1 82 LIGHT SCIENCE FOR LEISURE HOURS. 



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 

 eruption of 79 : ' The crater was five miles in cir- 

 cumference, 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 harboured. 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 taste- 

 less.' But in December, 1631, the mountain blew 

 away the covering of rock and cinders which sup- 

 ported these woods and pastures. Seven streams of 

 lava poured from the crater, causing a fearful de- 

 struction of life and property. Eesina, built over 

 the site of Herculaneum, was entirely consumed by a 

 raging lava-stream. Heavy showers of rain, generated 

 by the steam evolved during the eruption, caused in 

 their turn an amount of destruction scarcely less im- 

 portant than that resulting from the lava-streams. 

 For, falling upon the cone, and sweeping thence large 

 masses of ashes and volcanic dust, these showers pro- 

 duced destructive streams of mud, consistent enough to 

 merit the name of ' aqueous lava ' commonly assigned 

 to it. 



An interval of thirty-five years passed before the 

 next eruption. But since 1666 there has been a con- 

 tinual series of eruptions, so that the mountain has 

 scarcely ever been at rest for more than ten yeara 



