Page:Popular Science Monthly Volume 20.djvu/54

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process. Nor are volcanoes necessarily "mountains" at all; essentially, they are just the reverse—namely, holes in the earth's crust, or outer portion, by means of which a communication is kept up between the surface and the interior of our globe. When mountains do exist at centers of volcanic activity, they are simply the heaps of materials thrown out of these holes, and must, therefore, be regarded not as the causes but as the consequences of volcanic action. Neither does this action always take place at the "summits" of volcanic mountains when such exist, for eruptions occur quite as frequently on their sides or at their base. That, too, which popular fancy regards as "smoke" is really condensing steam or watery vapor, and the supposed raging "flames" are nothing more than the glowing light of a mass of molten material reflected from these vapor-clouds. The name of volcano has been borrowed from the mountain Vulcano, in the Lipari Islands, where the ancients believed that Hephæstus, or Vulcan, had his forge. Volcanic phenomena have been at all times regarded with a superstitious awe, which has resulted in the generation of such myths as the one just mentioned, or of that in which Etna was said to have been formed by the mountains under which an angry god had buried the rebellious Typhon. These stories changed their form, but not their essence, under a Christian dispensation, and Vulcano became regarded as the place of punishment of the Arian Emperor Theodosius, and Etna as that of Anne Boleyn, who had sinned by perverting the faith of King Henry VIII.

Volcanic phenomena can be studied to great advantage in Stromboli, whose crater, the edge of which is easily accessible, is in a state of constant moderate action, and can be watched for hours together without having the judgment warped either by an excited imagination or the sense of danger. It is an island of rudely circular outline and conical form, and rises to the height of three thousand and ninety feet above the level of the Mediterranean (Fig. 1). From a point on the side of the mountain masses of vapor are seen to issue, which unite to form a cloud over the summit, the outline of which varies continually according to the hygrometric state of the atmosphere and the direction and force of the wind. At the time the sketch was made, April 20, 1874, the vapor-cloud was spread in a great horizontal stratum overshadowing the whole island, but was clearly seen to be made up of a number of globular masses, each of which was a product of a distinct outburst of the volcanic forces.

The mountain is visible over the sea for a hundred miles. When it is watched from the deck of a vessel anywhere within this distance, "a glow of red light is seen to make its appearance from time to time above the summit of the mountain; this glow of light may be observed to increase gradually in intensity, and then as gradually to die away. After a short interval the same appearances are repeated, and this goes on till the increasing light of the dawn causes the phenome-