188 LIGHT SCIENCE FOR LEISURE HOURS. 



is the principal vent, we have a remarkable instance of 

 the deceptive nature of that state of rest into which 

 some of the principal volcanoes frequently fall for 

 many centuries together. For how many centuries 

 before the Christian era Vesuvius had been at rest, is 

 not known ; but this is certain, that, from the landing 

 of the first Greek colony in Southern Italy, Yesuvius 

 gave no signs of internal activity. It was recognized 

 by Strabo as a volcanic mountain, but Pliny did not 

 include it in the list of active volcanoes. In those 

 days, the mountain presented a very different appear- 

 ance from that which it now exhibits. In place of the 

 two peaks now seen, there was a single, somewhat 

 flattish, summit, on which a slight depression marked 

 the place of an ancient crater. The fertile slopes of 

 the mountain were covered with well-cultivated fields, 

 and the thriving cities Herculaneum, Pompeii, and 

 Stabiae, stood near the base of the sleeping mountain. 

 So little did any thought of danger suggest itself in 

 those times, that the bands of slaves, murderers, and 

 pirates which flocked to the standard of Spartacus 

 found a refuge, to the number of many thousands, 

 within the very crater itself. 



But though Yesuvius was at rest, the region of 

 which Yesuvius is the main vent was far from being 

 so. The island of Pithecusa (the modern Ischia) was 

 skaken by frequent and terrible convulsions. It is 

 even related that Prochyta (the modern Procida) was 



