As Judd remarks, from whom much of the information concerning some of the volcanic districts of the Mediterranean has been obtained, the flashing light of Stromboli differs from that of the ordinary flashing light in two important respects; viz., in the intervals that elapse between the successive flashes, and in the intensity of the light emitted. As you know, it is necessary that the different lighthouses placed near one another on a coast must have their lights of such a nature that they can be readily distinguished. In order to do this, the flashing light has been devised. In flashing lighthouses, the lights only appear at intervals, one lighthouse being distinguished from another in its neighborhood by the intervals between successive flashes, or, sometimes, indeed, by the color of some of the flashes. Now, in the case of Stromboli, the intervals between the successive glowings of the red lights are very irregular, varying between one and twenty flashes per second. Moreover, the intensity of the light also varies greatly from time to time. You naturally inquire as to the cause of these flashes of light that are emitted by Stromboli. If, as Judd suggests, you should climb to the summit of the mountain, during the daytime, and look down the inside of the crater, you could see its black slag bottom crossed by many cracks and fissures. From most of the smaller fissures the vapor of water is quietly escaping. This vapor rises in the air in which it soon disappears. There are, however, larger cracks on the bottom of the crater from which, at more or less regular intervals, masses of steam are emitted with loud snorting puffs not unlike those produced by a locomotive. From some of the openings molten matter is seen slowly oozing out, collecting in parts of the crater and moving up and down in a heaving motion. Every now and then a bubble is formed on the surface of this liquid. The bubble swells to a gigantic size, and suddenly bursts. The steam it contained escapes, carrying fragments of scum which are thrown high into the air. The masses of steam, formed below the surface of the sticky, boiling, lava, in endeavoring to escape, force their way through the mass, blow huge bubbles, which, on bursting, produce the roaring sounds that are heard, and throwing great columns of vapor in the air, produce the rounded masses of clouds you can see floating high up in the air over the mountain. At the same time the scum is partially removed from the red hot surface, its light illumines the lower surface of the overhanging cloud, which flings it back again to the earth. With the bursting of each bubble, and the clearing of the scum from the surface of the red hot mass, the light begins, increases in intensity, and then as the scum again begins to collect on the surface, decreases, and finally disappears, and not until the bursting of the next bubble is it again visible.