Aug. 10, 1883.] 



KNOWLEDGE ♦ 



81 



AN ILLUSTRATED ^^-^ JC^ 



MAGAZINE OF SCIENCE^ 



1^ RAINLrVyORDED -£XACTL|DES^RIB£D,, 



LONDON : FRIDAY, AUG. 10, 1883. 



Contents of No. 93. 



d Ischia. By E. A. 



Proctor 



The Birth and Growth of Myth. 



XIII. Bv Edward Clodd 



Pretty Proofs of the Earth 'a Eotun- 



dity. (/««».) By E A. Proctor 

 The Moon in a Three-Inch Tele- 



Bcopo (/iiiis.) ByF.E.A.S 



Weather Forecaate, and How to 



Make Them, Bv John Brownintj 

 The Fisheries Exhibition. IV. 



(Illus.) ByJohnErncst Ady ... 



PAGE 



The White Carna- 

 tion. (/;/(M.) ByT. Kimber 89 



A Steamer goes Safely Past Nia- 

 gara AVhirlpool 90 



Principles or Dress Eeform. By 



E. M. Kinf; 91 



Chemistry of the Cereals, III. By 



William Jago, F.C.8 93 



Editorial Gossip 94 



Correspondence 94 



Our Mathematical Colomn 95 



Our Chess Column 96 



VESUVIUS AND ISCHIA. 



By Richard A. Proctor. 



THE following pas.sages from an essay on Vesuvius, in 

 my " Light Science for Leisure Hours," may prove 

 of interest just now, when Vesuvius and Ischia have 

 shown the close connection which exists between them. 



" In the volcanic region of which Ve.suvius or Somma is 

 the principal vent, we have a remarkable instance of the 

 deceptive nature of that state of rest into which some of 

 the principal volcanoes frequently fall for many centuries 

 together. For how many centuries before the Christian 

 era Vesuvius had been at rest is not known ; but this is 

 certain, that from the landing of the first Greek colony in 

 Southern Italy, Vesuvius gave no signs of internal acti- 

 vity. It was recognised by Strabo as a volcanic mountain, 

 but Pliny did not include it in the list of active volcanoes. 

 In those days, the mountain presented a very different 

 appearance from that which it now exhibits. In place of 

 the two peaks now seen, there was a single, somewhat 

 flattish summit, on which a slight depression marked the 

 place of an ancient crater. The fertile slopes of the moun- 

 tain were covered with well-cultivated fields, and the 

 thriving cities Herculaneum, Pompeii, and Stabire stood 

 near the base of the sleeping mountain. So little did any 

 thought of danger suggest itself in those times, that the 

 hands of slaves, murderers, and pirates which flocked to 

 the standards of Spartacus found a refuge, to the number 

 of many thousands, within the very crater itself. 



" But though Vesuvius was at rest, the region of which 

 Vesuvius is the main vent was far from being so. The 

 island of Pithecusa (the modern Ischia) was .shaken by 

 frequent and terrible convulsions. It is even related that 

 Prochyta (the modern Procida) was rent from Pithecusa 

 in the course of a tremendous upheaval, though Pliny 

 derives the name of Prochyta (or " poured forth ") from 

 the supposed fact of this island liaving been poured forth 

 by an eruption from Ischia. Far more ])robably, Prochyta 

 was formed independently by submarine eruptions, as the 

 volcanic islands near Santorin have been produced in more 

 recent times. 



"So fierce were the eruptions from Pithecusa, that 

 several Greek colonies which attempted to settle on 



this island were compelled to leave it. About 380 

 years before the Christian era, colonists under King 

 Hiero of Syracuse, who had built a fortress on 

 Pithecusa, were driven away by an eruption. Nor 

 were eruptions the sole cause of danger. Poisonous 

 vapours, such as are emitted by volcanic craters after 

 eruption, appear to have exhaled, at times, from extensive 

 tracts on Pithecusa, and thus to have rendered the island 

 uninhabitable. 



"Still nearer to Vesuvius lay the celebrated Lake Avemus. 

 The name Avernus is said to be a corruption of the Greek 

 word Aornos, signifying 'without birds,' the poisonous 

 exhalations from the waters of the lake destroying all birds 

 which attempted to fly over its surface. Doubt has been 

 thrown on the destructive properties assigned by the 

 ancients to the vapours ascending from Avemus. The 

 lake is now a healthy and agreeable neighbourhood, fre- 

 quented, says Humboldt, by many kinds of birds, which 

 suffer no injury whatever even when they skim the very 

 surface of the water. Yet there can be little doubt that 

 Avernus hides the outlet of an extinct volcano ; and long 

 after this volcano had become inactive, the lake which con- 

 cealed its site ' may have deserved the appellation of " atri 

 janua Ditis," emitting, perhaps, gases as destructive of 

 animal life as those suffocating vapours given out by Lake 

 Quilotoa, in Quito, in 1797, by which whole herd.5 of cattle 

 were killed on its shores, or as those deleterious emanations 

 which annihilated all the cattle in the island of Lancerote, 

 one of the Canaries, in 1730.' 



"While Ischia was in full activity, not only was Vesuvius 

 quiescent, but even Etna seemed to be gradually expiring, 

 so that Seneca ranks this volcano among the number of 

 nearly extinguished craters. At a later epoch, -liilian 

 asserted that the mountain itself was sinking, so that sea- 

 men lost sight of the summit at a less distance across the 

 seas than of old. Yet within the last two hundred years 

 there have been eruptions from Etna rivalling, if not sur- 

 passing, in intensity the convulsions recorded by ancient 

 historians. 



" I shall not here attempt to show that Vesuvius and 

 Etna belong to the same volcanic system, though there is 

 reason not only for supposing this to be the case, but for 

 the belief that all the subterranean regions whose eflects 

 have been shown from time to time over the district 

 extending from the Canaries and Azores, across the whole 

 of the Mediterranean, and into Syria itself, belong to but 

 one great centre of internal action. But it is quite cer- 

 tain that Ischia and Vesuvius are outlets from a single 

 source. 



" While Vesuvius was dormant, resigning for awhile 

 its pretensions to be the principal vent of the great Nea- 

 politan volcanic system, Ischia, we have seen, was rent by 

 frequent convulsions. But the time was approaching 

 when Vesuvius was to resume its natural functions, and 

 with all the more energy that they had been for awhile 

 suspended. 



" In the year 63 (after Christ) there occurred a violent 

 convulsion of the earth around Vesuvius, during which 

 much injury was done to neighbouring cities, and 

 many lives were lost. From this period shocks of 

 earthquake were felt from time to time for sixteen 

 years. These grew gradually more and more violent, 

 until it began to be evident that the \olcanic fires w-ere 

 about to return to their main vent. The obstruction 

 which had so long impeded the exit of the confined matter 

 was not, however, readily removed, and it was only in 

 August of the year 79, after numerous and violent in- 

 ternal tliroes, that the superincumbent mass was at lenctli 

 hurled forth, Kocks and cinders, lava, sand, and scoria;, 



