48
THE POPULAR SCIENCE MONTHLY.
of earthquake-shocks in the country around, the vivid lightnings and thunders arising from the electrical action engendered by the column of steam, and the excessive rainfall which followed the condensation of the steam.
In both these volcanoes the active cause of all the phenomena exhibited is found to be the escape of steam from the midst of masses
Fig. 3.—Vesuvius in Eruption, as seen from Naples, April 26, 1872. (From a Photograph.)
of incandescent liquefied rock. The violence, the grandeur, and the destructive effects of an eruption depend upon the abundance and tension of this escaping steam.
The manner in which volcanic cones are built up is ascertained
