Jounston-Lavis—-The Eruption of Vesuvius in April, 1906. 183 
the north-east in face of wind blowing from that quarter. No reason is given 
in some cases for this oblique line of projection; but other writers attribute it 
to the lower truncation of the cone on the north-east side. It seems to me that 
the effect is taken by them for the cause. Even admitting that this difference in 
level of the crater-rim did have some influence, it would be out of all proportion 
to the remarkable limitation in the distribution of the ejecta. 
Various estimates are given as to the height that the uprising column of 
ejecta reached— 
Bassani and Galdieri put it at 4000 m. 
Luigi Conforti » 9» 4000 m. 
De Lorenzo 9 og §6=— WOO i, 
Lacroix yy» 9, 4000 m. 
Matteucci » 9, 10 to 13000 m. 
Mercalli Seni 4 to 5000 m. 
If we take 5000 m. as a fair average, it is hardly credible that the energy 
necessary to raise the fragmentary materials to that height could be much 
influenced by the relatively small difference in the level between one side of the 
crater and the other, which we might at that moment estimate to be under 100m. 
When I visited the crater, at the end of the eruption, the escape of the final 
puffs of dust and sand was occurring close to the west wall, but whether more to 
the north or to the south it was impossible to ascertain. I have already explained 
that the west and south-west parts of the crater-rim were highest in consequence 
of the larger amount of solid rock entering into their composition, whereas the 
north-east part was very friable and incoherent. What probably happened was, 
that the true eruptive axis at the time of the crater-formation was not that of the 
crater, since erosion took place on one side more easily than on the other. The 
result of this would be, that the crater-walls, being more resistant on the south- 
west, would tend to overhang the rent, and be diverted to the north-east, where 
the inner slope of the crater would be the more marked, and the edge of the 
crater lower—all favourable to the more easy projection of the loose materials to 
the north-east. 
This projection to the north-east, I repeat, could only be very limited in extent 
at any distance from the crater; and we have still left the elucidation of the 
spread of the ejecta far afield to the north-east, in what was supposed to be a con- 
trary wind. Those who observe Vesuvius will frequently perceive a phenomenon 
well known to meteorologists and aeronauts, namely, currents of air blowing in 
different directions. One may often notice the “smoke ”- of Vesuvius trend away 
in one direction, and, at a height of 500 or even 1000 to 2000 metres, bend over, 
and be traceable as a dark streak for fifty miles in the opposite direction. At 
