Page:Aspects of nature in different lands and different climates; with scientific elucidations (IA b29329668 0002).pdf/246

 *canic phenomena soon himself relinquished it. Observations made in mines and caverns in all climates, and which in concert with M. Arago I have collected in a separate memoir, shew that, even at what may be considered a very small depth, the temperature of the Earth is much above the mean temperature of the atmosphere at the same place. A fact so remarkable, and so generally confirmed, connects itself with that which we learn from volcanic phenomena. The depth at which the globe may be regarded as a molten mass has been calculated. The primitive cause of this subterranean heat is, as in all planets, the process of formation itself, the separation of the spherically condensing mass from a cosmical gaseous fluid, and the cooling of the terrestrial strata at different depths by the loss of heat parted with by radiation. All volcanic phenomena are probably the result of a communication either permanent or transient between the interior and exterior of the globe. Elastic vapours press the molten oxydising substances upwards through deep fissures. Volcanos might thus be termed intermitting springs or fountains of earthy substances; i. e. of the fluid mixture of metals, alkalis, and earths which solidify into lava currents and flow softly and tranquilly, when being upheaved they find a passage by which to escape. In a similar manner the Ancients represented (according to Plato's Phædon) all volcanic fiery currents as streams flowing from the Pyriphlegethon.

To these considerations and views let me be permitted to add another more bold. May we not find in this internal heat of our globe,—(a heat indicated by thermometric