540 G. Poulett Scrope — The Mechanism of Stromboli. 



Although I have hitherto spoken of the explosions of Stromboli 

 as equable, yet they do not by any means occur at precisely similar 

 intervals. These, though usually of from two to ten minutes, are 

 sometimes prolonged to thirty or even forty minutes. Nor is the 

 violence of the discharges always equal. According to information 

 furnished by the inhabitants of the island, the explosions are of a 

 more violent character in stormy weather, especially in winter ; and 

 there is a tradition, as old at least as Pliny, that they forecast the 

 weather for some days to come by the condition of the smoke, i.e. 

 the steam-cloud evolved from the mountain. I long since (Yolcanos, 

 ed. 1825, pp. 53-4) suggested that changes in the pressure of the 

 atmosphere on the elastic vapours, enclosed in the lava within and 

 below the volcano, might produce this effect. Mr. Mallet declares 

 this to be " impossible." But I am not inclined to renounce the idea 

 in deference to his arguments. Bearing in mind the well-known 

 fact — which appears to afford a strong parallel to the ease in point 

 — that a fall in the barometer is accompanied by the letting loose of 

 the elastic vapours confined in the vacant spaces of a coal-mine with 

 such violence as at times to force down masses of rock from the roof 

 of the workings, it seems not impossible that within or below the 

 chimney of a volcano communicating with the open air, similar effects 

 may be produced by the same cause.^ 



However this may be, the fact remains that the volcano is at some 

 times and seasons more turbulent than at others. The inhabitants 

 assert that in its eruptions of greatest violence lava is occasionally 

 discharged into the sea from the steep face of the great rent on the 

 north-west side, which bears the local name of the Schiarazza("the 

 great scar"). Hoffmann, as we have seen, confirms this fact; and Sir 

 W. Hamilton gives a coloured drawing of the island, taken by his 

 friend in the year 1768 (see Campi Phlegrgei, plate xxxvii.), when 

 a violent eruption was taking place, apparently from the whole 

 upper portion of the Schiarazza. Mr. Mallet, indeed, doubts that 

 lava can ever, in recent times, have been emitted by Stromboli, on 

 the ground that the crater must have been first filled to the brim, to 

 enable the lava to overflow it. There is reason to doubt the bottom 

 of the crater being much lower than the lowest part of its brim. 

 Even were this the case, it would be quite possible and consistent 

 with facts which I am about to notice, that lava may have flowed 

 into the sea from fissures broken through the bank which separates 

 the Schiarazza from the lowest hollow of the crater. Mr. Mallet, 



1 The attitude of philosophical caution which should be maintained by us with re- 

 gard to such questions was admirably pointed out by the late lamented Professor 

 Phillips in the following passage : — " It is a common belief among persons who do 

 not require strict proof of propositions which they accept, that the weather has 

 influence on such phenomena as earthquakes and -volcanos ; the same minds may 

 readily admit the influence of the moon on the weather ; and thus we arrive easily at 

 the opinion that Vesuvius is governed in its activity by the phases of the moon. On 

 the other hand, men trained in exact reasoning are apt to deride such notions as quite 

 unworthy of inquiry. Neither of these conditions of mind is right, when the problem 

 is one like that of volcanos, for which a just solution cannot be had without taking 

 into careful estimation all the known forces which may be influential on the epoch, 

 duration, and intensity of the effect." — Vesuvius, page 169. 



