THE GRAND ERUPTION OF VESUVIUS IN igo6 643 



The electrical phenomena. — An English acquaintance, in whose 

 statements the writer reposes confidence, reported to him that on 

 the morning of the 8th, when the large lava stream was overrunning 

 Boscotrecase, he followed the margin of the stream a considerable 

 distance in the direction of the crater. Almost continuous flashes 

 of Hghtning seemed to pass from the overhanging cloud nearly 

 straight downward toward the lava; and, if appearances were to 

 be relied upon, at no great distance. "^ On the 15th, when the writer 

 attempted to reach the new hocca by following up the stream of lava 

 from Boscotrecase, changes in the direction of the wind left him 

 for considerable periods enveloped in the ash cloud with surrounding 

 darkness too great for following the bad footing over the scoriaceous 

 surface, thus necessitating long delays. At elevations in excess 

 of 1,400 feet above Torre Annunziata heavy rumblings were heard 

 at intervals of from six to nine minutes, and in apparent corre- 

 spondence with the rhythmic uprush of steam and ash from the main 

 crater. Before the envelopment by the ash cloud the direction of 

 the crater had been ascertained to be in close correspondence with 

 the steepest slopes. The hoati always began in this direction as 

 low continuous rumblings, like the rolhng of heavy wagons over 

 hard and irregular pavements; but they soon moved away to the 

 southward and were transformed into reverberating crashes of 

 thunder so resembling those of a heavy electrical storm as to be 

 unmistakable. In a favorable shift of the wind an altitude of 2,200 

 feet was reached, when a quick change again brought the black 

 ash cloud and a patter of lapilli, so that further progress (now wholly 

 over fresh lava) was impracticable. 



Pliny mentions that in 79 almost incessant lightning flashes 

 accompanied the eruption. The rhythmic hoati of Vulcano during 

 its great eruption of 1888-89 lacked these striking electrical features, 

 at least at the time the volcano was visited by the writer in April, 

 1889; and apparently a smaller proportion of water vapor was 

 characteristic of the eruption. Professor Palmieri, the former director 

 of the Vesuvian Observatory, gave careful study through many 

 years to the electrical phenomena attending Vesuvian eruptions, 



I A friend who was in Pompeii during the great outburst of the 7th has erapha- 

 sized the grandeur of the electrical phenomena. 



