NATURAL PHILOSOPHY. 261 



4. The area of the ascending spiral movement in the vortex, as it leaves 

 the earth's surface, is by fur the smallest portion of the whirling body ; for 

 the reason that the rotation here is proportionally more active and intense, be- 

 ing 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.* 

 That 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 be- 

 comes visible, as in 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 ac- 

 tion of the tornado. In other words, there is a constant discharge from the 

 whirling body in the direction of least resistance. 



6. The spirality 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 or- 

 dinarily 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 por- 

 tions 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 docs not include the partial 

 and imperfect exhibitions of whirlwind action, which often occur ; nor the 

 various movements and phenomena which are collaterally associated with 

 tornadoes and whirlwinds, some of which are of much significance. 



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

 into smaller areas by its spiral involution, is that which pertains to other bodies 

 when revolving around interior foci towaids which they are being gradually drawn 

 or pressed nearer and rearer, in their involute course ; the line of focal or centri- 

 petal pressure, thus sweeping equal areas in equal times, at whatever diminution of 

 distance from the centre ; except as the velocity may be affected in degree by the 

 resistance of other bodies. Such resistance is of little effect iu a tornado, becauce its 

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

 into which the spirally descending and accelerated blast, near the contracted ex- 

 tremity 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. 



