VOL. XLI.] VHILOSOPHICAL TRANSACTIONS. 365 



Monday but little smoke and ashes. This day it began to rain plenti- 

 fully, which continued to Tuesday, and afterwards for many days : a circum- 

 stance which has constantly happened after the eruptions of times past. 



The damages done in the neighbourhood by this eruption of fire and ashes, 

 are incredible. At Ottajano, between 4^ and 5 miles from Vesuvius, the ashes 

 on the ground were 4 palms high. All the trees were burnt, or blasted, the 

 people terribly affrighted, and many houses crushed by the weight of the ashes 

 and stones that fell. 



After the description of this fiery eruption, the Academy of Sciences at 

 Naples made an accurate analysis of the matter, and of the salts, that were 

 collected in great plenty near the fissures; and, towards the discovery of the 

 truth, they made the following experiments : 



Exper. 1 . — Some of the stones of Vesuvius being pounded small, and the 

 loadstone applied to the powder, some few particles were attracted by it ; and 

 the same powder, put into aquafortis, caused a sensible effervescence; whence 

 it certainly contains no small quantity of iron : which was also found on trial 

 in another eruption by Tomaso Cornelio, But for the greater elucidation of 

 truth, one of these stones being applied to the magnetic needle, it turned to 

 the stone ; and then carrying it round to the opposite end of the needle, it 

 immediately turned from it, in the same manner as if iron was applied near 

 the compass. 



Exper. 1. — ^The stones are not all of the same density or colour; but various, 

 and of different ponderosity. Some are composed of real talc, others full of 

 marcasites : some are almost all sulphureous, others nitrose; some of a grey 

 colour, others red. 



Exper. 3. — The matter of the current is spongy at top, but very dense to- 

 wards the bottom ; which is a proof of its fusibility; the heavier bodies sub- 

 siding, and the lighter remaining at top. 



Exper. 4. — After growing hard, it retained part of the heat above a month, 

 though unequally : for in the interior parts, where the air had no free access, 

 and the matter was more compact, the heat was much stronger, than towards 

 the surface. 



Exper. 5. — ^Twenty days after the eruption, in divers parts of the mountain, 

 from the bottom to the top, there were seen to arise many pernicious damps, 

 [mofete] especially from the cavities, and the fissures of former torrents; as 

 also on the plain : but none were observed in the matter of this last eruption. 

 They issued out of the fissures under the appearance of a cold wind, and rose 

 about 3 palms high ; then they moved along the surface of the ground, and» 



