1852.] On Dust Whirlwinds and Cyclones. 267 



It seems probable, that the entire zone of a Cyclone is not equally- 

 charged at the same instant, nor throughout its whole extent, with the 

 electrical spirals ; but that on the side of progression they are diffused 

 or spread out, so as to occupy a large extent of surface ; while on the 

 looped side, or vortex of the Storm, there is a rapid convergence and 

 concentration of them, accompanied with increased intensity of action, 

 where conflicting winds and waves meeting, will, on the laws of inter- 

 ferences, destroy or counteract each other's effects — accounting for 

 many strange phenomena, well known to sailors, observable in that 

 quarter of the storm. 



The marked fall of the Barometer as the vortex is approached may, 

 possibly, be accounted for by the upward whirling motion imparted to 

 the air, by the action of the electrical spirals, which thereabouts, are 

 presumed to be highly concentrated ; and the modus operandi may 

 be thus explained. 



The electrical spiral rotating and working like a screw, from above 

 downwards, sets in motion by its centrifugal action a stratum of air 

 immediately surrounding it — outside this again, another circle of winds 

 will be found blowing centripetally ; and the two meeting will, by 

 their mutual action and reaction, continuous throughout, form an 

 ascending spiral current of air, working a reversed spiral upwards, the 

 two motions being well represented by two coils of wire wound in 

 opposite directions laid one over the other. 



At the outer verge of the side of progression, and at the tail of the 

 Storm, where the electrical spirals may be presumed to be in a great 

 measure absent, and the up-current consequently less, the Barometer 

 is reported to stand much higher, than it does elsewhere in the body 

 of the storm — the winds thereabouts being centripetal winds, blowing 

 with more or less obliquity in the direction of the Storm's track, and 

 caused by its action upon the air through which it has passed, as is 

 the case in smaller whirlwinds. 



This peculiar upward working spiral motion is, I think, the cause of 

 the ascent of dust, in whirlwinds passing over a dry sandy soil, and 

 of the ascent of water also in water spouts. 



The size and form of the ultimate spiral seems to be always the 

 same, and is about 12 inches in diameter and cylindrical; but its 

 energy appears to surfer increase and diminution, attributable, perhaps, 

 to the amount of electricity with which it happens to be charged. 



2 M 



