192 LIGHT SCIENCE FOR LEISURE HOURS. 



eruption wliicli 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. " He was at that time," 

 says his nephew, " with the fleet under his command 

 at Misenum. On August 24th, about one in the after- 

 noon, 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 afterward that it came from Yesuvius. 

 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 ; 

 occasioned, I suppose, either by a sudden gust of air 

 which impelled it, whose force decreased as it advanced 

 upward, or else the cloud itself, being pressed back 

 by its own weight, expanded in this manner. The 

 cloud appeared sometimes bright, at others dark and 

 spotted, as it was more or less impregnated with earth 

 and cinders." 



These extraordinary appearances attracted the cu- 



