

1852.] On Dust Whirlwinds and Cyclones. 141 



these electrical spiral threads, placed singly or in fasciculi, each and all 

 rotating independently as the whirlwind circles, onwards in its course ; 

 and the incurving of the winds oftentimes distinctly observable in 

 them when the whirlwind passes over a light dry soil, is occasioned by 

 the rotation of the electrical threads, Plate 2. 



The rotation of the spirals may now enable us to comprehend a 

 singular appearance sometimes seen in an approaching dust storm, 



A broad wall of dust is observed rapidly advancing, apparently com- 

 posed of a number of large vertical columns of dust, rolling onwards, 

 each preserving its respective position in the moving mass ; and each 

 column having a whirling motion of its own. 



This appearance is doubtless occasioned by the advance of a large 

 body of electrical matter in the form of spirals, rotating as they ad- 

 vance ; and this may actually represent the body of a Cyclone. 



The gusts that occur from time to time during a storm of this de- 

 scription, may be easily accounted for by supposing the passage of a 

 succession of these rotating electrical columns ; and it has been re- 

 peatedly proved to my satisfaction, that during the squalls that mark 

 these storms, the electrical tension is at its maximum ; for the electric 

 fluid then streams most furiously down the insulated wire, exactly in 

 accordance with the violence of the wind or gust at the time. 



I conceive therefore that the motive power in the Cyclone, may be 

 a zone of electrical matter, composed of innumerable spiral columns of 

 all sizes, single and compound, placed at intervals, rotating with the 

 body of the storm ; first from above downwards ; secondly on meeting 

 the earth's surface, whirling their eliptical or Cycloidal courses, each 

 preserving its respective position in the moving mass. Outside this 

 whirling zone of electrical matter, centripetal winds in all probability 

 exist, blowing from a circumference more or less extended, to the edge 

 all round, forming with it centripetal tangents, Plate 3. 



These straight-lined Centripetal winds blow, I should think, with 

 more regularity, greater force and longer continuance, on the side of 

 the storm's progression ; as that side will have a double set of forces 

 acting upon it, — the progressive and the rotatory. 



This side, may easily be determined when the track of the storm is 

 known, by attending to what seems the established law of the rotation 

 of the storms according to the Hemispheres — that those to the North 



