202 THE STORY-BOOK OF SCIENCE 



"An eruption is generally announced beforehand 

 by a column of smoke that fills the orifice of the 

 crater and rises vertically, when the air is calm, to 

 nearly a mile in height. At this elevation it spreads 

 out in a sort of blanket that intercepts the sun's 

 rays. Some days before the eruption the column of 

 smoke sinks down on the volcano, covering it with a 

 big black cloud. Then the earth begins to tremble 

 around Vesuvius; rumbling detonations under the 

 ground are heard, louder and louder each moment, 

 soon exceeding in intensity the most violent claps 

 of thunder. You would think you heard the can- 

 nonades of a numerous artillery detonating cease- 

 lessly in the mountain's sides. 



' ' All at once a sheaf of fire bursts from the crater 

 to the height of 2000 or 3000 meters. The cloud that 

 is floating over the volcano is illumined by the red- 

 ness of the fire ; the sky seems inflamed. Millions of 

 sparks dart out like lightning to the top of the blaz- 

 ing sheaf, describe great arcs, leaving on their way 

 dazzling trails, and fall in a shower of fire on the 

 slopes of the volcano. These sparks, so small from 

 a distance, are incandescent masses of stone, some- 

 times several meters in dimension, and of a sufficient 

 momentum to crush the most solid buildings in their 

 fall. What hand-made machine could throw such 

 masses of rock to such heights? What all our ef- 

 forts united could not do even once, the volcano does 

 over and over again, as if in play. For whole weeks 

 and months these red blocks are thrown up by Ve- 

 suvius, in numbers like the sparks of a display of 

 fireworks/' 



