323 
of Dust and Ashes. 
Campi Phlegrcei , says, that the column of fire and ashes 
during the great eruption of Vesuvius in August, 1799, 
was not less than three times the height of the mountain ; 
so that the whole elevation was nearly 15,000 feet. In 
1794, the height of the clouds of ashes and vapour over 
Vesuvius, when still, was calculated at twenty-five miles ; 
and Braccini calculated them, during the eruption of 
1631, to have an altitude of thirty miles. These state¬ 
ments occur in works easily accessible, and are too well 
recognised to require minute reference. 
]\ ow, if such be the case, it is impossible to limit the 
effect of violent currents of air blowing in certain 
directions upon these enormous columns of light and 
impalpable matter; ashes, dust, and sconce might be 
carried to astonishing distances ; so also might the fine 
impalpable dust of the desert be carried up, by the 
tremendous whirlwinds which there occur, to inaccessible 
heights in the air, and thence be wafted upon the wings 
of the wind to vast distances beyond their original lo¬ 
cality. 
But since in most great volcanic eruptions, as has been 
well maintained, there is not only a whirlwind produced 
in the crater, which ascends in constantly expanding 
gyrations till its strength is expended, but also a*pro¬ 
jectile force of great amount exerting itself upwards, it 
is certain that heavier matters may be carried higher and 
further by the volcanic outburst than by the whirling 
columns or sand-spouts of the desert; the presumption, 
therefore, will always be in favour of the former action, 
where there happens to be a choice of agents for the 
observer, and the character of the transported matter 
does not interpose a claim to another verdict. 
In A.D, 472, according to Marcellinus and Procopius, 
Vesuvius discharged such a quantity of ashes that all 
Europe was covered; and at Constantinople a festival 
y 2 
