Vesuvius, a volcano of southern Italy, on the E. shore of the bay of Naples, 8 m. E. S. E. of the city. It is the eastern extremity and the principal vent of a chain of volcanoes extending from it through the Phlegrasan fields to the islands of Procida and Ischia. Before the Christian era Ischia seems to have been the principal scene of volcanic disturbance in this district, and we have no record of any eruption of Vesuvius previous to that of A. D. f9, by which Pompeii and Herculaneum were destroyed. It is frequently mentioned by the older writers without reference to its volcanic character, but Strabo inferred from its structure that it had been a volcano, and Diodorus Siculus says it had " many signs of having been burning in ancient times." Viewed from Naples, Vesuvius appears to have two peaks, which are called respectively Somma and Vesuvius.

But the ancient mountain, according to Strabo, had but one, a truncated cone with an even outline; and it is to be inferred from Plutarch that it had a crater with steep cliffs, the interior of which was overgrown with wild vines. The flanks of the mountain were covered with cultivated fields, and on the bay at its foot were Pompeii and Herculaneum. The site of the latter is now occupied by the village of Resina. It is supposed that the walls of this ancient cone were destroyed in the eruption of 79, when the present cone was formed. In this eruption only scoriae and ashes were ejected, and there is no well authenticated record of a flow of lava from the mountain before 1036, when the lava is said to have reached the sea, although eruptions had taken place in 203, 472, 512, 685, and 993. In the eruption of 472 the ashes were carried as far as Constantinople, and in that of 512 to Tripoli. Other eruptions occurred in 1049, 1138 or 1139, and 1306, during the last of which terrible earthquakes shook the surrounding country, and destroyed Isernia and Brindisi and many thousand lives. In 1198 Solfatara was in eruption, and in 1302 Ischia, both discharging lava.

With the exception of a slight eruption in 1500, Vesuvius was quiet till 1631; but during this period Etna was unusually active, and in 1538 (Sept. 29 and 30) a volcanic cone, now called Monte Nuovo, was raised in the bay of Baiae 440 ft. high, covering an area 8,000 ft. in circumference. During the 131 years preceding the eruption of 1631 the sides of the crater became overgrown with trees and shrubs, below which was a plain where cattle were pastured. The eruption, which began in December, 1631, and lasted till February, 1632, was accompanied with many streams of lava and torrents of boiling water, which overflowed the towns at its base and destroyed many thousand lives. After this eruption the cone was 1,530 ft. lower than that of Somma, although it had previously been higher. During the last century the eruptions increased in frequency. That of 1779 is described by Sir William Hamilton as among the grandest of these phenomena. White smoke like heaps of cotton rose four times as high as the mountain, and spread about it to a proportional extent. Into these clouds stones, scoriae, and ashes were projected at least 10,000 ft. high.

On subsequent days columns of fire shot forth three times as high as the mountain, and large masses of rock were thrown out, one of which was 108 ft. in circumference. The eruption of June, 1794, destroyed the town of Torre del Greco by a stream of lava estimated by Breislak to contain more than 46,000,000 cubic feet, which flowed into the sea in a mass 1,204 ft. wide and 15 ft. high. Eruptions have occurred during the present century in 1804, 1805, 1809, 1812, 1813, 1817, 1820, 1822, 1828, 1831, 1834, 1838, 1841, 1845, 1847, 1849, 1850, 1855, 1858, 1861,1865, 1868, and 1872. That of 1822 broke up the whole top of the mountain, and formed an elliptical chasm about 3 m. in circumference, and supposed to be 2,000 ft. deep. In May, 1855, floods of lava descended as far as the village of Cercolo, committing great ravages in the cultivated fields. In May, 1858, an overflow of lava almost enveloped the hill on which stands the Hermitage. The eruption of December, 1861, was very violent. Eleven cones opened about ½ m. from Torre del Greco, from one of which flowed a stream of lava which threatened the town. Crevices opened in the streets, and many houses were shattered.

In March, 1865, the mountain was also in eruption, and again in December, 1867, continuing until the summer of 1868, when the cone attained an elevation of 4,253 ft. above the sea. On April 24, 1872, a great flow of lava succeeded an unusual outpouring of smoke and flame which had lasted for several months. A large tract of cultivated land was desolated, the villages of San Sebastiano and Massa were destroyed, and many lives lost. The streets of Naples were filled several inches deep with fine black sand. In December, 1875, the mountain again showed signs of activity, and in February, 1876, the disturbances of the instruments in the observatory indicated a speedy eruption, which began in the latter part of March. - Vesuvius stands alone on the plain of Campania, on a base about 30 m. in circumference. The ascent from the bay on the "W. side is by a gradual slope for about 3 m. to the base of the cone, where it attains a height of 2,300 ft. above the sea. Surrounding the cone on the N. and E. sides is the semicircular escarpment of Monte Somma, the ancient cone, with precipitous walls on the inside and sloping gradually on the exterior to the plain below.

On the S. side also of the cone is a terrace-like projection called the Pedamentina, supposed to be the continuation of Somma. The valley between Somma and the base of the cone is the Atrio del Cavallo, so called because horses are left there by those about to ascend to the summit. The cone rises at an angle of 25° to 40° to an additional height of 1,600 to 1,900 ft., varying greatly after eruptions. After that of 1845 its height above the sea was 3,876 ft., and after that of 1868 4,253 ft., the highest elevation ever reached up to that time. The top of the cone is truncated, the diameter being about 2,000 ft. The interior of the cone, or crater, slopes gradually to a depth of about 500 ft., which also varies greatly after eruptions. The lower strata of Somma are formed of compact tufa, composed of pumice and ashes, interspersed with fragments of limestone. Upon these lie beds of leucitic lava alternating with beds of scoriae, and intersected by dikes of compact lava. The cone of Vesuvius is composed of concentric layers of lava, scoriae, and sand, distributed around it with much regularity. According to Lyell, a greater variety of simple minerals are found in an area of three square miles around it than in any other place of the same dimensions on the globe.

Prof. Scacchi has reduced the number, once said to be nearly 400, to about 40 species, most of which are found in the ancient lavas of Somma. A meteorological observatory has been established since 1844 on an elevation near the Hermitage, 2,080 ft. above the sea, which contains besides meteorological apparatus delicate instruments for indicating earthquakes. It is now under the direction of Prof. Palmieri. In 1875 the construction of a railway from Naples to the summit of the mountain, over a line about 16 m. long, was begun. Ordinary locomotives are to be used for 14 m., and a stationary engine and endless rope for the remainder of the way. The last division is in two sections, the first of 2,300 yards extending to the Atrio del Cavallo, where the drawing machine and the necessary buildings will be placed, and the other of 1,200 yards ending a few steps from the crater. The station in the Atrio del Cavallo will be 21 ft. under the lava, and the rails are so guarded that the current of lava in case of an eruption will be turned from them. - The wine called Lachrymae Christi is produced on the slopes of Vesuvius, where also are most of the market gardens which supply Naples with vegetables. - See Schmidt, Vulcanstudien (Leipsic, 1874); Palmieri, Cronaca del Vesuvio (Naples, 1874); and Phillips, "Vesuvius" (London, 1874).

A. Astroni. B. Monte Barbaro. M. Monte Nuovo. S. Solfatara.

A. Astroni. B. Monte Barbaro. M. Monte Nuovo. S. Solfatara.