44 THE POPULAR SCIENCE MONTHLY. 



process. Nor are volcanoes necessarily " mountains " at all ; essen- 

 tially, 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 Hephaestus, or Vulcan, had his forge. Vol- 

 canic 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 Strom- 

 boli, whose crater, the edge of which is easily accessible, is in a state of 

 constant moderate action, and can be watched for hours together with- 

 out 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 direc- 

 tion 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 ob- 

 served 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- 



