That the loss of life remains so small is the more surprising in view of the fact that Vesuvius can by no means be trusted to discharge itself on all occasions by the main crater. In fact, the flanks of the mountain, strengthened and compacted as they are by the outflow of countless lava streams, are yet seamed and fissured by the rupture of the surface to form other vents. Occasionally these "bocche" mouths, as the Italians call them, have opened far down the slopes among the cultivated fields and vineyards. It was so in 1861, not fortunately one of the greatest of eruptions. The bocche of that year are on the hillside no great way above Torre del Greco. Nothing, in fact, is certain about the operation of volcanic forces, and this is a fact which may be borne in mind by those who elect to ascend the mountain during an eruption. Sir William Hamilton in 1767 had a narrow escape. "I was making my observations," he says, "upon the lava, which had already from the spot where it first broke out reached the valley"--that is, the Atrio del Cavallo--"when on a sudden, about noon, I heard a violent noise within the mountain, and at a spot about a quarter of a mile off the place where I stood, the mountain split, and with much noise from this new mouth a fountain of liquid fire shot up many feet high, and then like a torrent rolled on directly towards us. The earth shook, and at the same time a volley of stones fell thick upon us; in an instant clouds of black smoke and ashes caused almost a total darkness; the explosions from the top of the mountain were much louder than any thunder I ever heard, and the smell of the sulphur was very offensive. My guide, alarmed, took to his heels; and I must confess I was not at my ease. I followed close, and we ran near three miles without stopping." To run three miles over the broken and uneven lava reefs of the Piano, with a fiery torrent hunting close behind, is not an experience which would be relished by the ordinary tourist, however far it might be sweetened in the retrospect to the adventurous man of science. Yet happy is the man who in such a case gets off with a sharp run. In 1872 a party of tourists were less happy. The terrible eruption of that year deserves attention, being certainly the greatest within the present generation, and fortunately it has been described with knowledge and precision by Professor Palmieri who, with noble devotion to the cause of science, had spent so many years in the observatory planted on the barren ridge of trachyte which divides the two valley-arms which the Atrio del Cavallo projects towards Naples. Those valleys receive the streams of lava which are ejected into the Atrio, and when the volume of the flow is large, it has happened that the observatory has been almost engirdled with the red-hot torrents--a position of which, if the danger may be exaggerated, the awe certainly cannot, and which must fill all men with admiration for the illustrious scientists who endure it.