Since this great convulsion, which emptied the crater, Vesuvius has never again relapsed into a condition of total quiescence. At intervals, varying from a few weeks or months to a few years, it has broken out into eruption, sometimes emitting only steam, dust and scoriae, but frequently also streams of lava. The years 1766-67, 1822, 1872, 1906 and 1929 were marked by special activity. The extensive eruption of 1906 completely altered the conformation and aspect of the cone, considerably reducing its height.
The modern cone of the mountain has been built up by suc cessive discharges of lava and fragmentary materials round a vent of eruption, which lies a little south of the centre of the prehistoric crater. The southern segment of the ancient cone, an swering to the semicircular wall of Somma on the north side, has been almost concealed, but is still traceable among the younger accumulations. The numerous deep ravines which indented the sides of the prehistoric volcano, and still form a marked feature on the outer slopes of Somma, have on the south side served as channels to guide the currents of lava from the younger cone. On one of the ridges between these radiating valleys an observa tory for watching the progress of the volcano was established by the Neapolitan government (1844), and is now a national institution. A continuous record of each phase in the volcanic
changes has been taken, and some progress has been made in the study of the phenomena of Vesuvius, and in prognosticating the occurrence and probable intensity of eruptions. The foot of the cone is reached from Naples by electric railway, and thence a wire-rope railway (opened in 188o) carries visitors to within 150 yd. of the mouth of the crater.
See John Phillips, Vesuvius (1869) ; Pompei e la Regione Sotterrata dal Vesuvio nell' Anno 79 (Naples, 1879) ; L. Palmieri, Vesuvio e la sua Storia (Milan, 188o) ; H. J. Johnstone-Lavis, "The Geology of Monte Somma and Vesuvius" (1884), in Quart. Journ. Geol. Soc. vol. xl. p. 85; J. L. Lobley, Mount Vesuvius (London, 1889) ; F. Furchheim, Bibliografia del Vesuvio (Naples, 1897) ; T. McK. Hughes, "Hercu laneum," in Proc. Camb. Antiq. Soc. No. xlviii. p. 25 (Cambridge, 1908) ; A. Lacroix, Etude mineralogique des produits szlicates de l'eruption du Vesuve 1906 (1907) ; K. Burkhalter, Aus dem Reiche des Vesuves (Steffisburg, 1908) ; F. Zambonini, Mineralogia Vesuviana (Naples, 191o) ; F. A. Perrett, The Vesuvius Eruption of Iwo (Wash ington, 1924). (A. GEL ; T. A.)