470 1'bs Simoom. [Book V. 



with a loud voice, Fail upon your faces, for here is 

 the fimoom. I faw from the fouth-eaft a haze come,, in 

 colour like the purple part of the rainbow, but not fo 

 c.ompreffed or thick. Ic did not occupy twenty yards 

 in breadth, and was about twelve feet high from the 

 ground. It was a kind of bluih upon the air, and it 

 moved very rapidly, for I fcarce could turn u fall 

 upon the ground with my head to the northward, 

 when J felt the heat of its current plainly upon my 

 face. We all lay flat on the ground, as if dead, till 

 Idris told us it was blown over. The meteor, or 

 purple haze, which I faw, was indeed patted, but the 

 light air that (till blew was of heat to threaten fuffo- 

 cation. For my part, I found diftinctly in my breaft, 

 that I had imbibed a part of it ; nor was I free of an 

 afthmatic fenfation till I had been fome months in 

 Italy, at the baths of Poretta, near two years after- 

 wards *.' * 



Whirlwinds and water-fpouts have by many philo- 

 fophers been conlidered as entirely electrical pheno- 

 mena, while others have attributed them to a different 

 eaufe, and accounted for them upon the principles of 

 hydroftatics. It is poflible, however, that there may 

 really be two kinds of water-fpouts, the one the effect 

 ef the electrical attraction as defcribed in Book iv. 

 c. 6. and the other caufed by a vacuum, or extreme 

 and fudden rarefaction of the air. The whirlwinds 

 which I have obferved in this country, were, I 

 am perfuaded, of the latter kind; at leaft whatever 

 was the original caufe, the circumagitation or fpiral 

 motion of the air muft have continued long after every 

 electrical power had ceafed to act. 



It is well known that even a common fire produces 

 a kind of circulation of the air in a room, but in a 



* Brace's Travels, vol. iv. p. 553, 555. 



different 



