoric acid, and even pure hydrogen and oxygen and argon aro among the gases ejected by volcanoes. The molten matter, forced up from the bowels of the earth and poured out by volcanoes is mado up of various chemical substances, differing in different localities, and even in different eruptions of the same volcano. It consist j laigely of silicates of iron, lime, magnesium" aluminium, and the alkali metals, with possible admixture of nearly every other element. Some volcanoes eject "pitch" or "bitumen.'* When the molten matter cools interesting crystals of various "species" (i.e., of various chemical composition) usually form in the deeper part of the mass. The lavas of Vesuvius frequently contain beautiful opaque-white twelve_ided crystals of a siliceous mineral called 'ieueitc." Tho lavas of Niedermendig, on. the Rhine, havo bright blue transparent crystals (a mineral called Hauvite) scattered in their grey porous substance. The great "lavastreams, and even the "roots" of extinct yoicai.oe. which are of great geologic age, sometimes become exposed by tne change of the earth's surface, and great shoots of volcanic rock of various kinds aro thus laid bare. Basalt is one of these rocks, and it not infrequently presents .tself as a mass of perpondicular six-sided columns, each column 10ft or more high, and often a foot or moro in diameter. Tho "Giant's Causeway," in tho North of Ireland, and the"Payee dcs Geants," in tha Ardeehe. of Southern France, aro examples. Is is not easy to explain how the molten basalt has .omo to take thL- columnar structure on cooling.

Tho varieties of volcanoes and their products mako up a long story—too long to be told here. There arc from I*oo to -100 active craters in existence to-day—mostly not isolated, but grouped along certain great lines, a-* for instance, along the Andean chain, br in more irregular* tricks. If we add to tho list craters no longer active, but still recognisable, we must multiply it by ten. Vesuvius is tho only active volcano on the mainland of Europe — Hecla, Etna, Stromboli, Volcano, and the volcanoes of the Santorin group, are on islands. The biggest volcanoes are in South America, Mexico, Java, and Japan. Volcanoes and the related "earthquakes" havo been most, carefully studied with a view to the safety of the population in Japan. The graceful and well-beloved volcano, Fujiyama, is more than 12,000 ft high, but, unlike others in those islands it has been quiescent now for just 200 years. Tho most violent volcanic eruptions of recent times, with tho largest "output" of solid matter, are those of the Soufriore of St. Vincent in 1812, of the Mont Pelee of Martinique in 1502, and of Krakatoa in ISS3. A moderate eruption of the great volcano Mauna Loa, in Hawaii, nearly 14,000 ft high, represents a greater quantity of solid matter than Vesuvius has ejected since the destruction of Pompeii. Many hundred millions of tons of solid matter were ejected by Mont Peleo in 1902, when also a peculiar heavy cloud descended from the mountain, hot and acrid, charged with incandescent sand, and rolling along like a liquid rather than a vapour. It burnt up tho town of St. Pierre and its inhabitants and the shipping in tho harbour. In the eruption of tho volcano of St. Vincent in 1812 three million tons of ashes were projected, which fell on the Bahamas Islands 100 miles distant, besides what fell elsewhere. The great explosion at Krakatoa, lasting two days, blew an island of 1400 ft hicjh into the air. A good deal of it was projected as excessively fine ueedlelike particles of pumice with such force as to carry it up thirty miles into the upper regions of the atmosphere, where it was carried by degrees all over the world, causing the "red sunsets" of tho following year. The sky over Batavia, 100 miles distant, was darkened at midday "so completely that lamps had to be used. The explosions were heard in Mauritius, 3000 miles away. A sea wave 50ft high was set going by tho submarine disturbance, and reaching Java and neighbouring islands inundated the land and destroyed 36.000 persons. This wave travelled,in reduced size over a vast tract of the ocean, and was observed and recorded .at Capo Horn, 7800 miles distant from its seat of origin.