.Mechanism of Stromboli. 497 



being thus communicated, within certain limits, to the otherwise irregular 

 and accidental activity of the volcano. 



Passing ancient accounts, Stromboli has been visited in modern days, 

 amongst men of science, by Spallanzani, Dollomieu, Hoffman, Scrope, 

 Daubeny, and several others ; but no very full or exact description 

 of the crater and its adjuncts, much less any adequate explanation 

 of the curious mechanism of its action, has been given by any of these 

 writers. 



Hoffman's account of the phenomena witnessed by him, though far 

 from clear or satisfactory, is curious enough to deserve translation 

 here : " The volcano appeared to have changed into a hot mineral 

 spring ; then at irregular times we observed that the continually deve- 

 loping steam became stationary, and, with a jerking uncertain motion, 

 rushed back into the mouth of the crater. At the same time we felt a 

 terrifying trembling of the ground, accompanied by visible oscillations of 

 the loose crater-sides. Then followed a hollow roar, and a volume of 

 steam shot out of the crater, accompanied by a shrill crackling. Thou- 

 sands of lava-fragments, which had been carried up with the steam, spread 

 in the air like sheaves, and then fell back, either into the mouth or on 

 the surrounding cinder and sand walls. We could distinctly see (parti- 

 cularly on this occasion) the boiling, seething lava dash against the sides 

 of the shaft, separate into two streams, and then fall back ; but the lava 

 ejected in bubbles flew far through the air, twisting and tearing along, 

 foaming drops, bright as cooled glass, clattering as they rolled down the 

 declivity." 



Mr. Scrope makes the following remarks in his ' Volcanos ' (second 

 edition, pp. 332-334) : 



" The remarkable circumstance in this small but interesting volcano is 

 that the column of lava- within its chimney is shown, by the constant ex- 

 plosions that take place from its surface at intervals of from five to fifteen 

 minutes, casting up fragments of scoriform lava, to remain permanently 

 at the same height, level with the lip of the orifice at the bottom of the 

 crater, and therefore some 2000 feet above the sea-level. It is evident 

 from this that nearly a perfect equilibrium is preserved between the ex- 

 pansive force of the intuniescent lava in and beneath the vent, and the 

 repressive force, consisting in the weight of this lofty column of melted 

 matter, together with that of the atmosphere above it ; consequently a 

 very small addition to or subtraction from the latter, such, for instance, 

 as a change in the pressure of the atmosphere, must to some extent, how- 

 ever small, derange the equilibrium. It need not therefore surprise us 

 that the inhabitants of the island, chiefly fishermen, who ply their perilous 

 trade day and night, within sight of the volcano, declare that it serves 

 them in lieu of a weather-glass, warning them by its increased activity of 

 a lightening of the atmospheric pressure on the volcano equivalent to a 

 fall of the mercuiy and by its sluggishness giving them assurance of the 



