VOL. LXXXV,] PHILOSOPHICAL TRANSACTIONS. 503 



clouds. In the accounts of the great eruption of Vesuvius in ld31, mention is 

 made of the extensive progress of the ashes from Vesuvius, and of the damage 

 done by the ferilli, or volcanic lightning, which attended them in their course. 



I must here mention a very extraordinary circumstance indeed, that happened 

 rear Sienna in the Tuscan state, about 18 hours after the commencement of 

 the late eruption at Vesuvius on the 15th of June, though that phenomenon 

 may have no relation to the eruption; and which was communicated to me in 

 the following words by the Earl of Bristol, bishop of Derry, in a letter dated 

 from Sienna, July 12th, 179'i- " In the midst of a most violent thunder-storm, 

 about a dozen stones of various weights and dimensions fell at the feet of dif- 

 ferent people, men, women, and children; the stones are of a quality not found 

 in any part of the Siennese territory; they fell about 18 hours after the enormous 

 eruption of Vesuvius, which circumstance leaves a choice of difficulties in the 

 solution of this extraordinary phenomenon; either these stones have been gene- 

 rated in this igneous mass of clouds, which produced such unusual thunder, or, 

 which is equally incredible, they were thrown from Vesuvius at a distance of at 

 least 250 miles; judge then of its parabola. The philosophers here incline to 

 the first solution. I wish much. Sir, to know your sentiments. My first ob- 

 jection was to the fact itself; but of this there are so many eye-witnesses, it 

 seems impossible to withstand their evidence, and now I am reduced to a perfect 

 scepticism." His lordship was pleased to send me a piece of one of the largest 

 stones, which when entire weighed upwards of 5lb.; I have seen another that 

 has been sent to Naples entire, and weighs about 1 lb. The outside of every 

 stone that has been found, and has been ascertained to have fallen from the 

 cloud near Sienna, is evidently freshly vitrified, and is black, having every sign 

 of having passed through an extreme heat; when broken, the inside is of a light 

 grey colour mixed with black spots, and some shining particles, which the 

 learned here have decided to be pyrites, and therefore it cannot be a lava, or 

 they would have been decomposed. 



Until after the 7th of July, when the last cloud broke over Vesuvius, and 

 formed a tremendous torrent of mud, which took its course across the great 

 road between Torre del Greco and the Torre dell' Annunziata, and destroyed 

 many vineyards, the late eruption could not be said to have finished, though the 

 force of it was over the 22d of June, since which time the crater has been usu- 

 ally visible. After every violent eruption of Mount Vesuvius, we read of damage 

 done by a mephitic vapour, which coming from under the ancient lavas, insinu- 

 ates itself into low places, such as the cellars and wells of the houses situated at 

 the foot of the volcano. After the eruption of 1767, there were several in- 

 stances, as in this, of people going into their cellars at Portici, and other parts 

 of that neighbourhood, having been struck down by this vapour, and who would 



