XXVlil SUMMARY. VOLCANOS. EHODIAN GENIUS. 



mena. COMPARATIVE GEOLOGY OP 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 be- 

 tween 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 revolu- 

 tions 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 for- 

 mative 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 tempe- 

 rature) 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. 

 Barometric measurements on Vesuvius, comparison of the two crater- 

 margins and the Rocca del Palo pp. 376-379. Increase of temperature 

 with depth, being 1 of Fahrenheit for every 54 feet. Temperature 

 of the Artesian well in Oeynhausen's Bath (New Salt-works near 

 Minden), at the greatest depth yet reached below the level of the sea. 

 As early as the third century the thermal springs near Carthage led 

 Patricius, Bishop of Pertusa, to form correct suppositions respecting 

 the cause of calorific increase in the interior of the earth p. 379. 



VITAL FORCE, OR THE RHODIAN GENIUS; AN ALLEGORY. 



pp. 380-385. 



ILLUSTRATIONS AND NOTE pp. 386-389. 



The Rhodian Genius is the development of a physiological idea in a 

 mythical garb. Difference of views concerning the necessity and non- 



