CAUSES OF WHIRLWINDS, ETC. 257 



having been seen even to advance against a wind then slowing; and 

 when several waterspouts have been in sight at once, some have oeen 

 stationary, others running about without any common direction. 



In assigning these phenomena to the agency of electricity, there are 

 no conditions assumed, the existence of which can be disproved ; and it 

 cannot be denied that the cause is adequate to the effect attributed to it. 

 We may distinguish two kinds of them, according as the electricity has 

 accumulated in the earth, and discharges itself into the air, or, as the 

 electricity is emitted from a charged cloud, exercising a powerful induc- 

 tion upon the surface of the earth beneath, but without exploding. In 

 the former case, which is peculiar to land, the resulting action constitutes 

 the whirlwind or the pillar of sand, the different appearance of which is 

 owing to the nature of the soil from which they rise. Whirlwinds are 

 of most frequent occurrence in those countries not free from earthquakes, 

 and dry hot seasons during a limited time of the year, such as the wide 

 valley of the Mississippi. Compared with the pillars of sand they are 

 more terrible in their destructive energies, but they are more casual, and 

 are generally single. Pillars of sand are confined to the deserts of Africa 

 and Hindostan ; they are individually less dangerous, but they are not to 

 be despised if it be true that each of them may deposit a quantity of 

 suffocating dusts, forming a hillock of greater height than a man, and 

 that countless numbers may be stalking across the arid plain with 

 inevitable speed. 



The electricity, which we believe to be the prime mover of these 

 extraordinary spectacles, may possibly have different sources, and, we 

 are inclined to suspect, a less superficial excitation of that in the whirl- 

 wind. But, however, the charge may be derived, when it has 

 accumulated to such intensity that the electrical inertia of the air is 

 unable to repress it, it will rush upwards in a stream, communicating an 

 ascending motion to the air, and bearing along with it whatever light 

 mobile particles may be within its influence. 



If there were in the superincumbent atmosphere a sufficient mass to 

 supply by induction the requisite quantity of the opposite electricity, 

 then the accumulation might have been discharged in the ordinary 

 manner by explosion. In the absence of this, the electricity, taking the 

 direction in which it meets with least resistance, tends to dissipate itself 

 in a stream through the air so long as it can force a passage. The stream 

 expands in its progress by its own elasticity, so that its diameter is 

 greater as it recedes from the earth, often describing very exactly an 

 inverted cone. While the stream continues, the opposite kind of 



