1852.] On Dust Whirlwinds and Cyclones. 269 



The Aurora Borealis and Australis seen at the poles, may be due to 

 an accumulation of the Electro-magnetic spirals circulating in the 

 upper regions d the atmosphere at these particular points ; and the 

 ether, supposed to pervade space, may also be composed of this sub- 

 stance. 



An illustration of the opposite rotations in the two hemispheres, 

 which may possibly lead to the discovery of the laws themselves, 

 seems to be afforded by the motion of fluids. 



A body moved through water, from A to B, with moderate velo- 

 city, causes two eddies in the fluid, revolving in opposite directions, 

 and progressing on either side of the line of motion, with a tendency 

 as they advance, to be deflected from the line parallel to the line of 

 motion, and to assume parabolic curves, as described in Plate 1 2. We 

 have here three things : a fluid, — a motion imparted to it in a certain 

 direction, — and a resisting medium : the result being opposite move- 

 ments in the fluid ; seemingly of the very character of those which 

 influence the motion of the Cyclones. 



Corresponding to these, there is the atmosphere ; — the centrifugal 

 action of the earth's rotation from west to east, greatest at the Equator, 

 and uniform only on that line ; — and thirdly, the earth's translation, or 

 the impetus with which it is carried forward, in space, re-acting and 

 producing the effect of a resisting medium. The very conditions 

 requisite, perhaps, for giving these peculiar motions to the air at a 

 certain height, and for communicating the same to matter of which 

 the whirlwinds are said to be composed. 



The eddies so formed, being diverted downwards to the earth's sur- 

 face, just as we observe, under certain circumstances, the like motions 

 in water, continued downwards beneath the surface ; and once formed, 

 these rotatory movements will continue, till friction or other counter- 

 acting effects cause their cessation. 



Cyclones may be the means by which accumulated electricity in the 

 atmosphere is gradually discharged, and they may thus become power- 

 ful means by which evaporation on a large scale is effected, and rain 

 produced, and the Electro-magnetic spirals, having discharged their 

 electricity and water, may be again lifted up to the higher regions of 

 the atmosphere. 



