174 LIGHT SCIENCE FOR LEISURE HOURS. 



violent, until it began to be evident that the volcanic 

 fires were about to return to their main vent. The 

 obstruction which had so long impeded the exit of the 

 confined matter was not however readily removed, and 

 it was only in August of the year 79, after numerous 

 and violent internal throes, that the superincumbent 

 mass was at length hurled forth. Rocks and cinders, 

 lava, sand, and scoriae, were propelled from the crater, 

 and spread many miles on every side of Vesuvius. 



We have an interesting account of the great 

 eruption which followed in a letter from the younger 

 Pliny to the younger Tacitus. The latter had asked 

 for an account of the death of the elder Pliny, who 

 lost his life in his eagerness to obtain a near view of 

 the dreadful phenomenon. f He was at that time,' 

 says his nephew, ' with the fleet under his command at 

 Misenum. On August 24, about one in the afternoon, 

 my mother desired him to observe a cloud of very 

 extraordinary size and shape. He had just returned 

 from taking the benefit of the sun, and, after bathing 

 himself in cold water, and taking a slight repast, had 

 retired to his study. He arose at once, and went out 

 upon a height whence he might more distinctly view 

 this strange phenomenon. It was not at this distance 

 discernible from what mountain the cloud issued, but 

 it was found afterwards that it came from Vesuvius. 

 I cannot give a more exact description of its figure 

 than by comparing it to that of a pine-tree, for it shot 

 up to a great height in the form of a trunk, which 

 extended itself at the top into a sort of branches ; 



