224 Intelligence and Miscellaneous Articles. 



whirling body ; for the reason that the rotation here is proportionally 

 more active and intense, being impelled by the aggregated pressure 

 and momentum of the more outward portion of the whirlwind as 

 it converges from its larger area, on all sides, by increasingly rapid 

 motion, into the smaller area of ascending rotation*. 'I'hat this 

 interior portion of the whirl resembles an inverted hollow cone, 

 or column, with quiescent and more rarefied air at its absolute 

 centre, may be inferred from the observations which have been 

 made in the axial portions of the great cyclones. Into this axial 

 area of the tornado the bodies forced upward by the vortex cannot 

 fall, but will be discharged outward from the ascending whirl. The 

 columnar profile of this axial area sometimes becomes visible, as iu 

 the water-spouts so called. 



5. Accessions caused by circumjacent contact and pressure are 

 constantly accruing to the whirling body, so long as its rotative 

 energy is maintained. A correlative diffusion from its ascending 

 portion must necessarily take place, towards its upper horizon; and 

 this is often manifested by the great extent or accumulation of cloud 

 which results in this manner from the action of the tornado. In 

 other words, there is a constant discharge from the whirling body 

 in the direction of least resistance. 



6. The s])irality of the rotation and its inclination to the horizon, 

 in the great portion of the whirl which is exterior to its ascending 

 area, is not ordinarily subject to direct observation. Nor is the 

 outline or body of the more outward portion of the whirlwind at all 

 visible, otherwise than in its effects. 



7. In aqueous vortices the axial spiralities of the exterior and 

 interior portions are in reverse direction to those in the atmosphere, 

 the descending spiral being nearest to the axis of the vortex. Hence 

 lighter bodies and even bubbles of air are often forced downward in 

 the water, in the manner in which heavier bodies are forced upwards 

 in the atmosphere. 



The foregoing is simply a statement of results which I have derived 

 from a long course of observation and inquiry. It does not include 

 the partial and imperfect exhibitions of whirlwind action which often 

 occur ; nor the various movements and phenomena which are col- 

 laterally associated with tornadoes and whirlwinds, some of which 

 are of much significance. — Sillimans American Journal for January 

 1857, p. 23. 



* The law of increment in the velocity of the whirlwind, as it gradually 

 converges into sniuUer areas by its spiral involution, is that which pertains 

 to other bodies when revolving around interior foci towards which they 

 are being gradually drawn or pressed nearer and nearer, in their involute 

 course ; — the line of focal or centri))etal pressure, thus sweeping equal 

 areas in equal times, at whatever diminution of distance from the centre ; 

 except as the velocity may be eifected in degree by tlie resistance of other 

 bodies. Such resistance is of little effect in a tornado, because its revolving 

 mass is mainly above all ordinary obstacles, such as orchards and forests, 

 into which the spirally descendiny and accelerated blast, near the contracted 

 extremity of the inverted and truncated cone of the whirl, penetrates with 

 constant freshness and intensity of force, already acquired in the higher 

 and unobstructed region. 



