1 86 LIGHT SCIENCE FOR LEISURE HOURS. 



arrival at the bottom of the mountain, says Dr. Clarke, 

 'the whole current,' encumbered with huge masses 

 of scoriae, ' resembled nothing so much as a heap of 

 unconnected cinders from an iron foundry,' ' rolling 

 slowly along,' he says in another place, ' and falling 

 with a rattling noise over one another.' 



After the eruption described by Dr. Clarke, the 

 great crater gradually filled up. Lava boiled up from 

 below, and small craters, which formed themselves 

 over the bottom and sides of the great one, poured 

 forth lava loaded with scorise. Thus, up to October 

 1822, there was to be seen, in place of a regular 

 crateriform opening, a rough and uneven surface, 

 scored by huge fissures, whence vapour was continually 

 being poured, so as to form clouds above the hideous 

 heap of ruins. But the great eruption of 1822 not 

 only flung forth all the mass which had accumulated 

 within the crater, but wholly changed the appearance 

 of the cone. An immense abyss was formed, three- 

 quarters of a mile across, and extending 2,000 feet 

 downwards into the very heart of Vesuvius. Had the 

 lips of the crater remained unchanged, indeed, the 

 depth of this great gulf would have been far greater. 

 But so terrific was the force of the explosion that the 

 whole of the upper part of the cone was carried clean 

 away, and the mountain reduced in height by nearly a 

 full fifth of its original dimensions. From the time of 

 its formation the chasm gradually filled up ; so that, 

 when Mr. Scrope saw it soon after the eruption, its 

 depth was reduced by more than 1,000 feet. 



