741 



SCIENTIFIC SIDE-LIGHTS 



Vividness 

 Volcanoes 



visited Vesuvius not long before the erup- 

 tion of 1631, gives the following interesting 

 description of the interior: " The crater was 

 five miles in circumference, and about a 

 thousand paces deep; its sides were covered 

 with brushwood, and at the bottom there 

 was a plain on which cattle grazed. In the 

 woody parts wild boars frequently harbored. 

 In one part of the plain, covered with ashes, 

 were three small pools, one filled with hot 

 and bitter water, another salter than the 

 sea, and a third hot, but tasteless." But at 

 length these forests and grassy plains were 

 consumed, being suddenly blown into the 

 air, and their ashes scattered to the winds. 

 In December, 1631, seven streams of lava 

 poured at once from the crater, and over- 

 flowed several villages, on the flanks and at 

 the foot of the mountain. Resina, partly 

 built over the ancient site of Herculaneum, 

 was consumed by the fiery torrent. Great 

 floods of mud were as destructive as the 

 lava itself no uncommon occurrence during 

 these catastrophes; for such is the violence 

 of rains produced by the evolutions of aque- 

 ous vapor that torrents of water descend 

 the cone, and becoming charged with im- 

 palpable volcanic dust, and rolling along 

 loose ashes, acquire sufficient consistency to 

 deserve their ordinary appellation of " aque- 

 ous lavas." LYELL, Principles of Geology, 

 bk. ii, ch. 23, p. 374. (A., 1854.) 



3669. VOLCANO RENDERS SERV- 

 ICE TO MAN Buildings Cemented with Mor- 

 tar from Depths of the Earth. The quantity 

 of rain which falls during volcanic eruptions 

 is often enormous, owing to the condensa- 

 tion of the great volumes of steam emitted 

 from the vent. Consequently the falling 

 lapilli and dust often descend upon the 

 mountain, not in a dry state, but in the 

 condition of a muddy paste. Many volcanic 

 mountains have evidently been built up by 

 the flow of successive masses of such muddy 

 paste over their surfaces. Some volcanic 

 materials when mixed with water have the 

 property of rapidly " setting " like concrete. 

 The ancient Romans and modern Italians, 

 well acquainted with this property of cer- 

 tain kinds of volcanic dust and lapilli, have 

 in all ages employed this " puzzolana," as it 

 is called, as mortar for building. JUDD Vol- 

 canoes, ch. 4, p. 89. (A., 1899.) 



06 7 O. VOLCANO TURNS FRUITFUL 

 LAND INTO BARRENNESS Irredeemable 

 Sterility of Lava-stream. In the year 1302 

 [occurred the eruption] of a lava-stream 

 from a new vent on the southeast end of 

 the island of Ischia. During part of 1301 

 earthquakes had succeeded one another with 

 fearful rapidity; and they terminated at 

 last with the discharge of a lava-stream 

 from a point named the Campo del Arso, 

 not far from the town of Ischia. This lava 

 ran quite down to the sea a distance of 

 about two miles; in color it varies from 

 iron-gray to reddish black, and is remark- 

 able for the glassy feldspar which it contains. 



Its surface is almost as sterile, after a peri- 

 od of five centuries, as if it had cooled down 

 yesterday. A few scantlings of wild thyme, 

 and two or three other dwarfish plants, 

 alone appear in the interstices of the scoriae, 

 while the Vesuvian lava of 1767 is already 

 covered with a luxuriant vegetation. Pon- 

 tanus, whose country-house was burnt and 

 overwhelmed, describes tlm dreadful scene as 

 having lasted two months. Many houses 

 were swallowed up, and a partial emigration 

 of the inhabitants followed. LYELL Prin- 

 ciples of Geology, bk. ii, ch. 22, p. 365. (A., 

 1854.) 



3671. VOLCANOES EARTH'S SAFE- 

 TY-VALVES Rocks Crumpled Like Tissue- 

 paper by Internal Forces. No one who has 

 not studied the crushed, crumpled, frac- 

 tured, and altered condition of many of 

 the sedimentary rocks of the globe can 

 form the faintest idea of the enormous ef- 

 fects of the internal forces which have been 

 in operation within the earth's crust dur- 

 ing earlier geological periods. And it is only 

 by such studies as these that we at last 

 learn to regard the earthquake and volcanic 

 phenomena of our globe, not as the grandest 

 and most important effects of these forces, 

 but as their secondary and accidental accom- 

 paniments. " Volcanoes," it has been said, 

 " are the safety-valves of the globe " ; and 

 when we come to realize the real extent and 

 nature of the internal forces ceaselessly 

 working in the earth's crust we shall scarce- 

 ly be disposed to regard the simile as an 

 overstrained one. JUDD Volcanoes, ch. 10, 

 p. 289. (A., 1899.) 



3672. VOLCANOES IN MINIATURE 



Imprisoned Steam Escaping from Sulfur. 

 In the process of extracting sulfur from 

 the residues obtained during the manufac- 

 ture of soda, some very interesting phenome- 

 na are manifested. The molten sulfur is 

 exposed to a temperature of 262 F. and a 

 pressure of two or three atmospheres, in 

 the presence of steam; under these circum- 

 stances it is found that the sulfur absorbs 

 a considerable quantity of water, which is 

 given off again with great violence from the 

 mass as it undergoes solidification. The 

 hardened crust which forms on the surface 

 of the molten sulfur is agitated and fissured, 

 miniature cones and lava-streams being 

 formed upon it, which have a striking re- 

 semblance to the grander phenomena of the 

 same kind exhibited upon the crust of the 

 globe. JUDD Volcanoes, ch. 12, p. 356. (A., 

 1899.) 



3673. VOLCANOES, PRESENT NUM- 

 BER OF Seeming Quiescence Often Delusive. 

 What is the number of volcanoes which 

 are still vomiting forth lava during the 

 present period of the earth's vitality? It 

 is difficult to ascertain, for often mountains 

 have seemed for a long time to be extinct; 

 forests have grown up in their disused cra- 

 ters, and their beds of lava have been cov- 

 ered up under a rich carpet of vegetation, 



