1 84 LIGHT SCIENCE FOR LEISURE HOURS. 



on the outer circular mountain Somma, and on the 

 valley between. Falling, still red-hot and liquid, they 

 covered a district more than two miles and a half wide 

 with a mass of fire. The whole space above this 

 district, to the height of 10,000 feet, was filled also 

 with the falling and rising lava streams ; so that there 

 was continually present a body of fire covering the 

 extensive space I have mentioned, and extending 

 nearly two miles high. The heat of this enormous 

 fire-column was distinctly perceptible at a distance of 

 at least six miles on every side. 



The eruption of 1793 presented a different aspect. 

 Dr. Clarke tells us that millions of red-hot stones were 

 propelled into the air to at least half the height of the 

 cone itself; then turning, they fell all around in noble 

 curves. They covered nearly half the cone of Vesuvius 

 with fire. Huge masses of white smoke were vomited 

 forth by the disturbed mountain, and formed them- 

 selves, at a height of many thousands of feet above 

 the crater, into a huge, ever-moving canopy, through 

 which, from time to time, were hurled pitch-black jets 

 of volcanic dust, and dense vapours, mixed with cas- 

 cades of red-hot rocks and scoriae. The rain which fell 

 from the cloud-canopy was scalding hot. 



Dr. Clarke was able to compare the different ap- 

 pearances presented by the lava where it burst from the 

 very mouth of the crater, and lower down when it had 

 approached the plain. As it rushed forth from its im- 

 prisonment, it streamed, a liquid, white, and brilliantly 

 pure river, which burned for itself a smooth channel 



