Influence of travels in distant lands on the generalization of our ideas and on the progress of physical orology. Influence of the conformation of the Mediterranean on the earliest ideas respecting volcanic phenomena.—COMPARATIVE GEOLOGY OF VOLCANOS. Periodical return of certain revolutions in nature, the cause of which lies deep in the interior of the globe. Proportion of the height of volcanos to that of their cone of ashes in the Pichincha, Peak of Teneriffe, and Vesuvius. Changes in the height of volcanic mountain summits. Measurements of the margins of the crater of Vesuvius from 1773 to 1822; the author’s measurements embrace the period from 1805 to 1822—pp. 353–365. Circumstantial description of the eruption in the night between the 24th and 25th of October, 1822. Falling in of a cone of ashes more than 400 feet high, which stood in the interior of the crater. The eruption of ashes from the 24th to the 28th of October, was the most memorable among those, of which authentic accounts are possessed, since the time of the elder Pliny—pp. 365–371. Difference between volcanos that are of very diverse forms, with permanent craters, and the phenomena more rarely observed in historic times, in which trachytic mountains suddenly open, eject lava and ashes, and reclose, perhaps for ever. The latter phenomena are peculiarly instructive for geognosy, because they remind us of the earliest revolutions that occurred in the oscillating, upheaved, fissured surface of the earth. In ancient times they led to the notion of the Pyriphlegethon. Volcanos are intermittent earth-springs, the result of a permanent or transitory connection between the interior and exterior of our planet, the result of a reaction of the still fluid interior against the crust of the earth; hence the question is useless, as to what chemical substance burns in the volcanos, and furnishes the material for combustion—pp. 371–373. The primary cause of subterranean heat is, as in all planets, the formative process itself, the separation of the conglomerating mass from a cosmic vaporous fluid. Power and influence of the calorific radiation from numerous deep fissures, unfilled veins in the primordial world. Great independence, at that period, of the climate (atmospheric temperature) in respect to geographical latitude, the position of the planet towards the central body, the sun. Organisms of the present tropical world buried in the icy north—pp. 373–375. SCIENTIFIC ILLUSTRATIONS AND ADDITIONS pp. 376–379.