“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 acquainted with foreign languages.  He always retained a strong taste for literary pleasures; and when his continued illness retarded his scientific pursuits, he made literature his recreation.  In this manner he wrote Salmonia:  or Days of Fly-fishing, in a series of conversations, we gather from the Preface:—­“These pages formed the occupation of the Author during several months of severe and dangerous illness, when he was wholly incapable of attending to more useful studies, or of following more serious pursuits.  They formed his amusement in many hours, which otherwise would have been unoccupied and tedious.”  “The conversational and discursive style were chosen as best suited to the state of the health of the author, who was incapable of considerable efforts and long continued exertion.”  The volume is dedicated to Dr. Babington, “in remembrance of some delightful days passed in his society, and in gratitude for an uninterrupted friendship of quarter of a century:”  and the likeness of one of the characters in the conversations to that estimable physician abovenamed, has been considered well drawn, and easily recognisable by those who enjoy his acquaintance.