VOLCANOES, THEIR ACTION AND DISTRIBUTION 47 



molten material well out and sometimes flow outside of the crater, 

 with steam escaping, often in considerable quantities ; in some a vis- 

 cid or semi-liquid substance is seen seething, swelling up and form- 

 ing gigantic bubbles, which burst under occasional great rushes of 

 steam, carrying fragments of the scum-like surface of the liquid high 

 up into the atmosphere, almost precisely as takes place in a pot of boil- 

 ing mush. At night, " the smaller cracks and larger openings glow 

 with a ruddy light. Every time a bubble bursts, and the crust is 

 broken up by the escape of steam, a fresh, glowing surface of the in- 

 candescent material is exposed. If at these moments we look up at 

 the vapor-cloud covering the mountain, we shall at once understand 

 the cause of the singular appearances presented by Stromboli when 

 viewed from a distance at night ; for the great masses of vapor are 

 seen to be lit up with a vivid, ruddy glow, like that produced when an 

 engine-driver opens the door of the furnace and illuminates the stream 

 of vapor issuing from the funnel of his locomotive." 



These phenomena differ only in degree from those presented by 

 volcanoes which, like Vesuvius, are spasmodically more active. Occa- 

 sionally, the violence of the outbursts at Stromboli is temporarily in- 

 creased ; and at Vesuvius a series of small explosions, quite similar to 

 those occurring at Stromboli, were observed for some months before 

 the great eruption of 1872. French geologists, in fact, define the con- 

 ditions of activity of volcanoes by speaking of the " Strombolian " and 

 the " Vesuvian " stage as two degrees between which the passage is 

 by insensible gradations. The eruption of 1872, of which the accom- 

 panying view (Fig. 3) is from a photograph, afforded a fine example 

 of the intense Vesuvian stage. The activity of the forces at work 

 within the mountain had been on the increase for more than a year, 

 and reached its climax on the day the photograph was taken. During 

 the eruption the bottom of the crater was entirely broken up, and the 

 sides of the mountain were rent by fissures in all directions whence 

 liquid matter appeared to be oozing as from every part of the surface, 

 or as Professor Palmieri expressed it, " Vesuvius sweated fire." Enor- 

 mous volumes of steam rushed out from the crater and from some of 

 the fissures, to the height, as shown by the picture, of twenty thou- 

 sand feet, or nearly four miles, with a prodigious roaring sound that 

 frightened the inhabitants of Naples into leaving their houses and 

 seeking refuge in the streets. The roaring was produced by explo- 

 sions or detonations rapidly following one another, each of which sent 

 up a globe of white vapor, out of a mass of which globes the over- 

 hanging cloud was formed. Lava, or molten rock, rushed down the 

 sides of the mountain in great streams, whence enormous volumes of 

 steam continually rose, forcing the congealing rock as it escaped from 

 it into great bubbles and blisters, thus giving rise to the formation of 

 innumerable miniature volcanoes. 



Other phenomena accompanying this eruption were the prevalence 



