Page:Popular Science Monthly Volume 20.djvu/56

46 of about six hundred fathoms depth; as it rises to more than three thousand feet above the surface, it represents a conical mass of cinders and slaggy materials, six thousand feet high and more than four miles in diameter at the base. The crater may be approached by a flat slope called the Sciarra, which rises at an angle of 35° with the horizon, and ends abruptly at its edge. The accompanying sketch (Fig. 2) was



made from this point at the moment of an outburst. "Before the out-burst, numerous light, curling wreaths of vapor were seen ascending from fissures on the sides and bottom of the crater. Suddenly, and without the slightest warning, a sound was heard like that produced when a locomotive blows off its steam at a railway-station; a great volume of watery vapor was at the same time thrown violently into the atmosphere, and with it there were hurled upward a number of dark fragments, which rose to the height of four or five hundred feet above the crater, describing curves in their course, and then falling back upon the mountain. Most of these fragments tumbled into the crater with a loud, rattling noise, but some of them fell outside the crater, and a few rolled down the steep slope of the Sciarra into the sea."

Spallanzani and other later investigators carried on their observations from a point whence they could look down into the bottom of the crater, and, with a wind that would blow the vapors away, sit and watch for hours the wonderful scene. From this point, the blacky slaggy bottom of the crater is seen to be traversed by many fissures or cracks, from most of which curling jets of vapor issue quietly and gradually mingle with and disappear in the atmosphere. Besides, there are several larger openings, varying in number and position at different periods, from some of which "steam is emitted with loud, snorting puffs, like those produced by a locomotive-engine, but far less regular and rhythmical in their succession"; from others, masses of