1 84 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 supported 

 these woods and pastures. Seven streams of lava 

 poured from the crater, causing a fearful destruction 

 of life and property. Resina, 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 important 

 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 as- 

 signed to it. 



An interval of thirty-five years passed before the 

 next eruption. But since 1666 there has been a 

 continual series of eruptions, so that the mountain has 

 scarcely ever been at rest for more than ten years 



