238 
EEPOETS OF MEETINGS. 
On January 8th, 1885, Mr. William Hancock, F.L.S., 
F.R G.S., read a paper on “ The Volcanoes of Central America, 
with an account of the recent active phenomena observed in 
that region.” He alluded to the old and incorrect definition of 
a volcano as “ a burning mountain shooting forth smoke and 
flame.” A volcano was a hole in the outer crust of the earth, by 
means of which a communication existed between the heated 
interior and the surface ; and through which, from time to time, 
steam, gases, scoriae, and molten rock, or lava, were ejected. It 
must not be imagined, however, that the rocks of the interior of the 
earth were necessarily in a molten condition. Physicists rather 
inclined to the opinion that the interior of the earth was solid, 
though kept so only by the enormous superincumbent pressure, on 
the diminution of which the rock assumed the molten form. The 
fact has been established that water is an important, if not 
indispensable, agent in volcanic eruption. Relief of pressure 
causes the water, lield in a liquid condition within the rocks, to 
flash into steam, and give rise to paroxysmal, or continuous, 
eruptions. Variations in barometric pressure may in some cases 
determine a volcanic eruption. At Stroraboli a variation of 
2 inches of mercurial pressure has been noted in a short space 
of time ; and that would mean an increase or decrease of two 
million tons pressure per square mile. After describing the 
steam geysers in Formosa, in the tubes of which he had seen 
molten sulphur, the condition of which made possible an 
estimate of the temperature, Mr. Hancock gave a full and 
interesting account of the volcanic phenomena he bad observed 
in many parts of ('entral America. One of the most striking 
facts was that relating to a line of three volcanoes named 
Pacaya, Agua, and Fuego, of which that in the median position 
had never, within historic times been known to be in eruption, 
though the other two had frequently been active. The volcano 
of Jzixlco resembled Stromboli in being continuous in its action; 
