NOME II. VESICULAR LAVA. 



" I now return from this digression, which, Smoke, 

 though not indeed very short, appears to me 

 perfectly appropriate to the subject ; and pro- 

 ceed to resume my narrative. I shall first speak 

 briefly of a phenomenon relative to the smoke 

 which arises from the crater of Etna, and which 

 was seen differently by Mr. Brydone, Count 

 Borch, and myself. Mr. Brydone tells us that 

 " from many places of the crater issue volumes 

 of sulphureous smoke, which being much heavier 

 than the circumambient air, instead of rising in 

 it, as smoke generally does, immediately on its 

 getting out of the crater, rolls down the side of 

 the mountain like a torrent, till coming to that 

 part of the atmosphere of the same specific 

 gravity with itself, it shoots off horizontally, and 

 forms a large track in the air, according to the 

 direction of the wind." 



" On the contrary, the smoke when seen by 

 Count Borch, at the intervals when the air was 

 calm, arose, perpendicularly, to a great height, 

 and afterwards fell, like white fleeces, on the top 

 of the mountain. I shall not presume to doubt 

 these two facts, though I observed neither of 

 them. The two columns of smoke which I saw, 

 though bent somewhat from the perpendicular 

 by the wind, ascended with the usual prompti- 



