202 LIGHT SCIENCE FOR LEISURE HOURS. 



boiling up just as a caldron of water boils on the fire. 

 The fourth day it began to throw up again, and the 

 seventh day much more, but still with, less violence 

 than the first night. At this time many persons who 

 were on the hill were knocked down by the stones and 

 killed, or smothered with the smoke." 



And now, for nearly a century, the whole district 

 continued in repose. Nearly five centuries had passed 

 since there had been any violent eruption of Vesuvius 

 itself; and the crater seemed gradually assuming the 

 condition of an extinct volcano. The interior of the 

 crater is described by Bracini, who visited Vesuvius 

 shortly before the eruption of 1631, in terms that would 

 have fairly represented its condition before the erup- 

 tion of 79 : " The crater was five miles in circumfer- 

 ence, and about a thousand paces deep ; its sides were 

 covered with brushwood, and at the bottom there was 

 a plain on which cattle grazed. In the woody parts, 

 wild boars frequently harbored. In one part of the 

 plain, covered with ashes, were three small pools, one 

 filled with hot and bitter water, another salter than 

 the sea, and a third hot, but tasteless." But in De- 

 cember, 1631, the mountain blew away the covering 

 of rock and cinders which supported these woods and 

 pastures. Seven streams of lava poured from the 

 crater, causing a fearful destruction of life and prop- 

 erty. Resina, built over the site of Ilerculaneum, was 

 entirely consumed by a raging lava-stream. Heavy 



