The only grave objection that can be alleged is that of the memorable eruption of 1631, which surprised the neighbouring population so suddenly that many perished miserably, surrounded or covered with lava. But that terrible conflagration occurred after centuries of repose, so that trees had grown in the interior of the crater. No one suspected the possibility of danger. It took place, too, at the end of autumn, when the cone is usually covered with clouds, and, therefore, no one had an opportunity of observing any precursory phenomena. When the Observatory was established, I was able--in the first instance, at my own expense, and afterwards with some slight assistance from Government--to undertake studies more assiduous than any previously made. I had two instruments adjusted to indicate the internal efforts of the Volcano, viz., M. Lamond's apparatus of variations, which, by means of finely-balanced needles and methods of amplification proposed by Gauss, indicates the slightest trepidation of the ground, and my own electro-magnetic seismograph, a self-registering instrument of exquisite delicacy. These instruments, when attentively observed, give the most valuable information with respect to the activity of the adjacent Volcano. If the very slightest eruption occurs, these instruments manifest slight perturbation, increasing with the activity of the mountain. When the Volcano attains a certain degree of activity, and the instruments are proportionately disturbed, it is impossible to foresee a new phase of increase without constantly watching the changes in the intensity of the perturbations; and to effect this it is requisite to have upon the spot a staff of assistants sufficiently numerous, scientific and intelligent. If, therefore, on the night preceding the 26th of April the instruments had been properly watched, they would have undoubtedly indicated the great increase in the activity of the Volcano. The perturbations on the 23rd were steadily increasing, and on the evening of the 25th they were much stronger than on the 24th, but on the morning of the 26th they had become extraordinarily strong; they must, therefore, have increased considerably during the night. II. NATURE OF THE LAVAS. When the observer is near the source of the lava, he sees matter in a state of fusion, which, like a torrent of liquid fire, runs along, with more or less impetuosity, between two banks formed by itself. But as soon as the surface of the torrent cools to the point of congelation, it loses the splendour of its first incandescence. The part which begins to harden breaks readily in some lavas into fragments which float on the viscous fluid beneath; these, increasing in number with distance from the source, conceal the molten matter beneath and retard its progress, and at last nothing is seen but the more or less red-hot scoriæ moving along. These lavas I shall call "_Lavas with fragmentary scoriæ_."