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only of lava, but of immense volumes of volcanic ash, some of 
which became marked by ridges due to sliding. Other eruptions 
described were those of St. Vincent and Martinique in 1902, the 
destruction caused by these being largely due to the downward 
course taken by the hot ejected dust and gases; and that of 
Krakatoa in 1883, which was heard in Australia and in Ceylon. 
It was pointed out that the section of Rakata, which was exposed 
after the northern part of Krakatoa had been blown away, revealed 
in an exceptional manner the inner structure of a volcano and 
tended to confirm the “crater of eruption”’ theory. According 
to this view, a volcanic mountain is built up of materials ejected 
from the interior of the earth, and is not due to local inflation 
of the crust by subterranean forces. The various hypotheses 
which have been advanced to explain the origin of the earth’s 
internal heat were briefly discussed. Volcanoes are probably fed, 
not from any central source, but from local reservoirs of magma 
in a comparatively shallow part of the crust. It has been supposed 
that the heat for local fusion may be due to chemical or mechanical 
action, or to the radio activity of the rocks. The Hon. R. J. Strutt 
has shown that the average amount of radium in the rocks would 
supply sufficient heat to maintain the present thermal condition of 
the earth, if the crust were only about forty-five miles thick, with 
no radium below; but Prof. Joly holds that sufficient elevation 
of temperature near the surface for volcanic phenomena could 
not be obtained by any increased local radio activity of the rocks, 
unless of an order higher than seems probable from recorded 
observations. Reference was also made to the origin of vulcanism 
on the planetesimal theory of the earth’s formation, as suggested 
by Professors Chamberlin and Moulton of Chicago, and to the 
opinion of Prof. Arrhenius of Stockholm, according to whom the 
interior of the earth is mainly composed of gases—not gases as 
we know them, for, at the pressures and temperatures there existing, 
they would have a rigidity equal to that of steel. It should be 
remembered that volcanoes eject far more gases than anything 
else, and their action may be roughly compared to that of a bottle 
of soda-water when uncorked, for in both a release of pressure 
causes the pent-up gases to expand and rush out of the orifice, 
carrying some of the surrounding liquid with them. But, after 
all that has been written, it may be said that the real cause of 
volcanic action remains without satisfactory explanation. 
On Thursday, October 28th, the Annual Conversazione was 
held to inaugurate the Session 1gog-10. Mr. Walter Baily, 
