HARDWICKE'S SCIENCE-GOSSIP. 



13 



vent clear, as the vast bubbles rise through the viscid 

 mass, bursting at its surface, thus keeping up the 

 temperature of the lava column which it has traversed 

 by the heat brought up from below, and at the same 

 time preventing any permanent stagnation therein. 

 The vapour is generally to be seen carried away by 

 the wind in beautiful white clouds. When, however, 

 the eruption is of a more intense kind, these vast 

 volumes mount into the air at great heights, appear- 

 ing like a column of fire by night, carrying with 





g '^^■wM'wiim'/- /^, 





^C 



Fig. 12. — View of the crater of Vesuvius as seen from the highest point of Monte 

 Somma, on July ist, i88o. A, Crater; B, Cone of eruption ; C, Slopes of cone. 

 I, Spire-like fumarole ; 2, Irregular fumaroles along a fissure ; 3, Bocca 

 Grande, or vent ; 4, Edges and walls of crater (full) ; 5, Ash beds composing 

 cone ; 6, Cooled lava streams all thrown out since November, 1879. 



an ii-regular imbricated roll-like appearance to the 

 exterior. The surface is rapidly covered by bril- 

 liantly-coloured sulilimates, and the fumarole then 

 presents a very pretty spectacle. The author lately 

 was able to thoroughly watch the formation of such 

 a fumarole some 20 feet high, its decadence and disin- 

 tegration extending over a period of eight months. On 

 passing the arm down the central tube (i.e. the fumarole 

 was extinct) it could be felt very regular and smooth, 

 and having a pretty uniform bore of about nine inches. 

 After one slight eruption, the fuma- 

 role in question presented a very 

 curious phenomenon. Immediately 

 (about two to three seconds) after the 

 explosion from the main vent, there 

 came three terrific bangs, with a spout 

 of vapour from its apex, the last one 

 shooting out small fragments of still 

 Mquid lava. 



This continued without variation for 

 ^^^;. six hours that the author remained in 



the crater. The spire-like form may 

 be varied according to surrounding 

 circumstances. If the escape take 

 place along a fissure it will assume 

 on occasions a mitre-like form. There 

 are many other varieties in form, de- 

 pending on the variability of surround- 

 ing circumstances. 



them lapilli and ash often thousands of feet 

 above the mouth of the volcano, then 

 suddenly spreading out these vast clouds 

 give rise to the well-known appearance of 

 the Italian pine-tree. At the same time, 

 from every available fissure are seen to 

 issue little columns of vapour, adding their 

 small share to the grandest visible display 

 of force that nature has provided for our 

 amusement or peril. 



This brings us to the next point of 

 interest, the formation of fumaroles, which 

 may be considered as the effect of these 

 two agents last spoken of acting together. 

 In fig. 12 are seen two varieties, one 

 assuming a spire-like form. These may 

 make their appearance anywhere on the 

 volcano, but are usually situated in close 

 proximity to the vent. Their size varies from twelve 

 inches in height upwards ; generally from three 

 to thirty feet. They are commenced in the major 

 number of cases in the fissured crust recently formed 

 over still flowing lava. Here the vapour escapes 

 in spasmodic puffs, and by its force, a small 

 quantity of lava is forced up and spread out 

 around the aperture, which rapidly cools. It is 

 followed by another puff, and another oozing of 

 lava above and around the aperture of the first. In 

 this manner, layer by layer is built up, thus giving 



Fig. 13.— Crater of deposition. 



Fig. 14. — Crater of upheaval. 



It is now necessary to draw attention to the great 

 difference of opinion which has been expressed upon 

 a point for which we have very little data to support 

 either of two views of the question. 



Vulcanologists were for a long time divided into 

 two schools, which often waged war against each 

 other with considerable fierceness. 



The so-called upheavalists were led by such 

 eminent men as Von Buch, Elie de Beaumont, and 

 Humboldt, whereas those who held the opposite 

 view, Avhich will be immediately explained, claimed 



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