SOUFEIEEE, AND ON A VISIT TO MONTAGNE PELEE, IN 1902. 
50i) 
as 1229° but this, of course, is in the dry condition and under atmospheric 
pressure, not in a magma saturated with steam. 
The velocity of the black cloud is difterent in different parts of its course. So far 
as our observations go it is comparatively low at first, and increases as it sweeps 
down the hill till it is probably at a maximum just before it reaches the plains 
beneath, or the sea. Then it again diminishes, and rapidly slows down, as is well 
seen in St. Vincent by its effects on the trees. We have compared its violence to 
that of a hurricane or tornado, but in many w’^ays the comparison does not hold good. 
For ecpial velocities the destructive effects of the dust cloud must have been con¬ 
siderably greater than that of any wind, for the weight of tlie mass, or rather its 
momentum, is high, owing to the density of the mixture of gases and of dust. Tliis 
is much heavier than air, and flows along the ground, bnt lighter than water, on 
Avhich it always floats. 
There are a few facts which seem to show that the mere weiofit of the cloud did 
o 
much damage, as, for example, that the hatches of the “ Roraima ” were stove in.| 
We looked in St. Vincent for similar effects, but found none, even on Lot 14, which 
was nearest the crater. The roofs had in some cases collapsed, })robably with the 
weight of ashes which gathered througli the night. Many windows were broken, 
apparently by falling stones, as in Geoi'getown. There was no evidence that a great 
aerial shock, such as follows an explosion or the discharge of large guns, had broken 
the windows, though, as it was about mid-day, they were probaldy open, and may 
have escaped in consequence. 
Professor Lacroix and his colleagues | consider that the blast which destroyed 
St. Pierre covered a distance of 8 kilometres in three minutes. No very good 
evidence is available on which to base exact estimates. When the blast passed 
over the north end of the town it was travelling with a velocity certainly over 
100 miles an hour, Imt before it got to the Morne d’Orange, at the soutli end, it had 
considerably slowed. 
The fundamental question remains to be discussed—What is the source of the 
energy which drives the cloud along ? To this we believe there is only one answer— 
The motive power is supplied by the weight of the mass. It is in a condition 
comparable to that of a heavy and mobile fluid which has been elevated by the 
volcanic forces and poised on the edge of the crater, and proceeds to flow downward 
in obedience to tlie law of gravitation. This is, to our minds, the only conceivable 
explanation of what we saw’- on the evening of July 9th. The little black cloud rose 
from the crater exactly like a puff of steam, but lower and more globular. It did not 
* The melting point of hypersthene has not l)een ascertained, bnt that of enstatite, a less ferriferous 
rhombic pyroxene, is given as 1295° C. The melting point of difterent kinds of monoclinic pyroxenes 
ranges between 1187° C. and 1300° C. 
t ‘Cosmopolitan,’ July, 1902, p. 250. 
X “ Sur I’Eruption de la Martinicpie,” ‘ Comptes Eendus,’ vol. cxxxv., p. 425, 1902. 
