the action of air and water, give rise to volcanic fires, and to the
production of lavas, by the slow cooling of which basaltic and other
crystalline rocks might subsequently be formed." We have not space for
the details of these investigations, interesting as they would prove to
an unscientific reader; but we give an abstract of the result of Sir
Humphry's observations:

"The phenomena observed by the author afforded a sufficient refutation of
all the ancient hypotheses, in which volcanic fires were ascribed to such
chemical causes as the combustion of mineral coal, or the action of
sulphur upon iron; and are perfectly consistent with the supposition of
their depending upon the oxidation of the metals of the earths upon an
extensive scale, in immense subterranean cavities, to which water or
atmospheric air may occasionally have access. The subterranean thunder
heard at great distances under Vesuvius, prior to an eruption, indicates
the vast extent of these cavities; and the existence of a subterranean
communication between the Solfattara and Vesuvius, is established by the
fact that whenever the latter is in an active state, the former is
comparatively tranquil. In confirmation of these views, the author
remarks, that almost all the volcanoes of considerable magnitude in the
old world, are in the vicinity of the sea; and in those where the sea is
more distant, as in the volcanoes of South America, the water may be
supplied from great subterranean lakes; for Humboldt states that some of
them throw up quantities of fish. The author acknowledges, however, that
the hypothesis of the nucleus of the globe being composed of matter
liquefied by heat, offers a still more simple solution of the phenomena
of volcanic fires."[6]

We have hitherto spoken of Sir Humphry Davy as a philosopher. He was,
however, in every respect, an accomplished scholar, and was well