378 TVTiirltvinds excited by Fires. 



8. The velocity and strength of the wind in the rotative 

 action of a vortex, the axis of which is in a vertical position, 

 as in the above cases, greatly exceeds that which is exhibited 

 in other circumstances. 



9. We may perceive, also, in these cases, how eflFectually 

 the heated stratum of air nearest the earth's surface, may be 

 caused to penetrate a homogeneous and colder overlying stra- 

 tum of current, by means of the vorticular action ; a move- 

 ment which is otherwise physically impossible, except in a 

 partial degree, by means of other concurrent movements or 

 favouring circumstances. 



10. These considerations, and others which suggest them- 

 selves, will enable us to account for the sudden and rapid for- 

 mation of hail, in summer hail-storms and tornadoes ; and in 

 the structure of the hailstones, in successive layers, and their 

 occasionally fractured condition, we may perceive both the 

 evidence and the effects of the violent vortical action, and the 

 successive changes of temperature and hygrometric condition 

 in which they have been successively placed, before leaving 

 the vortex, and while falling to the earth. 



11. These cases, viewed in connection with the natural phe- 

 nomena which have been exhibited in a multitude of instances, 

 appear fullj^ to con&'m the opinion of Franklin, in favour of 

 the general identity of the columnar whirlwinds with the so- 

 called water-spouts. 



12. By the clue which is here afforded us, in the peculiar 

 noise and rumbling detonations of these violent whirlwinds, 

 we may become apprised of the existence of a violent vortical 

 action in the atmosphere, or within the envelopment of a 

 visible thunder-cloud, even in those numerous cases in which 

 the vortex or whirlwind does not reach the earth's sm'face. 



13. Perhaps we have also, in these noises, a clue to the 

 sounds which are ascribed to certain moving sands, in the heat 

 of summer, as in the case of Jebel Narkous, or the sounding 

 mountain, neai" Tor, on the Red Sea,* and also in the Beg- 

 ruwan, on a hillside, near Cabul, which is described by the 

 Emperor Baber and by Capt. Burnes. From the descriptions 



* Wellsted's Travels in Arabia, Load. 1838. Vol. ii. pp 23-27. 



